Chipload and DOC for small endmills

[Jonathan]

Probably true in your case Mark

:rofl:

I haven't found sub 3mm tooling in high helix with a rebate on the flutes and the carbide tinies tend to be coated with other than aluminium nitride so that helps not a lot.

That sentence took me a bit of time to decipher!

Even so, I wouldn't step drill it. Presumably you've turned a blank for the pulley and removed any surface hardening from the extrusion, if it isn't cast, and there is no oxide layer to wear an inconvenient slot in the flutes. Personally I'd go for around 2000 rpm, feed it at 1 -> 1.5 mm/s on a 3 flute, start with .25mm DOC, increasing if it seems good to go.

Yes I'm using aluminum bar, not cast. I wasn't aware of surface hardening being an issue with aluminum (iron yes), however now you mention it it makes sense. One anodises aluminum to make the surface harder (or prettier), so it follows logically that the natural layer of aluminum oxide will wear the tool.

42T pulley with 0.25mm DOC and 1.5mm/s will take 170 mins. Maybe a little less if I get rid of some rapids in Gcode, but not much.
Chip thinning may enable me to run the cutter a bit faster for the same chipload a significant amount of the time. I can quite easily add that to my program.

I'm warming to the make a tailstock (anyone got a spare!) and just use slitting saw idea. I can stop the 63mm slitting saw bending by machining some 50mm steel disks and sandwiching it between those on the arbor.

Standing over it with a blow gun, a pot of Rocol RTD and a brush could be an exceptionally good idea even if this temporarily suspends tea, fags and scratching

Who says I can't drink tea whilst doing that!