Rich Grise wrote:

Pete C. wrote:
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.

What depth of cut are you using? What is your chip load per tooth? What
is your cutter SFM?

You should never use an end mill smaller than you need, and from memory,
the knee crank "crown" could be milled with at least a 1/4" end mill
which will be stronger, have a higher SFM at your spindle speed and have
more chip clearance.

So, say I'm making a rectangular hole. Would I cut it with, say, a 1/4"
side mill, and finish up with a broach?

You would certainly need to finish with a broach if you need square
inside corners. If you can live with rounded inside corners of a small
diameter end mill you can certainly do a finish pass with a small end
mill, but it would be insane to try to mill say a 2"x3" pocket with an
1/8" end mill just because you need 1/8" for the finish pass.

At any rate, that is not relevant to Iggy's machining issue, since his
part does not have any inside corners. For his part he should be using a
3/16" end mill or slightly larger, milling the outside diameter, the
inside circular pocket, the radial bulk material removal cuts between
each section of the "crown", and then finishing by milling the exterior
of each "crown" island wedge. The limitation on the end mill diameter is
the spacing between the inner points of the "crown" islands which is
around .2".