Why does the machine retract so high when carving inside a deep pocket, and can I set a negative Z gap?

Why this happens

The Rapid Z Gaps (Z1 Clearance, Z2 Plunge) in Material Setup are measured above the material surface, not above where you're actually cutting. Carving detail at the bottom of a 0.625"-deep bowl with Z1 = 0.25" means every between-cut move retracts 0.625 + 0.25 = 0.875" above the work, and then plunges all the way back down. Multiply by hundreds of strokes in a V-carve and it is a large share of the job time.

As for a negative gap: the official documentation does not describe a way to make rapids reference the pocket floor in the same file, and negative Z gaps are not a supported way to do it. Use the fixes below instead.

The fixes, smallest to biggest

1. Shrink the gaps. Z1 needs to clear only what the bit actually crosses during THIS toolpath, and inside a recess that is nothing. Z1 = 0.1" and Z2 = 0.05" is a common starting point (keep more if clamps sit near the path).
2. Use the Plunge (Z2) gap. If you set Plunge (Z2) smaller than Clearance (Z1), the tool plunges at rapid rate down to the Z2 height and only then switches to the plunge rate. This can save a lot of time when Z1 has to be large to clear clamps. Some engraving machines cannot use this feature.
3. Raise the V-bit's plunge rate (tool database). With Start Depth set deep, the machine rapids to Z2 above the surface, then feeds the entire remaining distance at plunge rate on every single move, and that slow 0.65"+ plunge repeated over hundreds of moves is where the time goes. A plunge rate near the feed rate can cut deep-recess carve times dramatically for V-bits in wood (shop advice, test on scrap).
4. The re-zero trick (the real version of "make a separate file"): put the in-pocket carving in its own file, and at the machine zero Z on the pocket floor (touch off inside the bowl). In that file the V-carve uses Start Depth 0 and normal small gaps, so Z1 = 0.1" means the bit hops 0.1" above the FLOOR between moves. This is the way to get floor-referenced rapids.

• Safety rules: only in-pocket toolpaths go in this file (anything outside the recess would cut 0.625" too deep!); confirm the carve vectors stay inside the pocket footprint so the collet never meets the rim; label the files unmistakably ("ZERO ON BOWL FLOOR").

Pro tips

• Setting Start Depth = pocket depth is still required for correct carve depth when staying in one file (see the engraving-inside-a-pocket entry). The re-zero trick replaces it only in the split-file approach.
• The Estimate Machining Time tool can use your machine's Acceleration values to show the real cost of retract-heavy toolpaths. Compare before and after to see what each change buys.
• The same economics apply to deep relief carving (see the 3D speed entry).