View Full Version : How to fit oversize stock in 5C collets?

12-16-2012, 08:36 AM
Usually when I buy round stock, it manages to come out slightly oversize, e.g. 5/16=.314 and 3/4=.755. Sometimes it is a tight fit in a 5C collet, and sometimes it just won't go. I know that the grip range is not so large. What can I do?

12-16-2012, 08:43 AM
Sometimes you can go up to the next-larger collet, in 1/64th inch increments. They do collapse by about .010" to .015".

Better yet, just throw the 3-jaw or 4-jaw chuck on the machine?

12-16-2012, 09:07 AM
Are 5C collets available in metric sizes? If so might provide some in between sizes. Another solution would be to bore/grind some collets to enlarge their bores.

Lew Hartswick
12-16-2012, 09:14 AM
Usually when I buy round stock, it manages to come out slightly oversize, e.g. 5/16=.314 and 3/4=.755.
Consider yourself lucky. The stuff we get is usually under size by 1 to 5 thou.
:-( can't use it for shafts that go in bearings etc.

12-16-2012, 09:16 AM
They are available in metric sizes, but they can be harder to find here, more expensive and usually only the whole number 1mm increments.

12-16-2012, 09:23 AM
isn't that nice of them including extra material! Hopefully the rolling mills won't borrow the nasty trick from pricks who make lumber and start making it undersized

just get the next size up (1/64). Its a pita because you have to buy more collets....but its that or an emergency collet if you really need to hold them via collet. I've 2J (like 5c but a little bigger) and rubberflex collets; might seem like belt and suspenders but there are subtle differences when one will work and the other won't.....odd sized work like this is where the rubberflex shines so maybe long term that would a good shop addition

12-16-2012, 09:55 AM
"Stevenson's" ER32 / 5C collet adapter is one solution. Sounds like your need precludes the use of a normal 3-jaw---even if to only turn down a few inches on the bar end to nominal size? Otherwise for normal cold-roll steel, the stock tolerances are not so fine to generally gain any benefit from gripping in a collet rather than a three jaw scroll. Buying ground stock (which will be on size) is not always so much more costly than the cold-rolled. That is the other obvious solution.

In general, though, in my personal shop I approach the problem in the following manner. I acquired a nice set of Hardinge 5C's with my lathe in 32nds. I later bought the absolute cheapest set of 64ths I could find. I've never given a second thought, consequently, to springing those. Fits the bill great for oversize, undersize or otherwise stock :D The Hardinge's, of course, are reserved for ground stock.

Jaakko Fagerlund
12-16-2012, 11:30 AM
May I ask why the use of collet on a material that is not on size? If I buy cold-drawn round stock, it is h9 or h11 tolerance, meaning +0 and -something, depending on the diameter. This fits in collets etc. and costs next to nothing. If one wants exact stuff, then ground material is a choice.

12-16-2012, 11:42 AM
I just use the next size up like someone else mentioned. They run in 1/64th increments and cover everything down to the next size. A 1/2" collet covers up to 1/2" period. If I don't happen to have the next size sometimes I'll turn it down in a chuck first, but only if I need to remove and reinstall repeatedley. Otherwise just do everything while it's in the chuck.

12-16-2012, 12:30 PM
Whatever you do, DON'T FORCE oversized material into collets.
A few of the geniuses I work with do that with drills, cramming them into the wrong collets.
The result is a nice assortment of SPRUNG collets. :mad:

12-16-2012, 05:48 PM
Hardinge makes 5c collets in .001 increments.

But I have used a tapered punch to slightly spring collets and never had a problem using them.


12-16-2012, 06:21 PM
What is a "sprung" collet? Won't it compress back down when you pull the drawbar?

Also, I have read various opinions on the internet. Some say you can go a little oversize vs the stamped size, some say you can only go undersize.

12-16-2012, 09:20 PM
Why not use "soft jaws" in/on a 3-jaw chuck - if done correctly is should be as accutate as (m)any collets.

Other than that use ER-32 collets (metric) which are in 1mm (0.04") steps with an effective gripping range of 1mm (0.04") in a size range of 2>20mm (0.08">0.20").



12-16-2012, 10:02 PM
Many times I have used 5c collets with a 10 second cycle time in automatic lathes with air to open and close collets, no time to mess with stopping spindle and hand opening a collet. Lots of the time
collets have a spring in them to eject parts so you can reload new part without stopping spindle.


12-16-2012, 10:20 PM
What is a "sprung" collet? Won't it compress back down when you pull the drawbar?

Also, I have read various opinions on the internet. Some say you can go a little oversize vs the stamped size, some say you can only go undersize.
Complex issue---one I admittedly do not have the engineering background to address properly; however here is my understanding of the matter...

Depends on the way the collet is made. Not all collets are made the same regardless if they are all 5C or not. This is not a quality issue (although it surely could be). Some collets are made to collapse more to reach their nominal size when closed on the work. Some are made to collapse the fingers less. With those which open larger in the relaxed, open state, there is more of a leeway for oversize work. Up to a point.

Only at the condition where the collet is clamped on marked size is the bore ground into all the fingers parallel. The full depth of the bore is gripping the work evenly. For an oversize workpiece, the rear portion of the finger will contact the workpiece before the front while closing. As the collet is closed further, the fingers are distorted in being compressed into contact on the front portion. This has the potential to bend the finger---if it is bent past the yield point of the steel alloy used, the deformation becomes permanent. Likewise, undersize work contacts first at the front. The curvature bored into the fingers is not parallel and gripping the entire length of the seated work here either. The fingers can be bent past their yeild point here as well. As the rear part of the finger approaching the solid body of the collet is more supported, again the finger gets an unwanted curvature forced into it.

The overriding point to be made, though, is why use a collet at all? I can argue for two reasons: fine accuracy in workholding or convenience. Unless a collet is used with accurately sized work, there is no accuracy gained in using a collet! The fingers will contact the work over a limited distance because the collapsed bore in the collet is NOT parallel when it contacts the work. This lessens the security of the gripping force unless... The finger is further compressed to deform against the length of the bore and brought to grip the work its full inserted length. This, though, ruins the fine accuracy which the collet is designed to achieve. A scroll chuck is likely as accurate while providing a more firm grip on the work by which to drive it.

I fully understand that collets have other uses. This is what I was hinting at with my most-inexpensive-64ths-set previously mentioned. Sometimes you want to grip a short screw in the lathe to alter its length or turn down the head. I don't care if the mounting is super precise by any means. It is just more convenient and less distorting to the thread to grip in a collet. Soft jaws are great but less "fast" and convenient. Or maybe I have to hold something to use a wrench on it or file it or some other hand operation. I use a simple collet block gripped in the bench vise. Accuracy in concentricity, axial misalignment, repeatability---none of that matters to me in that instance. I would not expect, though, to use the same set of collets on work which does matter in those areas.

Hopefully something of the above is useful to you, and I don't come off as a pedantic obsessive :) Collets are an incredibly convenient and unobtrusive workholding device. You just have to pick your battles and balance the benfits to the consequences in a manner that suits your needs. Feel free to use all the oversize and undersize work you wish in your 5C collets. Just bear in mind, they may not perform up to expectation when they are absolutely required to if those boundaries are pushed far, often or without due caution.

12-16-2012, 11:45 PM

I bet you're using cheapo collets. They typically won't pass material of their marked size.

On occasions where I needed extra collets of a certain size I would take a piece of stock with me to the cheap collet store. Say I needed a 1/2" collet I would ask the clerk to bring out all their 1/2" . I'd go through all of them until I found some that would pass 1/2" material.

It's not unusual to find none of the collets will accept material. Actually, it's more likely they won't accept than will.

BTW, I'm talking about Lyndex collets which advertise as being made in Japan. Interesting only the boxes say "Lyndex, made in Japan", while the collet is only marked with it's size.

I had power collet closers on my lathes. We used only Hardinge collets for production runs. With a power closer, if the collet is closed with nothing in it it'll suck in so far It won't spring back open all the way. With Hardinge collets we used a screw driver pounded into the slots to open them back to normal size. No problems or loss of accuracy. I tried the screw driver trick a couple times on cheapo's, they split down the side, ruining the collet.

12-17-2012, 11:48 AM
I have no experience with Lyndex 5C's, but can confirm that their R8's, anyway, are definitely made to return closer to nominal dimension when fully relaxed. I can't help but believe this has some connection to the alloy and specific heat treatment they use in manufacturing. Hardinge collets are farther open in the relaxed state--they are meant to compress the fingers more to reach nominal diameter. The no-name 5C's I have used are a mixed bag but have always tended more toward the Hardinge side of the scale. I also have a number of pull-back collets made by Schaublin spanning a number of years. The current ones are relaxed roughly the same proportion to the Hardinge's. The older ones from the 70-80's were much closer on dimension when relaxed. Still, the Lyndex R8's definitely conform to nominal diameter in the relaxed state closer than any others I have used. I have been the complete cynic based on online rumors of the manufacturing origin for the Lyndex R8's in the past. Now less so; I have lost my certainty of such. I briefly owned a set of generic "Enco" R8's which were superfucially exactly the same in construction to the Lyndex variety but fit quite different. In the age of copycat manufacturers and obfuscation (whether intentional or not) for low-priced tooling... Hard to say. Could ultimately be that the Lyndex was the originator which the low-cost Chinese manufacturer decided to mimic. R8 end mill holders by Lyndex, on the other hand, are nicely laser etched with the Lyndex logo and "Made in Japan". So whatever... take it for what it is and make your own opinions, I say.

12-17-2012, 12:15 PM
I have used collets a lot over the years. Mostly R8 and 5C. The older quality brands of 5C like Royal, Hardinge, Lyndex, etc. used to come with a choice of whether they were sprung open or not. The ones that were sprung open a few thou. were for use on a lathe with a lever or air collet closer where you could change parts without stopping the machine. This is a big deal when you're running production and trying to make time. You will not get the part in a collet that is on size with it spinning. Over the years apparently they have stopped making ones that are sprung open. The ones that are not sprung are fine for static operations like on a lathe with a handwheel or keyed collet closer or mill fixture where the collet is not moving when you change parts. I have a full set of 5C in 1/64 increments, emergency collets in steel, brass and plastic, oversize ones that you can bore out to fit the part and recently the ER32 ones from Arc Eurotrade. Any time I have something that is not within + or - .001 of nominal on a regular collet, I go to the ER32 ones. They cover all sizes with just a few collets.

12-18-2012, 04:51 PM
I have used collets a lot over the years. Mostly R8 and 5C. The older quality brands of 5C like Royal, Hardinge, Lyndex, etc. used to come with a choice of whether they were sprung open or not. .................................................. .................................................. .................................................. .....................................

I was not aware collets were sold that way. I've been buying Hardinge for 30 some years and was never offered that option. I don't recall ever having a Hardinge collet that wouldn't pass nominally sized material.

I used to run a lot of extruded 5086 aluminum bar. Size-wise that was always a problem. Rather than fight with different collet sizes, over and undersize, I sent the bars out to be centerless ground undersize to the nearest fractional size.

12-18-2012, 05:02 PM
Your all doing it wrong! lol. (Yea just kidding)

If you use oversized 5C collets only the tip of the fingers make contact and the rest of the work is free to move around in the collet, only on size 5C collets hold work 'straight'

You need a double angle collet like ER32 if you want to collapse the collet much, those are designed to stay parallel and hold undersized work. (But won't hold short work unless you put a same sized plug in the back of the collet to keep it parallel)

That said, What I do is buy the next sized up hot rolled stock! Then turn it to whatever diameter I need.
Need a 1/2" shaft? Buy 5/8 hot rolled.
Need a 5/8" shaft? buy 3/4" hot rolled.

Its cheap as hell, you can turn it to the EXACT size you want, its decent stuff once you use your most disliked carbide tool to remove the skin in one gnarly pass (Or buy pickled hot rolled! no skin, very nice stuff, cheap, seems like cold rolled)