Laserscript user forum

I have an emerging problem when cutting a sheet of 3mm Perspex in that any cutting on the right hand side (especially the top RHS) of the workpiece doesn't cut through whereas the rest of the sheet cuts fine.

I have experimented long and hard over cutting speed and power for Perspex and have found a combination that worked, but I am now finding the above problem as well as the cuts are not square and I am left with a slight bevel on the cut edges.

I have shimmed the honeycomb bed and a spirit level shows the surface to be universally level, the mirrors and the rest of the machine are clean. I have a thermometer in the cooling water and it never gets above 19deg at this time of year.

I purchased the machine in May 2015 but it has only had very light use. Any suggestions would be gratefully received.

Regards, Richard

Check the mirrors are aligned ok. They only need very fine adjustment on the 3020.

Best
Dave

Hi! Thanks for that, I thought that might be a suggestion - however, I am frightened of touching the mirrors in case I mess up the machine totally!! Is there a set sequence/procedure for this or should I ask HPC to do it?

It is scary and I would allow a morning if it is your first time. On the 3020 the last mirror did/does not have any adjustment other than shimming it with thin card/paper.

There should be instructions that came with the machine, the idea is to get the beam to enter roughly in the centre of the hole in the head before the last mirror. I would take the last mirror out, place a bit of tape over the hole and text fire in all four corners (on a new bit of tape each time) this will give you an idea if it is out of alignment if the burn mark is moving. If it is not it could be the last mirror needs shimming so do the same (with the mirror back in place) but put tape over the exit hole of the nozzle.

Removing the mirror stops it getting smut from the test burns

Cheers
Dave

Thank you very much for your help - may I pick your brains further please?! I have removed the last mirror (the first time I have dared to do this but I guess it will seat correctly as there is no built-in adjustment) and placed tape over the head and fired test shots at top right (datum), bottom right, bottom left and top left. The result is rather disturbing as both RH shots are weak and scattered whereas the bottom left is seems central with probably a 50% white central circle and the top LH seems central with about a 10-20% white central circle. Does this point to a failing laser do you think?

I also note there are small scratch marks on the mirror I removed - I have only used IPA and cotton buds, but have inserted the cotton bud through the hole in the head.

Any thoughts would be most welcome

Best regards, Richard

Sounds more like alignment - if the tube was going the beam would be weak all over the bed on the 3020. Is the beam entering the head centrally?

The chances are the mirror was scratched by the cotton bud - depending how deep they are it could be scattering the beam. That mirror is adjusted by shimming.

If you do, don't remove the other mirrors when you clean as that can alter the alignment, if you have, it maybe worth checking they are all sitting right (not too tight - just pinched up).

Tape a bit of card over each mirror and see how central the beam is (the beam will be bigger until it hits the lens).

Best
Dave

Had a good start to the day - was testing the burn marks on each mirror and then cleaned the lens, went to do a test cut and - nothing! Turns out the last mirror above the head had shattered - a small mirror but a big price! I guess the very small scratch might have caused a weakness as I don't think the retainer was any tighter than before.

First time I cleaned that mirror I put it back the wrong way round It lasted about 30 seconds

Me again! I am extra frustrated now as I have just received my replacement mirror but the cut or lack of it on the RHS is even worse! I have even doubled the power from my well established level and it will still not cut through until I am at least 40mm in from the RHS.

When I make test shots at each mirror the marks all seem pretty central. My spirit level tells me the arm the laser travels on is dead horizontal and so is my shimmed honeycomb.

My puzzle is that if the laser and bed are parallel and the beam seems to be firing centrally how can there be such a variation unless the beam is weakening at its furthest distance?

Not sure what to do next - any further ideas please?

Regards, Richard

How old is the tube?
Have you cleaned the output coupler (BE VERY CAREFUL - don't use a cotton bud).

The beam will weaken the further from the source in theory. If the bed and mirrors are aligned it could be the tube - what sort of speeds and power are you using on which material?

When you say firing centrally - what part of the head are you centring on?

Best
Dave