Originally Posted by
Superman
RPM is calculated on the diameter of the cutter to suit the material being machined.
so... changing a cutter from 4 flute to 2 flute means that the feedrate is only to be altered ...altering the RPM changes the cutting speed that has designed for that cutter geometry.
[Most cutters can run fine in a fairly wide range of RPMs, but 2-flute cutters are designed for different materials than 4-flute ones. In general, you should run smaller tools faster than larger ones; this is based on SFM (surface feet per minute) which should be adjusted to yield an optimum chip size.]
you may not be locked in to what is specified by the tool manufacturers, but what works for your application/setup.
say... a 10mm dia x 2 flute verses 10mm x 4 flute.... both run at the same RPM but the 4 flute would be programmed at 2x the feed as a 2 flute
[I think you got that backwards. If the RPM is the same, then the 2-flute cutter would have to feed twice as fast to produce the same size chips.]
take material steel for example
a HSS runs about 25 m/min. so the RPM using 10mm dia is set around S800, dia 5mm would be S1600. if you double RPM, your cutter runs the risk of not lasting too long.
[That would depend on factors like machine rigidity and the material being cut, but you can't expect to take as big a chip with a small-diameter cutter as with a big one; your formula has to take that into account.]
That's not to say you cannot do it, you need to weigh the pros and cons.
The principle of thinking that doubling RPM is the same as halving feed is incorrect.... the time is quicker, but you have actually doubled the recommended cutting speed that the manufacturers have designed the tools to be optimally run best