cutting acrylic

[arthurvenet]

hi there, i am currently using 80 watt co2 laser with a dsp controler to cut 5mm acrylic. i seem to be having a problem cutting it, i need to do two passes at 95 % power at 10mm/sec to cut throw the 5mm acrylic i can slow the feed rate to 5mm/sec but the co2 tube barley has any power if i go below 10mm/sec, has any one come across that type of a problem.
thanks arthur.

[twehr]

hi there, i am currently using 80 watt co2 laser with a dsp controller to cut 5mm acrylic. i seem to be having a problem cutting it, i need to do two passes at 95 % power at 10mm/sec to cut throw the 5mm acrylic i can slow the feed rate to 5mm/sec but the co2 tube barley has any power if i go below 10mm/sec, has any one come across that type of a problem.
thanks arthur.

I have a 40w and I cut 4mm at 90% at 5mm/sec. Works nicely. There are these possible issues.

• 1. Focus - the focus is critical. Most of us try to focus half way into the material (2.5mm deep in your case)
  2. Depth of field - the height of the material that will remain in focus. Lots of calculations to get to this, but on my machine, with a 55mm focus lens, my depth of field is about 1.2mm, which means that the area from 54.4 to 55.6 is in perfect focus. Anything outside of that is less focused and therefore less powerful. To be in perfect focus (max useful power) for 5mm thickness you would probably need a 4" (100 mm) lens. Those are expensive. All of that being said, it you do get reasonable cutting outside of the perfect focus area. That is why I can do 4mm in one pass.
  3. Power supply is OVER driving the laser tube. My laser ps puts out way more than is expected for the tube I have. If I run it at anything over 60% (of PS capability) the actual power of my tube drops off a lot after a few seconds. The tube is not expecting that much power. So backing off the power setting may actually increase your actual tube power output. I have mine locked down to never go over 60% and I get great results on everything. The best way to check your power is to have an ma meter and see what it says at 90% (in cut mode). If it is over the recommended max for your tube, you will have to back it off. If you need a meter, Marco has them here on LightObject for under $15. Not something you use every day, but hard to test without it. (DON'T try to use a regular DVM - you will blow it up!)

With 80 watts, even a 55mm lens should cut acrylic like butter at nearly 10 mm/sec. So I suspect you are having one of the issues above. Start with #1 - make sure your focus is really right on. Then look at #3 - back off the power and see what happens. Maybe two passes at lower power (try 50% as a test) will work better than you 95%. If you have an adjustable table, you may want to focus on top, make a pass, raise table a couple of mm and make second pass.

When you make you tests, please report back here so others will benefit as well.

[arthurvenet]

hi tim i cleaned and ajusted all the mirrows i ajusted the focal lens to 50.8mm from the top of the acrylic which is the specified hight, i found by doing those three things it cuts heeps better,50% power at 12mm/sec 2 passes to cut throw 5mm acrylic not what i expected from a 80 watt co2 laser tube which has only worked 10 hours maybe its not a true 80 watt tube.i also noticed if i use the ph software i cannot go below 11mm/sec thats when the tube has no power, if i use only the dsp controler i can go down to 1mm/sec with full power no problems but still will not cut the 5mm acrylic it cuts about just over 3/4 of the way.once again thank you for responding.
arthur

[twehr]

hi tim i cleaned and ajusted all the mirrows i ajusted the focal lens to 50.8mm from the top of the acrylic which is the specified hight, i found by doing those three things it cuts heeps better,50% power at 12mm/sec 2 passes to cut throw 5mm acrylic not what i expected from a 80 watt co2 laser tube which has only worked 10 hours maybe its not a true 80 watt tube.i also noticed if i use the ph software i cannot go below 11mm/sec thats when the tube has no power, if i use only the dsp controler i can go down to 1mm/sec with full power no problems but still will not cut the 5mm acrylic it cuts about just over 3/4 of the way.once again thank you for responding.
arthur

Yep! Focus is critical - and clean optics from start to end. The fact that you can only go 3/4 the way through is probably do to the focal length limiting the depth of field (range of focus). A longer lens would definitely help that. (Marco - can you get longer length lenses [100mm?] at any reasonable price?)

I am not sure what you mean by use only the DSP controller and not the ph software. Do you mean you are downloading the file to a thumbdrive? The ph software is what generates the job to begin with, so I am curious what you are doing.

[arthurvenet]

hi tim if i use the ph cad software to ajust the speed below 11mm/sec the tube barily has any power only if i go below 11mm/sec, but if i use the dsp control panel to ajust the speed i can go all the way to 1mm/sec and the tube works fine if that maks sence.
tim what is the longer lense you are refering to is it the laser head? can you please let me no.
thanks arthur.

[twehr]

hi tim if i use the ph cad software to ajust the speed below 11mm/sec the tube barily has any power only if i go below 11mm/sec, but if i use the dsp control panel to ajust the speed i can go all the way to 1mm/sec and the tube works fine if that maks sence.
tim what is the longer lense you are refering to is it the laser head? can you please let me no.
thanks arthur.

The lens is in at the bottom of the laser head. It focuses the laser light into a fine point. You mentioned cleaning your mirrors - you need to make sure your lens is really clean as well.

I now understand what you mean about where you are setting the speed. The problem I have is understanding how the to are related. The speed you manually set at the control panel only controls the speed of the head when you press the arrow keys. Jobs still run based on the information that is downloaded with the job. So changing the settings at the control panel should have no effect on anything that is job related. How are you noticing the difference in power - running a job or pressing the laser button?

[arthurvenet]

i can still ajust the power and cutting speed with the control panel dont foget it is a stand alone system, you dont have to have a computer to run it.
ok, if i switch on the power to the dsp and i unplug the computer the file i created is still in the dsp memorey i can still procces that job and still set the cutting speed and power output .
arthur

[twehr]

i can still ajust the power and cutting speed with the control panel dont foget it is a stand alone system, you dont have to have a computer to run it.
ok, if i switch on the power to the dsp and i unplug the computer the file i created is still in the dsp memorey i can still procces that job and still set the cutting speed and power output .
arthur

I wil have to test it out, but I believe that it will continue to use the info that is stored as part of the job.

If I can't get it tested today or tomorrow, it will have to wait till late in the week. I will be moving the DSP to my new laser in the next few days.

[arthurvenet]

hi tim its good news, i can now cut up to 10mm acrylic at 6mm/sec at 95% power i can not belive it. it was all in the setup of the job,the cornner power was to low thats why it was not cutting the 5mm acylic i ajusted the cornner power the same as the cutting power, i set it at 6mm/sec at 40% power and with one pass it cut the 5mm acrylic all the way throw no problems at all.
thanks arthur.

[Tech_Marco]

Hey folks:

I just landed at Hong Kong/China. I'll try to quote some price for the longer focus length lens if available here.

Hey Arthur, what power supply are you using? Did you buy the PS from me also? What about the 80W tube?

By the way, I'm getting ultrasound cleaner and it should be good to be useed to clean lens and mirror. Try not be rough when cleaning lens/mirror with a cloth as scratches could harm the lens/mirror.


Marco

[arthurvenet]

hi marco i bourght the co2 tube and power supply from coletech, at that time i did not now about lightobjec. i just happen to stumble accross your webpage. i notice the dsp controler which i purchest two and some other items. also i want to say your forum has lots of information and intresting topics for us home builders which is grate keep it up guys good stuff. now that i work out the problems with my firt laser that work grate, with the help from you guys thanks so much, i will be starting my second co2 60 watt laser soon.
by the way marco when will the cleaning soloution be avaliable let me no please.
arthur.

[twehr]

So glad to hear you have it working. I'll file your solution away to remember next time.

[baccus61]

Hi Arthur,
Just a little heads up on cleaning your lenses and mirrors.
If you have the gold mirrors then you need to be really careful as the gold is soft and scratches very easily. You might have seen some video footage of a worker at a laser manufacturer site cleaning them with a cotton tip or Q-tip moistened with alcohol but it is not a good method if you want your mirrors to last a long time.

It's also a good idea not to have to clean them in the first place if you don't have to but when you do use a lens blower brush from a camera store to blow away the dust build up. Get a good quality squirrel hair one as the imitation ones are too coarse for the soft mirror surface.

The method used in industry is to WET some lens cloth with Isopropyl Alcohol and lay it flat on the mirror/lens and SLOWLY drag it off without applying pressure, just the surface tension of the alcohol.
Then use another piece the same way until the mirror/lens is clean.
This way you will not scratch them unnecessarily.

I used First Surface mirrors from a photocopier when I built my first one and they are coated with Aluminium and can take a lot more harsh treatment than the gold ones. I'm actually thinking of getting rid of the gold ones and going back to the aluminium ones as they are easier to look after but I've had no problems with the gold ones yet so I will keep them for a while longer.

I have also read that you must never use Acetone on the output coupler/mirror of your laser. I don't know why but my guess is that it is very bad for the AR (Anti Reflection) coating.

Chemists stock Isopropyl Alcohol and if you are lucky and get a bottle that is out of date then you get it cheaper. Does alcohol really go out of date???

Have fun with your build.
Richard.

[Tech_Marco]

hi marco i bourght the co2 tube and power supply from coletech, at that time i did not now about lightobjec. i just happen to stumble accross your webpage. i notice the dsp controler which i purchest two and some other items. also i want to say your forum has lots of information and intresting topics for us home builders which is grate keep it up guys good stuff. now that i work out the problems with my firt laser that work grate, with the help from you guys thanks so much, i will be starting my second co2 60 watt laser soon.
by the way marco when will the cleaning soloution be avaliable let me no please.
arthur.

Arthur:

I'm in China now and I found some low cost Ultrasound cleaning unit and I think it's a good candidates for cleaning laser lens and focus lens. With Ultrasound, there is no need to use cloth or paper to do clean and your lens/mirror hate the cloth/paper.

I'll do some test before I imported it. It cost less than $50 and I think it's a good investment for your laser machine as the optical parts cost a lot, especailly the ZnSe focus lens.

Any other item want to put it on your 'wish list'? I'll stay here till 26th

Marco