Tool post grinder - part 2, grinding chuck jaws
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- เผยแพร่เมื่อ 23 มิ.ย. 2022
- I complete my holder for the Bosch die grinder, and use it to correct the bell mouthed jaws on my 3-jaw chuck for the Harrison M300 lathe. This chuck however still has terrible run out, varying at different work piece diameters. So I think that is caused by the scroll having been over-tightened by previous owners.
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Adapt, improvise and overcome. Looks like a fun project.
Love your videos Samuel. On my Harrison when I’m parting I run the parting tool upside down and run the machine in reverse. Works much better cause the chips fall down and don’t get caught up between the blade and stock. I run the auto feed while regularly lubing the blade and it works a treat every time . I’m hoping to build a rear tool post in the future that I can do all my parting on! Keep up the videos Samuel. I look forward to your next one !
Seems the grind takes care of the one issue, but runout will only go away if you can either precisely cut the jaws for two results (grip and concentuality) or if you do as you did, correct the grip, then add or modify your back plate to allow for tru adjust type modification on the 3 jaw. Either case, it sure is nerve wracking when it comes to fixing these issues. Thanks for sharing!
Looks like a good result, when i put a bar in a 3 jaw chuck, I always tap it with a copper hammer to get it as concentric as I can, then fully tighten, I like how you don't edit the mistakes out too! well, another job done!
Looking forward to your next project, I hope you upload a video soon.
I got used to having a weekly update.
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You've really advanced rapidly. Nice job on the grinder. I had a new Dumore tool post grinder which I acquired but sold a few years ago due to only very light need for it. This is a nice option if you must grind. I strongly recommend disassembling and cleaning any chuck or tool holders in use during grinding. I've even used plastic drop cloth and tape to "box off" the grinding area. And a note on worn chucks. They are like chasing a rabbit across four seasons. From worn jaws to worn scrolls to worn slides, there's no stop until the chuck is on the shelf, used for holding milling work ... or perhaps holding the shop door open.
I see Mr Pete has lots of videos on Dunmore toolpost grinders - seem to be a US product. One available on ebay in uk right now but from US with £140 postage! Making a toolpost grinder would be a nice project.
I have a very similar parting tool on my M300. Just check that it's on centre and push harder. Also if you revisit the video (10:37) the second clamp from the end isn't tight. It's dancing wildly about, you are fighting rigidity. I might even tighten the carriage up so that rigidity isn't an issue where I do most of my cutting (near the chuck) and put up with the extra tightness at the tailstock end. Did you have the carriage locked in Z by the way when you were parting?
I used to be terrified of parting anything but case hardened cheesecake but once the tool starts to cut, push harder and keep the cut going. You will feel a sweet spot as far as feed rate is concerned and it's a very satisfying feeling.
There was a huge amount of bell on those jaws and I'd say the chuck has certainly had a long life. It might be worth considering another chuck. I managed to pick up a beautiful Pratt 4 jaw in as new condition from gum tree and it had the camlock backplate on it too.
I like your videos Samuel so please keep them coming.
Thank you for taking your time to produce them.
Topslide and saddle were locked. I think I only did up the first and fourth screws on the tool holder, thinking that with a 20x20mm shank more would make no difference. I must experiment with pushing harder but was frightened of breaking the tool. Probably the bell mouthing caused them to put a cheat bar on the chuck and do it up tighter and tighter, hence deforming the scroll. I actually bought a new Pratt Burnerd super precision chuck, but it isn't as wonderful as I had hoped!
Samuel, if you live anywhere close to Sheffield you are welcome to pop in and borrow a chuck or some tooling to allow you to narrow down and eliminate some of your problems.
I did not expect you would have trouble parting on this lathe. How wide is that insert? Myself I prefer the tool holders with the radial support for the blade, Reduces the depth you can get at large diameters but really improves the blade rigidity. We will have to work on it, I am sure we can do it better than you are doing here
Insert is 3mm wide. Tool cost me £54 and I don't like it - thought it was stronger from the photo. Yes, I think something like iscar "SGTFL 2020-3D 45" might be better, except that that tool only works for workpieces up to 45mm diameter and mine was 75mm. I probably didn't push hard enough, being frightened the tool would break if it dug in. Another problem is that the saddle is a bit loose because I did it up as tight as I could when it was over at the tailstock end of the ways, but then due to the 0.3mm (!) way wear it's loose when near the headstock. If I make it tight near the headstock then I couldn't move the saddle out of the way which one frequently needs to do.
@@samuelfielder my widest insert is 2mm, my insert that handles the largest diameter of 41mm is just 1.6
I work on the basis that there is a limit to the size I want to part off. Anything larger than 41 is handled another way. My manual lathe can handle 160mm, but that does not mean I expect to part off 160!
Wonder if the grinder could be used in a jig to do the ways
Possibly, but only with great difficulty. See Steve Watkins at th-cam.com/video/oQgxtSBXPxw/w-d-xo.html
@@samuelfielder Ive just seen I need 24T gear on the main feed box shaft. Bugger. I'm heading down same road as you and I'm not sure if I should cut my losses
@@jimspencer3072 Well, I don't regard refurbing the feed gearbox as a big problem - as I managed it! If your ways aren't terribly worn, then it may be worth persisting. It's just that fixing the ways is really hard for anyone to do in a home workshop, and doing it commercially costs around £1500.
@@samuelfielder I've almost solved the feed gearbox, the Delrin disks are freed and all marked, photos etc, had a broken pin in helical gear and very badly gunked. Just need to change the 24T and box is very good. Then I'll move to headstock and then saddle. Lead screw is good
My ways dip 0.018" that made me weep
SLOW DOWN WHEN PARTING
Charge on.
Maybe you would of been better dressing the stone in a clocked up 4 Jaw chuck before starting your Jaw dressing....
It might have made the grinding go quicker due to all of the wheel engaging with the workpiece. But because I ran the whole wheel over the full length of the jaws it shouldn't affect the accuracy.
Slow down when tree panning your going to have a nasty accident
Parting tool is at the wrong height. Waste of time grinding chuck jaws, purely and simply due to the fact they will only be accurate at the exact diameter they were ground at. The chuck is worn out, and is pretty much scrap. Never hand feed......the chances of any sort of uniform grinding are greatly reduced.
The purpose of grinding the jaws was to remove the bell mouth, which works at any diameter.
@@samuelfielder Ok, but wonder if a chuck which is not accurate, can ever be of much use? Vertex chucks are well made, and not that costly. Might be worth having a look at?
@@chrisstevens8431 I disagree the chuck is scrap, produced plenty good work in old chucks, if you need accuracy get some soft jaws and bore them
@@jimspencer3072 Scrap, unless you are doing very rough work with something like wood. Many people have the idea that boring a set of soft jaws, will produce totally accurate work. That is the case, but ONLY at the diameter the jaws were bored at.
@@chrisstevens8431 Obviously, you bore the jaws for a certain diameter, in industry any shafts that require precision are always finished on a surface grinder. Screws fit on the flanks not diameters so a little runout is usually OK. Of course for real accurate turning a new late helps but turners learn to compensate for lathe issues. Its nice to have an accurate chuck but it's never stopped me getting a job done.
Junk
Perhaps you could explain that. What is junk? It would also be useful if you could make your comments polite and constructive.