I’m testing some lettering for an epoxy sign I’m making, and I’ve found a case where pocket REST machining is doing way more work than needed.
The intent is that of an Advanced VCarve, but I’m using appropriately spaced vectors to Pocket the bulk of the work to reduce time.
Pocket is 1/4" - 2mm - 1mm REST machining. The 2mm pocket is cutting areas already cleared by the 1/4" bit. I’ve verified the geometry of the 2mm and 1mm bits, the diameter is correct on both.
You can see under the first row of text (just above the horizontal line), the 2mm is clearing areas already done by the 1/4" bit. There’s no geometry in there, all layers are visible.
The 1mm pocket seems to be having the same problem. The second row text starts with “Wire Fox”, and the areas internal to the “W” are being recut.
Here’s another area, the internal area of ‘o’ in the second row. Orange is a 2mm diameter circle. A 2mm bit should clear the vast majority of this area, so why is the 1mm bit doing the whole thing?
2mm toolpath (red):
As a final test case, I tried a 1/4" bit, REST machining with the previous bit also 1/4". I would expect this toolpath to be EMPTY, but instead it cuts this:
It appears the problem is that when looking for areas already cleared by the previous bit, the program is not looking at the original pocket, it’s looking at the pocket offset inwards by the radius of the current bit.
I took the pocket, offset by 1mm, and a pocket on that with a 1/4" bit . Blue is the 2mm path on the original vectors, red is the 1/4" path on the inset vectors. They match perfectly.
I’m having similar issues although mine might be exacerbated by CC not accepting Previous Diameters less than 0.250 mm.
Help me parse this:
“I took the pocket, offset by 1mm, and a pocket on that with a 1/4” bit . Blue is the 2mm path on the original vectors, red is the 1/4" path on the inset vectors."
Do you mean that after cutting the original pocket with the 1/4" bit, the 2 mm bit thinks the pocket which was cut is 1 mm smaller than it really is? And the 1 mm bit would think the 2 mm pocket is 0.5 mm smaller than reality?
Have you deduced any work-arounds for this? (Aside from creating new pockets for subsequent bites!)
Part of REST machining is deciding what areas the previous bit size has covered, and then using the current bit to cover what remains. It appears that the program is incorrectly determining what the previous bit size will cover.
The 2mm bit is using the right pocket - it’s covering the entire surface. The problem is that is using the ‘wrong’ pocket to determine what the 1/4" bit has already covered. The behaviour is as if the code is testing the 1/4" on a pocket that is smaller than the original, a pocket that seems equivalent to the original inset by the radius of the current cutter.
There appears to be a work-around. In my limited testing it appears that if you change the “Previous Diameter” value to be (Previous Diameter - Current Diameter), that the code works properly.
For example, if I am cutting 1/4" (6.35mm) then 2mm, then the actual previous diameter is 6.35mm. Instead use a value of 6.35mm-2mm, i.e. 4.35mm.
I ran a test with my new project using your insight, perfect!
I still can’t use it with bits smaller than 0.250 mm since CC Pro has limited this for some reason. But I redesigned my project to use 0.254 mm as my minimum bit size without too much compromise.
Since my rest machining agenda uses half size bits each time I merely used the current bit size versus the previous bit size for excellent results.
