ER COLLET sizes which to choose.

GoceKU

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I'm making a lathe milling attachment and want to find or make an ER collet holder to hold the end mills in the taper on my spindle it is an morse 6 taper, now the question is i need to source collets and looking at online stores the ER25 are half the price of the ER32 but go only to 16 mm, is 16 mm big enough or should i go to an ER32 and have 20mm capability ?
 
Er 40 goes to 1" , even that seems small for me? One of the nice advantages of collects in the lathe, they can hold material very precisely. If you think of collets as only holding mill cutters you may be limiting your options. When I bought mine, I knew I would be sharing them between the mill and lathe. For the lathe I have the ability to use them in the tailstock as well as spindle.

Just something to consider.

Rich
 
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I am wondering if the answer to your question might be dictated by what's available in the way of MT6 collet chucks.
 
My Tormach mill uses a 3/4" shank ER20 collet chuck which I mount in a 3/4" R8. Tormach also sells ER32 collet chucks. The advantage of the Tormach system is you have accurate and repeatable tool offset heights, providing you change out the chuck with the collet. I have about twenty different tool holders so I can have the whole set of pre-referenced milling tooling set up and switching out tooling during a job doesn't require re-referencing.

I modified my old mill to use the Tormach system as well. It simply involved removing some material from the face of a r8 R8 collet. My spindle face ran true so no modification was needed there. Tormach has a white paper on making this modification.

The tool holders will also work in a lathe but the disadvantage is the lack of a through hole. The solution would be to make or buy a spindle mounted ER chuck.

I opted for a 5C collet chuck for my lathe because I already had a set of 5c collets. Unfortunately, I had overlooked the limited grip range of the 5C collet and in order to have a complete set for work holding in the lathe, I would have to add, at least, the odd 1/32" collets and ideally, the odd 1/64" collets which would be 17 additional collets by 32nds or 51 additional by 64ths. Doing it over, I would have opted for an ER32 chuck or even an ER40 chuck.
 
I'll sort of echo RJS' sentiments. I had an ER-32 chuck on my bench lathe. Since I already had it, I later opted to buy a 5C chuck to handle 3/4-1" work pieces, and now use a thru-feed 5C to ER-32 adapter for 3/4" and smaller stock. Even though stock larger than 3/4" won't pass through my lathe's spindle, the 5C setup does give me a way to turn short pieces of 1" and longer pieces if I break out the tailstock center. In 20/20 hindsight, I should have bought an ER-40 chuck and collets, but I was sort of tunnel visioned into thinking the spindle ID was the practical limit for a collet system. It really doesn't have to be.

Tom
 
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