How do you set Start TC and Laser Off TC on a galvo laser?
Your fiber laser fills a square and every hatch line stops just short of the outline. Or it ends in a little scorch. Speed and power aren’t the problem. Start TC and Laser Off TC are, and you tune them on a test card, not from a forum post.
Applies to
- Process
- Galvo lasers: fiber, UV, CO₂ galvo
- Software
- EZCAD 2, EZCAD 3, LightBurn for galvo
- Settings
- Start TC, Laser Off TC (then Polygon, jump delay, NTC)
- Test stock
- Something that shows fine detail, like a metal business card
Why it matters
Every line a galvo draws goes: laser fires, mirrors start moving, line gets marked, mirrors stop, laser turns off. Start TC and Laser Off TC are delays on the laser, setting exactly when it fires and stops relative to the mirrors.
Start TC too long and the mirrors are already moving when the beam fires. Gap at the start of the line. Too short (or negative) and the beam fires before they move. A burned dot.
Laser Off TC is the mirror image at the far end. Too short leaves a gap before the contour. Too long sits and burns at the corner.
And the EZCAD tooltip says Start TC delays the mirrors. It doesn’t. It delays the laser. Alex at Laser Everything calls this out because it flips how people read the card.
What good looks like
- Hatch lines touch the contour at both ends: no gap, no bulge, no scorch
- Each value on the card is labelled
- The start corner of the outline (bottom left on a square) closes cleanly too
How to apply it
- Set jump delay to 500/500/500 with jump limit at 10. In EZCAD 2 it’s under Advanced; in LightBurn it’s in machine settings.
- Set every timing value to 0 except NTC, which stays at 100.
- Draw a 20 × 8 mm box, hatch it at 2 mm with Average distribute line checked.
- Mark it at Start TC 1000, label it, then step down: 500, 250, 100, 50, −50, −100, −250, −500, −1000.
- Look at each box under a USB microscope. Find where the gap closes just before the burn bulge starts. Split the difference between the two closest.
- Repeat the whole card for Laser Off TC with Start TC set. If the best value falls between two boxes, run a tighter card or split the difference.
- Save the values as your machine default (see below).
Test it on your setup
- Alex’s machine landed at Start TC 75 µs (gap gone at 100, bulge starting at 50) and Laser Off TC 175 µs (rounded cap at 100, a touch burny at 250). Yours will differ. He’s clear: don’t copy his values.
Exceptions & tradeoffs
LightBurn treats timing as global: set once in machine settings, override per layer or library entry if needed. EZCAD 2 and 3 store it per parameter, so set your tuned values as the default. Any parameter made before tuning has to be fixed by hand.
You don’t need a new timing set for every speed. In Alex’s testing, timings held steady up to about 4,000 mm/s, which is what most stock galvo heads are rated accurate to.
Common mistakes
- Tuning Start/Laser Off TC before parking the jump delaySet jump delay to 500/500/500 first; it skews the timing read
- Trusting the EZCAD tooltip that Start TC delays the mirrorsIt delays the laser; positive = later fire = gap
- Copying another machine’s timing numbersRun your own card; every machine is different
- Judging the card by eyeUse a cheap USB microscope; the differences are tiny
Frequently asked questions
- What does Start TC do in EZCAD?It delays when the laser fires relative to the galvo mirrors starting to move. Too long leaves a gap at the start of each line; too short burns a dot there.
- What is Laser Off TC?The delay before the laser switches off after the mirrors finish a line. Too short leaves a gap at the end; too long burns the end point.
- Do I need different timing settings for every speed?Usually not. Laser Everything found timings stayed consistent up to about 4,000 mm/s, the rated limit of most stock galvo heads.
- Does galvo timing work the same in LightBurn?Yes, the timing settings behave the same in EZCAD 2, EZCAD 3 and LightBurn. LightBurn just stores them globally in machine settings.
The timing settings beyond speed/power/frequency; same across fiber, UV, CO₂ galvo, EZCAD 2/3 and LightBurn — The COMPLETE Guide to Timing and Delay for Galvo Lasers ↗ at 01:37.
Jump delay baseline 500/500/500, jump limit 10; all timing at 0 except NTC 100 — The COMPLETE Guide to Timing and Delay for Galvo Lasers ↗ at 02:48.
What Start TC and Laser Off TC do; the EZCAD tooltip is wrong — The COMPLETE Guide to Timing and Delay for Galvo Lasers ↗ at 04:03.
Start TC test card: 20 × 8 mm box, 2 mm hatch, +1000 to −1000, read under a USB microscope — The COMPLETE Guide to Timing and Delay for Galvo Lasers ↗ at 05:13.
Laser Off TC card and splitting the difference between two values — The COMPLETE Guide to Timing and Delay for Galvo Lasers ↗ at 09:03.
LightBurn timing is global; EZCAD is per-parameter, so save as default — The COMPLETE Guide to Timing and Delay for Galvo Lasers ↗ at 26:57.
Everything here is from Alex’s video, including his advice to watch it all once before following along. Good advice. I split Polygon and jump delay into their own pages so each one has room for its own test card.