CO2 Laser Cuts Straight Lines but Misses Corners: Check Min Power

A cut that leaves tiny bridges at the corners raises an awkward question: why can the same CO2 laser tube cut the straight edges? The position of those bridges is a useful clue. Check whether they coincide with changes in direction before treating the job as a general loss of tube power.

On a glass-tube cutter with LightBurn and a DSP controller such as Ruida, Min Power is worth checking first. The advice below is for that combination. Find out which controller your machine uses before applying it.

Start with the job file

Put the failed sample beside a copy of its job file. In the cutting layer, note speed and both power values, including Min Power even if you normally only adjust the maximum. Write down the speed units as well. A setting in mm/min cannot be compared directly with the same number in mm/s.

There is one extra detail for Ruida users. LightBurn has a Default Power switch that tells it to use the controller's default minimum and maximum values. With that switch on, the numbers you are editing in the layer may not be the ones used for the job.

The corner uses a different part of the power range

A turn changes the head's speed. Supported DSP controllers adjust power between the minimum and maximum values as the head accelerates or slows. A clean straight section therefore does not tell you what power was used at the corner.

An insufficient Min Power setting can leave a shallow cut there. A completely blank gap can mean the setting has gone below the level needed to start firing. At the other extreme, excessive minimum power leaves scorching where the motion slows. Neither symptom, by itself, establishes that a tube needs replacing.

Start Speed is another setting to read. At or below this speed, the controller uses Min Power; above it, power starts moving toward Max Power. Your machine's stored value matters here. There is no need to overwrite it with a value found in someone else's setup.

Make the next sample useful

Use an offcut of the same approved material and thickness. Keep the focus setup, speed and Max Power as they were. The test outline needs a turn and a straight section; a straight line on its own misses the feature you are investigating.

For the first comparison, change only Min Power, by a small amount within the manufacturer's permitted range. This remains an attended cutting job: the enclosure stays closed and the cooling and extraction must be working. Record the change beside the result. Did the corner separate? Did the cut become wider or darker? If it chars, further increases are the wrong direction.

LightBurn suggests equal Min and Max Power for very slow cutting. This is still a material-specific cutting setting, not permission to exceed the tube's operating limits. Surface marking needs a different balance because a strong corner burn can damage the appearance.

If the problem extends beyond corners

Weak straight edges or a cut that fades during a longer run call for checks beyond Min Power. At that point, return to the machine's cooling and optics checks rather than continuing the corner test. Ask a qualified technician to investigate any suspected electrical fault.

When contacting Puri Laser, send the saved settings and sample photos together. Add the tube and controller models, material thickness, and the operating current if it is already safely displayed on the machine. A panel percentage is not a current measurement. A photo showing the good straight edge beside the incomplete corner is more useful than simply reporting that the tube has lost power.