Doesn't exist? -- 8 TPI threaded chuck to fit an 80mm HF faceplate (w/ picture)

[bcrimmins]

@Alcap Were it me I'd cut the tang off, drill and tap the end for 1/4-20 or maybe 3/8-16 (if there's sufficient material) so that a drawbar of threaded rod could be used.

That's a good thought.

Is it OK that the cones will hide the edges of the ring? Should you consider an expanding mandrel type setup?

You don't want the 'cones' to be too high. But it depends on whether you're using ring blanks or if your cutting them entirely out of raw material. That said, ring mandrels of this kind I car about (mostly using ring blanks) usually come with multiple sets of 'cones' for different size rings.

Expanding mandrels are great too. I made a wooden one but it was wonky. The metal ones are often sold in sets in order to cover all the ring sizes and so they can get quite expensive. Like this:

IMHO, this is the most-brilliant design of all of them. $125.

 

[rwm]

That is beautiful and clever! I have made simple expanding ring mandrels to cover the common sizes I use and then I just chuck it in a 4 jaw and dial it in.

Flat head screw expands it just fine. I made the cut on a bandsaw. Simple.

 

[WobblyHand]

@Alcap Were it me I'd cut the tang off, drill and tap the end for 1/4-20 or maybe 3/8-16 (if there's sufficient material) so that a drawbar of threaded rod could be used.

That was the LMS link that I provided. Comes drilled and tapped for 3/8-16, $12.95. Fat end is 1.5" diameter, 1.5" long. MT3. I'll probably order one, just because. Seems like a handy thing to have. Could probably turn it to size, slit it, thread it, and make a tapered pin to expand it. A short version of the Breakheart tool.

 

[bcrimmins]

View attachment 394009
That was the LMS link that I provided. Comes drilled and tapped for 3/8-16, $12.95. Fat end is 1.5" diameter, 1.5" long. MT3. I'll probably order one, just because. Seems like a handy thing to have. Could probably turn it to size, slit it, thread it, and make a tapered pin to expand it. A short version of the Breakheart tool.

I agree... worth having around. I just order this one on amazon. https://www.amazon.com/dp/B06WRVKWYP/

 

[homebrewed]

The "expanding" mandrel with the matching tapered fingers is a pretty cool solution. If the commercial version is too expensive, I don't think it would be too difficult to make one (depending on what other machine tools you've got). I wouldn't think it would require a lot of accuracy to shape this kind of jewelry so a DIY version should be feasible. Don't over-engineer it if it's not required

 

[Firebrick43]

That's a good thought.

You don't want the 'cones' to be too high. But it depends on whether you're using ring blanks or if your cutting them entirely out of raw material. That said, ring mandrels of this kind I car about (mostly using ring blanks) usually come with multiple sets of 'cones' for different size rings.

Expanding mandrels are great too. I made a wooden one but it was wonky. The metal ones are often sold in sets in order to cover all the ring sizes and so they can get quite expensive. Like this:

View attachment 394003 View attachment 394005

IMHO, this is the most-brilliant design of all of them. $125.

View attachment 394006

to bad they have such a nice looking product and have such crappy knurling on the thumb screw

 

[bcrimmins]

I'm sad. I drilled out the shank and tapped at 5/16 - 24. Used my CO2 laser to cut an acrylic version of the awesome ring mandrel. Spun it up... and IT WOBBLES!!! The hole is offset by about 2/100's of an inch. I think what happened was that the face of the shank has a pilot dimple and I trusted that to be the guide for the point of the drill. In retrospect, I think I should have shaved the face flat and then drilled my own pilot hole with, say, a 1/8 bit. But I'm a lathe newby so I'm grateful for any wisdom y'all want to throw my way.

And, of course, I now have a shank with a tapped 5/16 hole in the wrong spot. I don't think I can re-drill it because the existing hole will drag the new drill off center. Although maybe an end mill bit moved in slowly would keep true? This also presents the opportunity (read, 'excuse') to experiment/learn with a boring head. Am I right that this would be a use case for a bore?

I could also just buy a new shank... which is way cheaper than a boring head. And besides, the ring mandrel I've designed kinda needs a 5/16 rod to be effective -- if it's any bigger, then the 'jaws' will need to be thinner or else small ring sizes won't work because I'd have to the diameter of the jaws to account for the relative weakness of the acrylic.

I probably should just have shelled out the dough for one of the awesome mandrels... .but trying to fabricate one is a fun opportunity to learn to ue my new mini lathe.

 

[Firebrick43]

Probably not the drill but the tap. You will always get wobble like this. Drill and ream a hole (next stock size up) in your soft shank. Use green locktite to retain the new piece of stock(say 3/8 if your doing 5/16 threads). After it sets up for 24 hours cut the glued in shank down to 5/16. Cut threads single point but not under where the ring sets. Just like the unimandrel above. Even better, don't cut any threads under any part of the mandrel at max extension(smallest size ring you will do) and use spacers under the nut for bigger rings

 

[Alcap]

How deep did you drill the hole ? Could you just face off threads ?

 

[rwm]

.020" is pretty bad. To get a hole dead center, it should be drilled undersized and finished with a boring bar. You would need one of those tiny boring bars for a hole this small.
You could start over with a new shank or loctite a plug in place as suggested above. Either way you should use a boring bar to center the new hole.
Keep this in mind:
Drilling is for making a rough hole.
Boring is for making a hole on center.
Reaming is for making a hole to exact diameter.
Sometimes you need to do all 3.