Where Those Random Dots in Engravings Come From

My assumption (and I know what that word means :grin:) has been that a commercial laser will arrive from the seller with its power supply twiddlpot preset to the maximum current for the laser tube in that machine. Similarly, a “60 W” replacement supply will arrive preset for more-or-less the correct current for a “60 W” tube from that seller. In either case, there’s no consumer interaction required or expected.

Which seems true for the three HV supplies I have. They all produce about the same 25-ish mA max current, but each has a different twiddlpot setting: the factory techs definitely adjust the pot to produce a specific current. We all know 25-ish mA is how OMTech (and others) wring an alleged 60 W out of a 1 m tube: having a twiddlepot doesn’t preclude overdriving the tube!

Conversely, anyone inclined to tinker inside / “improve” a laser or build one from scratch must do a whole bunch of system-level integration / configuration / testing far beyond the consumer level, so it doesn’t seem unreasonable to expect those folks to perform what’s ordinarily a factory adjustment. Setting the current does not require opening the power supply, doesn’t expose you to high voltages, and uses only common tools. Admittedly, it might require adding a DC milliammeter to the HV circuit, but the OEM supply in my laser included a digital meter and tinkers generally add a meter as one of their first mods.

So it seems reasonable to think the twiddlepot is intended to (and actually does) set the maximum recommended / allowed / peak tube current, with the PWM / analog value scaling the operating current between 0% and 100% of that current. The usual caveat about improving the tube’s lifetime by rarely exceeding 70% of its maximum current translates into a sensible, consumer-friendly meaning of rarely exceeding a 70% “power” level. OEMs setting the twiddlepot to an “optimistic” current just take advantage of the situation.

Choosing a different twiddlepot setting can certainly make the supply harder to use, but what’s the point in that?


One would hope that’s the difference between the top-dollar supplies found in high-end commercial machines and the bottom-dollar cost-reduced supplies we have. It would be interesting to measure what goes on in those machines, but my toy budget won’t stretch that far.