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I may be stupid but

Tightening a 3 jaw chuck.

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Andrew Tinsley24/06/2022 21:14:11
1615 forum posts

Thanks Diogenes,

I did wonder if it might be a TOS chuck. I have a conventional 3 jaw TOS chuck which came with an almost identical box?

However I would expect a TOS chuck to have the manufacturers name on the chuck. I would also doubt that TOS would make such a chuck, unless it was for a very special application.

It seems to be quite well made, I expect it will stay a bit of a mystery.

Regards,

Andrew.

peak424/06/2022 21:39:32
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1787 forum posts
193 photos

I have a feeling that one or more of the Rohm designs has just the one pinion, which might fit with the German writing.
Have a look at the catalogue HERE P3024 (28 of 94 in the pdf) Economy - ZG-ZGU
https://www.roehm.biz/fileadmin/content/pdf/products/en/Lathe_chucks_Independent_chucks_en_web.pdf

It's a bit more obvious in the photo of the 4 jaw SC chuck, that there appears to only be one pinion at the top.
Since it's presumably not labelled on the chucks being discussed here, I wonder if they might be Chinese copies??

Similarly these TOS 4 jaw ones
https://www.shop.santool.de/en/clamping-tools1/chucks-tos/four-jaw-lathe-chucks.html 
Bill

 

 

Edited By peak4 on 24/06/2022 21:41:52

Andrew Tinsley25/06/2022 10:25:38
1615 forum posts

Thanks Peak 4,

As there is no identifier on the chuck, I would think it is probably Chinese. I must make a backplate for it and see if it is any good.

Regards,

Andrew,

Hopper25/06/2022 11:14:07
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6696 forum posts
347 photos
Posted by Andrew Tinsley on 25/06/2022 10:25:38:

Thanks Peak 4,

As there is no identifier on the chuck, I would think it is probably Chinese. I must make a backplate for it and see if it is any good.

Regards,

Andrew,

It might be a bit like those Chinese DTIs that look like a Mitutoyo, come in a Mitutuyo-like orange and white box, but don't actually say Mitutoyo on them, because they are not exactly Mitutoyo. Which doesn't mean they are junk necessarily. Mine has worked satisfactorily in the home shop for years but it's no Mitutoyo to be sure.

SillyOldDuffer25/06/2022 18:22:21
Moderator
8903 forum posts
1999 photos
Posted by Andrew Tinsley on 25/06/2022 10:25:38:

Thanks Peak 4,

As there is no identifier on the chuck, I would think it is probably Chinese. I must make a backplate for it and see if it is any good.

Regards,

Andrew,

Could be from almost anywhere. If it's last century East Germany or the communist bloc is a distinct possibility, but almost every country in the world with any kind of industry once made or is still making chucks, most of them unbranded, ranging from cheap and nasty to first class.

Where it came from is almost irrelevant. Try it and see - if it turns smoothly and holds work firmly with typical 3-jaw run-out, it's a bargain. Otherwise, poor performance speaks for itself.

Dave

Andrew Tinsley25/06/2022 20:13:38
1615 forum posts

Hello Dave,

Despite your theorizing, I would lay a large bet that it is of Chinese origin. I am not really bothered if it is good bad or indifferent. I didn't even realize that it had come with a job lot that I had purchased, so not a loss, if it is a load of junk.

My main interest is its single pinion and why it was made thus and by whom.

Regards,

Andrew.

SillyOldDuffer25/06/2022 20:38:38
Moderator
8903 forum posts
1999 photos

Posted by Andrew Tinsley on 25/06/2022 20:13:38:

...

My main interest is its single pinion and why it was made thus and by whom.

...

Any chance it can be taken apart? It may not be a scroll chuck, perhaps a different mechanism designed to save time because it doesn't need 3 pinions to be tweaked in turn for maximum tightness:

Dave

Andrew Tinsley25/06/2022 21:15:38
1615 forum posts

I didn't bother to strip and clean the single pinion chuck as it appeared to be brand new and still in the manufacturers grease. However I am curious to know more about it, so a strip down is in the offing. I will pass on the results.

Regards,

Andrew.

Steviegtr26/06/2022 01:21:05
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2460 forum posts
341 photos

From a miriad of answers, i have decided to have a go at some measurements to see the difference of tightening 1 keyhole & doing all 3. I guess the best way will be using a torque wrench to make sure each jaw gets the same tension.

The next would be to see the difference to the workpiece, maybe using 2 different diameter pieces to make it fair.

I have already started to take some dims but found my wonderful griptru bernard chuck has moved somewhat since i last set it up. That maybe from a big jamup i had while trying to part some stainless steel. So the 1st thing is to try & get it running true 1st.

I will video all the results & hope it gives a definitive answer once & for all. Although i doubt it will because everyone has a different chuck with different results.

I also need to check my bearing clearances as you all know a Myford has a tapered bush at the chuck end & bearings at the rear. These may also need checking as i noticed that if i pulled on the chuck face i got a slight variation on the DTI. Meaning maybe the bearing clearance needs adjusting since i rebuilt the head.

If you own a Myford or any lathe that has a tapered brass/ bronze front bush. Which many lathes have , will know that you will always have a very slight movement of the chuck, over a lathe with say tapered bearings at each end. Not quite a achilles heal but something to bear in mind.

Steve.

SillyOldDuffer26/06/2022 19:18:53
Moderator
8903 forum posts
1999 photos
Posted by Steviegtr on 26/06/2022 01:21:05:

From a miriad of answers, i have decided to have a go at some measurements to see the difference of tightening 1 keyhole & doing all 3. ...

Steve.

Good idea, experiments are always fun. I suggest there are two possibilities to investigate:

  1. Tightening the pinions one after the other causes one or more jaws to move and alters the job's concentricity.
  2. Tightening the pinions one after the other increases the grip.

The first we can all test by clocking a rod in the chuck, First note how far the needle deviates min to max when the first pinion only is tightened, then same measurement after the other two pinions have been tweaked to take up any slack.

Second is harder, because we have to detect an increased pressure on the workpiece after the second and third pinions are adjusted. I suggest a narrow diameter manometer might be good enough. The apparatus is a steel tube sealed at one end and held in the chuck. The other end is connected by a hose to a clear U-tube, and the whole filled with water dyed red. When the steel tube is squeezed, the water level in the U-tube will register the pressure change by rising. I predict tightening all three pinions will increase the pressure on the tube. The thickness of the steel tube's wall determines the system's sensitivity. Some maths will tell us how much extra pressure, if any, is applied.

pressuresensor.jpg

Dave

 

Edited By SillyOldDuffer on 26/06/2022 19:19:13

Neil Lickfold26/06/2022 20:23:16
892 forum posts
195 photos

We have an old 3jaw chuck at work. If you use 1 key on some bright bar, it will be around 0.15mm to 0.2mm tir. Then tighten first on the jaw by the logo (Pratt) then rotate chuck clockwise(away from you) then just nip onto the next two keys, it will generally be better than 0.02mm. Until I was shown about this, I would not have believed it. It was a great trick to learn of this particular chuck. So it seems that as they wear, different trick can be used and they become individuals as to how they work. The aspect I like about the grip tru series, is that it adjusts the chuck in the plane and the swash of the part remains the same. With old 4jaw chucks, you need 2 indicators to try and get the part running true. Any chuck that is over tightened by holding onto a part that is just using the very front of the jaws, (lost of parts 2nd ops ) don't grip it so tightly. It will last a very long time.

Regular maintenance and cleaning of the scroll and pinions will make them last a lot longer, even on a 4 jaw chuck. Using a vacuum cleaner will also help if cutting things that are dusty and dry.

Andrew Tinsley27/06/2022 11:10:50
1615 forum posts

Hello,

I have just checked out the single pinion chuck. It is a conventional scroll type and 4" diameter. I don't need to make a back plate as it has a Myford thread!

So screwed it onto the lathe and checked it out with a DTI and different diameter silver steel rod. Average run out was 3 thou, so I am MORE than happy with that!!! I still think it is of Chinese manufacture, no identifier, only a couple of numbers. The finish on the scroll looks excellent, but then all the machining looks very good.

Maybe the Myford thread is a clue?

Andrew.

Mike Poole27/06/2022 11:53:51
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Moderator
3383 forum posts
77 photos

I think the runout of a three jaw chuck should not really matter, even if it can be improved by a tightening regime there is nothing you can do if it is out unless you have a griptru chuck. A three jaw chuck is a quick and dirty device to hold a job to be turned at one setting. If further operations are required and concentricity is important then remounting in a collet or 4 jaw independent is required. Working between centres is the best option if the job is suitable. It may be the case that concentricity is not critical so replacing the job in a 3 jaw will not matter but other jobs will require perfect concentricity in which case the three jaw will not be the tool for the job. It may be interesting to explore the performance or a three jaw at various diameters and tightening regimes but unless you are going to clock the job every time it matters then you can never be certain where you are. Even if you establish that a chuck has low runout and repeats accurately you never know when it may have collected an embedded chip in the scroll unless you check every job that is critical.

Mike

Andrew Tinsley27/06/2022 13:00:06
1615 forum posts

Mike,

I am well aware that a 3 jaw scroll chuck is a quick and dirty solution to work holding with any accuracy. I quoted the low run out, because it implies that the chuck was manufactured with more than the usual degree of accuracy. The chuck is unused as far as I can tell, so what it would be like after extensive use, I don't know.

Regards,

Andrew.

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