How does VCarve Pro & Aspire handle multi-pass cutting (pass depth control) and when should I use multiple pass depths vs a single deep cut?

Understanding pass depth is critical for clean cuts, long tool life, and machine health. The software calculates multiple-pass toolpaths automatically based on tool settings.

What is Pass Depth?

Pass Depth is the maximum depth of cut the tool can take in one Z-level pass. It is set in the Tool Database for each tool, and can be defined per machine and material depending on machine rigidity and material hardness. If the Cut Depth is greater than the Pass Depth, the software divides the cut into multiple Z-level passes.

Example from the official documentation: a pocket 1 inch (25.4 mm) deep with a tool whose Pass Depth is 0.25 inches (6.35 mm) makes 4 passes.

How Passes Are Calculated

• The software uses the tool's Pass Depth to work out how many passes are needed to reach the Cut Depth.
• By default, the software may also change the exact step down by up to 15% in either direction if that reduces the total number of passes. This saves machining time.
• If you need exact steps (for example, when cutting into laminated material), check Maintain Exact Step Depth in the Edit Passes dialog, and the software will not vary the step size.
• The final pass reaches the Cut Depth.

Choosing a Pass Depth

The right pass depth depends on your tool, material and machine. These are starting points to test on scrap, not rules:

• Start at about half to one tool diameter per pass for an end mill, then adjust to what your machine cuts cleanly.
• Hard materials usually need shallower passes than soft ones such as MDF or plywood.
• Deep pockets: use multiple passes to reduce bit deflection and burning.
• V-carving deep text: the software calculates multiple Z-level passes automatically where the V-carve needs to go deeper than the tool's Pass Depth.

Customizing Pass Depths

For Profile toolpaths, you can override the automatic pass calculation:

1. Open the toolpath form
2. In the Passes section, the software shows the number of passes it calculated
3. Click Edit Passes to add, delete or edit individual pass depths. Double-click in the passes diagram to add a pass, and use Set Last Pass Thickness to define the last pass by the thickness of material left for it.
4. Example: instead of 3 equal passes, set a light first pass and deeper later passes for harder materials.

Note that setting the number of passes with the list utilities discards any custom passes you added.

Custom pass use case: for profile cutouts in hard material, a light first scoring pass can reduce chipout on the top surface, then deeper passes remove material efficiently. This is shop advice, so test it on scrap.

Do Separate Last Pass (Profile Toolpath)

The Profile toolpath has an option called Do Separate Last Pass. Enter an allowance and every pass except the last is held that far off the line (they undercut, leaving a thin skin of material). Only the final pass cuts to the exact vector boundary. This can give a cleaner edge because the final pass removes only a thin skin. The software warns if the allowance is more than one third of the tool diameter, and it should ideally be much smaller.

3D Toolpaths and Pass Depth

• Texture toolpath: Pass Depth is not used. The full Max. Cut Depth is cut in one pass, so keep it within what the tool can handle.
• 3D Finish toolpath: the official documentation says the finishing toolpath is always a single pass and does not use the tool's Pass Depth. Set the 3D Rough toolpath's Machining Allowance appropriately for the finishing tool so the finish bit is never asked to cut more than it can handle.
• 3D Rough toolpath: Z Level roughing removes material in Z-level steps. Reduce the roughing step if you see big leftover steps for the finish tool.

Signs a Pass Depth Is Too Deep

• Tool burning (smoke, scorching)
• Bit deflection causing wider-than-expected cuts
• Excessive machine noise or vibration
• Broken bits
• Fuzzy or torn edges instead of clean cuts

If any of these occur, reduce the pass depth (for example by 25 to 50%) and try again.