ShopBot post processor — OpenSBP .sbp

File: .sbp
Controls: ShopBot Control · SB3 · FabMo
Machines: ShopBot PRS alpha / standard · ShopBot Buddy · ShopBot Desktop · ShopBot Max

What the post writes

SA for absolute coordinates, and MS for cut speed in units per second — XY and Z set separately.
JZ, J2 and J3 for jogs; MZ, M2 and M3 for cuts.
CG for arcs and circles about a centre, where I and J are the centre’s offset from the start point and the diameter is written as well, so the circle is unambiguous.
TR for spindle rpm, then the control’s own C6 spindle-on routine with a two-second pause to come up to speed, and C7 at the end. A machine with no VFD simply ignores TR.
&Tool = n with the control’s C9 tool-change routine, or a PAUSE that names the bit for a hand change.
A unit guard — IF %(25)=1 THEN GOTO — that halts the file when the control is set to the other unit.

Conventions chosen, and why

Where the public description of this format left a token ambiguous, the conservative reading was taken — the one a mistake cannot bury a bit under. Each is written into the program's own header too, so it can be read on the machine before a scrap cut. Check these against your own setup sheet.

The file never SETS the control’s units. ShopBot’s unit values are calibration values, and writing a wrong one miscalibrates the machine rather than converting the program — so the post guards with %(25) and halts instead.
A hole wider than the bit is STEPPED, not helixed: plunge one pitch, cut one flat full circle, repeat. CG carries its own plunge parameter, but the public Command Reference does not make its sign certain, so it is not used.
Arc direction is derived from the geometry the simulator enforces, never from the source opcode.

Where this program comes from

WoodWright has one toolpath planner. The Xilog generator plans the program, the simulator clears it, and every post below translates that cleared program op for op — never a second planner with a second set of rules. Whatever your machine reads is the same toolpath every other machine reads.

Every file this post writes is read back by the post’s own parser and compared to the source program move for move — same XY, same depth, same order, every bore accounted for. A translation that does not survive its own re-read is not a program, and is not offered.

Written from public format documentation only. No vendor post-processor was copied, decompiled or referenced.

Questions

Straight answers

Which ShopBots does this work with?

All of them, as far as the file format goes. ShopBot put OpenSBP in the public domain and every ShopBot — PRS, Buddy, Desktop, SB3 or FabMo — reads the same flat subset this post writes. What differs between machines is the tooling and the spindle, which live in your own setup rather than in the file.

Does the file change my machine’s inch or millimetre setting?

No, deliberately. ShopBot’s unit values are calibration values, so a post that wrote the wrong one would miscalibrate the machine rather than convert the program. Instead the file checks the control’s unit setting on the first line and halts if it does not match what the program was written in.

How are holes bigger than the bit cut?

Stepped, not helixed: plunge one pitch, cut one flat full circle, plunge again. A helix would be faster, but the arc command’s plunge parameter has a sign the public Command Reference does not settle, and guessing it wrong on a plunging move is the kind of mistake that ends in the spoilboard.

Was a ShopBot post file copied to make this?

No. It is written from ShopBot’s public Command Reference only — no vendor post was copied or referenced. Where the reference left a token ambiguous, the conservative reading was taken and written into this page and into the program’s own header, so the shop reading it before a scrap cut can see the assumption.

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