Hi all,
(I did not find any answer regarding pitch, please point me to possibly existing threads I was not able to find. Thx)
I’m beginning with my first cuts and I’m a bit confused about how to select pitch (its Zahnvorschub in german - feed per tooth).
I had a medium sized quite rigid 'hobby’machine a few years ago. There I just used the pitch recommendations and cutting speed for the material to calculate RPM and feedrate.
However, if I do so, I get quite large feedrates, which I think are not sensible on the mpcnc (see below).
I could reduce cutting speed (which gives lower RPM and hence feedrate) and/or pitch which I think should be reduced as it determines the force necessary to drive the cutter into the material - not?. However, the pitch actually depends on the tool, and not using the recommended pitch might result in bad results or tools getting blunt quickly.
Are there any recommendations how to select the initial values (which might then get optimized per machine/tool)? E.g. material cutting speed recommendation *1/3 and pitch * 1/3 ?
Example:
8mm endmill (spiral).
MDF: I have a material cutting speed recommendation of 450m/min.
This gives 17.9k RPM (quite sensible for my spindle).
However, the pitch for mdf is given as fz=0.4 mm/tooth. Spiral endmill means #tooth=2 in the following formula
vf (Fxy in estlcam) = RMP * #tooth * fz= 14320 mm/min = 239 mm/s which is about a factor of 8 above the 30mm/s I find in the mpcnc estlcam 2.5D tutorial.
Using 1/3 for cutting speed and 1/3 for pitch I get 6k RPM (which I could do with my spindle) and vf=26.6 mm/s which would be sensible.
BUT: in the tutorial RPM=18K which is a factor of 3 compared to the above which means pitch was reduced by 1/9, while not reducing the cutting speed. This is far from the typical pitch recommendation.
On the other hand, my gut feeling is this could be necessary as the mpcnc is not too stiff.
What do you think?