Ned Simmons wrote:

On Sun, 20 Feb 2011 23:28:01 -0600, Ignoramus17758
wrote:

I am trying to make a dog clutch that mates with the knee crank and
replaces the crank handle:

http://igor.chudov.com/projects/Brid...-8057.jpg.html

I wrote a G code program that makes such a clutch from a flat block of
metal, with a 1/8" end mill.

In machinable wax, it does a great job, zips through it, and makes a
surface that mates with the crank handle perfectly, I was very
impressed.

In steel, however, this little 1/8" endmill works for a while, then
breaks after 1/2 hour.

1/8" end mill
4 flute
1 IPM feedrate
2,000 RPM
plenty of coolant
unknown steel, but feels like 1018.

I am sure that something simple and stupid is wrong. I am not really
sure how to approach this.

I will, first, get a known best quality endmill, they are still
somewhat affordable in 1/8". I am thinking, get a 2 flute, 1/8"
endmill, 1/2" DOC. I am thinking TiN coating?

In addition I will get a known 1018 block, I only need a small piece.

I do not want to up the RPM beyond 2,000: at 2k RPM, the spindle is
nice and barely warm to the touch, and at higher RPMs it gets
warmer. Since this is a job that takes forever to complete, I would
prefer to keep the sipndle cool.

Any ideas?

I know that I could make the program run faster with tool changes and
a larger end mill doing boring and such. But I wanted to learn more
about small work.

i

First thing that strikes me is that the feed rate is extremely low. It
sounds like you're dulling the tool with a way too conservative DOC.

Chip load, not DOC. Agree, the tool is rubbing more than cutting and as
a result is rapidly dulling, deflecting more and more as it dulls and
eventually snaps.