[ravix]

I recently completed a CNC conversion of a Shopfox M1111 Benchtop Mill (basically an SX3). The maximum spindle RPM is 1800.

I've been researching speeds and feeds and trying to get a feel for it on my machine.

My only intention is to cut aluminum, I don't have much desire to cut steel with this machine. For aluminum, many people seem to be using RPM's in the 3000-6000 range.

Can I achieve similar results using a proportionally slower feed rate at a lower RPM? I'm not typically in a hurry to get pieces finished, but if I'm going to be constantly fighting other issues (surface finish, worn tools, etc) with 1800rpm I'll do something to address it.

Lastly, I think I should tend to use larger diameter endmills at lower RPM's, does this make sense? Right now I'm primarily using a 3/8" carbide high helix endmill.

[Jim Dawson]

I would stick with the 3/8 endmill. Yes, just decrease the feed rate to keep the chip load in a reasonable range.

[hackish]

My experience has been that you need both RPM and rigidity to be successful. People often under-size both when dealing with cutting aluminum. It might be soft, but you still need to provide a certain number of RPM to keep that head from moving around. I feel like the lower RPM causes the head to oscillate more. I know when I had my bridgeport, I could mow through material at 1800 RPM and it would just go through. Currently, my PM25 seems to be a lot more affected by exactly the same settings. At a higher RPM and more feed, it does fine.