Collets: Incremental Work Holding

Get a few "emergency" collets of brass or soft steel and bore them to suit if you need a special size.

--Gads, if you can afford these, you can afford to shoot me a check for ten grand or so, heh. My advice: don't bother buying one until you need it. Get a couple of machinable blank 5-Cs if you must, but that's it.

I find that collets provide a good quality control device for me. Frequently I will machine a section of a shaft and then part off and flip the part around and machine the other end. This requires that I hold the machined part in the collet that matches its machined diameter. these are typically standard sized collets, but gripping on a machined rather than stock diameter. If the correct sized collet (ie the size of the spec'd shaft) does not hold the work precisely, the piece is not to tolerance and typically is scrapped. These are relatively simple parts but with many people of different skill levels performing the machining, if the collets don't hold I assume the part is worthless.

Woodworker88 Student Machinist Los Altos High School "Eagle Strike" Robotics Team

I find that collets provide a good quality control device for me. Frequently I will machine a section of a shaft and then part off and flip the part around and machine the other end. This requires that I hold the machined part in the collet that matches its machined diameter. these are typically standard sized collets, but gripping on a machined rather than stock diameter. If the correct sized collet (ie the size of the spec'd shaft) does not hold the work precisely, the piece is not to tolerance and typically is scrapped. These are relatively simple parts but with many people of different skill levels performing the machining, if the collets don't hold I assume the part is worthless.

Woodworker88 Student Machinist Los Altos High School "Eagle Strike" Robotics Team

My 5C collets are every 16th, have never needed an in-betweener. Yet.

Recommend you don't buy them just to buy them.

Lately I've been using my 5C indexer quite a bit. If you want to spend money on workholding, I suggest you get some really good quality 5C workholding stuff. I have (and use, and like) the 5C square and hex bars, a 5C solid horizontal/vertical mount (like an angle plate that holds a 5C collet), and a 5C indexer. I use 'em all. If you had a 5C nosepiece for your lathe that might be a different story. I have every 3C collet (except the 1/64", don't really envision turning a workpiece that small; if I do I can grab it in a pin chuck and rechuck that) for my 9" South Bend.

The thing about workholding with collets is you have to grab the part tightly, and if the workholder isn't made well, you may have real trouble getting it tight enough.

GWE

Just to give the other opinion, I wouldn't be without a full set by /64s. Then you can grip anything, they will collapse that much. I hate not having the tool I need when the job comes up. (If you don't get work you got to do NOW, things might be different) Of course, I waited and bought at Ebay pricing.

Karl

I find that collets provide a good quality control device for me. Frequently I will machine a section of a shaft and then part off and flip the part around and machine the other end. This requires that I hold the machined part in the collet that matches its machined diameter. these are typically standard sized collets, but gripping on a machined rather than stock diameter. If the correct sized collet (ie the size of the spec'd shaft) does not hold the work precisely, the piece is not to tolerance and typically is scrapped. These are relatively simple parts but with many people of different skill levels performing the machining, if the collets don't hold I assume the part is worthless.

Woodworker88 Student Machinist Los Altos High School "Eagle Strike" Robotics Team

When I used to run a lathe in production work, both manual and CNC, the companies I worked for used a range of 5C collets with .005" increments, although we could go to +.010" w/o getting in trouble with the foreman. More than that and the collet would spring and no longer close and grip consistently. We didn't have every size .005" increment up to an inch, just the most common ones, but if we needed an uncommon one, we'd buy or bore the correct size.

David

My understanding is that collets should be sized appropriately for the diameter you are gripping, within some tolerance of course. The angle of the collet is supposed to match up with the angle the collet seats into. If the angles don't match, then the collet is only secured on 1 point. I tried to cheat with a R8 collet once. I put in a drill bit that was to small for the collet. It wouldn't even hold. I took some brass shim of the appropriate thickness and wrapped it around the drill bit. Then I put it into the collet. That worked great! Buying some brass shim stock is a lot cheaper than buying the in-between collets. And you can even go more in-between.

Wayne D.

No one has mentioned what the acceptable tolerance is for collet and work, but it seems convenient to have whatever collets you need handy, rather than having to order one every time the work size is not to standard. So I guess the more is better approach is best.

And the collets I already have(which are said to have an accuracy of .0006), are hardened and ground throughout, and have outside threads at

1.245 x 20 RH; and Inside threads at 1.047 x 24 RH.(I can't seem to find specific mention of these exact numbers for the threads in the newsgroups, but I assume that they are the 5C standard).

Nevertheless, I don't know if I can duplicate such a collet with my equipment anyway. (Especially since the collets I have are fully ground).

Does anyone know the acceptable tolerance for boring a hole in an "emergency collet", and if this changes as the size of the collet/work change?

Thanks.

Darren Harris Staten Island, New York.

****************************************************************************************************** Wayne wrote:

It's an emergency collet. Try not to analyse it too thoroughly, it'll get in the way of getting anything done.

They get bored usually on the machine that they will be used on. The accuracy will be as good as the maker can get, or as good as is needed for the job, more to the point, then it'll be chucked in the drawer (hopefully somewhere near the pins for it) and done over for the next job that comes along, provided that job is the same size or larger. That's all, really.

You are not going to find a bible somewhere that says in flaming letters "THOU SHALT NOT BORE A COLLET LARGER THAN .0005 OVER DESIGNATED DIMENSION"

Cheers Trevor Jones

A full set would be something to behold

Mark Rand RTFM

I just don't want to be anywhere near the bill for that set. Hardinge is pretty proud of their work, as good as it is.

Cheers Trevor Jones