Steel Squeel?

[peter.blais]

Hello guys. I usually cut a lot of aluminum, but am currently making some steel parts. These ones are A36, which is soft as hell, but I seem to have the same problem in virtually any material. I've even machined post heat treat 4340 etc up to 45-50 Rc and the issue is the same, just slower.

Anyways, on these particular parts I'm doing a round ID pocket. I'm spiraling down into the part, then using a "true spiral" toolpath. What's odd to me is that 75% of the time, the tool cuts very nicely and quietly- the other 25% I get howling banchie that I can hear all the way from my office in the front.

Sometimes it's even just going around a constant circle, with the same tool radial engagement, and yet there are a few spots here and there it will screach at.

The final finish looks fine, but the finish pass doesn't make any noise either.

Specs: ~Very low hours VF2
1/2" SGS Z Carb AP
Maritool ER32 Collet / Holder - Finish seems great all said and done
39 IPM, 3900ish rpms
.5 DOC
anywhere from .25 to .45 width of cut

Changing the speed and feed just seems to result in an orchestra of different pitched squeels. I can never seem to eliminate it that way. I just changed the radial engagement down to like 30%, and it helped a little, but it's still there.

So, my questions are- does anybody actually know what is causing this or have seen similar symptoms? Is this just a bad noise, or is it chatter? Could it damage my spindle over time, or should I just ignore it?

I've tried straight / zig zag type tool paths, all sorts of things. No matter what, I seem to get a mixed bag of quiet / loud as hell.

Thanks in advance!

Pete

[Delw]

try using a collet tool holder instead of a screw lock one., Just assuming you are cause you said it does it in alum also.

[Matt@RFR]

Sounds like chatter to me. .500 deep and .150 stepover is still a chatter-prone cut in steels in my experience. (I'm on a '07 VF-2ss) If that endmill is AlTiN coated, I just had great results with these parameters in A36, with a Lakeshore Carbide 4 flute with R.030 corners in an endmill holder:

6100 RPM
127.5 IPM
1.125" deep
.050" stepover
Airblast, no coolant

This is actually taking it easy, no chatter whatsoever, and fast. The stepover could be increased slightly, and / or the feedrate could be increased substantially. Chip thinning is your friend, as well as current coatings, and will make your Haas much more steel friendly.

[peter.blais]

Guess I'll just reduce the stepover some more until I can get it to quit, then start working up the speed & feed as you suggest.

Yes, it's coated in AlTiN- they are also a variable helix blah blah blah.

I guess when slotting the solution would be less axial DOC and that's about all we can do?

I've got a little AJX style insert high feed insert cutter that I need to try out- shallow but fast cuts seems like a match for the haas. It's just odd because I never thought it would have an issue with a 1/2" cutter.