Feeds, Speeds and Depth of cut.

[jthelen]

First let me say There is a lot of valuable information here on the forum and I appreciate the advice and help.

I did some searching today for different feeds and speeds people use on the various materials.
Most of the time 3 components are given. Feed rate, RPM's, and the bit size. (1/8, 1/4, 3/8,1/2 Etc)
There were many times I would get the end and say "at what depth?"

Is depth of cut per pass a standard thing that I am not aware of? Like assume one material thickness or 1.5 times bit diameter per pass. If someone says 2.5 IPS at 18,000 RPM's with a 1/4 inch bit don't you find yourself wondering at what depth? Is not the depth per pass an important component in this calculation too?

Thanks.

Jim

[wemme]

Gidday I am new to the shopbot and would like to optimise my cutting, make the most of tool life and cut quality. can any one point me to a FAQ or other info regarding feed rates, cut depth, etc. I mostly cut MDF but would like to look at other materials too.

[mrdovey]

As far as I've ben able to determine, the important variables are feed, speed, and cutter geometry.

The feed speed is limited by how rapidly the material ahead of the cutter is being removed - and this is determined by how fast the cutter is rotating and how much chipload the gullet behind the cutting edge can carry and release. Bit sharpness is a significant factor.

That gullet appears to vary according to manufacturer and bit type/style.

Chip removal rates are important also for heat removal - perhaps counter-intuitively, it's the chips rather than air that carry away the bulk of the generated heat. I strongly suspect that the heat capacity of the workpiece material may sometimes also be significant.

So - for any given cutter, a too-high feed rate will attempt to move the bit faster than the material ahead of it can reasonably be removed resulting in bit flexing and/or breakage.

Also for any given cutter, a too-low feed rate will produce unnecessary frictional heating and insufficient heat removal resulting in workpiece burning and/or bit breakage.

Onsrud Cutter has a calculator and chip load data on their web site. It's really handy but you need to be aware that it's specific to OC bits and may or may not be accurate for other manufacturers' bits.

...Morris