My purchased file V-carves too deep no matter what Start Depth I enter: what's the right fix?

The misconception (you're turning the wrong knob)

Start Depth does not limit V-carve depth. It pushes the carve deeper. Start Depth is the depth at which the V-carving toolpath is calculated, and its real job is carving or engraving inside an already-cut pocket (for example, Start Depth = 0.5" to carve into the bottom of a 0.5" deep pocket). If you've been raising Start Depth trying to fix a too-deep carve, set it back to 0 for cutting directly into the surface.

The reason no depth number seems to work: V-carve depth isn't entered, it's geometric. The angled bit goes down until its sides touch both edges of the vector gap, so depth is set by the width of the shape and the bit angle. Wide areas of the design force the bit deep; narrow lines stay shallow. This is not a bug. Approximate depth for a stroke of width W:

• 60° bit: deepest, depth is about 0.87 x W
• 90° bit: depth is half the width (0.5 x W)
• 120° bit: shallowest, depth is about 0.29 x W

A 1"-wide stroke with a 90° bit goes 0.5" deep, by design.

The real fixes, in order

1. Set a Flat Depth in the V-Carve/Engraving toolpath form (a common starting point is 0.1 to 0.15", shop advice). This limits the depth everywhere: wide areas get a flat bottom with angled sides. For big flat areas, add the optional clearance tool (end mill) in the same form so they clear quickly and cleanly. If no clearance tool is selected, the V-bit clears the flat areas as well.
2. Check the bit angle against what the file was designed for. Purchased files are usually designed around a specific bit, commonly 90° or 60°, so check the listing or readme. A 60° bit on a file designed for 90° cuts about 73% deeper than intended (0.87 divided by 0.5). Match the bit, or switch to a wider angle (90° to 120°) to make everything shallower (see the 120° V-bit entry).
3. Verify the tool database angle is the bit's real included angle. Mislabeled bits and per-side-versus-included confusion produce exactly this symptom (see the V-bit angle entries).
4. Scale the design down. This reduces every cut depth proportionally, which is sometimes the right call for a file designed bigger than your board.
5. Use a thinner-stroke font or shrink the artwork so the gaps are narrower.

Before recutting

Run Preview Toolpaths and check the widest areas of the design. When the simulated depth looks right, the cut should match. If the preview is right but the wood is wrong, the cause is Z-zero or the machine (see the entry on V-carves deeper than the preview).

Pro tips

• Flat Depth plus a clearance tool is a common recipe for big dimensional letters and large logos.
• If the flat bottom shows tool marks, take a finishing pass with a slight (0.01") step down on the clearance tool.
• The pass depth for V-bits comes from the tool database entry (see the entry on V-carve multi-pass control).
• Purchased-file checklist: read the listing for the intended bit and depth, then open the toolpaths it shipped with (if it is a job file) and inspect their tool settings before trusting them on your machine.
• Deep-carve look without deep cuts: Flat Depth plus a stain or paint fill reads just as bold.