A bas relief set into a pocket used three bits: 1/8” upcut, 1/16” ball nose and 1/32” ball nose. Using VCarve Pro:
-Pocket depth 0.1875, model height 0.1825 and depth ABOVE the model = 0.005.
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Roughing bit Machining Allowance = 0.0
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“Rest Machining” minimum detail = 0.001
On the first try, the ball nose bits didn’t clean up the cut lines of the roughing bit. The Z=0 was set (for each bit) with the aluminum block made for that purpose.
On the next try, after setting the second bit with that block, I used the ‘paper’ method to confirm the same Z=0; but the methods didn’t agree. When the bit touched the wood (preventing movement of a bit of paper) the controller said the bit was at 0.014. In other words, it said Z=0 was that distance BELOW the surface of the material. Again, the second bit didn’t clean up marks from the first.
On the third try, I deliberately set the second bit 0.017 below the surface and told the controller that this is the real Z=0. The smoothing bit did a better job, but still not perfect. I feared it would cut into the bottom of the pocket at the model edge (but it didn’t).
- Why does the aluminum block (for setting depth) differ from the ‘paper’ method by so much?
2. Which setting should I change: Machining allowance? Rest Machine detail?
3. Would a down-cut spiral do any better for this than an upcut?