While making some test pieces for our CNC drilling machine, we had a few problems with the laser cutter. It was nothing serious, except the cutter seemed to be losing power when cutting anything more than a simple few circles. We slowed the speed down from 20mm/sec to 10mm/sec and ramped up the power dial from 15mA to 20mA but to no avail – even making two passes didn’t slice through a 3mm acrylic sheet.

The first thing that came to mind was mis-aligned mirrors. Unless the laser beam is correctly focussed, cutting power is only a fraction of maximum. But re-aligning mirrors is a real pain to get right – so before we messed about with that, we thought we’d give the old “turn-it-off-and-turn-it-on-again” approach a go.

Whenever we start using our laser cutter, the first thing we do is check for air bubbles in the laser tube.
Cutting with an air bubble can cause the tube to overheat and eventually crack or rupture. This is one thing we’re quite paranoid about, so we always make sure there are no bubbles in the tube before starting!

A quick inspection of the tube and we found the problem.
There was a massive air bubble in the tube. But how did that get there?
It seems that our run-silent aquarium pump (supplied with the cutter to provide cooling water) wasn’t in fact running.

To avoid getting bubbles in our water, we keep both the pump and the return pipe from the cutter fully submerged in water. This is great when everything is working – but when the pump stops running, there’s no immediate indicator that the water isn’t getting pumped round the laser tube.

Overheating (or cooling water that’s got too warm) is another cause for power loss with a laser cutter. And that’s exactly what was happening here. The laser tube wasn’t getting any cooling water, and so just getting hotter and hotter!

We left the cutter switched off for about half an hour, then got the water pump up and running again (we didn’t do it straight away, in case quickly cooling the glass laser tube caused it to crack). After leaving it for a few minutes, and checking that there were no more air bubbles in the glass tube, we fired up the laser.

It was soon cutting 3mm acrylic at 20mm/sec as usual as if nothing had ever gone wrong!
So just a word of warning to anyone suffering from poor performance – check your tube! We were lucky this time – an overheating tube can easily crack if you continue cutting with it;
it looks like we caught ours just in time. But we know to check our water pump is working, as well as getting rid of any and all air bubbles in the tube from time to time.