Up to this point I’ve worked in the lathe and the mill without worrying too much about speed and rpm calculation, trusting in my own experience and “feeling”, as a lot of hobbyists, I guess. Tooling wearing wasn’t ever an issue to me; carbide tools seemed to last almost forever. Until I grasp Machinery’s Handbook and read “tool life for milling… should be approximately 45 minutes” (!!). So clearly in the cnc world choosing the right cutting parameters matters.
The cutting setup of my first cnc project involves:
- 5052 Aluminum sheet, 1mm thick
- 2mm, 3 flute uncoated carbide end mill
- 1mm DOC
- 2800 RPM
- No coolant, just a some WD40
This LMS table states a speed of 165 FPM for 6061 aluminum (I guess it’s for HSS). So RPM = (165 x 4) / 0.0787 = 8386. Now, according to this, 0.002 IPT (inches per tooth) is suggested for 0.05 DOC, 1/8″ hss end mill over aluminum (closets size); 0.0015 IPT for my 2mm endmill seems reasonable. So using the max rpm’s (2800) gives me a feed of 2800x 0.0015 x 3 = 12.6 IPM or 320 mm/min.
Of course, due to the complex nature of this topic, suggested parameters for material/end-mill can vary a lot. American-Carbide suggest a feed of 16.000 rpm / 11.8 IPM for this cutting setup. And Whitney Tool states a cutting speed of 600 FPM for hss and 1200 FPM for carbide. As always Practical Machinist is a good source of knowledge.
Now some real world experience in the Sherline world. This guy broke his 2mm carbide endmill at 8 IMP, 0.5mm DOC. This other guy broke his 1/8″ 4 fl endmill at 6000 RPM 14 IMP, 1.27mm DOC. In a test in my manual mill three turns per second (7 IPM) doesn’t seem to break the tool.
So i think I will stick to 7 IPM for now and see what happens, and maybe later I get a set of teen end mills to do some testing and push further. Also, It’s clear I need to order the 10.000 RPM pulley set.