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Hello Dick:

I made an ER32 holder for my unimat from a CAT40 holder. That way I didn't have to thread anything but the M12x1 mounting hole.

Here is the full story in pictures:

/g/Unimat/album?id=195716

Also since the clamping range is so broad, it also doesn't mater if they a Metric or Imperial.

Carl.

I just remembered I have a full set of ER32 Imperial collets with closing nut and also a full set of ER25 Imperial collets with closing nut. I could make a chuck for each size to fit my DB200 Unimat and thereby eliminate the need for a three jaw scroll chuck and have very close T.I.R.
My ER25 set has guaranteed T.I.R. of .0002”.
I would still have the Unimat 4jaw independent chuck for larger workpieces.?

Dick

The following files and folders have been uploaded to the Files area of the [email protected] group.

• /jaw_lapping.png

By: Julius Henry Marx <sawbona@...>

Description:
This is a facsismile from a tip posted in the January 1924 issue (p. 86, lower right) of Popular Science magazine and already posted here. This version comes from an on line source - thank you 8^) - and has some writing on top of the article but it is quite readable.

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Hello Dick:

I have several Unimat SL1000 lathes and would never be able to tighten the three jaw chucks without the tommy bars. I wish the knurled scroll had four holes instead of just the one.

I would suggest that the damage to the holes is from using under sized bars, etc. or excessive tightening. I read once that wrenches are sized ( length ) to limit the torque a normal person can put on a nut.

Carl.

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Ill fitting (undersized) or partially inserted tommy bars will quickly bell mouth the tommy bar holes. It is so hard to resist using something random if the proper tommy bar can't be found.

I have often thought it would have been better had the Unimat 3 jaw chuck never had tommy bar holes or been supplied with tommy bars. These items are the instruments of destruction. The knurled surfaces are sufficient to hand tighten the jaws and prevent damage.
Of course this is my opinion only!
Dick

Years ago I had an article that showed a way to make up the scroll side of 3 jaw chuck jaws.??

It appeared to be a little involved but not too hard to do.

Unfortunately a drive failure lost that article.

I thought making up some soft jaws may be useful but I've never found it since.
Perhaps some one else has a similar article stashed away or has already done that job.

Regards,
Brian.

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Hello Gang:

This looks like a great fixture, and not too hard to make. On the production grinder I designed we had a similar fixture and the carbide jaws would be reground every 1000 parts. At two parts every 15 seconds this would happen every 34 hours. Since we ran 24/7 that meant the jaws were reground every day and a half. To save the cost of special jaws we used round carbide lathe tool bits and could rotate them twice before recycling them.

Grinding near the part diameter is important since other diameters depend on the consistency of the scroll.

Carl.

Hello:

Hello:

Thank you both for the prompt reply.? 8^)

On Mon, Jan 16, 2023 at 11:11 AM, OldToolmaker wrote:

... appears to have suffered abuse | ... tommy bar holes have been deformed ... | ... chuck jaws themselves are not closing ...

Indeed ...
43 years after, that's the gist of it.

... can’t see the scroll, but there could be trouble there ... | ... disassembly and inspection is in order ...

Here you go.
I took it apart and put the pieces on my scanner's bed (!) to get accurate images of each one's critical surfaces.

Jaw surfaces do not look too good.
I probably have some responsibility for part of this damage as once or twice a long rod flew off the chuck, probably because the jaws were already in bad shape and did not hold the piece properly. ?



Asides from the scanning software pixies, scroll teeth seem to be (?) in decent shape.



Same could be said for the scroll itself.



To my untrained/unexperienced eye, what looks bad are the jaw surfaces.
ie: I cannot make out any issues with the scroll or the teeth running on the scroll but you chaps know better.

On Mon, Jan 16, 2023 at 11:30 AM, Carl wrote:

... lapping procedure should work ... | ... make the mandrel guide the diameter to slide in the head stock hole.

And avoid the use of a pilot, right?

... doesn't look like the Unimat 3 tailstock has any adjustment ...

Quite so, much to my chagrin.
I think have the bed ie: headstock/tailstock reasonably well aligned.
After a couple of surface passes on a steel rod mounted between centers, I get a 0.05mm deviation when I run a comparator dial from point 'A' to point 'B' 125mm away.

... suggest taking the jaws out. |? ... back of the jaws should be square to the clamping surfaces and you could grind them that way.

I'm afraid I don't understand how that whould be done but I have time to spare.
If you could please enlighten this amateur ...

The only methods I have seen (on-line) are with the jaws in place and a rotating cylindrical element grinding each jaw as the chuck rotates.
ie: one at the time and preloading, requiring some sort of jig to get them tight/with no slack while holding nothing to let the stone do its work.

All are more or less like one I found in the 'U3 Notes' folder I put together while I was trying to decide whether to the purchase the Unimat 3 or not.

What makes the lapping method from 1924 quite different is that it will grind all three jaws at the same time, keeping the surfaces concentric and avoiding the need to preload the jaws as their full length press on to the grinding surface at all times.
That would be one less thing to worry about if the jaws are in the right place/position when grinding.

Thanks in advance.

Best,

JHM

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Hello JHM:

The lapping procedure should work fine. You could make the mandrel guide the diameter to slide in the head stock hole. It doesn't look like the Unimat 3 tailstock has any adjustment, so nothing to fix there. Since there is such a gap I would suggest taking the jaws out. The back of the jaws should be square to the clamping surfaces and you could grind them that way and save a lot of lapping time.

Good luck, Carl.

Hello Julius,
The chuck appears to have suffered abuse over the years. The tommy bar holes have been deformed and the the chuck jaws themselves are not closing as they should. I can’t see the scroll, but there could be trouble there as well. A good disassembly and inspection is in order here. Please let us know what you find.
Dick

Hello:

The OEM 3-jaw chuck that came with my ca. 1980 Unimat 3 does not seem to be in good shape.
Granted, it is 43 years old and it may have been subjected to some abuse, no way of knowing just how much.

While attempting to diagnose the source of chatter I could not find, I noticed this:


?
A so-so photographer and a a so-so camera makes it look worse than it is but there is a good amount of axial play there, probably one of the sources of the chatter I often (too) get as well as deviations when drilling a small diameter length wise hole with a drill bit.

Looking for a possible solution I came across this *.pdf file with a scan of an article published in the January 1924 (!) issue of Popular Science.

Has anyone here actually done this on a Unimat 3?
I ask because it would seem to me (?) that this method would be highly dependent on the tailstock and the headstock being properly aligned.
ie: to within a tight tolerance

That said, I am not being able to make out how the pilot bushing would work in a Unimat 3.?

I'd appreciate comments on this.

Thanks in advance.

Best,

JHM

Hi Jay,
Thank you the first link worked for me, very interesting I have just been playing about with some steppers on my SL but I am trying some single axis drivers to be honest so far not very impressed with them, would it be possible to see a screenshot of how you have powered up the lathe and the controller you are using.


Thank you
Phill

The two attached screen shots are from the BBC program The Repair Shop.? A few seconds of video show a Unimat being used to hand turn multiple wood pieces(maybe checkers).? No CNC here.? It is not often that a Unimat makes it to TV.

I had to do something simpler, but without CNC, making quantities of small flywheels on my U3. I found it was a big advantage to use collets, so everything ran true, and then found that the brass bar I bought was very accurately round, and to size, so I didn't have to do any finishing on the top diameter. I used 6, 7, 8 & 10 mm diameter bar, and parted it off with a 0.8 mm wide tool that I was given.

I assume the bar is so accurate so it can be used reliably in CNC production machinery. The only snag I did find was that, although the bar was all to the same spec (CZ121), the larger diameters were softer in the centre, which had some effect on drilling for the shaft. However, this is to be expected with cold drawn materials.

Jay,
The link you provided was not an active link. Could you provide an active link?
Thanks
Dick