shim material for tiny work holding in collet

ironhoarder · Nov 10, 2019

I had to do some machining on some small stock today- 0.118 steel rod.
I have a 1/8" Hardinge collet and my next smaller size is 1/16. I can tighten the 1/8" collet down enough to hold to work for cutting some e-clip slots, but I also need to thread one end with a die, and the 0.125" collet couldn't quite hold the 0.118 work from turning.

So- my question- for small work like this, what is a good way to shim the work so the collet will bite it a little better? I guess wrapping the work with a few turns of paper would be one approach, but maybe better would be to wrap it in a small piece of emery cloth?

I didn't bother because I figured it would be hard to shim such small work evenly and keep it concentric, which would defeat the whole purpose of using a collet instead of a chuck.

I thought about putting some heat shrink tubing on it, but that would probably make it too thick.

What to do when you work falls between your available collets, esp when the work is very small?

naru · Nov 10, 2019

Use a larger collet (not much) and face a piece of stock then drill and ream it. Cut a slit or two in it with a bandsaw. Reinstall it then go about your business. That or if possible, use .125” stock and turn it down for each part. Really depends on how many you need to make. If you need to make a lot of them, just order a .118” collet from Hardinge. Shimming it will take time and may not yield results that are satisfactory.

Lee J · Nov 10, 2019

A 3mm collet should work & be a stock item.

dgfoster · Nov 10, 2019

I have made a “collet” to go inside a collet in this circumstance. In other words I took a piece of ,say,1/2” drill rod and bored to the needed size. Relieve it so the 1/2” factory collet it slides into bears on the insert collet at its tail stock end 2/3. Slit the insert with three racial cuts to .118 hole just like a standard collet. A little lip on the outside (make from 5/8 rod instead and turned to 1/2 except for the outside last 1/16”) will keep the insert from sliding out of reach into the factory collet. Provides excellent centering (ESP if Loctited and bored in situ to ID final size) and very good grip. A lot of trouble, true. But a very skookum work-around that does the job if the job warrants the effort.

Denis

thermite · Nov 10, 2019

What was said. Go enough LARGER that it is less of a PITA to make a sub-collet.

When you have TIME, order-up a straight-shank ER set you can grip IN one of your largest collets. ER-11 is tiny. I use ER-20. (and ER-40..)..

Collapse range is continuous. There ARE NO "gaps", ER system. One needs only a fraction as many collets.

CAVEAT: ER are slow to operate, so not a substitute for my 2J or 5C, just an extension or "problem solver".

NB: ANY "spring collet" system, 3C, 5C, 2J.. wotever.. one should have one, if not three "emergency" collets put-by. Order replacements first iime one is actually USED. (..up..).

Steel, Brass/Bronze, Nylon, for example.

Milland · Nov 10, 2019

For what you're describing, a single layer of regular printer paper (~.003" thick) formed into a loop (strip ~.5" x 1" wrap around rod with 1" length) and the excess tail tucked into one of the collet slots should work well. You can get a surprising amount of clamping through a sheet of paper.

Keep a supply of brass shim on hand. Assortments are cheap, common sharp scissors will cut it to ~.015" thickness with clean edges. Use as above when needed. Almost always will give a fine concentricity if using just one layer.

JohnMartin · Nov 10, 2019

I’ve made reducer bushings for small collets, starting with drill bushings. Make sure the drill bushings you get are not counterbored - they should be on size full length. I use the headed bushings. You’ll want to use a bushing quite a bit larger than the bore - at least 1/4”, maybe 5/16”.

Slot them from each end. Since the drill bushings are already hardened, I use a thin cutoff wheel on my surface grinder. Bushing held upright in a piece of drilled and slotted round, which is itself held in a collet fixture.

Mechanola · Nov 11, 2019

Aluminium foil is your friend. No overlap, butting ends

L Vanice · Nov 11, 2019

Lee J said:
A 3mm collet should work & be a stock item.

naru said:
Use a larger collet (not much) and face a piece of stock then drill and ream it. Cut a slit or two in it with a bandsaw. Reinstall it then go about your business. That or if possible, use .125” stock and turn it down for each part. Really depends on how many you need to make. If you need to make a lot of them, just order a .118” collet from Hardinge. Shimming it will take time and may not yield results that are satisfactory.

Hardinge claims to stock 5C collets in increments of .001 inch, but the 3 mm collet will be cheaper, especially if you get an import. I have a Hardinge .300 inch 5C collet I needed for a particular job. Or the emergency collet is cheaper yet.

Larry

rons · Nov 11, 2019

Would use a 1/8" piece of aluminium or brass in the 1/8" collet and drill a hole through the size of your small piece. Now insert small wire.

I have a few emergency collets that are plastic and steel. Emergency collets can be reused with progressively larger holes in the same collet.

I have a pin vise with a shaft that is 4" long. Used to hold tiny rods to press small pins like for watch bands. Insert shaft into larger size collet
(about 1/4") and then use small vise jaws to hold piece. The one I have is like this with a larger opening.

High Precision Micro Pin Vise

dgfoster · Nov 11, 2019

Mechanola said:
Aluminium foil is your friend. No overlap, butting ends

An easy way to avoid overlap that allows for more positive manipulation of foil or paper, should you use it, is cut a piece of paper/foil bout 1 inch wide and a couple inches long. Pinch the ribbon of paper between your fingers overlapping the ends and cradling the round stock in the fold. Snug the loop of paper around the stock and then push the paper and stock into the collet allowing the long ends of paper to slide into one of the slits in the collet. You don't have to push the paper all the way into the collet and it is easier if you don't. Tighten up the collet. The first turn or two of the lathe will sweep away any paper hanging out the collet. I used to try the no-overlap butt method and it works fine on large stock 1/2" or so, but, for me at least, is very fiddly on something like 1/8" stock.

Denis

Bluejeep · Nov 11, 2019

This is why it's handy to have metric set of collets on hand.

jim rozen · Nov 11, 2019

I always keep a couple of brass 5Cs around for just such kinds of jobs.

Milland · Nov 11, 2019

dgfoster said:
An easy way to avoid overlap that allows for more positive manipulation of foil or paper, should you use it, is cut a piece of paper/foil bout 1 inch wide and a couple inches long. Pinch the ribbon of paper between your fingers overlapping the ends and cradling the round stock in the fold. Snug the loop of paper around the stock and then push the paper and stock into the collet allowing the long ends of paper to slide into one of the slits in the collet. You don't have to push the paper all the way into the collet and it is easier if you don't. Tighten up the collet. The first turn or two of the lathe will sweep away any paper hanging out the collet. I used to try the no-overlap butt method and it works fine on large stock 1/2" or so, but, for me at least, is very fiddly on something like 1/8" stock.

Denis

That's what I was trying to describe in #6, I guess you did a better job of it.

dgfoster · Nov 11, 2019

Milland said:
That's what I was trying to describe in #6, I guess you did a better job of it.

Now that I re-read your post #6 I see exactly what you were saying. I gotta tell you I was struggling to describe the loop and tuck method in my post. It is one of those commonly encountered situations where clearly verbally describing a very simple procedure is not so simple. Standing shoulder-to-shoulder with someone and showing them requires no words and is simple as can be. But then put what you mean into words... I would have drawn a picture but I am traveling right now and doing so was not convenient. Anyway, I think we both put forth a pretty useful technique once learned is not forgotten.

Denis

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