[Jjiveturkey]

Hi all, I'm running right now in a 3-inch thick 10.25" Diameter block of 4140. I have to mill out about 60 small parts that are about .95" TK, so I'm using a 1/4" 4-Flute AlTaN coated endmill, running about 4,000 rpm and 18.5 Inches a minute, ramping at 0.15 of a degree. The overall run takes about 12 hours, but the tool only cuts about 8 parts before breaking from excessive chip-buildup. I'm blasting coolant from four ends down into these tight slots, but it's just not doin the trick. So I'm asking you guys if you have run into anything similar?

Thanks!
-Weston

[jimmyjames1981]

your sfm is too high for 4140 and slotting, is it 4140 or is it prehard 4142? either way, small endmills hate 4140. is 1/4" your maximum tool size? you say its ramping at .15 degree, that doesnt tell me anything, depending on your part size your depth of cut could be way too deep. sounds like you need a 1/4" rougher if 1/4" is the biggest tool you can use. a 1/4" rougher can go roughly 3/16" deep or more at 12ipm through 4142/4140/d2/a2/etc. id have too look and see what the rpm is, cant remember. would have to be in an endmill holder though, it would pull out of a collet.

[Jjiveturkey]

Well I reduced the speed and feed by 25% and was actually able to get my cutter through the parts. Sorry if I confused you with the ramping angle, I wasn't making a slot cut I was actually doing a ramp cut. I had to mill the parts out kind of like barnacles and then use a saw to remove them from the main chunk of 4140. It is also regular 4140, it wasn't prehard 4142. But yes, I agree with you that small endmills hate 4140, I also work with a lot of D2 (un-hardened and hardened), and have found a great speed and feed for cutting cavity's and internal corners using ramp cutting, similar to what I'm doing here. But I appreciate your response, it just took a bit of finicking and plenty of headaches to find somethin to work for this guy.

Cheers!