What is best bit to use

[wrechin2]

I am cutting some .500 X 5.00 slots in 3/8 aluminum. What would be the best tool for the job and at what RPM? I have used a 4 and 2 flute end mills but it is slow and the sides are not neat/clean. Would a ball mill do a better job? Thanks to all that answer!

[Geof]

A two flute high helix carbide, GAR 242M or equivalent, running at 10,000rpm or faster with flood coolant.

[wrechin2]

Which for dry? I don't have flood coolant. Fastest my mill will go is 5500. Thanks for the info!!

[Geof]

Which for dry? I don't have flood coolant. Fastest my mill will go is 5500. Thanks for the info!!

I figured you probably couldn't meet the rpm I suggested; 5500rpm is acceptable.

Don't do it dry this is where your poor finish comes from. You can try spraying on WD40, I don't think it works as well as brushing on Dexron ATF along where you will be cutting. Or get some proper coolant that is intended to be mixed with water and just brush this on neat.

Also for the best finish use a 5/16 (or 1/4") cutter; take a couple of passes down the centerline of the slot going 0.25" deep for each one. Then move sideways to get to the 3/8" width and finish both by climb milling; this mway you don't have the chips jamming in the cut and making a mmess of the opposite side of the slot.

[wrechin2]

DANG!!!! That makes sense. My edges are being "beat" up by the chips. My width is 1/2 in 3/8 thick material. Would a solid carbide bit work ok? Guess I will use a 3/8 cutter then move out to my finish size. Just looked at my MSC book and they have a ton of bits just for aluminum. Thanks for the info! Makes sense.

[Geof]

.... My width is 1/2 in 3/8 thick material....

And I should read straight; 1/2" slot, 3/8" material. I read it as 3/8" slot 1/2" material; have you ever heard of dyslexia? A d**n nuisance sometimes.

Yes use a 3/8" cutter with coolant/lubricant and you should get a good finish. Solid carbide and as I mention the high helix style, these cutters lift the chips out of the cut and have more of a shearing action in the cut.

[wrechin2]

Thanks again! Been a big help. Most of this is simple one you are told!!!LOL!! Later
James