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- เผยแพร่เมื่อ 14 ส.ค. 2023
- MrCrispin Merchandise available at www.mrcrispinenterprises.com
Instagram: mr_crispin
In this video I regrind a 1970's Pratt Burnerd 3 jaw chuck. The grinding carried out uses a No.44 Dumore Tool Post grinder and an Aluminum Oxide wheel. Discussion topics around chuck grinding and operation are also discussed.
The lathe featured is a Harrison 190
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The "Mr Crispin Jaw Dolly Clamping System" is an inspired work of genius !
The humor in these videos is dryer than a martini. Im here for it.
I don't drink either, but is it drier than port?
I have discussed this multiple times and I believe Robin has talked about it too. Scroll chucks are made with a master key. For best results you need to tighten the master with a torque wrench and then grind. The same torque needs to be applied every time to get the best repeatability because the torque deflects the chuck and jaws.
When you are opening, and closing your chuck you are relying in the accuracy of the scroll to keep the jaws concentric. I believe the level of accuracy you attained is about the best you can expect from a scroll chuck.
Was just about to say the same, the scroll isnt ever going to be perfect and how linear it is depends on its quality of manufacture and if that employee was in a rush to get himself home that day
There will be a different runout at every diameter due to compound inaccuracies in the scroll, worms, and jaw teeth.
Robin renzetti always talks about two things about the chucks he uses. He uses the same tightening position as he ground with and also uses a torque wrench to tighten his chucks. Some food for thought. Enjoyed your work as always.
Thanks
I recall he also mentioned the concentricity will change as the chuck clamps any diameter that is different from one during grinding. The cause of that is imperfections in the grooves in the scroll plate.
MR CRISPIN!
Great to have you back. Hope the absence wasn't a forced one.
Informative, educational , and entertaining as usual. Thank you.
You were missed.
Pleased to be back
Nice video mate just a quick tip for your search for ultimate precision , when i worked as a machinist many years ago we used to mark each chuck so that we used the same chuck key pinion every time.
we were machining to tolerances to the value of a few tenths of a thou ( old school ) so you are on the right track m8 . loved your solution of the jaw dolly clamps pure genius keep up the good work
Thanks
The jaw clamping dowel invention is a brillant idea. Way back when I was being trained I remember our instructor used to always tell us to use all three pinions every time when tightening. To get the work piece more true.
Glad to see you back and the project complete. I was beginning to think you had moved on to other interests. I found the jaw loading discussion particularly helpful.
No don't worry, if I was going to get bored of machining I would have done it by now!
Following the example/advice of other content creators, I have moved my angle grinding operations OUT of the shop to a portable work table to minimize the abrasive filth that gets spread around the shop. I also employ an N-95 mask to minimize the abrasive filth that gets into my respiratory system. Nice job on the tools.
Good to see you again, sir!
All is right with the world, the English Island still exists and Mr. Crispin is back in the shop. God save the King.
you are 100% correct. The scroll wear WILL contribute to runout as well as how much play are in-between the outer surfaces of the jaws. Meaning the non-grooved sides riding in the chuck body. At our company we used to spend a lot of time doing what you do did but soon realized wear plays too much of a factor. Hence we also went the dowel way where we removed the jaws from the chuck and then ground them in a jig. Our dowel jig system held the jaws flat, on their sides but in a circular jig, if you know what I mean.
There's a certain amount of slop in the scroll in the chuck body, and of course the wear on the scroll working surfaces will not be even, so it would depend a lot on where the jaws were located in their travel when they were ground. If you can get a self centering chuck to centre within 2 to 3 thou you're doing well, even if the chuck is unworn. I notice on my old Burnerd 3 jaw one of the scroll gear stations has a punch mark... probably the most accurate spot last time the jaws were ground. Love your little dollies.... must make myself a set... brilliant...
Thanks
I forgot where it says in the machinist manual that chucks can also be used as a vice. 😄
Very fortunate that you had the large ring available, from your brother's automobile. He always has the proper tools. 😊
I'm pleased to see you appear roundly chuffed about being back. Cheers!
Yes it's good to be posting videos
Welcome back Mr Crispin. Fascinating stuff as usual. So, a round file in the tail stock…. No, I’ll not go there. LOL. Learned so much about a lathe chuck during this series. Thanks for sharing and stay well.
From Australia - Great to see you back doing stuff.
Even if you are a Brit 😉
From Britain - Wanker. 😁
The best solution to an old problem that I ever saw.
So happy to see you again. I sure did miss you.
WOW!!!!!! YOU ARE SO METHODICAL, IN YOUR ANALYSIS!! MUCH APPRECIATED!!! BRILLIANT WORK!!! THANKS FOR SHARING!!!
The Mr Crispin Jaw Dolly is a fabulous piece of kit. Thanks for the demonstration. 👍👍😎👍👍
Nice to see you back Mr Crispin, interesting video.👍👍
Thanks
Very, very ingenious. If I was wearing a hat I'd take it off to you
Thanks for sharing. Your thought process is very insightful. It points out to me that a machinist is always dealing with less than perfect tools.
WOW! He can really work fast when he wants to!
In addition to the factors that you have mentioned, realize that grinding only yields concentricity for that one exact jaw diameter. If you change rhe diameter, the jaws are held by an entirely different section of the scroll.
Absolutely Brilliant! You have been sorely missed.
Robin had mentioned, possibly in the same regrinding video, to always using the same key slot to tighten and only using one rather than tightening all 3. Seems you’ve proven the theory. A good one to ponder. Great to see you again!
That's the case with most chucks. Pretty much all good quality chucks I've seen have a pinion marked 0. On my Harrison, using a Pratt chuck made in this century, starting at the pinion marked zero and supporting the part correctly will see most items come in under 20 microns of runout. I swaped ends on a part 145mm diameter and 120mm long earlier and it was 10 microns out just by holding it in place and tightening it down correctly.
Personally I round file 3 jaw chucks that are worn out or keep them for holding round parts on the mill. Pissing about grinding them is not worth it compared to spending £600 on a new chuck, more so when you're earning money with it.
Chuckception pt2 the grinding of the rings continues. Thanks for taking your time to produce these videos they are intresting and very useful
Many years ago, i went through exactly the same processes with exactly the same disappointing results. My conclusion was that it is due to wear in the scroll plate. Making a new scroll plate sounds like an interesting project !!! . Glad to see you back
Yes it does but I think I'll try and get back to that Locomotive instead!
You hooked me with "Do you have bar sag?" 😂😂😂
Good evening Mr Crispin,
And welcome back !
I have given the matter of work-holding concentricity in the three jaw chuck some thought previously, and I offer my thinks . . . .
1. Three jaw chucks from Pratt Burnerd are supplied with matched jaws, having a unique reference number, and I deduce that this is for a reason.
2. The quality standard of accuracy is given in different grades ; the higher accuracy of run-out is obtained with the precision series of chucks, which is reflected in their price . . . .
3. The scroll is a circle of continuously changing radius and more importantly, curvature, whereas the mating teeth on the back of the jaws can only be produced with one curvature. It follows that there can only be one radial position where each tooth curvature matches that of the scroll ; at all other positions, contact is at best at one or two points. When the points are small, loads will induce deflection, which appears as movement of the gripped component away from concentricity.
I perceive that full contact may well occur at different radii for each of the jaws, which might further affect concentricity of components of differing diameter . . . .
This implies that attempts to true up the jaws at one radius may not necessarily produce a similar improvement at all radii ; indeed, it could make some worse . . . .
4. As others have pointed out, age-related wear and tear will increase the “float” in the scroll on its locating spigot, and our concentricity is ultimately dependant on where the scroll positions the jaws, with respect to a fixed point, which is the axis of the spigot. It follows that increasing float will allow the jaws to take up different positions, depending upon which of the key pinions is tightened first, and by how much . . . .
Grinding the jaws will offer no improvement in this instance . . . .
5. Jaws which are “bell-mouthed” are either showing signs of wear in the slides, or have been badly strained at some point in their lives . . . .
It follows that, whilst not doomed to failure, grinding the jaws is not going to restore the chuck to its original manufactured accuracy, but as long as this is borne in mind, it will certainly yield some improvement.
6. Three jaw chucks should be treated as precision items, and kept away from anything other than truly circular or hexagonal bar stock !
My thoughts, but I humbly invite debate !
Kind regards,
Steve A.
Great to see you back, very interesting to see your thought process when you tackle these things, something I will never do but interesting all the same, hope to see you back more regulary
Yes it's been quite an exercise in thinking!
You kept your promise...good man!! Lol Thanks for the new video!!
Adam of Abom79 found with a new six jaw chuck that all three tightening lugs must be used for best concentric for near zero runout. Thanks for your explanations and your wonderful invention. 😊
Astonishing. A wealth of information and an innovative and very well thought out solution.
Thanks
I took a different path after grinding with three bolts and nuts adjusted on opposing jaws on the 45 degree chamfer of the jaws.
Similar results.
Copied John Mills from double boost and machined 5 thou off the backplate spigot and improved it by drilling and tapping 8mm holes on the periphery of the chuck body.
Fitted setscrews and it is a simple method to slightly loosening the backplate screws and adjust with setscrew and retighten the backplate.
Essentially a set tru chuck for precise setup.
I really like the jaw dollies. I have a six jaw that I wasn't looking forward to trying to drill for pins. Stefan Gotteswinter has done a few things about using a single pinion for best accuracy, and that it is mentioned in some chuck documentation and that some top made chucks still have only a single pinion to ensure things.
Well done Crispin, neat little aids, great design. Constant battle with larger chucks, a handful of different thickness shims now you have parallel clamping is advisable, helps you get to near zero quite quickly as usually only one jaw needs correction. I use this method quite often. Cheers, Jon
Cheers John
What a superb idea! For years, I have been mulling over how to put pressure on the jaws so that I could accurately grind them. Voila, the elegant solution.
Our patience has been rewarded!
I hope you had some earplugs in for the angle grinding job, those things are loud!
Mr crispin i see you after long time.
Mr. Crispin, brilliant work. Thanks for another superb job!
In my time as a centre lathe turner in the UK we had two piece jaws that accepted a machinable bolt on top that could be indexed forward or backwards using serrated faces. You would position the jaws to the size of the component and then m/c the jaws very lightly to match. We would still use internal/external rings to eliminate backlash in the scroll. This would eliminate scroll wear and distortion of the scroll caused by previous over tightening. I would suggest that if you used a test piece that matched the clamping position that you used when grinding the result would be a lot better.
The most thorough, yet enjoyable, course on getting a lathe & chuck find common… ground! Grind! oh bother… Anyway, thank you again for taking us along!
P.S. I think Clough42 has met your brother…
Excellent! I had always wondered how accurate one of these old chucks could be (re)made. Per results, 0.0015 appears to be the answer. I find it amazing that the thread in the scroll and the jaws is that repeatable!
Welcome back Mr Crispin, it’s been a while. Thank you for another entertaining and educational video. Have a good one 👍🇦🇺
Always good to see a new video from you. Thanks.
Awesome. Glad to see more content. It's been WAY to long! :) I've been curious about this situation in my shop. Thanks for sharing some great ideas.
Great to see you back Mr C. Thanks for another informative video.
Really nice work and explanations.
Great video, enjoyed your technique and explanations, a great enlightenment on our humble 3 jaw chucks. Cheers Mr. C!
So glad you're back!!! 👍👍👍
You'v been mist
Good to have you back , and its never dull, hope to see you more often.
Mr Crispin, could you tell us about your work at Rolls Royce?
we'd love to hear about what you do there, the types of machines you work with etc.
I'm pleased to see a new video on your channel!
When he said he took his series 2 Land Rover Brake Drum and cut it in two so he could get a ring big enough for preloading while maintaining the original radius, I had the thought: “Ah, He is one of my people 😂” -> Subscription Clicked!
Glad to see you back just wanted to thank you for all the great information 😊
Thanks
What a Bobby-dazzler Mr Crispin, well done.
Thank you my good sir for the brilliance...
welcome back to the videos and great video I actually learned something very interesting. Thank You
It's good to see you back sir
He's alive!!! Glad to see you back MrCrispin. Love your content.
Very well thought out, thank you for this, it has now become part of my machining world view
Yes I like it before viewing it, exactly what i was looking for for years THX
Quite informative, thank you. Love the music.
very helpful info and a very thorough investigation. thank you for taking the time to investigate these phenom. this clears up a lot of questions ive had but didnt know how to analyze.
Nice grinding fixture for the internal preload Mr C. There is another style I have seen recently that worked on the same principle but was built on a large dia ring. Yours is much simpler to make. The outside ring from a brake drum is some good stuff as well. Well done sir
I was taught to always use the same position on the chuck to cut the the jaws with a spider as you do when gripping the part . I have managed to get consistent concentricity of around 0.01mm with this method .
Basically grip the spider using the key in the position where the chuck badge is then once done grip the part using the same chuck position with the badge .
It'll work 👍 24:20
I have at least one chuck with one of the pinions marked with a zero. This is the pinion that should always be used for final tightening of a workpiece and for truing the jaws. The theory I have read regarding this is that the scroll will always be pushed in the same direction against its internal bearing surfaces, there is always some clearance otherwise it would not rotate and this gives consistent closing of those clearances.
@@martinconnelly1473 exactly mate .Over the years we have made lots of sets of bespoke welded up jaws for hundreds of jobs and using this method taught by my old mentor it always worked well 👍
Impressive as usual.
Great idea mate 👍
Fantastic work! Really clever solution with the Jaw Dolly.
another great video - thank you!
Great video Mr Crispin. Brilliant solutions in setting up the chuck for grinding. Glad you showed the final results, as I recently checked my Myford chucks run-outs. Pleased that they are well within the tolerances compared to yours. Glad you're back with your videos. Cheers Nobby
excellent idea. thank you for sharing. best regards.
Fascinating. Educational and entertaining from beginning to end. Thank you sir 👏👏👍😀
Thanks
I found this video quite interesting. I believe that a 3JC with even moderate use will ONLY be true if the scroll and jaws are in the exact position in which the grinding was carried out. Also, the radius ground into the gripping surfaces should, ideally, match the test pin. Additionally, the same torque should be applied to the master pinion. All that said, you achieved VERY good results in my humble opinion. Thanks for sharing.
Thanks
"match the test pin" or larger circumference I would think would do but like my dad always said, reassemble exactly the same order and position it was taken apart, at least it can't be any worse. 😄
There are also carbide grades that are suitable for turning hardened steel. Are also available as indexable inserts in various sizes. It is therefore not always necessary to grind. Even better are plates with CBN (cubic boron nitride), but they are very expensive.
thanks i learnt a lot from an honest man .... 100%
Brilliant information.
I must confess that I just zipped through this video because I already knew the problems you were going to need to address and I wanted to see your solutions. When I came to the part where you realize that concentricity can be lost depending on which pinion you turn to tighten the chuck I thought I should add a comment. I recently retired after a 45 years or so of being a machinist, being self employed for most of those years and I specialized in high precision lathe work, so maybe my comment will have some weight. Anyway, the main problem with using different pinions to tighten the jaws is because the scroll inside the chuck will shift some when the chuck is tightened and the direction it shifts changes depending on which pinion is used to tighten the jaws. The scroll shifts because it must have some clearance to rotate and then it wears over time which only adds to the running clearance. So, to get the best repeatability the same pinion must always be used to grind and then tighten the jaws. In my opinion decent lathe chucks should only have one pinion for tightening. Also, I should say, all of the lathe chucks in my shop are adjustable for concentricity. Except for one that came with an antique lathe that I am restoring. The lathe and chuck were made in 1899 and I'm not sure adjustable 3 jaw chucks were made in 1899.
Cheers,
Eric
Thanks for the info, I think we can agree that a master pinion is the solution for a non adjustable chuck
About time! THANKS and a great video
It is, in fact, your big head that makes your videos so compelling!
Now this is cool . Didn’t think about holding the jaws like that for interior( the firt grind) . I saw a pipe whit 3 slots that use that angle of the jaw for normal pretension. But you’re idea is easier, I will just cut on laser of the profile and weld a pin on it. Tanks .
Thanks for posting this. I ground the jaws of my 3 jaw chuck a while ago and was most disappointed to find that things had apparently not improved. However armed with the knowledge from your post I checked all the tightening positions and one produced a run out a quarter of that of the others. Much grief saved!
👍 brilliant idea with the jaw clamps!
Mr Robyn Rens would say to pick a drive location and stick with it.🙂 The scroll needs to stay biased in same way.
The legend, the hat, the man! in no particular order.
Thanks for your thorough investigation and demonstration of this ... thoroughly complex business! I like your Jaw Dolly Clamping System which deals effectively with the important issue of biasing the preload "parallelism" situation. Resulting in much stronger and truer grip on the workpiece. As to all the other variables, I tend to use a shim on one jaw, or two if required. Beyond that - its back back to the independent 4-jaw!
In any case, good to have you back. See you soon again Mr Crispin!
Good to see you back!
Your results are pretty much what I achieved. The big benefit I got was the jaws before grinding appeared bell mouthed and did not grip short pieces at the tip of jaws. After grinding I had good support at the tips. My machine was essentially new so I suspect the OEM Chinese jaws had never been ground.
Great to see you today
I just saw you for the first time today. My first reaction is how much you and your general presence resembles the guy from Photonic Induction. You must be from the same general region, you have the same charm. Looking forward to following.
Good to have you watching
Great idea on the 3 plates to grind the ID on the chuck jaws. I have found that i always use the same key to open and close it works well ,great presentation
nice and educational work. young man!
also its reassuring that British industry is still producing decent/excellent manual machinists and not just button pushers.
is the scroll the main issue?
Yes probably the wear in the scroll, the jaw teeth, and the general play between all the components
is there a way to regrind the scroll? ive never seen this in any machinists video. it would make an epic project!
come to think about it . repeated tightenings. wear, interrupted cuts, etc would impact the scroll. has anybody anywhere done a vid about regrinding/cutting a chuck scroll? .. why not give it a go?
@@MrCrispinEnterprises
Thoroughly stimulated
MR. Crispin, i've found that a couple of good whacks with a soft blow hammer on the chuck helps move things around on certain parts, but not all. my Chinese 3 jaw has a zero stamped on one of the scrolls, if you use that one to tighten it first it runs pretty true and consistent. if you use ay of the other 2 it has 3 or 4 thou runout.
As below, wear in the location diameters of the scroll is most likely the issue. Turning the pinions imparts a radial load on the scroll as well as a tangential one so any clearance in the scroll will allow the jaws to move. I was always taught to find the truest pinion on any chuck (where the jaws were ground) and just use that one (usually the one adjacent to the nameplate pad on burnerd chucks)
Regrind the insides of the jaws intentionally using one pinion and see how you get on.
Nice video though, glad you're back
Thanks
So, just a little tip, you always use the key hole on the chuck that you tightened when you ground the jaws, that's how I was taught!
Very clever solution to the clamping of the jaws with the jaw dolly!
About bloody time