Lapping a Unimat 3-jaw chuck

JHM I recall that the thread on my Dremel when I made the holder for it was an odd thread that matched no standard. I ended up just measuring the diameter and the pitch and screwcutting a thread to match it in a piece of aluminium. But I think you could just make the the hole smooth with no thread and put a cut in it and a pinch bolt so you clamp it.

I bought a small 50 or 60mm chuck like yours with a 14mm thread for the spindle off Aliexpress for peanuts and it is actually very nicely made. Made in China rather than India I believe but not sure.

My toolpost Dremel holder. Bit of a tart's handbag with the jewelled finish but it was a an experiment to try different ways of doing it. I reckon you could just clamp rather than screw the front mount though.

Hello:

Seems it is an odd thread, but a chap that makes holders says that (most) are either 3/4" x12tpi or 3/4" x16tpi (with some exceptions) so that sort of settles it as it matches what I have measured here with my Dremels.

But while I was going about all this, I wondered if I could not just chuck a decently made 8 or 10mm stone or diamond grinding bit on the tailstock. I have a brand new ca. 1990 Czeck 8mm chuck I recently (and successfully) bored to M14.

It would be working right up close to the tips of the jaws so I guess head/tailstock alignment would not (?) be an issue.

I would then very lightly adjust the jaws till their rear part touched the bit and turn the U3 on at a slow speed.

Done that, I would move the grinding bit very slowly/gently forward/back with the tailstock screw till I could hear no more grinding.

After inspection to check exactly what went on, I would again lightly adjust the jaws till their rear part touched the bit and repeat the procedure.

The job would be finished once the front end of the jaws touched the bit as it was being drawn out.

Does this make sense/sound feasible to you?

Thanks in advance.

Best,

JHM

You can't adjust the jaws if they are held in place by the clover leaf plate.

Tailstock has too much overhang and too much slack and is often not overly well aligned with the bed. i would not use that method.

To work properly a grinding stone needs to be spinning fast. It will not work well held stationary inthe tailstock.

I have seen other Dremel holders that just clamp around the body. Easy enough to make.

Hello:

Thank you very much to all who pitched in to help. 8^)

Best,

JHM

Edited By Julius Henry Marx on 18/01/2023 18:54:41

Thta does look promising Julius & your video plays fine for me.

My "solution" for a Dremel mount is a work-in-progress & it won't be as "high tech" as Hopper's :

A 3D printed adapter to suit a Dickson toolpost - the photo has come in sideways, but it doesn't really matter.

The formation to mate with the toolpost fits very nicely & with 6 perimeters the print is solid enough to resist similar clamping lever forces to a steel holder. The printed M5 threads in the body & height adjuster required a tap running though them to remove a very small amount of plastic to get a screw to fit snugly. The thread for the Dremel needs work - the example above is M18x2, which is the nearest to the M19x2 or 1/2" x 12 thread usually quoted for the Dremel nose from the "standard" threads in FreeCad. I used this with the idea of opening up the thread with a tap (1/2" x 12 BSF, as M19 x 2 taps are pricey ! ), but will re-visit this aspect on the "Threads workbench" to try to define a custom thread that fits the tool without need for a tap.

Unfortunately my PC was stuffed by a failed Windows update on Saturday (thanks Microsoft ! ) & the 3D model was one of the files that the repairer hasn't saved (the nature of the failed restart after the update required specialst help - a unfortunate first for me & I wasn't up to date with backing up ), so will have to start the project again from scratch. Should go easier this time (until I get to the custom threading bit anyway) but I do need the practice with FreeCad !

Nigel B.

Hello:

So is mine, which I may eventually need for something else in the future.

But ...

I think that Dremels are too large and heavy for what the Unimat 3 is, the older Model 328 much more than the Model 395.

So I will make a holder for the flexible shaft atatchment which will only need an easy to tap 1/2" x 20 hole or an equivalent common steel nut.

I'll probably have a piece of 8mm steel plate laser cut with an adequate profile, turn most of the hex part of the nut to a suitable diameter and then braze it or press fit it into a hole made on the holder.

It will be much easier to work with the Dremel in the Unimat 3 that way.

My only concern is that the flex shaft is not mounted on bearings, so any *precision* jobs will probably not have too much of that due to the inherent lack of rigidity unless passes are very light.

Best,

JHM