[patrick31]

I have a Precision Mathews PM-25 MV that is converted to CNC. I installed a custom Jian-Ken brand 3KW, 12k RPM spindle on the machine. It's powered by a 2.2kW VFD, a WJ200. The new spindle is a direct drive.

I'm getting a lot of chatter and looking for recommendations. Trying to machine a 5.5" x 5.5" pocket 1.15" inch deep in a piece of 6061 aluminum. I bought a 1/4" carbide end mill with a 1.25" LOC, and it chattered pretty bad and snapped off in 2 minutes, broke off right where it was clamped to the collet.

The cutting edges were not damaged! I even checked them under a USB microscope, the cutting edges are perfect. The cutter just snapped off. I'm guessing this means I was too aggressive with my feeds and speeds?

What would be a good feed and speed to run for this cutter? I was running 0.25" DOC, .075" WOC, .0023" chip load, 12k RPM, which works out to 108 IPM and 1.92 MMR.

[shooter123456]

You are probably pushing that cutter a little bit hard. 5x diameter cutting edge is a little bit high, so you will need to back off of it a little bit. You might want to step up the diameter to a 3/8" and step off the WOC a little bit.

I regularly run a 3 flute 3/8" carbide end mill at .375" DOC, .05" WOC, 10,000 RPM, 90 IPM. That is .003 IPT, 1.69 MRR.

I have a video with mine running a .25" end mill with .25" DOC, .035" WOC, at 110 IPM and it is cutting just fine. https://www.youtube.com/watch?v=sbE0DkhU60s&t=225s

Did you have any coolant running? That will be needed for sure if you are trying to push it with aluminum.

I hope that helps.

[dazp1976]

I'll be in the same position when mines running.
Watch a few Tormach videos.

I read somewhere about using 50% DOC & 30% WOC of cutter diameter.
Nothing is really definitive, it's all a bit trial and error.

I think you need to back off both rpm and woc at least.

[ChrisAttebery]

Do yourself a favor and buy FSWizard Pro. It's well worth the $20 he charges for it. I run about 80% of his recommended feed at the maximum speed I can.

5x depth is pretty extreme.

[patrick31]

You are probably pushing that cutter a little bit hard. 5x diameter cutting edge is a little bit high, so you will need to back off of it a little bit. You might want to step up the diameter to a 3/8" and step off the WOC a little bit.

I regularly run a 3 flute 3/8" carbide end mill at .375" DOC, .05" WOC, 10,000 RPM, 90 IPM. That is .003 IPT, 1.69 MRR.

I have a video with mine running a .25" end mill with .25" DOC, .035" WOC, at 110 IPM and it is cutting just fine. https://www.youtube.com/watch?v=sbE0DkhU60s&t=225s

Did you have any coolant running? That will be needed for sure if you are trying to push it with aluminum.

I hope that helps.

Thanks! I am going to try some new settings. I actually discovered I was clamping the part wrong and it was vibrating in the vise. I reclamped it, put a busted up worn our 1/2" end mill in the spindle, and was able to run the exact same feeds/speeds etc with that cutter and no chatter. So I ordered some new 1/2" and 1/4" cutters to try out. May buy a 2 piece vise as well so I can clamp parts lower and get the z column down to improve rigidity and clamp things better.

I'll be in the same position when mines running.
Watch a few Tormach videos.

I read somewhere about using 50% DOC & 30% WOC of cutter diameter.
Nothing is really definitive, it's all a bit trial and error.

I think you need to back off both rpm and woc at least.

Thanks. Yeah it's trial and error.

Do yourself a favor and buy FSWizard Pro. It's well worth the $20 he charges for it. I run about 80% of his recommended feed at the maximum speed I can.

5x depth is pretty extreme.

I went ahead and bought FSM Advisor, it comes with that for free. I ran his trial a while back and it was good, but expired. So now I got a liscense.
Thanks for the tip!

In the future, I'm going to do some testing with a 1/4", 3/8", and 1/2" rougher and see how they do with parts clamped better.

[patrick31]

As an update, it turns out my vise clamping was not correct. I fixed that, and got a new 1/2" rougher, used HSM advisor for feeds/speeds, and was able to do 3 cubic inches per minute no problem at all. Could probably do twice that! I am having chip recutting so I'm upgrading the cooling pump now as the current pump isn't strong enough.