Need Help!- LS3020 Perspex Edges

[fullingdale]

Would like to hear the thoughts of others on the best way to get a clean cut on the edges of prespex ... I am getting mixed results, quite possibly down to the settings that I am using.

When I have used thicker perspex (6mm) I find that the cut is melting the perspex and it tends to pool a little under the cut, which is making the back edges a little messy. I did think that perhaps I would be getting a better result if I used something like blu-tac to lift the perspex off of the metal grill.

Do you find that you get better results from cutting the outline in a number of passes, or by hitting it in one go?

Similar, when I am working on thinner material (1mm) I am finding that the edges are getting a little scortched.

Any guidance, appreciated

[KPBadger]

Hello

you dont tell us what wattage your laser is?
i will assume a 40W water-cooled tube.

can you upload a photo of the cutting results?


i use 60W tube in a chinese 6090 machine and find the following settings to be ideal ( could go faster with higher power, but i find taking it easy makes the edge better - this is the best quality i have managed on the particular work pieces which are quite intricate - i would go faster/more power on simple shapes ). Some forum members will probably have slightly different ideas on the matter, and of course for different laser tube power the settings should be adjusted proportionally. Even if you have only 30 watt it should be well capable of cutting 5mm perspex in one pass. ( or 6mm indeed )

3mm Perspex
Speed 7 mm/s , Power 30%,20%(corner)

5mm Perspex ( i refer to 5mm since thats what i normally use )
Speed 5 mm/s , Power 40%,30%(corner)



1. lift the material off the metal bed to avoid back-flash as you suggest- i use offcuts of acrylic but you could use anything - with bluetack it will be harder to get the material perfectly horizontal. watch for the material sagging ( and thus loosing focus ) if you do this - might need support in the middle.

2. Make sure the acrylic is "perspex" "repsol" "Plexiglas" or other brand name quality product. some inferior product is very poor for cutting by these type of low power CO2 laser.

3. your 1mm material - what is it? are you absolutely sure its acrylic? 1mm cast acrylic should cut very nicely - but it is quite expensive material!
unless someone can tell me cheap UK supplier!?!?!?!

4. have you checked all the 'usual suspects' like beam alignment, focus length, dirty mirrors/lens ?

5. Air Assist - YES DEFINITELY.

6. masking film - best to remove but can leave the back film on to prevent scratching on the machine bed.

7. "melting" - i have noticed that some perspex will exude a liquid when cut.
(short lived, evaporates quickly )
is this what you refer to? in fact some of the blue colours seem to create a dark red liquid which is quite worrying - thought i cut my finger or something! best to raise the material by means already discussed so that the 'liquid' cannot track along the back by capillary action.



hope this ramble is of some assistance!


regards
KPB

Originally Posted by fullingdale Would like to hear the thoughts of others on the best way to get a clean cut on the edges of prespex ... I am getting mixed results, quite possibly down to the settings that I am using. When I have used thicker perspex (6mm) I find that the cut is melting the perspex and it tends to pool a little under the cut, which is making the back edges a little messy. I did think that perhaps I would be getting a better result if I used something like blu-tac to lift the perspex off of the metal grill. Do you find that you get better results from cutting the outline in a number of passes, or by hitting it in one go? Similar, when I am working on thinner material (1mm) I am finding that the edges are getting a little scortched. Any guidance, appreciated

[KPBadger]

I should have mentioned - the power settings refer to a 2 year old tube, but seems to perform much as it did when new.

[ru-alright]

Hi
I have a 3020. You must raise acrylic above metal honeycomb bed. I was getting the same results are you until I did so. I use 4 scrabble tiles, one in each corner. Currently I'm cutting at approx 80% (machine amp meter reading 21) and set machine at 12 speed via newly draw. I also set cut order for each of my designs. I always cut internal bits first leaving the last outline til last 'cos the internal bits fall out. Usually I get a very nice clean cut, no melting underneath. I leave the backing on what will be the front of the piece and cut on the back side sometimes with backing on, smells a bit more though. If you cut on back side with backing off, 'flip' the image to cut in reserve. Any slight acrylic smutt (staining of surface) will be on back, backing comes off front giving nice front finish. Also check your height. Remember the piece of plastic on the machine keys in a height guide. Align to top of laser head mounting = 62mm. I still do this for everything I cut.