Need advice on surface finish

[Robin Hewitt]

It's called "chatter". A sort of sympathetic vibration and you've got it bad.

The easiest way to get chatter is big overhangs, reduce your overhangs.

Apart from that you can either increase the rigidity to damp it out or change the frequency either by adding flutes, as bogstandard suggests or by changing the RPM.

A radical spindle speed change before the finishing cut might help but chatter does tend to echo through on to the next cut.

With that much chatter, I agree, cutting uphill is probably a no-no.

Robin

[FatFreddie]

Thanks everyone for the suggestions, I've been trying different feeds and speeds and more flutes as suggested and I have improved things by running 4 flutes at minimum speed (about 300 RPM I think) - feed doesn't seem to make too much difference except that it has to be fairly slow at that speed to avoid machining marks. Locking the quill doesn't make too much difference but I assume the resultant cutting force is downwards which is against the feed mechanism so it's fairly rigid in that plane.

I wouldn't even consider climb milling with this rig :-)

Looking at the milling head, the part of the casting that connects the main body of the machine to the spindle is just two thin vertical plates - I might try and bolt some cross members in to stiffen it.

I think I can make some improvements with work holding as well though the vice is good and solid.

I'll also try and source some 6 flute cutters - any recommendations?

Thanks again,
Mark