Setting up gSender for a 32-bit GRBL CNC router centers on three workflows that materially change how you run the machine: conductive touch-plate zeroing for repeatable $X,Y,Z$ origins, the integrated surfacing tool that auto-generates spoilboard-flattening G-code without leaving the control interface, and guided EEPROM step-per-mm tuning ($100, $101, $102) to eliminate accumulated positioning error. These features are especially useful on machines like the TwoTrees TTC450 Pro, which uses a 32-bit GRBL mainboard with USB serial connectivity and is designed to work with open-source G-code senders.
Connect gSender to a 32-bit GRBL controller (COM port, Baud, status)
gSender communicates with GRBL over a serial link. On Windows this appears as a COM port; on macOS/Linux as a /dev/tty* device. For TwoTrees desktop CNCs with 32-bit GRBL boards, set Baud rate to 115200 in gSender's Config → Basics before connecting.
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Power on the CNC controller, then connect the USB cable to the computer.
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In gSender, hover the "Connect to CNC" button and select the serial port that appears (do not use network/Ethernet on first setup unless you have already validated serial).
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If the connection fails or behaves oddly: close other programs that may hold the port (UGS, Candle, Easel, Arduino IDE), reseat the USB cable, and confirm Baud = 115200.
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Once connected, confirm the console responds to
?(status report) and that jogging moves the machine.
Safety check before heavy cuts: verify the emergency stop and feed-hold behave as expected in gSender, and confirm your soft-limit travel values ($130, $131, $132) match your machine to prevent rapid-move alarms.
Conductive touch-plate probing for repeatable $X,Y,Z$ zero
gSender includes guided probe routines that use a conductive touch plate to set workspace zero reliably. This is distinct from "paper touch-off" because the software detects the electrical contact and sets the offset automatically.
Configure the probe in gSender
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Open Config → Probe (or the probe settings area in your version).
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Enter your touch-plate thickness as the Z-offset. Typical plates are 1–5 mm; use the actual measured value.
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Set a safe retract height after probing (e.g., 5–10 mm) so the bit clears clamps and the plate on rapid moves.
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Ensure your GRBL firmware has probing enabled ($30–$32 settings control probe behavior; many 32-bit boards ship with probing active).
Run an $X,Y,Z$ probe sequence
A practical sequence that avoids collisions:
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Home the machine if your controller supports homing ($22=1).
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Jog to a known corner of the spoilboard or fixture.
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Run Z-probe first: place the plate under the bit, start the Z probe, and let gSender detect contact and set Z zero with the plate-thickness offset applied.
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Run X and Y probes using the edge of a known square or fixture; some users run single-axis probes by touching one side, setting zero, then repeating on the orthogonal side.
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Save the result to a work coordinate system (G54–G59) if your workflow uses multiple jobs on the same setup.
Always verify the result by jogging a small distance and re-probing to confirm repeatability. If results drift, check bit deflection, plate flatness, and that the probe circuit is clean (no dust or finish between plate and bit).
Built-in surfacing tool: flatten spoilboards without external CAM
One of gSender's highest-leverage features is the surfacing tool, which generates a raster/zigzag toolpath for spoilboard or wasteboard flattening directly inside the UI. This removes the need to open a separate CAM program for a routine maintenance operation.
How gSender calculates the surfacing toolpath
You provide the physical dimensions and bit parameters; gSender computes a raster pattern that covers the defined area with a specified stepover, then outputs G-code with constant-Z passes.
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X & Y: enter the spoilboard dimensions (e.g., 1245 mm × 1220 mm for a large bed).
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Cut depth per pass: keep this conservative (≈1 mm or less) when using large-diameter bits to avoid uneven surfaces and excessive load.
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Max depth: total depth to remove from the highest point (often 1 mm for routine maintenance; more if the board is badly dished).
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Stepover: set overlap as a percentage. Around 40% overlap is common; larger overlap (smaller stepover) yields a smoother finish but takes longer.
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Spindle RPM and feedrate: choose values appropriate to your bit and material. For MDF with a fly cutter or large surfacing bit, ~20,000 RPM and ~8000 mm/min is a typical starting point on rigid machines; adjust based on chip load and machine rigidity.
After generating the G-code, preview the path in gSender's visualizer, then load it to the main screen and run a dry run (air cut) with the Z offset raised to confirm the machine stays within bounds.
Practical surfacing tips
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Use a rigid fly cutter or surfacing bit; avoid long stick-out to reduce deflection.
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Clamp the spoilboard firmly and check that the bed is mechanically square before surfacing.
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If your machine has a large work area, consider surfacing in sections to reduce cycle time and tool load.
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After surfacing, re-probe Z zero on your actual workpiece or fixture, since the spoilboard height has changed.
EEPROM step-per-mm tuning ($100, $101, $102) for accurate travel
GRBL stores step-per-mm values in EEPROM as $100 (X), $101 (Y), and $102 (Z). If these values are off, the machine will consistently over- or under-travel, which shows up as dimensional errors in parts and misaligned spoilboard surfacing. TwoTrees' 32-bit GRBL boards are designed to respond accurately to these adjustments, supporting positioning precision on the order of 0.05 mm when tuned correctly.
Measure commanded vs actual travel
Use a dial indicator, digital caliper, or a precise ruler and a sharp V-bit for best results.
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Command a known distance on one axis (e.g., 100 mm) using gSender's jog or console.
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Measure the actual physical travel with your instrument.
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Compute the corrected steps/mm:
new_steps_per_mm=current_steps_per_mm×measured_distancecommanded_distanceFor example, if $100 = 800.000 and you commanded 100 mm but measured 99.0 mm, the corrected value is:
800.000×99.0100≈808.08
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Apply the new value in gSender's console, e.g.
$100=808.08, then save with$$.writeor the controller's save command. -
Repeat for Y ($101) and Z ($102). For Z, use a fixed-height gauge or a precision block to measure vertical travel.
Re-test after each change to confirm improvement. If errors persist, inspect mechanical causes: loose couplers, belt stretch, lead-screw backlash, or frame flex.
Common setup pitfalls and how to avoid them
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Wrong Baud rate: If gSender connects but the machine behaves erratically, confirm Baud = 115200 for TwoTrees 32-bit GRBL boards.
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Port conflicts: Other software can lock the serial port. Close UGS, Candle, Easel, or any terminal before connecting gSender.
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Probe offset ignored: If Z zero is consistently off by the plate thickness, re-check that the plate-thickness value is entered correctly and that the probe routine is set to apply the offset.
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Surfacing out of bounds: Always preview the generated toolpath and run a dry run with Z raised before cutting into the spoilboard.
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Calibration drift after mechanical work: Any change to couplers, belts, or lead screws can alter effective steps/mm. Re-run the $100–$102 calibration after mechanical adjustments.commons.
When gSender is the right controller (and when it isn't)
gSender excels as a modern GRBL/grblHAL interface for 2.5D routing, spoilboard maintenance, and workspace management. It is not a full CAD/CAM suite and does not replace 3D relief-carving toolpath generation. [brief] For complex 3D surfaces, continue using a dedicated CAM program to generate toolpaths, then use gSender to send, probe, and manage the job.
If your workflow relies heavily on automated spoilboard surfacing, conductive probing, and straightforward EEPROM tuning, gSender provides a cohesive environment that reduces context-switching and keeps critical setup steps inside one interface.
