Chatter question

[tbaker2500]

I'm doing some pocketing, having to remove a fair piece 'o aluminum. The material is 6061 T6, mounted in step jaws, 3"x13"x0.75". The bit is Atrax Carbide 1/2" 2 flute EM 1"LOC , with about 1.25" of the bit sticking out of a TTS set screw holder.
I've been finding that when slotting (have to, to start the pocket) I'm getting some serious chatter on the tool IF I'm cutting with a depth of cut of greater than 0.15". 0.15" DOC or less, I can crank through with 27ipm or even 36ipm. But once I go deeper than that (today was 0.188" DOC), it chatters/squeals something horrible, no matter how much I slow it down, even to 10ipm.

I'm willing to accept this as my limit, if this is normal. What do other people get away with for DOC?

Thanks
Tom

[underdog]

Tom,

I don't have my black reference book of successful cutting parameters with me but, you're going the right direction. Chatter is too much load so the boring bar, toolholder, frame of the machine, etc. Whatever can't handle it. OR there is too little load, so the tool bounces along the surface and does not cut. But .150 DOC at 36 IPM sounds pretty good to me on a 1/2" EM and yes, slotting is VERY severe service for any cutter.

You might want to try corkscrewing (helixing) into the pocket if your programming system and controller parameters support it (or the old way - drilling a starter hole and dropping in on center of that!). On the helixing, if you make the Z advance light enough and keep the helix tight, the chips are light from the light DOC and there is always chip clearance out the open side of the cut, because if you cut a helix around a .375 base circle, then .125 of the cutter is always in the clear and its almost like side milling.

Oh one last thing, a set screw holder gives less support than a collet, but you have to weigh that against it spinning in the collet or pulling out with aggressive millling. That's why they came up with milling chucks, hydraulic holders and thermal holders - best of both worlds but expensive.

Good luck.

[TXFred]

I have a 1/2" Cleveland end mill that behaves very similarly to what you describe. So I think it's just a machine limitation.

Be careful about the chatter. My end mill has several times chattered so badly that it somehow caused the spindle to shut down. In those cases, Mach didn't notice anything, and kept on feeding even though the end mill was quickly coming to a halt.

I don't know exactly why this happened, but believe that the vector drive faulted out somehow due to rapidly changing loads from the chattering.

Frederic

[beanbag]

Make sure that the tool holder hasn't pulled out very slightly. You have to crank on the drawbar pretty good.

[tbaker2500]

Thanks. I did have the holder pull out slightly during the chatter, but I suspected it was because of the chatter, not the cause of it.
I was getting the chatter even when doing a 65% step over, not just on full slotting.

The rule of thumb I seem to be slowly homing in on, is that shallow DOC with higher feed rate = happier PCNC.

[David Bord]

I had limitations with .5" em as well. I purchased the Tormach 17mm center cutting insert em. That thing RIPS! Look for my post on it. I posted a video as well.

David

[Steve Seebold]

I do slotting work with my machine all the time. First thing I do is drill a hole the same size of the cutter you're using, then I create a drilling program and use the Z axis to ruff stuck out of the pocket. It goes a lot faster than trying to side mill the pocket. You can use .150 to .225 step over and a fairly high feed rate. I think I use 4500 RPM and about 30 IPM.

[tbaker2500]

I ran more of this project today, and if I keep my DOC below .15, it cuts like butter.
So I guess that's the limitation of this cutter on this machine.

[beanbag]

I bet it would work well in a regular r8 collet.