In CNC milling, there are many variables that you must adjust.
The first one you'll encounter right away is how deep to cut. If you try to cut too deep, you'll break the
endmill or router bit. I like to start at about 1/2 of the diameter of the cutter and adjust from there. If I'm using a 0.050"
endmill, I'll set the cut depth to 0.025" per pass. That seems to be a good starting point for me.
The two other big factors are feedrate and spindle speed. Feedrate is how fast the cutter
moves though the material. Spindle speed is how fast the spindle is spinning. Feedrate and spindle speed, together
with how flutes the cutter has, determine chip load. If you move a cutter that is spinning too fast (RPM) through
hardwood too slowly (feed rate), it will build up heat and burn the wood. Instead of tiny chips (which carry away heat),
you'll just be making dust and then smoke. If you move a cutter too quickly that is spinning too slowly through the wood,
the cutter will bog down break.
The mistake I think a lot of people make is to have the router (RPM) too fast and the feed rate
too slow. This causes the bit to heat up and burn the wood. Most of the time, I cut with the router at about 12,000 rpm
(half speed for mine) with a feedrate of 30 inches per minute (which is as fast as my little table will go).
There are methods to determine the optimal feed & speed for router bits. There is a great article
on how to do this at: