Thanks to all those interested viewers that made suggestions on how to overcome the out of square issues I am having with this toolholder. Rather than answer each comment individually, I thought it would be better to summarise answers to the most common suggestions and what I have tried so far. 1. There is a relief groove machined into the pocket that aligns and supports the blade. The relief groove accounts for the thicker part of the tee section and allows the blade to sit *Almost* vertical. Due to a very slight taper in the grind, the blade is likely a few arc seconds of a degree out of vertical but I cannot measure it and it seems unlikely that this would account for the amount of out of square I am getting on the cut. 2. The cutting edge of the blade had the factory original grind on it and it was sharp and not chipped. I did recently regrind it and I checked it with a good light and an engineers square and as far as I can tell it's square. 3. Since publishing this video I have tried different speeds and feeds, so far with no improvement on the original test cuts I made. 4. I machined the overhang off the top mounting block so that now there is a continuous surface from the top support block down to the face of the BXA tool holder. This eliminated the gap between the blade holder and the face of the BXA tool holder. This did not make any difference. 5. I changed the position of the blade clamping washer so that now it grips on the thicker part of the blade (the wider part of the tee section) and I moved it as far forward as I could on the blade clamping plate. This did make a difference but now the face of the stock closest to the chuck is convex instead of concave! 6. On all the new tests the carriage was locked and I checked the alignment of the blade with an indicator. It is dead square to the axis of the lathe. 7. An indicator on the side of the blade during a cut shows that the blade is flexing sideways enough to cause the issue but I don't know what is initiating the sideways movement. 8. I hate to admit defeat and I seem to be the only one who has made one of these tools that seems to be having a problem. The only other thing which I haven't tried yet is to grind the top edge of the blade flat, removing the shallow half round groove from the top surface. It seems unlikely that this will make a difference but other than some fundamental physics thing that might be going on with the flexure in the blade mounting plate, I don't know what else to try. Finally, I have two other parting systems on my lathe that work fine so it's not like I have no other options. I just wanted to show that Mark Winquist's design was a good one. If my version is a fail, don't write off his design. His works perfectly. Mine is a dog!
I have one of Winky’s sprung parting tools as well and I love it. Cuts perfectly and hasn’t flinched at anything I’ve thrown at it. Very fast and low drama parting. Mine is working flawlessly. Can’t say enough good things about this design.
Quinn, Mark did tell me that he had sent you one of the AXA versions. During the first cut I did with mine I figured that it was doing it's thing perfectly. I was feeling quite smug but then I noticed the amount of taper in the face. It was consistent no matter what I did to eliminate it. I have some ideas to try now though. I was terrified that I would have a catastrophic failure on camera which is kind of why I stopped. Regards, Mark
Thanks for posting this Mark. I have also used this style of cut-off blade, on a Maximat Super 11 and BXA toolpost. I don't see whether you have compensated for the taper section of the blade, to ensure the vertical centerline stands truly vertical. If not, the cup shape of the cutting edge engages unequally, causing the blade to deflect. This leads to the convex cut that you are getting, and might jam up the swarf curls. In short: They can work well but are critical in: 1. Ensuring the (resharpening) grind of the cutting edge is perfectly square to the blade and 2. Clamping the blade truly vertical, e.g. by shimming the lower edge under the clamping screw. My penny's worth, lol. I now always gravitate towards my 2mm insert in springsteel blade.
I agree. My rear parting tool holder gives me almost no issues and I was worried about making a tool that had so many variables. I did include a relief for the top thicker tee section and the centre line of the blade should be very close to vertical. The amount of sideways deflection seems excessive and of all the other parting tools that I have used, this is the first time I have seen one behave like this. To be fair, it produced very little chatter and the chips came out mostly uniform in shape and size. I clearly need to do a lot more experimenting. Regards, Mark
I believe if you tested the blade vertically you will find that it’s slightly tilted to the left. The washer you made is pressed against the tapered surface of the blade. It’s not a huge difference, but tapered non the less. That’s what I think is your trouble to put it simply. Great work as always Mark. Enjoyed the conversation.
Thanks. I am sure the way I have clamped the blade has some effect but my rear parting blade has a similar geometry and it tracks straight. The rear toolpost has a different clamping system but it is probably still a bit off vertical. I have a lot more testing to do but I got a bit discouraged and I needed to end the video. I will revisit this. Regards, Mark
@@Preso58ypu mentioned that there was a slight gap at the back of the tool. Could the combination of that gap with an off vertical cutting edge be causing the blade to cant when the holder flexes?
Thanks for that. I have received your stickers and I am looking for a video to add them to my door. I have two videos almost finished so I will see if I can squeeze it into the next one. Regards, Mark
Good Show Mate: As per normal. Glad to see collaboration between two of my favorite TH-camrs. I have to like Winky's stuff. We are both reformed printers. You have to be a Jack of All trades in that business. Dead lines and broken machines are normal. Fixing stuff all the time. I have turned many parts for presses and folders and binding machines. Just a fact of life.
Thanks. I have been discussing Mark's work in the printing industry with him. I did study a bit about it during my teacher training and it has always fascinated me. Such big and powerful machinery at work in that trade. On a recent holiday in New Zealand we came across a newspaper printing shop in Greymouth on the west coast of the South Island. The entire front of the two storey building was glass and you could look in off the street and see all the workings on display. Unfortunately it wasn't operating when we were there though. Regards, Mark
I suspect that the curvature cutting issue is cause by the flexure being offset from the centerline of the parting blade. This is likely allowing the paring blade holder to twist when loaded.
I was seeing that in the CAD analysis but out of three other similar toolholders that have been made to Mark's design, mine is the only one giving this result. I sort of suspect the gap behind the tool holding plate and I will eliminate that first to see if it's a culprit. Regards, Mark
Yes, there is something fundamentally different about my version. I believe Mark Winquist sent an AXA version to Blondihacks and she reported that hers worked fine. Regards, Mark
I’ve found with the 3/32” blade it flexes vertical and horizontally and twists in the holder, especially when cutting over 3/4” dia. stock. Shimming the blade to support both the tapered and ‘T’ style profiles improves the ‘squareness’ of the cuts but never quite matches a thicker blades at all diameters. A fresh sharpening improves the cut most times but not consistently. Many broken blades from HSS/cobalt blades to insert styles, in several different holders, in various steel alloys and non ferrous materials and coolant/ lubrication efforts. I have watched the sprung style holders with interest but do not have one, yet. The gods do not smile on my sacrifices. Just my observations and I share your frustrations. Take care n play safe.
Hi, Mark. Great video as always. The design you just built is remarkably similar to a toolpost-mounted lathe dynamometer that I fabricated years ago when I was in engineering school. It used a dial indicator attached to the top rear of the flexure component and the plunger set to bear on the back of the movable part. It was calibrated by weights suspended on the business end of the tool. From my work back then I can offer that the dished profile on your workpiece is likely because the cutoff tool is cantilevered on the headstock side of the flexure element. In use this will create torsion as well as the expected downward tool deflection. If you model this viewing from the top you may be able to observe it to a degree. As you use power infeed the forces can become higher as you approach the centerline of the workpiece so the effect may be most noticeable as you go inward. Cheers.
My suspicion is that you’re right about the side to side flex because of the clearance. The front to back section of the holder is enough to allow the blade to flex vertically and it looks to be even smaller in the side to side dimension. I look forward to seeing the solution because while my lathe is actually very good at parting I’m very reluctant to use power feed to do it and it sometimes gets tedious feeding the tool manually if I have a lot of parting to do.
My thinking is the tool blade is tapered, so when you tighten the lower clamp onto the blade the upper cutting surface is higher on the side closest to the tool holder and the side closest to the chuck is lower. When you set centre height the edge closet to the tool holder will be on centre and the edge closest to the chuck will be lower. When the tool is cutting this impart a turning force into the blade toward the chuck, pushing the blade further into the work piece. As the diameter gets smaller the effective speed of material past the cutter lowers, so the force goes up, making the blade push into the work more. I also think the point of deflection is the edge of the drilled hole because in order for it to flex there must be no material to compress. If you want it to flex around the point you indicated, extending the slot through the hole would do that.
Thanks. I had wondered about the thinning towards the bottom of the blade and that will be a factor. The amount of sideways deflection seems to be excessive though. My rear toolpost has a similar but smaller cross section blade and doesn't have anywhere near the same amount of deflection. Regards, Mark
It is definitely twisting. The blade is located sideways from the holder and the blade itself is quite thin. The flexure also does not add rigidity. 16:55 also shows the load is located on one side of the blade
I think that the issue is the gap that you mentioned. As more force is applied to the blade, the holder is flexing as it should, however, since there is a gap between the blade and QCTP, the blade holder is allowed to over flex causing the blade to slightly twist inward. I really don't know what the issue is, but it makes sense to me clear as mud 😅
We had a commercial cutting tool holder that had a Simler relief and it would do the same thing. Our machinist had experience with Simler and the same thing had happened. He brazed the relief cut up and it would cut Strate every time.
See my pinned comment at the top of this video for what I have learned since publishing this video. I suspect that there is something strange going on with the blade spring design on my version but two other people with the same design that Winky came up with report that there's work perfectly. It's a mystery so far. Regards, Mark
My two cents is there is some flex happening (obviously). I see two points of attachment at the top of the blade holder and the rest is flopping in the wind so to speak. If you shimmed the space it might stop flexing. I have given up on those "T" blades. Your rear parting tool holder and the accompanying procedure is the best I've seen. However there is no room on my Rockwell late to use one. Thanks for the video and the tests. You'll get it right! Loved Mr. Snake!
yes, the blade is not perpendicular to the work because of the taper towards the bottom of the blade, side clamp means the blade leans into the work on the chuck side
See my pinned comment which I have added since publishing this video. It outlines what I probably didn't mention in the video and what I have tried since then. Regards, Mark
Parting off is the one job I hate doing. Like you I also seem to get the best results using my rear tool post. Over the years I’ve made two tool height gauges similar to yours. I do prefer the one I made from a Hemingway Kit. So easy to use. Didn’t like the way that snake was looking at you. I guess it was wondering how it could get you in it’s belly 😅 Cheers Nobby
Thanks Nobby. This tool really has me stumped. See the pinned comment for what I have tried since publishing this video. It's still not right and I do at least have the rear parting tool which works fine. Regards, Mark
Fascinating video and problem. I'm very interested in seeing the resolution or explanation if it can be discovered. Such a mystery for such a seemingly simple tool, fascinating. From half a world away my view of Australia is that of an entire continent of strange, very strange, wildlife. Non-venomous? Fine, still creeps me out.
Thanks. We see a lot of those big carpet pythons. We have had one living in our roof for many years. It only comes out to moult and I am guessing it lives on frogs and mice. I was doing some work in the roof space one day and was kneeling on the roof truss when it slithered by my hand in the gap between the insulating batts and the edge of the truss. It's the old story though. if you leave them alone they are quite harmless. I only wanted to relocate this one because it was headed under our house and there are lots of chemicals and garden products stored under there. Regards, Mark
I recently made the axa version, scaled down a bit, and it works great. I can't see how yours is going off track though, unless it's not sitting vertical in the holder. Don't stress about your tool height setting tool, mine has got an indicator built in. It's over the top but it works for me 😂
Thanks, I have some ideas now to make some improvements, or at least some things that can be tested to eliminate them as suspects! An indicator on your tool height setter? You're my kind of man...😁 Regards, Mark
I immediately started to question if the tool holder was rotating at the flexure. So I am in agreement with your diagnosis. I would eliminate the space as you described. However, it could rotate the other direction after that correction?
Hi Mark I would say with all the metal been removed, the blade is only hanging on about a 1/4 of the up right. making the up right to twist because of the gap behind . Good luck dude
Does the slot match the T or angle profile of the blade? If your washer clamp is pushing the narrow bottom of the blade over against the flat slot, then your blade will be tilted slightly and will tend to steer itself through the cut.
See my pinned comment I have just added. It outlines some things that I didn't mention in the original video and what I have tried since. Regards, Mark
G’Day Preso, at this stage I see the majority of comments suggesting a slight vertical tilt in the parting blade. I tend to agree with that suspicion because the cut drifted in the same direction in each sample. 👍
I need to do a lot more testing but I kind of got discouraged and I was running out of time to get the video under 30 minutes. I will revisit this subject though. Regards, Mark
Hi Mark, firstly thanks for the shout out in your video. Note that the email I sent you today was sent before I watched your video, so now I have more insight in the tool you built. 1) I don't think the gap that you have between the tool holder and the part holding the blade has anything to do with the issue. When I built my tool I had to mill some off the tool holder as it was sticking out more than the blade holder. Having a gap there is fine and the design from Mark does not rely on those surfaces touching. 2) Although you have a similar blade clamping system that Mark has, I wonder if there is some flex occurring from the single bolt clamp? If you discover that that is the case you could try adopting a twin bolt clamping method like on my tool. I only did mine like that because I'm using a different blade, but I'm sure it adds a lot more clamping pressure and support for the blade. 3) I see you tested with some 32mm round stock and the blade stick out was 25mm. 25mm is not a lot of stick out but in your testing you could try choking up the stick out a bit. I just measured the stick out on my parting tool and it is 16-17mm. I was parting a 25mm piece at the time. Perhaps reducing the stick out to 20mm may help? If it does, then that could be more evidence of blade flex and where to focus on troubleshooting. I hope these suggestions help in your testing.
Thanks Jon. I haven't given up yet but this project has had to go on the back burner for a while. I take your point about the blade clamp and that is something I want to try. I did shift the existing blade clamp to the top and front of the blade groove but it was still cutting out of square, although now it cuts the concave the opposite way. Regards, Mark
It's really clear, the tool was designed for the northern hemisphere. For ideal cutting, you need to turn the tool upside down and rotate it two times 180 degrees, counterclockwise.
Did you say the blade is slightly tapered under the top shape in the area you clamp it? If you clamp that on to a vertical face, might the groove running down the top be introduced to the metal in a way that has a tendency to cut to one side. Maybe a longer clamp to replace the washer would stiffen it.
There is some taper towards the bottom of the blade. My rear parting tool is similar though and it tracks very straight. I probably need to redesign the clamp to impinge on the top, wider section of the blade. Regards, Mark
Hey Mark, can you look at a couple of things: 1. is there relief for the wider cutting top surface, if not the cutting blade will have a twist when looking from the front - this may be the cause of blade deflection and cupping of the parted surface. 2. go to the next higher spindle speed.... the issue seems to start at 1/2 way through the cut.... indicating insufficient surface speed at the cut. Good luck sorting it out.
I did add a relief for the thicker top section of the blade. I did not try a different cutting speed though. That's something that is going on the list of things to try. Regards, Mark
It's square. However I have used parting blades with an angular grind so that you can control which part is left with a clean face and they don't go off track as much as this one does. Regards, Mark
It's likely, but the amount that it is tracking off line still seems excessive. It's probably one of those cases where there are several contributing factors and you need to eliminate them one at a time. I am going to run out of material doing test cuts! Regards, Mark
I have one of those blades but set in a rigid holder and at an angle of , if i remember right, about 5-7 of top rake. It works beautifully and i never saw the logic of having a flexing holder, and suspect they are thought to work better than rigid because the owners have more confidence and keep a constant pressure in the cut, rather than timidly pussyfooting about.😉
Same here. I gave my flexible holder away and bought the Aloris AXA holder with the 7 degree top rake. It works beautifully. Better than the flexible one.
It took me a long time to trust using power feed when parting off. It seems kind of counterintuitive but the theoretical geometry of the spring parting holder does work in simulation. However there are all sorts of other factors at play, like flexing at the various interfaces from the bed right up to the tip of the tool and the flexing action may not be able to cancel out those other factors. To be fair, there was no hint of chatter during the cut. At first it seemed to be a completely trouble free cut. Regards, Mark
@@Preso58 I should clarify, I know the tool comes out of contact, but if you continue the cut you end up with a negative rake tool, or a sudden extra deep feed when it tries to lift.. Working out how stiff the flexure should be for best results could be a long process, as Winky found out.
I do have drawings but I am unwilling to share them due to the issues I am having with my version of the build. See the pinned comment above which summarises what I have done to try to resolve it. If you check Winky's Workshop channel he has some drawings of the AXA version which you can download. Regards, Mark
Could your revised clamping washer be over-constraining the tool and causing the side of the tool to cup? Would that give you two springs and harmonics causing the tip to swim in the cut?
I am going to eliminate the gap at the back of the tool mounting plate first and see how that goes, then I will change the tool clamping washer to bear on the top of the blade. If that doesn't work I will have to use a clamping system like I use on my rear parting tool. It squeezes the blade between the top and bottom edge and it works fine. Regards, Mark
I am going to try clamping the blade from the top on the thicker section of the tee profile. There is a relief for this part of the blade so it should give a more positive clamping action. Regards, Mark
I don't know much about machining, but is the blade perpendicular, or is it at an angle due to the taper? This, I would think, would tend to steer the blade.
There is a relief for the top, thicker section of the tee, but there is almost certainly some vertical misalignment but I would have thought it was not nearly enough to produce the deflection I was seeing. Regards, Mark
You say that you are locking the saddle, but are you locking the top slide as well? Any backlash in the top slide lead screw will allow lateral movement of the parting blade. But apart from that the design of the holder allows for a lot of flexibility in the side to side position of the blade as well as in plan rotation of the blade. In other words, the deliberately designed flexibility that is supposed to cause the blade to back out rather than dig in is also making it flexible in just about every other direction. The designed flexibility still has to overcome any tendency for the top slide to roll towards the workpiece with any increase in the cutting load. It's hard to beat a rear tool post for parting on a small lathe. Cheers
I cannot lock my compound slide easily but the inverted Eccentric Engineering parting blade that I have doesn't have a problem when mounted in the BXA mount on the front tool post. I am puzzled! Regards, Mark
It is not clear what the profile of the tool slot is but I suspect with a simple flat surface you have introduced a vertical cant to the blade. In commercial items it is common for the blade seat to have a V shaped groove with the intension to keep the blade vertically aligned. I also believe you would benefit from using a thicker spring plate and not solely relying on bolted connections. A monoblock design which incorporated the spring joint and toolpost clamping dovetail would seem to be the most compact and rigid solution.
I did machine a clearance slot at the top of the blade pocket for the thicker part of the tee profile. If the top cutting edge is tilted it would be very minor which wouldn't seem to account for the amount of flexing that the blade is exhibiting. I do know that those people who own one of the olde worlde forged spring parting tool holders swear by them. It's a bit strange that mine seems to be the only one that isn't playing ball our of the three or so others that have been made. I haven't given up yet though. I just ran out of time in the video to find a solution. Regards, Mark
It's possible that is a factor but the amount that it tracks sideways seem to be way out of proportion to what is probably only a few arc seconds of angle. Regards, Mark
Hey Mark, what if you put a dti at the opposite end of the parting blade to see if the holder is flexing? The dti will show the movement very easily than if you put it on the holder itself.
I am going to do a lot more testing with the DTI. I just sort of ran out of time on the current video and I was not really expecting it to behave the way it did. Regards, Mark
Preso, have you ever checked the spindle bearing pre-load on your lathe? It's a decent sized lathe and it's surprising you suffer with chatter to this extent. On my little South Bend lathe utilizing early 1900's technology, an oiled fibre washer was used to help control end thrust but I quickly replaced it with a needle bearing setup and parting-off became much more predictable. Was the rear tool post a success? I added a T-Slotted cross slide to my lathe last year, so adding a rear tool post is easy enough although I'm not sure if it's worth the bother. Did you find it gets in the way of normal lathe operations?
The Colchester Student lathes use a very sophisticated Gamet bearing system and after tearing down the lathe for the first time (I have done it twice) I did not add sufficient preload on the spindle bearings and I was getting terrible finishes on my facing cuts. I subsequently tightened up the rear lock ring and this improved things out of sight. However I cannot find any factory instructions on how to accurately set the preload to factory specs. Most of the forums just suggest tightening the rear lock ring until the headstock bearings feel warm after a machining session. It all sounds very subjective but putting an indicator on the end of the spindle and trying to move it produces no measurable result with the metrology I have. Regards, Mark
@@Preso58 Ahh yes, forgot the Colchester's used those in-house Gamet bearings. Probably best not to screw with the bearing pre-set too much on basically unobtainable bearings especially if the finish looks good.
Very informative as always Mark. I suspect the clamping button is either putting the parting blade at a slight cant and/or allowing the parting blade to twist slightly about the clamping point Could you analyze that in Autodesk Inventor?
I must say I don't have the expertise to fully analyse the data that Inventor provides in the stress simulations. My observations are very rudimentary in that environment. I am going to look harder at the blade clamping system though. Regards, Mark
I did add a relief for the thicker section at the top of the tee. I need to do some inspection on the way the blade is clamped but if it is tilted it must be very very minor. Regards, Mark
@@Preso58 I would think that if it is tilted that the cutting forces would have a lateral component in the blade's weaker plane. Not a machinist, just a nerd into vectors ;-)
There may be some tilt in the blade but it has to be very minor. I added a relief for the thicker section of the top of the "tee" I doubt if I could even measure how much tilt there was. Regards, Mark
Did you relieve the groove for the thick part of the blade? I always put a shim under the thin side to prevent it from cocking. which helps keep cuts square and not binding. I don't usually have any issues with parting but its still a interesting concept and project. Thanks for the video!
I did add a relief for the thicker part of the tee section. If it is tilted it must be very minor. The amount of flexing seems to be out of all proportion to the way the blade is clamped. Regards, Mark
Nice effort Preso. Are you sure your cross slide is exactly perpendicular? Loose gibs in the cross and/or top slide? I'm sure you will find the cause. 👍
It could be a bit worn. It's an old lathe but I don't have the same issue with the either of my inverted parting tools. It's still a mystery but I need to do some more tests. Regards, Mark
I checked that first. It's the factory grind and it is square. I could grind it progressively off square to find a suitable angle but that seems like introducing one error to control another. Regards, Mark
I checked that first. It is square. I have used parting blades with an angular grind on the end of the blade (so as to ensure that one face or the other is finished without a centre pip) and they don't track off line as much as this setup. Regards, Mark
It might have been fun to use a conventional parting tool and mount just so you can demonstrate the problem that this "loose" holder is supposed to solve.
I must say that my rear parting tool holder is sort of the gold standard for me. It rarely gives any trouble but I wanted to try this style of tool just as a comparison. Regards, Mark
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Thanks to all those interested viewers that made suggestions on how to overcome the out of square issues I am having with this toolholder. Rather than answer each comment individually, I thought it would be better to summarise answers to the most common suggestions and what I have tried so far.
1. There is a relief groove machined into the pocket that aligns and supports the blade. The relief groove accounts for the thicker part of the tee section and allows the blade to sit *Almost* vertical. Due to a very slight taper in the grind, the blade is likely a few arc seconds of a degree out of vertical but I cannot measure it and it seems unlikely that this would account for the amount of out of square I am getting on the cut.
2. The cutting edge of the blade had the factory original grind on it and it was sharp and not chipped. I did recently regrind it and I checked it with a good light and an engineers square and as far as I can tell it's square.
3. Since publishing this video I have tried different speeds and feeds, so far with no improvement on the original test cuts I made.
4. I machined the overhang off the top mounting block so that now there is a continuous surface from the top support block down to the face of the BXA tool holder. This eliminated the gap between the blade holder and the face of the BXA tool holder. This did not make any difference.
5. I changed the position of the blade clamping washer so that now it grips on the thicker part of the blade (the wider part of the tee section) and I moved it as far forward as I could on the blade clamping plate. This did make a difference but now the face of the stock closest to the chuck is convex instead of concave!
6. On all the new tests the carriage was locked and I checked the alignment of the blade with an indicator. It is dead square to the axis of the lathe.
7. An indicator on the side of the blade during a cut shows that the blade is flexing sideways enough to cause the issue but I don't know what is initiating the sideways movement.
8. I hate to admit defeat and I seem to be the only one who has made one of these tools that seems to be having a problem. The only other thing which I haven't tried yet is to grind the top edge of the blade flat, removing the shallow half round groove from the top surface. It seems unlikely that this will make a difference but other than some fundamental physics thing that might be going on with the flexure in the blade mounting plate, I don't know what else to try.
Finally, I have two other parting systems on my lathe that work fine so it's not like I have no other options. I just wanted to show that Mark Winquist's design was a good one. If my version is a fail, don't write off his design. His works perfectly. Mine is a dog!
Nice collaboration. Two of the smartest guys on the internet.
I have one of Winky’s sprung parting tools as well and I love it. Cuts perfectly and hasn’t flinched at anything I’ve thrown at it. Very fast and low drama parting. Mine is working flawlessly. Can’t say enough good things about this design.
Quinn, Mark did tell me that he had sent you one of the AXA versions. During the first cut I did with mine I figured that it was doing it's thing perfectly. I was feeling quite smug but then I noticed the amount of taper in the face. It was consistent no matter what I did to eliminate it. I have some ideas to try now though. I was terrified that I would have a catastrophic failure on camera which is kind of why I stopped.
Regards,
Mark
I definitely haven’t encountered any taper. Let me know if you want me to measure anything off mine to see what might work on yours
The idea that the blade holder is twisting makes perfect sense. Time to do some mesurement setups and see what happens.
Thanks for posting this Mark.
I have also used this style of cut-off blade, on a Maximat Super 11 and BXA toolpost.
I don't see whether you have compensated for the taper section of the blade, to ensure the vertical centerline stands truly vertical. If not, the cup shape of the cutting edge engages unequally, causing the blade to deflect. This leads to the convex cut that you are getting, and might jam up the swarf curls.
In short: They can work well but are critical in: 1. Ensuring the (resharpening) grind of the cutting edge is perfectly square to the blade and 2. Clamping the blade truly vertical, e.g. by shimming the lower edge under the clamping screw.
My penny's worth, lol.
I now always gravitate towards my 2mm insert in springsteel blade.
I agree. My rear parting tool holder gives me almost no issues and I was worried about making a tool that had so many variables. I did include a relief for the top thicker tee section and the centre line of the blade should be very close to vertical. The amount of sideways deflection seems excessive and of all the other parting tools that I have used, this is the first time I have seen one behave like this. To be fair, it produced very little chatter and the chips came out mostly uniform in shape and size.
I clearly need to do a lot more experimenting.
Regards,
Mark
You say you releaved for the taper but how acurately, an inaccuracy here would surely cause a side force
A collaboration between my favorite two “Mark’s” on TH-cam is a great idea. Thanks for sharing with us!
I believe if you tested the blade vertically you will find that it’s slightly tilted to the left. The washer you made is pressed against the tapered surface of the blade. It’s not a huge difference, but tapered non the less.
That’s what I think is your trouble to put it simply.
Great work as always Mark. Enjoyed the conversation.
Thanks. I am sure the way I have clamped the blade has some effect but my rear parting blade has a similar geometry and it tracks straight. The rear toolpost has a different clamping system but it is probably still a bit off vertical. I have a lot more testing to do but I got a bit discouraged and I needed to end the video. I will revisit this.
Regards,
Mark
@@Preso58ypu mentioned that there was a slight gap at the back of the tool. Could the combination of that gap with an off vertical cutting edge be causing the blade to cant when the holder flexes?
Right on 👍🏻. I, myself, like your centering tool. Cheers
Thanks. It works for me!
Regards,
Mark
Well happy days Preso 🎉 great bit of kit for the smaller lathe, Winky is a great guy too, thanks for sharing
Thanks for that. I have received your stickers and I am looking for a video to add them to my door. I have two videos almost finished so I will see if I can squeeze it into the next one.
Regards,
Mark
Good Show Mate: As per normal. Glad to see collaboration between two of my favorite TH-camrs. I have to like Winky's stuff. We are both reformed printers. You have to be a Jack of All trades in that business. Dead lines and broken machines are normal. Fixing stuff all the time. I have turned many parts for presses and folders and binding machines. Just a fact of life.
Thanks. I have been discussing Mark's work in the printing industry with him. I did study a bit about it during my teacher training and it has always fascinated me. Such big and powerful machinery at work in that trade. On a recent holiday in New Zealand we came across a newspaper printing shop in Greymouth on the west coast of the South Island. The entire front of the two storey building was glass and you could look in off the street and see all the workings on display. Unfortunately it wasn't operating when we were there though.
Regards,
Mark
Always love the endings Mark. I think your analysis about it needing to be supported by the holder is correct. I think that will help a little.
Thanks, that is the first thing I am going to try.
Regards,
Mark
Thanks Mark for demonstrating the issue. I’m certain you will discover the slight design issue and resolve it. 👍😎👍
I suspect that the curvature cutting issue is cause by the flexure being offset from the centerline of the parting blade. This is likely allowing the paring blade holder to twist when loaded.
I was seeing that in the CAD analysis but out of three other similar toolholders that have been made to Mark's design, mine is the only one giving this result. I sort of suspect the gap behind the tool holding plate and I will eliminate that first to see if it's a culprit.
Regards,
Mark
Very interesting. That looks like a handy tool. Nice work
I've watched all 3 of the builds now, they certainly seem to work well, most of the time.
Yes, there is something fundamentally different about my version. I believe Mark Winquist sent an AXA version to Blondihacks and she reported that hers worked fine.
Regards,
Mark
I’ve found with the 3/32” blade it flexes vertical and horizontally and twists in the holder, especially when cutting over 3/4” dia. stock.
Shimming the blade to support both the tapered and ‘T’ style profiles improves the ‘squareness’ of the cuts but never quite matches a thicker blades at all diameters.
A fresh sharpening improves the cut most times but not consistently.
Many broken blades from HSS/cobalt blades to insert styles, in several different holders, in various steel alloys and non ferrous materials and coolant/ lubrication efforts.
I have watched the sprung style holders with interest but do not have one, yet.
The gods do not smile on my sacrifices.
Just my observations and I share your frustrations.
Take care n play safe.
I like your tool height set.... I will build one for myself.
Great! It works for me.
Regards,
Mark
Hi, Mark. Great video as always. The design you just built is remarkably similar to a toolpost-mounted lathe dynamometer that I fabricated years ago when I was in engineering school. It used a dial indicator attached to the top rear of the flexure component and the plunger set to bear on the back of the movable part. It was calibrated by weights suspended on the business end of the tool. From my work back then I can offer that the dished profile on your workpiece is likely because the cutoff tool is cantilevered on the headstock side of the flexure element. In use this will create torsion as well as the expected downward tool deflection. If you model this viewing from the top you may be able to observe it to a degree. As you use power infeed the forces can become higher as you approach the centerline of the workpiece so the effect may be most noticeable as you go inward. Cheers.
My suspicion is that you’re right about the side to side flex because of the clearance. The front to back section of the holder is enough to allow the blade to flex vertically and it looks to be even smaller in the side to side dimension. I look forward to seeing the solution because while my lathe is actually very good at parting I’m very reluctant to use power feed to do it and it sometimes gets tedious feeding the tool manually if I have a lot of parting to do.
My thinking is the tool blade is tapered, so when you tighten the lower clamp onto the blade the upper cutting surface is higher on the side closest to the tool holder and the side closest to the chuck is lower. When you set centre height the edge closet to the tool holder will be on centre and the edge closest to the chuck will be lower. When the tool is cutting this impart a turning force into the blade toward the chuck, pushing the blade further into the work piece. As the diameter gets smaller the effective speed of material past the cutter lowers, so the force goes up, making the blade push into the work more. I also think the point of deflection is the edge of the drilled hole because in order for it to flex there must be no material to compress. If you want it to flex around the point you indicated, extending the slot through the hole would do that.
Thanks. I had wondered about the thinning towards the bottom of the blade and that will be a factor. The amount of sideways deflection seems to be excessive though. My rear toolpost has a similar but smaller cross section blade and doesn't have anywhere near the same amount of deflection.
Regards,
Mark
It is definitely twisting. The blade is located sideways from the holder and the blade itself is quite thin. The flexure also does not add rigidity.
16:55 also shows the load is located on one side of the blade
Great job Mark, don’t give up there is an answer there somewhere
I think that the issue is the gap that you mentioned. As more force is applied to the blade, the holder is flexing as it should, however, since there is a gap between the blade and QCTP, the blade holder is allowed to over flex causing the blade to slightly twist inward. I really don't know what the issue is, but it makes sense to me clear as mud 😅
I am going to eliminate that gap. It will at least rule it out as a cause.
Regards,
Mark
We had a commercial cutting tool holder that had a Simler relief and it would do the same thing. Our machinist had experience with Simler and the same thing had happened. He brazed the relief cut up and it would cut Strate every time.
See my pinned comment at the top of this video for what I have learned since publishing this video. I suspect that there is something strange going on with the blade spring design on my version but two other people with the same design that Winky came up with report that there's work perfectly. It's a mystery so far.
Regards,
Mark
My two cents is there is some flex happening (obviously). I see two points of attachment at the top of the blade holder and the rest is flopping in the wind so to speak. If you shimmed the space it might stop flexing. I have given up on those "T" blades. Your rear parting tool holder and the accompanying procedure is the best I've seen. However there is no room on my Rockwell late to use one. Thanks for the video and the tests. You'll get it right! Loved Mr. Snake!
it is because you have a side tilt in your blade so that the cutting edge is not parallel to the centerline of the work.
yes, the blade is not perpendicular to the work because of the taper towards the bottom of the blade, side clamp means the blade leans into the work on the chuck side
See my pinned comment which I have added since publishing this video. It outlines what I probably didn't mention in the video and what I have tried since then.
Regards,
Mark
Parting off is the one job I hate doing. Like you I also seem to get the best results using my rear tool post. Over the years I’ve made two tool height gauges similar to yours. I do prefer the one I made from a Hemingway Kit. So easy to use. Didn’t like the way that snake was looking at you. I guess it was wondering how it could get you in it’s belly 😅 Cheers Nobby
Thanks Nobby. This tool really has me stumped. See the pinned comment for what I have tried since publishing this video. It's still not right and I do at least have the rear parting tool which works fine.
Regards,
Mark
Fascinating video and problem. I'm very interested in seeing the resolution or explanation if it can be discovered. Such a mystery for such a seemingly simple tool, fascinating. From half a world away my view of Australia is that of an entire continent of strange, very strange, wildlife. Non-venomous? Fine, still creeps me out.
Thanks. We see a lot of those big carpet pythons. We have had one living in our roof for many years. It only comes out to moult and I am guessing it lives on frogs and mice. I was doing some work in the roof space one day and was kneeling on the roof truss when it slithered by my hand in the gap between the insulating batts and the edge of the truss. It's the old story though. if you leave them alone they are quite harmless. I only wanted to relocate this one because it was headed under our house and there are lots of chemicals and garden products stored under there.
Regards,
Mark
The parting blade is a triangle and your locking ring is bowing/bending the blade. Just my thougs off the problem. Thanks for the video!
I recently made the axa version, scaled down a bit, and it works great. I can't see how yours is going off track though, unless it's not sitting vertical in the holder. Don't stress about your tool height setting tool, mine has got an indicator built in. It's over the top but it works for me 😂
Thanks, I have some ideas now to make some improvements, or at least some things that can be tested to eliminate them as suspects! An indicator on your tool height setter? You're my kind of man...😁
Regards,
Mark
I immediately started to question if the tool holder was rotating at the flexure. So I am in agreement with your diagnosis. I would eliminate the space as you described. However, it could rotate the other direction after that correction?
Hi Mark I would say with all the metal been removed, the blade is only hanging on about a 1/4 of the up right. making the up right to twist because of the gap behind .
Good luck dude
Outstanding inventiveness.
But not yet a substitute.
Does the slot match the T or angle profile of the blade? If your washer clamp is pushing the narrow bottom of the blade over against the flat slot, then your blade will be tilted slightly and will tend to steer itself through the cut.
See my pinned comment I have just added. It outlines some things that I didn't mention in the original video and what I have tried since.
Regards,
Mark
G’Day Preso, at this stage I see the majority of comments suggesting a slight vertical tilt in the parting blade. I tend to agree with that suspicion because the cut drifted in the same direction in each sample. 👍
I need to do a lot more testing but I kind of got discouraged and I was running out of time to get the video under 30 minutes. I will revisit this subject though.
Regards,
Mark
Hi Mark, firstly thanks for the shout out in your video. Note that the email I sent you today was sent before I watched your video, so now I have more insight in the tool you built.
1) I don't think the gap that you have between the tool holder and the part holding the blade has anything to do with the issue. When I built my tool I had to mill some off the tool holder as it was sticking out more than the blade holder. Having a gap there is fine and the design from Mark does not rely on those surfaces touching.
2) Although you have a similar blade clamping system that Mark has, I wonder if there is some flex occurring from the single bolt clamp? If you discover that that is the case you could try adopting a twin bolt clamping method like on my tool. I only did mine like that because I'm using a different blade, but I'm sure it adds a lot more clamping pressure and support for the blade.
3) I see you tested with some 32mm round stock and the blade stick out was 25mm. 25mm is not a lot of stick out but in your testing you could try choking up the stick out a bit. I just measured the stick out on my parting tool and it is 16-17mm. I was parting a 25mm piece at the time. Perhaps reducing the stick out to 20mm may help? If it does, then that could be more evidence of blade flex and where to focus on troubleshooting.
I hope these suggestions help in your testing.
Thanks Jon. I haven't given up yet but this project has had to go on the back burner for a while. I take your point about the blade clamp and that is something I want to try. I did shift the existing blade clamp to the top and front of the blade groove but it was still cutting out of square, although now it cuts the concave the opposite way.
Regards,
Mark
Is there an Australian drape snake to match the carpet? hehehhe. Love your videos as always. Thank you, from Qc, Canada!
It's really clear, the tool was designed for the northern hemisphere. For ideal cutting, you need to turn the tool upside down and rotate it two times 180 degrees, counterclockwise.
If only it was that simple! 😁
Regards,
Mark
Did you say the blade is slightly tapered under the top shape in the area you clamp it? If you clamp that on to a vertical face, might the groove running down the top be introduced to the metal in a way that has a tendency to cut to one side. Maybe a longer clamp to replace the washer would stiffen it.
There is some taper towards the bottom of the blade. My rear parting tool is similar though and it tracks very straight. I probably need to redesign the clamp to impinge on the top, wider section of the blade.
Regards,
Mark
Hey Mark, can you look at a couple of things:
1. is there relief for the wider cutting top surface, if not the cutting blade will have a twist when looking from the front - this may be the cause of blade deflection and cupping of the parted surface.
2. go to the next higher spindle speed.... the issue seems to start at 1/2 way through the cut.... indicating insufficient surface speed at the cut.
Good luck sorting it out.
I did add a relief for the thicker top section of the blade. I did not try a different cutting speed though. That's something that is going on the list of things to try.
Regards,
Mark
Is the leading edge of the blade square or angled ?
It's square. However I have used parting blades with an angular grind so that you can control which part is left with a clean face and they don't go off track as much as this one does.
Regards,
Mark
Hi Mark, is it possible that tool is leaning to the left because it's thinner at the bottom causing it to pull towards the chuck as it is cutting ?
It's likely, but the amount that it is tracking off line still seems excessive. It's probably one of those cases where there are several contributing factors and you need to eliminate them one at a time. I am going to run out of material doing test cuts!
Regards,
Mark
What about makeing a bigger clamp disk. Is the cutting too twisting?
I have one of those blades but set in a rigid holder and at an angle of , if i remember right, about 5-7 of top rake. It works beautifully and i never saw the logic of having a flexing holder, and suspect they are thought to work better than rigid because the owners have more confidence and keep a constant pressure in the cut, rather than timidly pussyfooting about.😉
Same here. I gave my flexible holder away and bought the Aloris AXA holder with the 7 degree top rake. It works beautifully. Better than the flexible one.
It took me a long time to trust using power feed when parting off. It seems kind of counterintuitive but the theoretical geometry of the spring parting holder does work in simulation. However there are all sorts of other factors at play, like flexing at the various interfaces from the bed right up to the tip of the tool and the flexing action may not be able to cancel out those other factors. To be fair, there was no hint of chatter during the cut. At first it seemed to be a completely trouble free cut.
Regards,
Mark
@@Preso58 I should clarify, I know the tool comes out of contact, but if you continue the cut you end up with a negative rake tool, or a sudden extra deep feed when it tries to lift..
Working out how stiff the flexure should be for best results could be a long process, as Winky found out.
Hi Mark will there be drawings available for this build. What a great project looking forward to the build.
I do have drawings but I am unwilling to share them due to the issues I am having with my version of the build. See the pinned comment above which summarises what I have done to try to resolve it. If you check Winky's Workshop channel he has some drawings of the AXA version which you can download.
Regards,
Mark
Maybe a clamp for the top of the blade as well? Thanks for sharing.
Could your revised clamping washer be over-constraining the tool and causing the side of the tool to cup? Would that give you two springs and harmonics causing the tip to swim in the cut?
I am going to eliminate the gap at the back of the tool mounting plate first and see how that goes, then I will change the tool clamping washer to bear on the top of the blade. If that doesn't work I will have to use a clamping system like I use on my rear parting tool. It squeezes the blade between the top and bottom edge and it works fine.
Regards,
Mark
Would a bigger clamping button help, clamping the tool nearer the cutting surface rather than half way down which may allow the blade to flex?
I am going to try clamping the blade from the top on the thicker section of the tee profile. There is a relief for this part of the blade so it should give a more positive clamping action.
Regards,
Mark
If the blade is tapered top to bottom does that mean it has a small amount of 'tilt' on its side?
I don't know much about machining, but is the blade perpendicular, or is it at an angle due to the taper? This, I would think, would tend to steer the blade.
This. Exactly.
There is a relief for the top, thicker section of the tee, but there is almost certainly some vertical misalignment but I would have thought it was not nearly enough to produce the deflection I was seeing.
Regards,
Mark
You say that you are locking the saddle, but are you locking the top slide as well? Any backlash in the top slide lead screw will allow lateral movement of the parting blade. But apart from that the design of the holder allows for a lot of flexibility in the side to side position of the blade as well as in plan rotation of the blade. In other words, the deliberately designed flexibility that is supposed to cause the blade to back out rather than dig in is also making it flexible in just about every other direction. The designed flexibility still has to overcome any tendency for the top slide to roll towards the workpiece with any increase in the cutting load. It's hard to beat a rear tool post for parting on a small lathe. Cheers
I cannot lock my compound slide easily but the inverted Eccentric Engineering parting blade that I have doesn't have a problem when mounted in the BXA mount on the front tool post. I am puzzled!
Regards,
Mark
An indicator would show you twisting during the cut.
I do need to do that but I sort of ran out of time to do more testing in this video. I will do a follow up.
Regards,
Mark
It is not clear what the profile of the tool slot is but I suspect with a simple flat surface you have introduced a vertical cant to the blade. In commercial items it is common for the blade seat to have a V shaped groove with the intension to keep the blade vertically aligned. I also believe you would benefit from using a thicker spring plate and not solely relying on bolted connections. A monoblock design which incorporated the spring joint and toolpost clamping dovetail would seem to be the most compact and rigid solution.
I did machine a clearance slot at the top of the blade pocket for the thicker part of the tee profile. If the top cutting edge is tilted it would be very minor which wouldn't seem to account for the amount of flexing that the blade is exhibiting.
I do know that those people who own one of the olde worlde forged spring parting tool holders swear by them. It's a bit strange that mine seems to be the only one that isn't playing ball our of the three or so others that have been made.
I haven't given up yet though. I just ran out of time in the video to find a solution.
Regards,
Mark
Button holding the blade forcing a cant on it presenting the cutting edge at an angle to the part.......................is my guess
Isn't the cutting blade canted left by half the taper width in the blade? Maybe that is forcing it to flex?
It's possible that is a factor but the amount that it tracks sideways seem to be way out of proportion to what is probably only a few arc seconds of angle.
Regards,
Mark
Hey Mark, what if you put a dti at the opposite end of the parting blade to see if the holder is flexing? The dti will show the movement very easily than if you put it on the holder itself.
I am going to do a lot more testing with the DTI. I just sort of ran out of time on the current video and I was not really expecting it to behave the way it did.
Regards,
Mark
Preso, have you ever checked the spindle bearing pre-load on your lathe? It's a decent sized lathe and it's surprising you suffer with chatter to this extent. On my little South Bend lathe utilizing early 1900's technology, an oiled fibre washer was used to help control end thrust but I quickly replaced it with a needle bearing setup and parting-off became much more predictable.
Was the rear tool post a success? I added a T-Slotted cross slide to my lathe last year, so adding a rear tool post is easy enough although I'm not sure if it's worth the bother. Did you find it gets in the way of normal lathe operations?
The Colchester Student lathes use a very sophisticated Gamet bearing system and after tearing down the lathe for the first time (I have done it twice) I did not add sufficient preload on the spindle bearings and I was getting terrible finishes on my facing cuts. I subsequently tightened up the rear lock ring and this improved things out of sight. However I cannot find any factory instructions on how to accurately set the preload to factory specs. Most of the forums just suggest tightening the rear lock ring until the headstock bearings feel warm after a machining session. It all sounds very subjective but putting an indicator on the end of the spindle and trying to move it produces no measurable result with the metrology I have.
Regards,
Mark
@@Preso58 Ahh yes, forgot the Colchester's used those in-house Gamet bearings. Probably best not to screw with the bearing pre-set too much on basically unobtainable bearings especially if the finish looks good.
Very informative as always Mark. I suspect the clamping button is either putting the parting blade at a slight cant and/or allowing the parting blade to twist slightly about the clamping point Could you analyze that in Autodesk Inventor?
I must say I don't have the expertise to fully analyse the data that Inventor provides in the stress simulations. My observations are very rudimentary in that environment. I am going to look harder at the blade clamping system though.
Regards,
Mark
You mentioned that the blade was tapered (and stepped by the look of it). Is the slot the inverse of this taper?
I did add a relief for the thicker section at the top of the tee. I need to do some inspection on the way the blade is clamped but if it is tilted it must be very very minor.
Regards,
Mark
@@Preso58 I would think that if it is tilted that the cutting forces would have a lateral component in the blade's weaker plane. Not a machinist, just a nerd into vectors ;-)
Mark, could it be because the blade is at an angle because of the blade taper.
There may be some tilt in the blade but it has to be very minor. I added a relief for the thicker section of the top of the "tee" I doubt if I could even measure how much tilt there was.
Regards,
Mark
Did you relieve the groove for the thick part of the blade? I always put a shim under the thin side to prevent it from cocking. which helps keep cuts square and not binding. I don't usually have any issues with parting but its still a interesting concept and project. Thanks for the video!
I did add a relief for the thicker part of the tee section. If it is tilted it must be very minor. The amount of flexing seems to be out of all proportion to the way the blade is clamped.
Regards,
Mark
No one will ever know, except for the many people who watch the video 😆We’ll keep your secret Mark.
Nice effort Preso.
Are you sure your cross slide is exactly perpendicular? Loose gibs in the cross and/or top slide? I'm sure you will find the cause. 👍
It could be a bit worn. It's an old lathe but I don't have the same issue with the either of my inverted parting tools. It's still a mystery but I need to do some more tests.
Regards,
Mark
I think the blade is set a a angle in the holder ie the top of the blade is thicker than the bottom of the blade
See my pinned comment for some further insights.
Regards,
Mark
Check the grind on the tip of the parting blade, maybe it's not square to the blade?
I checked that first. It's the factory grind and it is square. I could grind it progressively off square to find a suitable angle but that seems like introducing one error to control another.
Regards,
Mark
You have an angle cut on the end of the cutoff blade.
I checked that first. It is square. I have used parting blades with an angular grind on the end of the blade (so as to ensure that one face or the other is finished without a centre pip) and they don't track off line as much as this setup.
Regards,
Mark
Try moving your right foot a little to the left. And close your eyes. Works for me.
It might have been fun to use a conventional parting tool and mount just so you can demonstrate the problem that this "loose" holder is supposed to solve.
I must say that my rear parting tool holder is sort of the gold standard for me. It rarely gives any trouble but I wanted to try this style of tool just as a comparison.
Regards,
Mark
The carrage is not moving the tool is bending sideawys
Eppur si muove! Though not likely the planet is the cause of your woes. At least not in an immediate sense...