we are testing our v bit for some simple text engraving with Fusion 360 at different feeds and speeds. We have already been advised by our v bit manufacturer that a good starting point for feeds and speeds on ply is about 18k rpm @2000 mm/min, however we just wanted to see the effects of varying feed and speed while keeping approximately the same ratio between the two.
As you can see we have not observed large differences across the whole rpm span of our makita, howevere what’s more interesting here is the appearance in some cases (12000 and 17000, see labels below each letter “a”) of a curved edge at the top left and bottom right tip of the letter “a”. All the sketches and the toolpaths have been copied from the first one so this appears quite difficoult to understand to us… Do you have hints about what this effect may be caused by?
Interesting… also, for the 10000 and 12000, the line that forms the ‘hollow’ in the centre of the ‘a’ has a pointy bit on it that doesn’t appear on the 20K+ series:
Perhaps your machine has a belt/wheel issue that means those physical locations for the cutting area have glitches/bumps?
It might be worthwhile creating an array of small circles that covers the same dimensions, and positioning the stock in exactly the same place. After cutting, see if there is any correlation between the defects you see here and the defects (if any) in the circles?
I think it all has to do with the banding of grain in the wood in your examples. I treat my 60V like a typical endmill for SFM/RPM the smaller the engrave the faster I turn it.
The wood type and sharpness of the bit also has a lot to do with your issues.
In addition to what was mentioned I would suggest to run a surfacing pass after the stock has been installed on the machine and before v-carving. This will remove any local height difference on the stock surface, which can translate to similar artefacts. If those curved edges are still present then, you will know it’s a mechanical issue.
