The flycutter is simply being pushed too fast through the hard bits to cope and it's taking the edge off.
What do you think?
I think you might have hit the proverbial nail on the thumb. I was using the smallest of a set of 3 flycutters, it has a cutting-edge-diameter of about 1.5" and I may well have been running the speed a little hot ( not having a rpm meter I set the speed on what seems to give the best finish along with what feels and sounds right ) Then I changed over to a 14mm 4 flute end mill.
What sort of speeds are we looking at for fly cutting, (depending on radius of flycutter of course)?
Thanks
Gordy
On my little flycutter mentioned above ( I havent yet sharpened up the other 2 larger ones ) I would run at a max of just under half speed on my belt-drive-converted-X2, ( that's about as fast as I can get it without it causing vibrations to set in ) without a meter to tell me the exact rpm I would guestemate that would be about 1300-1500rpm.
However ( and that's a big however ) that would be on taking light ( and I mean light for a flycutter ) cuts on soft materials like brass and Ali. On harder stuff you need to slow down even more.
A handy little online calculator for working out just what the actual surface-feet-per-minute is
Here And near the top of
This page there is a basic table of cutting speeds for different metals.
Looking around, there seems to be a lot of variations in what people say should be the cutting speed you should use on a particular metal, I guess the best you can do is to get it roughly right and then let the machine ( lathe or mill ) tell you if it is too fast.
Tim