gSender Workflow: Setting Zero, Running Jobs, and Recovery
What Is gSender?
gSender is Sienci Labs' free, open-source CNC control software. It's the interface between your computer and your CNC machine — you jog the machine manually, set work coordinates (zero point), load G-code files, and run jobs from it. It runs on Windows, Mac, and Linux.
This guide covers the complete workflow from power-on to finished cut.
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1. Connecting to Your Machine
- Launch gSender
- Connect your CNC via USB
- Select the correct COM port (Windows: Device Manager → Ports; Mac/Linux: /dev/ttyUSB0 or similar)
- Select Baud Rate: 115200 for most GRBL machines
- Click Connect — status bar shows "Connected" and machine position appears
If connection fails: check USB cable, check that no other software (Candle, UGS) is using the same port, try a different USB cable.
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2. Homing the Machine
Most CNCs have limit switches that let the machine find a known reference position (home).
Click Home in gSender. The machine will:
- Move Z up to the limit switch (safe first move)
- Move X to the limit switch
- Move Y to the limit switch
- Stop at machine home (usually back-left corner)
After homing: machine coordinates (MPos) are now known. Work coordinates (WPos) are still wherever they were last set.
If no limit switches: skip homing. You'll rely entirely on work coordinates you set manually.
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3. Jogging the Machine
Use the jog controls to move the machine manually:
- Arrows: X and Y movement
- Z+ / Z-: move the spindle up and down
- Step size: 0.1mm for fine, 1mm for normal, 10mm+ for fast travel
- Speed: how fast jog movements happen
Move the machine to your desired work origin (the X0, Y0, Z0 point your G-code was programmed from).
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4. Setting Work Zero (XYZ)
Work zero is the reference point your G-code uses. It's separate from machine home — you can set it anywhere.
Setting X0 Y0 (the corner of your workpiece):
- Jog the bit directly over your desired XY origin (usually bottom-left corner of the workpiece)
- Click Zero X and Zero Y (or Zero XY together)
- The WPos display now reads X0.0 Y0.0 at this position
Setting Z0 (the surface of the material):
- With a paper feeler gauge method: jog Z down until a piece of paper just barely slides under the bit with slight resistance. Click Zero Z
- With a touch plate / probe: place the touch plate on the material surface, connect the clip to the bit, click Probe Z in gSender. It auto-zeroes within 0.01mm accuracy.
- Raise Z 5-10mm after zeroing so the bit isn't sitting on the surface
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5. Loading and Visualizing Your G-code
- Click Open and select your G-code file (.nc, .gcode, .tap)
- The visualizer shows the toolpath in 3D — rotate with mouse drag, zoom with scroll
- Check the toolpath makes sense — does it match your design? Are the cuts in the right places relative to origin?
- Dimensions display shows how big the job is — verify it matches your expected part size
Simulating the job: gSender can run through the file without moving the machine. Click Start with the spindle disabled (or use a dry run mode) to simulate. Watch for any path that goes outside your material boundary.
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6. Pre-Flight Checklist
Before pressing Start:
- [ ] Spindle/router is running (turn it on manually)
- [ ] Work zero is set correctly
- [ ] Workpiece is secured (tape, clamps, screws)
- [ ] Bit is correct for the job and tightened
- [ ] Collet is tight (should not spin by hand)
- [ ] Dust collection is running (if you have it)
- [ ] Bystanders are clear
- [ ] You know where the emergency stop is
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7. Running the Job
Click Start. The machine begins moving.
During the cut:
- Watch the first pass carefully — does the bit engage material correctly?
- Listen: smooth machining sounds correct. Chatter, squealing, or excessive vibration = stop and investigate
- Check your first few cuts: are they at the right depth?
Feed rate override: while running, you can adjust feed rate in real-time using the override slider. Reduce if something sounds wrong. Increase if cuts are going well and you want to speed up production.
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8. Recovery: When Something Goes Wrong
Machine alarms (limit switch triggered):
- Don't panic — the machine stops safely
- Click Unlock in gSender to clear the alarm
- Jog away from the limit switch
- Re-home if needed, reset work zero
Power loss mid-job:
- DO NOT re-home while the bit is in the material
- Note the approximate position
- gSender has a Start from Line feature — you can re-enter the job at a specific line number after re-establishing position
Bit breaks mid-job:
- E-stop or click Stop immediately
- Raise Z
- Replace bit (same type, same diameter)
- Re-zero Z on the same surface reference point
- Resume from approximately the line where the break occurred
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Useful gSender Features
Outline: traces the XY boundary of your job at a safe Z height (not cutting). Verifies your material is large enough and positioned correctly.
Macros: save sequences of G-code commands as buttons. Useful for going to a safe home position, turning on/off accessories, running a probe sequence.
Start from Line: re-enter a job after a failure without re-running completed sections.