Clear acrylic not cutting clean

Community Laser Talk
1

I have some 12mm clear cast acrylic that was given to me. It’s frosted on both sides. I was experimenting with cut settings on my 100W C02 and have a strange issue, at least it seems strange to me. The top 3mm or so of the cut is very rough / frosted and everything below is nice and clear. I have experimented with different focal heights, both closer and further way as well as different speed/power settings and do not notice any difference in the results. Looking for guidance.

I have not noticed this issue with 3 or 6 mm material.

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2

Turn your air assist off or, like mine, down low enough for only lens protection.

What length of lens are you using?

A 4" lens has a depth of focus (dof) of a little over 10mm, shorter lens, shorter dof.

That would be a starting suggestion.

The thickest I’ve cut is 10mm, but I have less than half you’re power.

:smiley_cat:

3

Using a 4" lens. I did have air on, although regulated to 15 PSI. I will try it with air off (only bleed through) and see what happens. Thanks.

4

You are aware of the start speed effect on minimum/maximum power levels?

My only solution, from Russ Sadler, was to reduce the air flow. Hope it helps.

:smiley_cat:

5

I discovered that during testing. It was only running at 4ma at 70%. Took me a while to find the issue.

6

Tim..
I cut 15mm Clear acrylic, setting Speed 3mm/s power 70%
130W monport machine
UPDATE: Nozzle distance to the material is 10mm…
The shorter distance seems to help the flame ups with the focused minimul airflow.

But I use a 3" lens it seems to work well on most of my cutting…
I tried a 4" lens but it it reduced the cutting powerand the 3" seemed to work
well with small kerf so I use it now…

But I do keep the air on low about 5-10psi to help keep the flame ups down.
I also raise the material off the homecomb for airflow.

Lastly i put some shelf liners on the unsused sidesof the cutting to help
focus the air-pull down and also assist in reducing the flame-ups.

Since it is cutting at the lower speeds it has more time to ignite the acrylic vapors…

let us know what you discover…

1 Like
7

I had some time for testing today. I ended up turning off air assist and reduced the bypass air so that it just barely came out of the nozzle. I ended up at 4 mm/s @ 70% power with 2 passes. That solved the frosted edge problem.

I did have a couple small fires though, which I don’t like. They went out as soon as I stopped the laser so no damage done. Definitely not something to walk away from.

1 Like
8

I’ve put a dish of water and stuck the nozzle in and watched it bubble..

Reducing air pressure was the only way I could get rid of the frosting on thicker pieces of acrylic.

I usually try to get the fastest speed at the highest power so I can do it in one pass..

Have fun :tada:

:smiley_cat:

9

That was interesting so I did a quick search. It seems that Cast will frost more easily than Extruded.