1. Home
  2. ⏣ General Metalworking
  3. Machining Expanding 5C Collets?

Machining Expanding 5C Collets?

I need to hold a part with a 1/2" bore to finish machining the outside. I bought an Eagle Rock expanding 5C collet, but it didn't come with any instructions on the correct way to turn it to size. The "1/2 inch" collet is about 0.55" in diameter, and has to be turned down. I did some digging on-line, and there are several different manufacturers. Most provide no instructions on how to turn them to size, and the ones that do all seem to have varying approaches specific to their design.

My concern is how to set the drawbar/expander tension while I turn it. Hardinge apparently provides a ring that fits on the end that you expand against so that everything is tight & solid while you are turning it. If the collet is turned as is, the expanding fingers will be free to twist and flex, and you won't necessarily get a very round result. I also don't know if I should turn it with a little pre-load on the expander to minimize this.

Because I'm actually only going to turn down the end a bit and not the full length, I could make a ring for the collet to expand against that would fit over the back, but that's a pain in theneck, and if it was that critical, I assume somebody would provide instructions mentioning it.

For now, I'm just going to tighten the expander plug slightly, then use a sharp tool & light cuts, but I'm curious as to what other folks do with these things.

Thanks!

Doug White

Reply to
Doug White
Loading thread data ...

Sounds good to me. Randy

Reply to
Randy Replogle

Use a pipe/Jubilee clip to restrain the collet while turning to size.

Mark Rand RTFM

Reply to
Mark Rand

Reply to
Jim Sehr

I'd just quick turn a ring of maybe 1/4" or so (whatever will fit in the uncut part of the collet) with an inside of .55" and slide it on. The outside really doesn't need to be anything specific and the depth doesn't need to be exact either. Grab a chunk of 3/4 stock, bore a bit (don't worry about the center area) and cutoff the ring and it's ready. Also, don't forget that if you do it too wide, you can always cut it as part of the cut on the collet.

-- Yeppie, Bush is such an idiot that He usually outwits everybody else. How dumb!

Reply to
Bob May

One more thing. If you cut it with the ring on there, you'll know that whatever you turn the collet to will fit well in the work you need to do as the collet would have been firmly torqued to tension while holding the ring.

-- Yeppie, Bush is such an idiot that He usually outwits everybody else. How dumb!

Reply to
Bob May

Well, taking light cuts on the collet seems to work. I still have to be very gentle with the part I'm machining, or it slips. I'm going to try cleaning all the residual oil off everything and then applying some rosin for added insurance. The rod that expands the collet is only about a #6 bolt (if that), so I can't tighten it too much.

Doug White

Reply to
Doug White

The problem with this approach is that it holds the base of the expanding fingers, when what you really want it something out at the tips.

Hardinge has a neat dodge for this on theirs. The ring fits over a turned down section at the end of the collet. The ring is sort of a cap, smaller than the minumum diameter the collet is rated for. This gives you something to tighten against right where you want it. If I was doing anything particularly critical, I think I'd try that approach, but it means modifying the collet (and losing some length), in addition to having to make a matching end cap.

It also would have been an issue for my present application, because I needed to counterbore the piece. Having a protruberance on the end of the collet would have reduced the gripping length I could use & still get a boring bar inside.

Doug White

Reply to
Doug White

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.