I’m 3D roughing a job in poplar and I noticed that it’s dust. The chip load was super low. I have a chip load range chart by material type, but I’m having a hard time believing it, because the only way I can seemingly get it in the range is by increasing the FPM beyond what I’d expect or by dropping the RPM below what I’d expect.
For instance, I had it at 80 FPM and 19k RPM.
If I plug in 100 FPM and 5k RPM I get .01, but 5k RPM? Can the be real?
Aspire, OF Elite with stiffy, .25 ball nose for this case.
If I plug in 100 FPM and 5k RPM I get .01, but 5k RPM? Can the be real?
Yes that is real for a 2 flute cutter. It would be 400 IPM feed at 20000 RPM.
I used to shoot for .01" per tooth ( and have tried 400 IPM ) but I don’t anymore. See why below.
Formula for chip load per tooth is Feedrate / ( RPM x # of teeth ).
But bear in mind that is the chip load out at the edge of the cutter.
You are using a ball cutter. In the center closer to the center of the ball the surface speed of the tool comes close to zero. This means the high feedrate can get to be way too much for the center of the ball to clear out. You will get tearing of the wood instead of cleanly cutting it.
I would recommend roughing with an endmill and just finishing with a ball. Unless you are doing just a little bit of roughing then I would slow feedrate down because of the ball.
What this formula won’t account for is load on the spindle. For that you have to consider the the depth of cut per pass.
DOC x stepover x feedrate. Then you end up with the material removal rate.
What this all means is to keep the chip thickness high but reduce the load on the spindle one method I prefer is to reduce the depth of cut.
For the woods like walnut I use:
.250” upcut endmill 2 flute
20000 RPM
.100” DOC
150”/min feedrate
.230” step over per pass
This ends up being .0038" per tooth so it is not too aggressive but the chips definitely look like chips - not dust.
For hard maple I reduce DOC to .080" to reduce load.
I have tried deeper cuts and slower feedrate but it ends up being dust as you say ( which is harder on the cutter ) and the load is higher on the motor. I have a 1HP Makermade Makita clone.
I have tried feed rates up to 300 IPM and found it’s a little on the aggressive side, but the motor did handle it - but just. So for a 1HP motor I don’t try for .01" chip load any more. .003" to .005" is good. Mainly why I go with 150 IPM is the OF can’t keep it going any faster if there are any curves involved.
I have settled on .230" stepover because the difference between that and full load ( .250" width ) is minimal - such as when the cutter hits an inside corner or when starting the next pass in a pocket and it’s cutting full width. So the load remains the same in those situations.
Well, I ran at 150 ipm today, which was the first time I’ve ever ran over 100. I made some lovely chips and the carve went well. Will continue to learn the limits of my machine.