Speeds, feeds, plunge rates

Not necessarily, pine is not the best material (to put it kindly) and is quite susceptible to tearout when using upcut endmills. What endmill did you use for the first slot on the left ? Any chance you used a downcut endmill for that one ?


It broke on the lateral movement after about 3 minutes into the project at the highest RPM, I think 18000. It was a fairly new Amana 46176-K

Are you using a router? Which one?
You may be running closer to 30k rpm and generating excess heat.


The first was carbides #251. Aren’t all of carbides starter pack endmills down cut?

Actually #251 is the only downcut.
So it makes sense that this one would have clean top edges, while for the others you get tearout since they are upcuts.

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I’m using the carbide compact router on the #6 setting. I use the 6 for almost all my bits I didn’t think RPM mattered too much, please correct me if I’m wrong

Oh… Okay that makes sense. I am mostly using common board for practice.

The 3 is 18,000 rpm on that router. There is a speed guide in the back of the manual.

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You’re right though, never thought to check the RPM levels 30000 is the highest for my carbide compact. Is that RPM to high to use?

The C3D router is a clone of the Makita. Here is the speed chart for the Makita.

Makita 0701
Dial # 1 2 3 4 5 6
RPM 10k 12K 17K 22K 27k 30K

That Amana 46176-K is a 2-flute 1/8", so at 35ipm feedrate like you mentioned, and if you had the RPM maxed out at 30.000RPM, the chipload was 35 /2 x 30000 = 0.00058", which is at the lower end of the recommended comfort zone (lower than that and on a non-perfectly-sharp cutter you get an increased risk of rubbing rather than cutting, and then “heat happens” and then all bets are off)

Working at max RPM (if you can bear the noise level) is actually a best practice I learned from @gmack, BUT if you do you need to bump your feedrate compared to the recommanded values for lower RPMs (e.g. if you see a recommanded setting of say, 30ipm at 15.000 RPM, you will need to use 60ipm feedrate at 30.000RPM to get the same chipload)

So I tend to think you would have been fine by feeding faster, actually (CNC is weird like that).


CNCcookbook.com There is a ton of info. there.

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