The KaVo collet, revisited

5 Bears Home Homebrew CNC bench mill

Quite a while ago, I attempted to make a collet for the KaVo 4041, in 1/4" diameter bore. The KaVo collets are available, but expensive, and I wanted to see if I could make one of adequate precision. I proceeded to completion except for the collet slot cuts, as measuring the runout of the bore revealed about 0.001" runout, horrible and unacceptable for a cutter designed to rotate upwards of 50,000 RPM. Recently, while lubricating and cleaning some of my mill fixtures which I hadn't used in some time, I was working on this wonderful Hardinge spacer, and decided to put it to use while it was out. Dragging out the failed collet, I decided to see if slotting the collet and actually mounting a cutter would improve things.

This particular indexer has a hardinge taper nose as well as a 5C drawtube. Since the body of the collet was metric and I didn't have an acceptable collet, I mounted my lathe chuck on the indexer and centered the collet to 0.000".

Mounting the thinnest slotting saw that I had, which was 0.023" thick, I proceeded to slot the collet on 3 spots spaced by 120 degrees, the same as the factory collets.

The slotting was uneventful, with about 0.020" depth per pass working fine. Here, the saw has almost cut through to the bore. This type of mill operation is a lot of fun.
Deburred and polished, the collet looked nice. I was concerned that the collet wouldn't have enough "flex" to grip the cutter under the KaVo's pneumatic drawbar, but it worked fine.
The rear of the collet reveals the M10 female threads for the pneumatic drawbar. I had some hope that mounting the cutter, and applying a 0.0001" indicator to the cutter shank, would reveal a much lesser runout than the 0.001" that I had originally measured on the unslotted collet.
Shown here with a 1/4" shank carbide end mill.

Sadly, the cutter, once mounted, still had the original 0.001" runout. It was obvious on the indicator, and it was very obvious from the vibrations it created! Rather than try again, I am resigned to buying what collets I'll need to really tool up this particular spindle. Like so many other machining adventures, into the scrap box it went, with nothing gained except the experience.