View Full Version : Collets

patty boy
01-02-2009, 01:06 AM
I have very little experience using collets in either a lathe or milling machine. I have two questions:

1. Can regular 5C or R8 collets successfully hold a drill? This assumes the collet matches the drill size. Or will the drill slip? Same question for holding a straight-shank boring tool?

2. Are conventional collets preferred (though it takes a lot of them), or would I be better advised to invest in a set of expanding collets (and holder) such as the ER ones?

01-02-2009, 01:32 AM
1. Yes, you can hold a drill in either of the collets and ditto for a boring bar. Both these collet series are sensitive to size, so a drill larger or smaller than nominal will not be held as accurately or tightly.

2. This question is a matter of great debate and you may have inadvertently removed the lid from this can of worms (again). In my opinion, the ER series is nice because of the good grip over a range of sizes. On the other hand, 5C collets are so prevalent that they can be bought less expensively.

Expanding collets are different, in that they're intended to grip on the ID of a a part to be machined. These are also much more available for the 5C series than others. For special needs, soft collets can be had which are then machined as required like soft jaws on lathe chucks.

Paul Alciatore
01-02-2009, 03:01 AM
The best solution is what is best for you.

R8 collets are commonly used in smaller milling machines. Milling cutters generally come in a limited range of shank sizes so a set of collets by 1/16s or even by 1/8s would be good for most cutters you are likely to use. I believe even most metric sized cutters are available with fractional inch sized shanks.

Drills are another story. They come in a wide range of sizes and generally, the shank size is the same as the drill size. So it would either require a very large set of 5Cs or several sets of the ERs. My personal solution is to have several drill chucks with R8 taper adapters for the mill and several others with 2MT and 3MT tapers for the lathe.

Yes, ERs do cover overlapping ranges of sizes, but there are several different series of ER collets and to cover all drills from a #60 up to 1" you may need two or even three of these series. And here's the kicker, each requires a different sized collet holder. For instance, the ER-32 series is perhaps a good choice, but it will only hold from 3/32" to a bit over 3/4". If you want larger sizes you will need to buy some ER-40s and for smaller sizes you will need a smaller series (ER-25, ER-20, ER-16, or ER-11). Even the ER-11 only goes down to about 1/32" so smaller drills would still require another solution. $$$$$.

Drill chucks are a lot cheaper for holding drills. ERs are considered as work holding collets. This is not a hard and fast rule, just how they are generally used. I have a set of ER-11s for my Unimat lathe and some 1Cs for my SB lathe. I also use the ERs for holding small milling cutters in the Unimat. But I always use drill chucks for drills. I have not decided on a replacement for the 1Cs for my SB, but the two choices I have considered are the ERs (probably ER-32 or ER-40) and the 5Cs. I discussed the ERs above. One advantage of the 5Cs is the lower prices and availability of other shapes such as square and hex.

At present I do not have any boring heads for the mill but when I do get one it will most likely have an R8 adapter on it.

But that is my solution. Your needs may be different.