# Confused about Collets



## kjk (Jul 20, 2010)

I have been looking around the net for information about the various types of collets and collet chucks and am confused by the number of alternatives and the nomenclature used.

Can anyone enlighten me or point me to a site that has a good description of the types and their specific advantages? 

My lathe has a MT4 spindle and so an MT4 collet chuck is the easy part, but what type of collets do I want? I thought initially that the difference between ER32 and ER16 for example was capacity, but that doesn't seem to be the case and there are of course many other types. 

I don't have a milling machine yet, and clearly being able to use the collets on both the lathe and a future mill would be an advantage.

I've been following the thread on building a collet chuck, but I don't think I'm ready for that project yet.

My reasoning for wanting a collet chuck is just safety at this point. 

It's a real newbie question, but then that's what I am.


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## mklotz (Jul 20, 2010)

ER collets are a good choice but don't instantly dismiss C5 collets...

Widely available in a range of prices.
Can accept stock longer than the collet. (R8 can't)
Easily fitted with a collet stop. (Can ER use a stop? Don't know.)
Can be had with square and hex holes. (Square collets will save mounting and centering the 4jaw in many cases. Hex are nice but not essential. I've never seen a square ER but they may exist?)
Emergency collets (blanks you bore to your required size) and pot chucks are available.
(Again, I've never seen them for the other collet types but that doesn't mean they might not exist.)

On the mill, can be used with collet blocks (super useful) and Spindex (very useful).


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## ksouers (Jul 20, 2010)

Hi Woodguy,

I'll try to answer and hope I don't add to the confusion.

I use 4 different collet systems in my shop: R8, 5C, MT3 and ER40.

R8: The most common (by far) taper collet used for milling machines in North America. Thus, the tooling is readily available and affordable in the new and second hand markets. I've never seen an R8 taper on anything but a mill. The collets require a draw bar to pull them up tight so they are closed end. The collet is released by backing off the draw bar and tapping it with a dead blow hammer.

5C: Quite common on production sized lathes, this is a self-ejecting pass-through collet. Though similar in appearance to an R8 the body is larger and the taper is slightly sharper and more abrupt. The outside far end of the collet is threaded for a draw tube that is connected to the locking/ejecting mechanism.

MT3/4: These are Morse Taper collets. The taper is rather shallow and locks quite firmly using a draw bar. They are closed end. Releasing the collet is similar to the R8 but may require a rather sharp smack to release as they can grip very tight because of the slight taper.

ER series: All of the ER series are similar in design, the difference is the physical size of the collet and capacity. These are a pass-though and self-ejecting design. The collet itself has two tapers and is shaped somewhat like a truncated diamond. A nut with a ring in it locks into a groove in the collet, the nut screws onto the chuck pressing the collet into the taper. The collets for each "step" (ER11, ER16, ER32, ER40 etc) are not interchangeable with each other.


The R8, 5C and MT collets have very little tolerance for off sized work. Your material/tool must match closely the size of the hole in the collet. The ER series is much more forgiving in this regard allowing as much as a millimeter variance in size.

There are many more collet systems used throughout history and the world but these are the most common, you will be able to find any of these at reasonable cost at any of the major tool vendors or on Craig's List/ebay.


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## kjk (Jul 20, 2010)

Thanks Marv and Kevin - exactly the kind of info I was looking for.


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