Threaded shank are needed only if you have an Autolock or Posilock type milling chuck – they screw into the collet and actually tighten it. They will however fit plain collets such as ER style.

2 (or 3) flute cutters are able to cut at their centre, so can be plunged straight into a surface. They are good for cutting slots, also seem to be the best choice for aluminium. Sometimes called slot drills. 4 flute cutters generally need to cut from an edge as they can't be plunged.

ER collet systems are about as good as you will get for holding plain shank milling cutters, there are lots of suppliers of these about,

Some 4 flute cutters can plunge!!

HTH

Shaun

If you sacrifice the ability to plunge, sharpening the 4 flute is relatively easy.

What do you do with the "bit in the middle" then? Where the cutting edges meet. If you simply don't grind up to that point wouldn't you leave a "pip" or high area in the centre? Making sort of a counterbore in the centre to take that area out would be good but I don't know how you could do it practically.

(Speaking in ignorance because although I've fashioned several devices for sharpening end mills I haven't seriously knuckled down to doing it properly yet).

First question, what mill do you have and what shape is the spindle nose? If you have an R8 spindle (or haven't yet bought a mill and have the option to get one with R8) I'd recommend using R8 collets with a drawbar. You don't need a huge range of sizes anyway, R8 collets are quite cheap, they grip like b*****y, don't get stuck, and best of all they are almost flush with the end of the spindle when holding a cutter, which maximises the headroom you have.

If your spindle is morse taper, you can get MT finger collets which need a drawbar and have many of the same benefits of the R8, except they don't grip quite so well and the taper can get stuck (but you can make/get an ejecting drawbar design).

Finally you can get an ER chuck on a shank to fit your spindle. If your spindle is R8 then in my view there's no point in using ER, it just eats up headroom and reduces rigidity. For an MT spindle then at least you don't have the problem of ejecting a stuck taper to change the cutter if you use ER. Depending on the machine and the biggest size cutter you want to use, most people seem to use ER25 or 32.

Most of the usual ME suppliers have collets and chucks, Arc Eurotrade, RDG, Chronos etc. Personally I normally buy from Arc as they've always given good service and have good quality stuff. I bought my R8 collets from J&L Industrial Supply. Or you can buy through eBay, with the usual caveats.

Personally I have R8 on my Myford VMB and have never seen the need for anything different except for drills that won't fit in a standard collet. My little CNC Novamill has an Int30 spindle taper so I use an ER16 collet chuck in that (you can't use collets direct in an Int30 taper).

As John states depends somewhat on the type of spindle your machine has, I would add also depends on the maximum size of end mill it is capable of working with. If max size is 10mm then there's no point in buying an ER25/32/40 type holder, the greater diameter closing nut may prevent access to the part being milled/drilled.

I believe any of the suppliers mentioned by others will provide similarly accurate low cost products but you may have to accept differing amounts of run-out on the cheaper end collets.

Emgee