Building a cnc router

[sanddrag]

Originally Posted by DonRotolo

Contrast that with sheet aluminum (6061), with my 1/4" bit I can cut 1/4" thick material single-pass at 50 IPM...As long as the coolant mist and compressed air are on. Chip management is critical for Aluminum, or bits will break.

I take it this is slotting, full width, with an Onsrud single flute bit? Still, that seems like a rather hefty cut. FSWizard tells me to go something like 18,000 RPM at 34 inches per minute for 6061 aluminum, a 60 degree helix angle 1/4" single flute bit, in 1/4" 6061 aluminum, full depth, slotting. It says it will take 0.6 Horsepower for this cut. I wonder if my Porter cable would be able to do this cut.

[DonRotolo]

Yes. Specifically, I did the calculations for an Onsrud 63-620 (1/4" diameter) single-flute upcut bit for Aluminum, with a 1" stickout, running at 16,000 RPM and a straight-line cutting speed of 60 IPM. Under those conditions I can cut as much as 0.300 of material in a full slot. I know it sounds crazy, but it really does it. Less than 0.001" deflection. I didn't calculate the HP, but it is well under 2, maybe even less than 1.

But an Onsrud 63-760 (1/8") for polycarb with 1" stickout at 10,000 RPM and 64 IPM can only cut 0.020" deep slots. It is weird, but the thinner bit really deflects so much more compared to the 1/4" bit.

Both assume a fairly strong stream of air to blow chips out of the slot, and a vacuum system to whisk them away. For the aluminum, add mist coolant to the mix. Allowing the bit to cut chips twice is almost asking for it to shatter.

34 IPM doesn't give you the chipload you need, it is 0.0019 and Onsrud specifies 0.003-0.006. Reduce RPMs or run faster. Never any harm in taking a smaller depth of cut if .250 gets you nervous.

[CENTURION]

Originally Posted by DonRotolo

34 IPM doesn't give you the chipload you need, it is 0.0019 and Onsrud specifies 0.003-0.006. Reduce RPMs or run faster. Never any harm in taking a smaller depth of cut if .250 gets you nervous.

Quoted for truth. Get your chip load correct, then step up your DoC until you get uncomfortable (or it starts making bad noises).

I'm currently designing a router for BadgerBOTS. Still wrangling sponsors, but I've been working on the paper design/CAD since January.

Here's the latest render from a couple nights ago. Still very WIP.

Eventually I'll scan my whole engineering notebook on this design and upload it. If you guys want, I could scan what I have some time this weekend, but as I said, the design isn't exactly complete. There will also be a build log when it comes to that, but it may be a while.