I may be stupid but

[SteviegtrParticipant @steviegtr]

Posted by Bountyboy on 24/06/2022 06:43:40:

Hi Steve,

I agree with Nigel, you’re not stupid. Anyway I thought you had an Albrecht chuck, the Rolls Royce of keyless chucks. 😀

No Bountyboy i was refering to the main lathe chuck which is a Bernard griptru, that came with the lathe.

[SteviegtrParticipant @steviegtr]

Well from all the feedback here, it would seem a good idea to give each key hole a nip.

Thanks for all the replies to my question.

Steve.

[VicParticipant @vic]

Posted by Mike Poole on 24/06/2022 09:38:15:

Posted by Rex Hanman on 24/06/2022 08:02:16:

If one hole is adequate, why would the manufacturer add others? There must be an advantage other than convenience.

I bet if chucks had a single hole then there would be a thread about what a great idea it would be to have 3 holes so there was always one on top for immediate use. On a larger geared head lathe it could be something of an effort to rotate the chuck, I seem to remember setting one of the gearbox levers to a halfway position to effectively disengage the gearbox when setting up a 4 jaw job.

Mike

Edited By Mike Poole on 24/06/2022 09:44:30

Many wood turning scroll chucks only have two holes. Some use a pinion like an engineering chuck but my two of differing makes don’t have them, the key drives the scroll directly.

[peak4Participant @peak4]

I've not seen any formal manufacturers instructions on conventional 3 jaw chucks, other than for Griptru or similar designs.
These are effectively just a high quality cuck on a separate, but integrated mount for adjusting concentricity.

The Pratt Burnerd instructions give directions for adjusting the chuck body, and then say that any pinion may be used, "when it is not essential to maintain concentricity within the very fine limits mentioned."
https://prattburnerd.com/wp-content/uploads/2022/01/PBI-GRIPTRU-MANUAL.pdf

I read that as, use any pinion, but if you set something up using one, then continue to use that one, if you want repeatability for a given diameter.
I always use the same pinion on each chuck I have, and seem to get the best concentricity.

A drill chuck however seems to benefit in holding power, by using each key hole, but that seems to be about internal friction and holding power, rather than concentricity.

Bill.

[Martin KyteParticipant @martinkyte99762]

As has been said tightening all 3 for Jacobs chucks is the correct proceedure and will result in a lot less ruined drills which have slipped in the chuck. For 3 Jaw lathe chucks I only do this for tapping larger holes especially with BSW threads and even then there is a limit. 3 Jaw lathe chucks have quite a limited holding power.

regards Martin

[not done it yetParticipant @notdoneityet]

I tighten all the way round. But I don’t yank up the first position absolutely tight. I look at from the point of view that less force on each point is better than forcing on a single point on the scroll.

[BazyleParticipant @bazyle]

Owing to the movement of the scroll as mentioned by SOD above you should first do some tests on different diameters to see which jaw to use as teh last one that gives the best concentricity at each diameter and use that when it matters.

If the chuck was previously used by a brainless gorilla then the scroll will be distorted at common diameters like 1", 1/2" etc.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, this argument has been going on for many years, even in industry, with both drill and lathe chucks. My father (who worked for a well known bearing manufacturer) taught me the way he was taught in his apprenticeship, that the correct way was to slightly tighten each of the three holes and then go round again to give each hole a final tighten. When others that I have worked with, just use one hole on a pistol drill chuck and they get a hole that the drill snags in (which was quite often) the drill would stop and the chuck would spin, eventually resulting with chewed drill shanks, I never got that happening, unless I was forced to use a drill that was already chewed up. I have always adopted tightening the chucks the way my father taught at work and at home.

Regards Nick.

[colin hawesParticipant @colinhawes85982]

Most times that I use the three jaw chuck I only tighten it in one place and it is accurate, however, if I have particularly heavy machining to do I have found that if I use all tree key holes the job is held more firmly. Can this be due to three times the friction at the scroll gears ? Colin

[HopperParticipant @hopper]

Posted by Nicholas Farr on 24/06/2022 12:37:22:

Hi, this argument has been going on for many years, even in industry, with both drill and lathe chucks. My father (who worked for a well known bearing manufacturer) taught me the way he was taught in his apprenticeship, that the correct way was to slightly tighten each of the three holes and then go round again to give each hole a final tighten. When others that I have worked with, just use one hole on a pistol drill chuck and they get a hole that the drill snags in (which was quite often) the drill would stop and the chuck would spin, eventually resulting with chewed drill shanks, I never got that happening, unless I was forced to use a drill that was already chewed up. I have always adopted tightening the chucks the way my father taught at work and at home.

Regards Nick.

So, tighten all 6 holes then.

[Dave HalfordParticipant @davehalford22513]

I've got two 5" lightweight chucks with only a single pinion on each.

[David George 1Participant @davidgeorge1]

I was told that it was a balance thing to have equal weight and not to have one pinion throwing it out of balance. I have always used one pinion to tighten the chuck whenever I went it to run true as that one marked O is the one which was used when the chuck was set up. That was what we were instructed to when I was an apprentice and carried on doing so.

David

[Andrew TinsleyParticipant @andrewtinsley63637]

Like Dave Halford, I too have a 5" chuck with a single pinion. It must have come with a job lot, because I only spotted it 3 weeks ago when I decided to clean my chucks, I was very much surprised at this! No name on the chuck and it was in a light blue box with a German language print saying 3 jaw chuck. Looks unused to me, still in makers greased condition.

Anyone know the origin of these oddball chucks?

Regards,

Andrew

[DC31kParticipant @dc31k]

Posted by peak4 on 24/06/2022 11:42:50:

I read that as, use any pinion, but if you set something up using one, then continue to use that one, if you want repeatability for a given diameter.

In a recent thread about manufacturer's chuck test certificates (long vee and short vee), I suggested people seek out Indian Standard IS2876-1999, which is a parallel of the ISO standard for scroll chucks.

In that Standard, it states that the tests on which the certificates are based should be carried out using the master pinion.

—-

There seems to be some confusion on the three-pinion issue. Everyone is talking about tightening the chuck. My chucks work in a bi-directional manner, loosening as well as tightening. Not having to spin the chuck around is a big advantage when removing the work.

[old martParticipant @oldmart]

Because of the unavoidable clearances required for the mechanism to work, there is likely to be a slight difference in the workholding accuracy dependent on which pinion is used to tighten the jaws. Only by testing using accurate test pieces can the master pinion be found. That is the least inaccurate one. I use the test bar which is about 3/4" diameter and a Morse taper socket with a 2" diameter ground cylindrical outside. Simply tightening the jaws on a workpiece is not good enough, you should move it in a circular motion as the jaws come in contact until tight. Tests should be made on each pinion and the best results recorded. As many different diameter test pieces as possible will check the accuracy of the scroll.

If setting up to grind the jaws in situ, then one of the pinions should be chosen and that will be the master. Unless the chuck is well worn, the differences between pinions will be minimal and having a master jaw would only be needed for critical work. For instance, turning and boring and then parting off without disturbing the workpiece in the chuck will be exactly the same with any chuck, good or bad.

[DiogenesIIParticipant @diogenesii]

Posted by Andrew Tinsley on 24/06/2022 18:05:04:

Like Dave Halford, I too have a 5" chuck with a single pinion. It must have come with a job lot, because I only spotted it 3 weeks ago when I decided to clean my chucks, I was very much surprised at this! No name on the chuck and it was in a light blue box with a German language print saying 3 jaw chuck. Looks unused to me, still in makers greased condition.

Anyone know the origin of these oddball chucks?

Regards,

Andrew

..TOS come in a blue box with German language labels.. ..some of the smaller Toolmex also had single pinions, not lucky enough to know what colour boxes they come in though.. ..both are good chucks..

FWIW I was taught to tighten on the master and use any to release.. ..also not to wring the life out of a 3 jaw..

Edited By DiogenesII on 24/06/2022 20:50:14

[Andrew TinsleyParticipant @andrewtinsley63637]

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.

[peak4Participant @peak4]

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 TinsleyParticipant @andrewtinsley63637]

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,

[HopperParticipant @hopper]

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.

[SillyOldDufferModerator @sillyoldduffer]

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 TinsleyParticipant @andrewtinsley63637]

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.

[SillyOldDufferModerator @sillyoldduffer]

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 TinsleyParticipant @andrewtinsley63637]

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.

[SteviegtrParticipant @steviegtr]

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.

[Author]

Posts