Minimum spindle RPM?

[bsilva]

Hey all!

I have a PRS with an HSD 2.2HP spindle (great unit) and I was wondering if anyone knew of a minimum RPM for this unit? Or issues with spindles at low RPM in general?

I have a cut I'm planning with lots of complex curves in Acrylic, so I'd like to keep the feedrate low. But I do not have a single flute bit in the diameter necc, so I was thinking of using a two flute bit at 4250RPM at 1IPS. (target chipload .007).

There's nothing mentioned in the manual I found at HSD's site and I'm aware that the torque will be lower, but since I'm running a small bit, It seems like I should be fine.

Opinions?

Thanks,
Brad

[bcammack]

I don't know that there's an absolute minimum save for the precipitous drop off in torque (HP) once you get south of about 10k RPM. We were running our 5HP Colombo at 7-9K RPM and it was making less than 2HP at that speed. Had to have a spindle custom-made to meet our needs.

I agree that it sounds like it should be okay with acrylic. What sort of depth of cut are you planning?

[harryball]

I run my 4HP HSD at 5000 RPM for one drilling job with an 1/8" drill bit. I don't think there is any reason I couldn't run a slower but I found that speed with trial and error to get the best hole quality. Any faster on the RPM and it starts burning even with Z at 3 ips. So I peck drill with Z at 3 ips and 5000RPM

/RB

[bsilva]

Brett; I havn't decided what depth yet. Start shallow and play with it. I've using an 1/8 down spiral and I'll probably start with .04 Z cut.

I have lots of scrap for testing!

Brad