Depths and oversize
Start and end depth
Every operation cuts from its start depth to its end depth, in mm down from the stock top, whatever the Z zero is.
- Rule: 0 ≤ start depth < end depth.
- Passes: the cut goes down in equal passes no deeper than the step down, and the last pass is exactly at the end depth. Start 2, end 6, step down 2 gives passes at 4 and 6 mm.
- Cutting through: an end depth below the stock bottom goes into the spoilboard. That’s allowed up to Max depth below stock (Job settings), with a warning; deeper is refused, so a typo can’t reach the machine bed. For 12 mm board, an end depth of 12.3 cuts 0.3 mm into the spoilboard. The Through button next to the end depth sets it to the stock thickness plus that allowance.
- Going down: from safe Z the tool rapids to 1 mm above the stock top, then goes down at the plunge feed. The air between the stock top and the start depth is crossed at the plunge feed too: Chipload doesn’t know whether another operation already cleared it.
Oversize
Oversize is how much more than drawn is cut, in mm: the cut moves into the material
that is kept by that much. Positive removes more; negative leaves material. In the project
file the field is clearance. Other CAM programs call the opposite “stock to leave” or
“allowance”: there, a positive value leaves material.
| Operation | Positive oversize | Negative oversize |
|---|---|---|
| the pocket larger all round, islands smaller | the pocket smaller, islands larger | |
| Profile, outside | the part smaller | the part larger: stock left for a later cut |
| Profile, inside (a hole) | the hole larger | the hole smaller |
| Profile, on the line | not allowed | not allowed |
- How: the tool’s centre runs at its radius minus the oversize from the drawn line.
- Limit: an oversize of the tool radius or more is refused. Use a profile on the line, or a smaller tool.
- Corners: inside corners of the kept material stay as round as the tool. Outside corners get rounded with the oversize as radius, because the tool reaches past them.
- Use:
- a little positive oversize gives a fit, such as a lid that drops into its box;
- a negative oversize leaves stock for a finishing pass (see also the profile’s finishing pass).