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

开云体育

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

Haven't used the Unimat in a while. Needed 10 brass pieces so pulled in out and fired it up.

Here's a 3 minute video of the final operation. Prior to this I had center drilled, drilled, and bored out a close tolerance feature on the inside.

Jay

https://www.dropbox.com/s/zecw0bmqpe95r5v/20230108_151911.mp4?dl=0

Many of the cheap speed controllers have the facility to use a 0 - 5 V input rather than the pot. Therefore a bit of electronics, maybe nothing more than a resistor and a capacitor will give a short (or long) acceleration. Using an integrator would give a linear acceleration, and a comparator would stop the ramp when it is equal to the speed demand from the pot. What might also be useful is a mild braking action when stopping - not too much or the chuck will spin off. The simplest way to do this is to switch off with a relay, which drops out and short a resistor across the motor, providing a braking load. Integrating the two together would be possible.?
.

Hello:

For all of us here, I have never heard of any typical home use lathe with anything other than a regular(non-soft?)start motor.
In any case, the suggestion is too find a mixer and take it apart.? Now checking Ebay, if you are lucky you can get a used Kitchenaid for under $100(and shipping, tax).? For those who are curious, you can find everything you want to know, with photos and videos on Kitchenaid mixers disassembly.? Figure out what you have to do to mount it.
Now what is wrong with using my power supply to just start my $35 scooter motor at a slower speed?? I never would, but isn't this easier?? I can start a Sherline with the built-in speed control knob.

Hello:

Seems that something happened on the way to the upload ...

The image Carl was referring to is this one:



Sorry about that.

Best,

JHM

Hello:

How did almost every lathe owner in history get by without this?