Changed laser tube, now wider kerf on right hand side of cuts

Hi, we run a Shenhui 1280 and just changed from old 100W RECI to 100W EFR, along with changing all the mirrors. We also removed the collimator lens for the inline red dot as it often didn't work well anyway. The combination of new tube mirrors, alignment has given a nice increase in cutting performance, but we have a problem.

As per picture, on the right side of cuts we notice a little burning as though the kerf width is wider or the beam distorted.

Air supply is as previously (2 bar for wood) through cone extension to 10mm from the surface of the cut. Most of the smoke from the underside where there is no problem, and the direction of the burning is at a right angle to the direction of extraction.

Happens with various lenses, but this picture shows a new 75mm lens.

We have tried altering the focal distance. We have made sure that the beam is coming through the centre of the cone as we suspected reflections. The beam is hitting the centre of the mirrors and cuts are good, straight and clean.

Having considered the above points, I'm asking for other ideas.

Thanks!
Attachment 375798

do a rough check on the beam mode John, where it exits the tube, stick a bit of thick white card in front and see what state the emitted beam is straight from the tube

On thin tape it looked circular and central. Will try with thicker material. Are you thinking the collimator removal is an issue?

was wondering if the beam had a particularly poor mode from the new tube, unlikely but the easiest thing to rule out for zero cost.

next test will be rotate the tube by 90 degrees (making sure you don't cause an air bubble in the ends) to see if the effect moves 90 degrees as well

Attachment 375945
30% power brief press of pulse button. Tried a few and they all have the lower left quadrant like this. Holding any longer and the whole thing would set on fire. TEM20?

Full reflector to output coupler looks a bit off in that one, shouldn't make too much difference though once it's been through the final lens.

Something else to try, try cutting something without the cone, the airflow can sometimes cause sideburn (obviously don't go setting anything on fire) ;)