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lazlo
08-29-2009, 11:05 PM
Bruce Griffing organized an awesome visit for the Austin Metalworking Club to CDN Systems (an industrial surplus dealer) today, and I ran across a lot of Hardinge 5C serrated collets.

The serrations look like splines cut into the bore of the collet, and the serrations are also cut cross-wise. Bruce and I were puzzled over these, and he suggested that perhaps someone had EDM'd them for a one-off job.

But I just checked Hardinge's web page, and 5C serrated collets are a (specialty) stock item: What are these used for?

Hardinge collets are through-hardened, so any material softer than hardened tool steel is going to end up with a waffle pattern on it. Are these maybe for gripping slippery pastic material, and you just cut-off the section held in the collet?

http://i24.ebayimg.com/05/i/001/02/e4/9be4_12.JPG

Boucher
08-29-2009, 11:49 PM
How many did you take home and when can we expect a performance report?

nheng
08-29-2009, 11:52 PM
I suspected what it was for but had to Google it to be sure. They are for hot rolled, for cast and forged materials or those with irregular surfaces to give an extra grip. Den

Jim Shaper
08-29-2009, 11:54 PM
You answered your own question - kinda.

The serrations reduce the force needed to grip the stock, so you don't need to crank on it so much to hold it while turning your parts out of the end. Think production jobs where you're making doohickey after doohickey.

oldtiffie
08-30-2009, 12:02 AM
Yep.

Same reason for serrated jaws on a bench vise and smoother ones on a machine vice.

Same as serrations on pliers and pipe vises etc.

But I was a bit bemused to see serrations on a C% collet which are not very forgiving at all as regards variations from nominal sizes. I'd have expected it more in ER collets which have a "gripping range" of 1mm (~0.040").

When you think about it, it is no different to the serrated teeth on standard 3 and 4 -jawed chucks - for probably similar reasons.

lazlo
08-30-2009, 12:02 AM
They are for hot rolled, for cast and forged materials or those with irregular surfaces to give an extra grip. Den

Ah, Den gets the prize! :) Thanks guys!


The serrations reduce the force needed to grip the stock, so you don't need to crank on it so much to hold it while turning your parts out of the end. Think production jobs where you're making doohickey after doohickey.

But on bar stock, normal 5C collets grip just fine, and are often used in full-blown production. That's the whole point of the closer -- to apply the correct amount of pressure to clamp the collet without springing it.

Or put another way, serrated collets seem to be exceedingly rare, which would imply a special purpose, like Den explained...

Bruce Griffing
08-30-2009, 12:44 AM
Robert-
Did you buy any of the serrated collets?

lazlo
08-30-2009, 12:52 AM
No, they weren't ready to be sold :)

Seriously, they were pretty nasty, and they were on the tech's bench -- he was just starting to clean them up. I did buy that Akro Mills cabinet with all the stainless fasteners, so when I go to pick it up, I'll check on the serrated collets.

Not sure what I'd do with them, but that's never been an issue before. :p
Did you want a couple?

Bruce Griffing
08-30-2009, 01:01 AM
I am not really interested in buying a serrated collet - it was just more of a curiosity. I should have looked at it more closely when I had it in my hand.

Rustybolt
08-30-2009, 11:26 AM
They grip tighter. Anybody who has worked screw machines or bar fed CNC has had the experience of the stock being pushed back into the spindle, especially when pushing a big drill. So a serrated collet will hold tighter for the same amount of clamping force.

Rustybolt
08-30-2009, 11:36 AM
The radial grooves are made while the collet is being turned by a special forming boring tool. The linear grooves are broached.

If you want a good puzzle. Are the collets honed/ground before or after they're slit? If so, are they slit before or after they're heat treated?

lazlo
08-30-2009, 11:50 AM
If you want a good puzzle. Are the collets honed/ground before or after they're slit? If so, are they slit before or after they're heat treated?

Yeah, I wondered that too. That's why Bruce was thinking they had been EDM'd, but that wouldn't explain the cross-wise slits.

By the way, are these worth having in the home shop? I've never needed them before...

Rustybolt
08-30-2009, 03:26 PM
I can't see where it would hurt. I wouldn't pass up a hardinge collet for the right price as long as it was the size I needed.

The way we used to do it was to slit it almost all the way. just leave a little web at the end. Then finish the collet; heat treat, grind ,and hone/ grind the ID. The last step was to take an brasive cut off wheel and very carefully remove the last of the web.