1 · Hold it down

The lab uses two holds. Pick one, then tell SRM-CAM which, under Set up the job › The copper › Held down by: it decides whether the cut is deepened (section 3).

Best: double-sided tape

Lay double-sided tape across the whole back of the board and press it flat onto the spoilboard. It is the easiest to set up, and because the whole back is held, nothing can arch: the probed surface is the surface that gets cut. In SRM-CAM: Held down by › Bonded across the whole back (tape), which adds no extra depth. It is the default.

Second best: four disc clamps

1. Beside the board, not through itEach clamp is a plastic disc with a chamfer round its side. Put its screw through a spoilboard grid hole just beside the board's edge, into the threads of the metal plate underneath.
2. Turn it inTurn the disc until its chamfered side presses on the board's edge, pushing it down and in.
3. One on every sideUse all four: the clamping force has to come from all sides, or the board slides away from the open side.
4. Tell SRM-CAMHeld down by › Screwed or clamped at points. A board held at its edges can arch in the middle, so the cut is deepened a little (section 3).

2 · Tell SRM-CAM where the copper is

Under Set up the job › The copper: the board thickness from calipers, then the sheet's width and height. Then its front-left corner. Find the corner with the probe (the walk is on Milling a board), leave the bit there, and press Set the corner from the tool. It only reads the machine's X and Y: nothing moves, and the work origin is not touched. Then Where it sits on the bed › Centre it on the copper puts the job in the middle of the part of the sheet the spindle can reach.

3 · A board held at points gives under the cutter

Clamped at its edges, the board can arch over air between the clamps. The probe measures that arch with a static tool at almost no force; the cutter arrives spinning and pushing down, and the unsupported part gives a little instead of being cut. So, held at points, SRM-CAM deepens the cut:

• Screwed or clamped at points, with the probe map applied: a quarter of the arch the map shows (what a flat, tilted plane cannot explain), capped at 0.12 mm, plus the 0.035 mm copper foil. The number is on the setup page.
• The map not applied: nothing cancels the tilt, so the whole range of the map is charged, plus the foil. Apply the map.
• Bonded across the whole back (tape, the lab's best hold): there is nowhere for it to go, so nothing is added.

Untick Set up the job › The copper › Work the extra depth out from the probe map to set Cut deeper by yourself, down to nothing, if the board keeps coming out too deep or too shallow. How to measure the map is on Bed levelling.

4 · Prove it before you cut

Every single-sided export writes <name>_airpass.nc, step 0 of the plan: spindle off, bit held 5 mm up, tracing the outline slowly enough to follow. If it wanders off the copper, stop and re-place the stock. Twenty seconds, before every job.

Which one do I need?

When you are done, leave the machine as you found it: Leave it as you found it.