PM-25 recommended feed and speed?

[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.

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[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.

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.

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.