strange edge when cutting acrylic

[zoefie]

Hi i've got a strange problem when cutting thick (10 mm) acrylic

I use a 60 watt CO2 china-laser, when i vector cut something the edge looks very strange to me ( see attached jpg)


The cutting edge seems to be a bit hollow.
I don't understand what could cause this kind of edge

I have tried all different kinds of settings checked the beam alignment as good as i can but i keep getting this edge.

The drawing represents the edge of the acrylic cutout, this cutout was made at 80% power and a speed of 4mm/sec.


Has anybody got any idea what could be causing this?

Best regards,
Ferry...

[zax15uk]

It is likely just the beam profile, although there could be some other factors (heating or alignment etc).

Do you have a longer focal length lens available?

If not, you could focus into the material to compensate. You may have to experiment to get the optimium setting.

Zax.

[ocp]

What cad program are you use? Do you have corel draw? IMO thats one of the easiest programs to use. If you are using corel, see about putting the file up for us to look at.

[zoefie]

@zax : I hope to get a 100mm lens this weekend (the original one is 55mm FL)

@ OCP : I don't think it has anythiong to do with the cad program, even when i cut a straigt line directly from lasercut 5.3 the edge looks like it is hollow.

I appears that the beam is at it's widdest in the middle of the material. I would expect the cut to be like an hourglass or even a bit tapered, but nothing like what i'm getting at the moment.

I will conduct soem more test's this weekend and try to shoot some pictures of the results.

Best regards,
Ferry.........

[RCaffin]

Hi i've got a strange problem when cutting thick (10 mm) acrylic

Funny stuff, acrylic.
Have you tried cutting something else for comparison? Al, steel?
It could be the transparency and lack of conductivity.

Cheers

[zoefie]

No, CO2 will not cut any metal.

But i will try some plywood or mdf this weekend to see if it's material related or machine related

[zax15uk]

Well not quite true, CO2 cuts metal very nicely... you just need a LOT more power than your machine has (several kW for 10mm steel).

You are correct that an hour glass or taper would make more sense, but if the alignment isn't dead center on the lens it could be similar to your drawing.

Zax.

[zoefie]

Oke, i didn't expect that.

I'm gonna recheck the alignment tomorrow.

thanks for thinking it over.

Best regards,
Ferry........

[RCaffin]

No, CO2 will not cut any metal.
But i will try some plywood or mdf this weekend to see if it's material related or machine related

Try cutting some opaque plastic then - a bit of black UHMWPE or even some PVC. (Mind the fumes.)

Cheers

[vivinar]

do your machine made of steeper motor or belt?
and you also can check the linear guide to make sure it fixed well.if the linear guide is loosen,it also will effect the cutting.and check the beam at the alignment.
hope you can deal with it well quickly.
Vivinar

[zoefie]

UPDATE :

If been busy all weekend to align the tube and mirror's as best as i could get them.
I've found out that indeed the beam was not striking the lens exactly deadcenter.

Now it's almost perfect (althoug it's hard to see if there is any difference in striking point from point to point) and the quality of the cut is much better.
It's still not exacly what i hoped for.

But i'll try to improve the alignment further.

I find it difficult to see exactly where the unfocused beam is striking the mirror.
I have used diffrent kinds of detection, plain-paper, thermal faxpaper (seems the best)

Anyway thanks to all of you who gave me advise

Best regards,
Ferry....

[zax15uk]

I'm glad to hear you're making progress. Initial alignment can be a challenge but it should remain stable unless you move the machine.

The hardest part is getting everything parallel so the beam stays centered across the entire table. The best method is to align it with the longest beam path and progress from there.

Zax.