Documentation / Reference

Sender software with the Twinwright controller

This page is for people who want to drive the MC-1 from a G-code sender of their own (bCNC, gSender or Universal G-code Sender) instead of from Studio. The MC-1's controller is the Twinwright controller (kernel), compatible with the Grbl 1.1 serial protocol and the extensions current senders use, so these senders work with it, with the few settings and caveats below.

Everything here was tested on the MC-1 digital twin, which runs the same controller code as the machine. Checking it on a real machine is still to come. Tested versions: bCNC 0.9.16, gSender 1.6.4, UGS Platform 2.1.27.

Connect

What the controller says about itself:

• Its welcome line is Grbl 1.1f ['$' or '$HELP' for help], like a classic Grbl controller. Senders look for a welcome line that starts with "Grbl" to notice that the controller restarted (see section 3).
• Its name is in the answer to $I: [VER:Twinwright 1.1f.…] and [FIRMWARE:Twinwright]. Senders that show the firmware show "Twinwright".

Pick the firmware in the sender

After an alarm or a reset

• E-stop. The MC-1's E-stop opens the power contactor. Release it, press the machine's Start button, then reset in the sender and home. Until Start is pressed the alarm (ALARM:10) does not clear.
• ALARM:11 (homing required). Home ($H). Unlocking with $X is refused (error:46).
• ALARM:2 (soft limit). The program asked for a move outside the travel. Homing leaves Z at the top of its travel (machine Z 0), so any move above it, such as G53 G0 Z5, raises ALARM:2. Reset, then home or unlock.
• bCNC recovers after any reset: it sees the "Grbl" welcome line and forgets the lines that were still on their way, so $H goes out.
• bCNC after Stop. bCNC's Stop is a feed hold, then a reset. Afterwards bCNC sends the modes it had before (coordinate system, units, tool length offset) back to the controller in a line or two, and in a few cases the controller refuses them, as other Grbl controllers do: with a tool length offset (G43.1) in effect the line gets error:24 (bCNC sends a G43.1Z... of its own after its first Stop, so from the second Stop on it always happens); under G80, G43.1Z... gets error:31; with scaling (G51) in effect, G51:X gets error:1. After an error every G-code line that follows gets the same error until an empty line, a $ command or a reset. So after a Stop, check the coordinate system, the units and the tool length offset with $G and $# before you jog or carry on. If they are wrong, set the zero again and measure the tool length again (tested on the twin, 2026-10-06).
• UGS with its other firmware choice. After a reset that UGS did not send itself, for example one from Studio's window or the controller restarting by itself, press Soft Reset once more in UGS before Home. Until then Home does nothing. With that choice UGS treats only another welcome line as a restart. A reset from UGS's own Soft Reset button is fine. On the MC-1 itself such resets are rare: it has no reset input and one USB host. With the firmware set to "GRBL" this does not happen: after such a reset UGS shows CONNECTING, and Home works at once (tested on the twin, 2026-10-06).

Tool changes (M6)

None of the three senders, with their default settings, lets the MC-1 change the tool and measure the new one:

More about UGS and M6:

• It also stops at an "M6" inside a comment, such as FreeCAD's ( M6 T1 ).
• A second M6 that comes right after a tool change can slip past it to the controller. The controller then waits in the Tool state for a confirmation that UGS never sends, and no button in UGS's window works any more. On the MC-1 only the E-stop ends it: press it, release it, press Start, then Soft Reset and Home in UGS.
• If the controller is reset during a UGS job before UGS has reached an M6, UGS may report the job as complete, but its tool-change dialog still comes. Dismissing it can start the whole program again from the beginning. After a reset in the middle of a job, close the file in UGS before you go on.

Measuring tool length on the MC-1's tool setter

The tool setter is at the back left of the table; G59.3 is stored right above it.

• bCNC, Manual tool change (TLO). Tool change position above the tool setter. Probe position G59.3. Probing distance 50 mm, seek 200 mm/min, slow 25 mm/min (the MC-1's $342–$344), command G38.2. Measure the first tool with "Calibrate" before running the program. bCNC then sets G43.1 for each new tool.
• gSender, Fixed Tool Sensor. Sensor location G59.3. Measure the initial tool in the wizard. gSender then shifts the work Z for each new tool (G10 L20) instead of using a tool length offset. It takes the length from where the axis stopped after the touch, not from the trigger point the controller reports, so each change can be a little off. In the twin, run tool changes at 1× speed: gSender reads that position after a fixed short pause, and a twin running faster can give it one from before the stop.
• Start at least 0.1 mm below the top of Z (machine Z −0.1 or lower) when the tool change begins. Both senders return to that height after measuring. Starting right at the top, the small scatter of a measurement can put that return above the soft limit, and the job stops with ALARM:2 before it cuts.

Setting work zero with a touch probe

• UGS (its probe module) works out the zero from the trigger points the controller reports ([PRB:]). This is the right way.
• gSender (3D probe) and bCNC (its probe page, then its Z=0 / X / Y buttons) set the zero where the axes stopped after the touch. The machine always runs on a little past the trigger before it stops, and the faster the final touch, the further. Use a slow final touch, or set the zero with Studio's probe cycles, which use the trigger points.
• UGS's hole centre (its probe module's Hole Center): from where you leave the probe it probes -X, +X, -Y and +Y, each by half the hole diameter you type in, and sets the centre midway between the slow touches' trigger points. How far it reaches depends on that diameter: the start may be at most (typed diameter - actual bore) / 2 + the ball's radius from the centre. With the bore's own diameter typed in, that is only the ball's radius (1 mm for a 2 mm ball); type it a few mm larger (24 to 26 for a 20 mm bore) to allow for placing the probe by eye.
• When UGS's hole centre does not reach the wall (finding 192, UGS's own behaviour): that probe ends in ALARM:5 and UGS stops. But it set G54's X0 Y0 at the start point before probing, and as the cycle did not finish, G54 stays there. After unlocking, set the zero again before cutting. Its probe cycle also stays half-way: disconnect and connect again before probing again. It also takes a point the controller reports as not touched ([PRB:...:0]) for a touch.
• Calibrate the probe first (Studio's probe cycles: a ring gauge). An uncalibrated probe reads every bore larger and every boss smaller by twice its pretravel.

Other things to know

• bCNC over the network. On Windows, bCNC reads a TCP connection only about every 2 seconds, so its display can be 2 seconds old. "Idle" in bCNC does not mean the machine has stopped. A USB connection does not have this delay.
• gSender, M0. An M0 within the first 10 lines of a program does not pause (gSender turns it into a comment). M1 always pauses.
• gSender, continuous jog. Holding a jog button is refused on the MC-1 (error:15): gSender asks for a long jog beyond the travel. Jog in steps. On some Grbl controllers, $40=1 (limit jog commands) ends long jogs at the soft limits instead of refusing them; the MC-1's controller does not act on that setting yet and still refuses them (tried with gSender on the twin, 2026-10-06).
• UGS, long lines. UGS never sends a line longer than 127 characters: the job stops without a message. Keep lines shorter (UGS removes comments first).
• UGS, M30. UGS removes M30. A program that relies on M30 to stop the spindle and coolant leaves them running: end programs with M5 and M9 before M30.
• UGS, comments. If a line has two comments, UGS also removes the code between them.
• Disconnecting during a job. The controller keeps running the lines it already has. gSender and UGS send no stop when you disconnect, so the machine runs on, with the spindle turning. Stop the job before you disconnect. bCNC holds and resets before it closes the connection.
• Comments with non-ASCII characters (such as Chinese, "Ø", "–"): all three senders remove comments before they send, so these characters never reach the controller. The controller itself reads UTF-8 text in comments and in (MSG,...) as text, never as a real-time command.