Collet-in-collet

[azamiryou]

This is a tip for when you need a collet size you don't already have, and you don't have the time (or money) to get a new collet. I've been thinking about it for a long time, and today I actually had need for it - so I tried it, and it worked great!

Basically, I just made a custom-size cylindrical "collet" to fit in my 3/4" collet.

1. Start with a piece of 3/4" round stock. I used delrin for dimensional stability, but almost anything will work fine.

2. Cut off a piece the length of your regular collets. This is not a precise measurement.

3. Chuck it up in your 3/4" collet and square the end. If you feel like it, turn it around and square up the other end, too.

4. Drill or bore a hole the size you need. You may want to start a little smaller than you need, then sneak up on it, test-fitting your target piece until you get a good fit.

5. make a cut lengthwise in the piece for more than half its length. I made a simple jig to do this with a hacksaw by cutting a slot in a piece of wood, then drilling a 3/4" hole down the slot (but not all the way through the wood). I drop the tube into the hole, and cut down the slot.

6. turn the tube around, and cut a similar slot from the other end, rotated 90 degrees from the first one.

To use it, chuck up this tube in your 3/4" collet, then put target piece in the tube. As you tighten the collet, the custom "tube collet" tightens on the piece.

Apologies if this is a well-known "trick", but I've never seen it mentioned before.

 

[juteck]

I've seen it used with 4-jaw chucks, but not in a collet. Great idea for those small diameters. Thanks for taking the initiative and doing it, and posting it. Great tip!

 

[Sylvanite]

I made similar collets (to use with a scroll chuck) before I bought a collet chuck and collets. I found it better to cut the slots first, compress it in the chuck, and then drill with the minimum size bit you want to hold. That yields a little better concentricity. Also, if you're going to use it in a scroll chuck, mark the orientation so you always align it with the same jaws.

A real machined collet is still much more accurate and secure, though.

Regards,
Eric

 

[jd99]

I make collets for custom sizes all the time but I just machine a straight bushing close to or the exact size of the part for the ID, and the OD is a standard size to fit one of the other collets I have, (or I use them in a chuck to keep from marking delicate parts), then I make a cut through one side lengthwise, and cut a groove 180 degrees from that on the other side.

The trick is to not make the wall thickness to thick, (or too thin that it collapses in a chuck, and marks your part).

 

[azamiryou]

I make collets for custom sizes all the time but I just machine a straight bushing close to or the exact size of the part for the ID, and the OD is a standard size to fit one of the other collets I have, (or I use them in a chuck to keep from marking delicate parts), then I make a cut through one side lengthwise, and cut a groove 180 degrees from that on the other side.

That may be simpler to make than mine. No jig required, anyway. (With the jig, mine is pretty quick.)

 

[azamiryou]

Here are some photos of the tube ("inner collet"? "collet liner"?), the jig for cutting slots in the tube, and the tube mounted in my collet chuck holding a work piece.