Hi,
No, that is correct, its meters per minute. That is the surface speed not the speed of advance of the tool or cutting speed.
The surface speed is the velocity of the tool tooth or tool surface relative to the material. So as the rpm's go up so does the
speed of the surface of the tool that rubs the material.
Each material has a recommended surface speed. Roughly:
Titanium and Superalloys 20-40m/min
Stainless 50-70m/min
Mild Steel 100m/min
Aluminum 200-500m/min.
Note these surface speeds are for plain carbide. Coated carbides will tolerate more surface speed as a rule. HSS tools rather less, about 1/2 to 2/3.
I like HSMAdvisor so much I bought it.
https://hsmadvisor.com/
Cutting speed is all about how big a chip you are trying to peel off.
You are using a four flute endmill, so for each revolution it will take four chips. If each chip were 5um thick then the tool would advance:
d=4*5um
=20um
or 0.02mm.
At 6222rpm the cutting speed would be:
CS=6222* 0.02
=124mm/min
The thickness of the chip, called chipload, is dependent on a number of factors including the strength of the tool, both bending AND torsion,
the power of the spindle and the rigidty and thrust of the machine. I would suggest download HSMAdvisor (demo) and input the parameters of your
machine and experiment a bit with it.
What I have found is that the surface speed is the most important.....you can vary by 10-20%, but if you try to spin the tool too fast then you risk
overheating and wrecking the tool. It does not usually hurt to spin a tool slower than the recommended surface speed would indicate, and often with small
and very small tools your spindle can't spin as fast as you would like.
You can reduce the cutting speed to accommodate your machine or spindle which may be a bit too light. What I do not recommend however is trying to take very
light or slow cuts.....what happens is you just give the material a good 'rub' and workharden it WITHOUT really peeling off a chip.
I have made that mistake......having a high speed spindle I have settled on a high rpm well exceeding the recommended surface speed and so to compensate
tried to take very light cuts very slowly. It didn't work!
A lot of the literature recommends NOT cooling carbide, the thermal shock of the carbide it supposed to hurt it.
That is not my experience. With my mill whenever I use flood cooling my machining has improved VASTLY! I have had various conversations with other hobbyists
and most use some sort of lubrication. I'm quite keen to have a go with M(inimum)Q(uantiy)L(ubrication) as a result. I'm less convinced that lubrication
is the real point but rather using a fluid, be it cutting fluid or compressed air, to blow the chips out of the cutzone.
Craig