What tool/feed/speed for case hardened steel?

[67Charger]

I have to cut a .064" deep step into some 2"x.75" case hardened steel pieces. The hardening is about .015 deep. The cut goes from the bottom edge in about .65 at a 15° angle across the bottom. The step must be square so a sharp cornered tool is necessary.I was using an uncoated carbide Atrax 2 flute 1/2" endmill at 2500rpm and 3.5fpm feed, and a flood of ValCool, but after 4 pieces there are no corners left on the endmill. I need to do 250 of these. The machine is a Cincinnati 5vc-750 (5HP).

[fizzissist]

Rough it with an insert tool, then finish with a solid carbide coated endmill.

[DMF_TomB]

your doing 2500 rpm with a 1/2" carbide end mill on hardened steel ??
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me i would try slowing down. see how far you get at 1000 rpm or even slower

[Shane123]

i would save your sharp corner for cleanup. maybe a tain coated fine tooth roughing endmill for the first pass?

[H.A.S.]

Originally Posted by DMF_TomB your doing 2500 rpm with a 1/2" carbide end mill on hardened steel ?? . me i would try slowing down. see how far you get at 1000 rpm or even slower

I agree. Corner breakdown is also caused by heat and lack of rigidity, if you have a lot of pieces, snug up the gibs even more. It won't hurt your machine to run with the gibs a little tighter, you can always adjust them back.

Are you using a four flute carbide? High quality cutters?

[67Charger]

Update:

The job is done for now, but there will be another 500 - 1000 in the near future. Attempt 2 involved using a 1.25" 4 flute insert cutter at 650 rpm and 3.5fpm feed to rough it out then finish with the 1/2, but I lost the corners of the 1/2" cutter again. #3 traded the 1/2" cutter for a 7/8" 4 flute solid carbide and had better results, but still was eating the roughing tool pretty bad. About 150 parts in the tool changer arm decided to drop my 7/8 cutter and holder onto the vice and shattered the end of the tool. Out of morbid curiosity I reprogrammed it to use just the roughing tool and do a roughing pass and a finish pass, and the results are a good as using 2 separate tools. I went ahead and ran the rest of the batch and took a sample over to the heat treaters. Interesting tid bit. What we thought was case hardened steel turned out to be through hardened steel coming in between 48 and 55 HRc.

I'm currently using a Kennemetal 4 flute 12 insert 1.25" diameter cutter with XDCW 2322 and SDCW 322 inserts, but I'm only getting about 25 pieces before having to rotate the inserts, and since the XDCW are rectangular I only get 2 edges per insert. The inserts are flat. Knowing that it is through hardened, should I use an insert with some tooth to it rather than flat? how about the feed and speed? I am really not used to working with hardened materials.

The parts were finished beyond the customers expectations, but it cost me nearly $100 in inserts and tool sharpening on a $1000 job.