step collets vs bezel chuck

[JGrainger]

Aside from one tool with internal and external stepped jaws vs having a range of step collets (and stepped expanding arbors) in incremental ranges, is there any noticeable benefit to either over the other?

I'll eventually want to machine the parts of a silver watch case and I can't really justify the price of a nice brand bezel chuck. My own setup would either be 5c collets on a 9" swing, larger version of WW type bench lathe, or I could dig out a dormant WW lathe to fit a small bezel chuck if thats a much better option and one was affordable.. The big lathe could also/alternatively be fitted with one of the 100mm 6 jaw chucks from China - I've been advised that soft jaws are available, or maybe I could try to machine the factory jaws to be 2-piece.

[nickelsilver]

I suggest finding a 100mm Maprox 6 jaw step chuck. They crop up regularly on Ebay. Probably still run you a few hundred bucks but you'll never regret it. The jaws are machinable and replaceable, if you're lucky you might get both internal and external jaws, if not Maprox has them. These were often branded "JF", sometimes Alina, sometimes both. The jaws can be machined without need of a clamping ring, due to their clever design.

 

Step collets are great, but you need a bunch and the steps are still rather large. You can get blank step collets of course and machine them as you like.

 

If you are really on a budget and like making tooling Schaublin has a kind of step chuck-y type thing that's fairly simple and ultra precise. You can see in the pics it's an arbor that has a tail end identical you your lathe collets (W20 here, 5C for you). The front has a taper, 15-20 degrees is fine. Then there is a piece that slides on the arbor with a very close fit, with a taper to fit your spindle nose  and a taper to go in the "collet". The "collet" is the brass piece (Schaublin furnishes blanks in steel, I make them up as needed in brass as it's usually for a onesie-twosie thing). The collet has a bore to pass freely over the arbor, and tapers at each end. It's slotted as far as possible in 3 spots. When you chuck it in your lathe it expands of course, very precisely. To machine it you just tighten the drawbar slightly, or if you want to be more secure you can make a ring that will slide on and expand to grip that. Schaublin's is naturally hardened and ground all over, but if you start with decent steel like Stressproof you don't need to harden it or grind it, just careful turning work and it should last decades.

 

 

[JGrainger]

The Maprox chucks look nice but will probably be above my budget for the next few months - unless there's a bunch listed at once, I've emailed a supplier for a price and will keep checking ebay.

Would a bezel chuck have an advantage over a step collet when in use?

The Schaublin expanding arbor looks a great idea, and more economical than the usual forms of expanding arbor.. thank you for the suggestion, I'll probably be make one of those.

For external gripping the 5c blank step collet blanks should probably squeeze 0.5mm, so 6 or 8 with rings stepped at 1mm intervals should keep the clamping movement within 0.33/0.25mm and keep the runout minimal while covering all the fractional millimeter sizes from say 25-65mm.. individual import 5c blanks are pretty cheap but the total cost is heading towards that of a bezel chuck.. luckily I could choose to make the size ranges needed one at a time until the set of 6 or 8 is complete

- while I'd like to think I'll eventually be able to make enough money from working on watches to afford nicer tools, between a bit of regular repair and servicing I'm presently trying to focus on being able to complete difficult, interesting, or unusual tasks as a way of self validation and to be able to later use for publicity pictures.

Edited June 11, 2020 by JGrainger
addition

[nickelsilver]

Would a bezel chuck have an advantage over a step collet when in use?

The real advatage of a bezel chuck is convenience. I have a 100mm maprox for my 102 and it gets used all the time. I also have a full set of step collets for external diameters that get used sometimes. The maprox "out of the box" is so accurate I don't touch the jaws very often. I do share my machine with several other watchmakers so there are times when someone (nobody ever knows who haha) has put a ding on it or retouched the jaws without pretension or something, I've had that one about 15 years, give a kiss on one or another of the steps every couple of months.

They are for light work though.

Try to google up some videos on Martin Matthews, he was a case maker in England who worked very traditionally. Most of his chucking was with wood (bow powered lathe too). He'd make what's called friction chucks in wood, and sort of snap the part in/on, then machine it. It's a simple method that's super accurate. I do it often, but with plastic bar stock, when I need to modify acrylic crystals to fit a chrono chapter ring inside or slightly touch up the OD. Leaves no marks and is spot on since I machine the "chuck" in place.

But I do hold the plastic "chuck" in a- bezel chuck. Haha.

[JGrainger]

Thank you for going into some detail about the maprox chuck, I'll keep an eye open for one - hopefully once I've got more money. My upcoming case project will probably have to be done with the other methods but in the long term it's not practical to be without some method of convenient and accurate workholding - a chuck would satisfy those criteria, and I guess that saving space with fewer collets would be nice.

I have seen a little bit of video with people using wooden chucks but hadn't given them much thought, I do have a reasonable length of plastic bar stock so will give it a go.

[rodabod]

That Schaublin brass ring is smart. You could make something like this without too much difficulty in brass. 
 

Back to the original question, I think simply that ring/stepped collets are going to be more accurate. But there are advantages to using an adjustable chuck - you may get deeper jaws and you can customise your own jaws. I made a set of smaller brass jaws for one of my Burnerds last week so that I could increase the maximum capacity. I also prefer brass jaws on some watch cases.