Need help/tips/advice to get a super clean edge on acrylic cuts!!

[Dylan Hall]

I made an account on here because everyone seems very helpful and i am hoping to get some help myself. We have a Gravograph LS900 80watt laser that we are using to cut out 1/8" 1/4" and 1/2" acrylic. We are getting a somewhat textured side to the acrylics which i will include some pictures of and other than using a torch with map gas i haven't found anything else that has any better results. The deeper it cuts the worse the lines and will even kind of make the bottom jagged. I will include a screenshot also of the settings i am currently using. Thanks for any help!

- Dylan

[Dylan Hall]

More info. I am actually using the red line on vector (forgot to change it) and it is cast acrylic.

[Rich Harman]

I'm curious to hear some solutions.

The only one that I know of is to cut slower in order to put more heat into the edge, or use another tool such as a jointer to shave a bit off. I have used progressively finer grits of sandpaper starting with 80 and ending with 1000 (or higher) to get a polished edge.

[Mark Hennebury]

Sand and polish to a fine finish, or sand to flatten it then flame Flame it to finish clear. I worked in a sign shop on acrylic for a while, and we used to sand and flame it. I also worked many years ago polishing acrylic blocks.

[Kev Williams]

First of all, the pic shows your driver set to RASTER every color but blue and orange, your red needs to be set to VECTOR.

Second of all, with 80 watts on tap- and it'll be closer to 90 watts if your machine has a Coherent tube in it- your speed of 1.5% seems a bit on the slow side, even for 1/2" thick- but all machines are different...

I'm curious--what kind of table- pin, honeycomb, flat aluminum- are you doing the cutting on?

Your driver is much newer than my newest GS driver, I note you have a 'Vector DPI' setting under the raster res settings I don't have... in your pic it's grayed out because you have nothing chosen to VECTOR--

So now I'm REALLY curious if you actually cut the plex in your pics in RASTER mode? :) (or the actual VECTOR settings you used!)




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[Ross Moshinsky]

You need to slow your machine down. The trick to cutting acrylic and getting a smooth finish (other than making sure your focal distance is right and your air assist pressure is right) is slowing down the cut speed.

I can see on your sample the bottom edge is barely cut through. That's a bad sign when cutting acrylic. You want to go well beyond that limit. So let's pretend 5% speed cuts through your acrylic clean, you need to drop the speed to maybe 2 or 3% to get a glossy finish.

I can tell you the acrylic mfg I work with on bigger orders ultimately ends up diamond polishing edges whenever possible. It gives you a "perfect" result every time.

[Dylan Hall]

First of all, the pic shows your driver set to RASTER every color but blue and orange, your red needs to be set to VECTOR.

Second of all, with 80 watts on tap- and it'll be closer to 90 watts if your machine has a Coherent tube in it- your speed of 1.5% seems a bit on the slow side, even for 1/2" thick- but all machines are different...

I'm curious--what kind of table- pin, honeycomb, flat aluminum- are you doing the cutting on?

Your driver is much newer than my newest GS driver, I note you have a 'Vector DPI' setting under the raster res settings I don't have... in your pic it's grayed out because you have nothing chosen to VECTOR--

So now I'm REALLY curious if you actually cut the plex in your pics in RASTER mode? :) (or the actual VECTOR settings you used!)




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Any speed over 2% will either need a second pass to cut through the 1/2" and/or give an even worse finish to the sides. I made a comment right after i posted saying i use the red line as vector and the dpi is usually at 1000. We are using the standard honeycomb bed with it. thanks!

[Dylan Hall]

I am running the vector cut out at 1.5% speed, should it usually be slower than that? I am using a 4" H laser lens and on my vector cuts it is 100 power 1.5 speed 1 pass and dpi 1000

[Dylan Hall]

So sand it down with a fine grit and then what kind of gas? Does it matter if i am using map gas torch?

[Dylan Hall]

We have slowed it down to 1.5% speed with the 1/2" acrylic. now the air assist pressure i am not sure about we have an electric fan motor that just pulls the fumes and debris out. Is there a way to test the air pressure and any way to adjust it? It seems like i just have the option of turning on the air assist but not changing any settings with it.

[Bruce Volden]

?? Could you try focusing into the piece instead of on top?? Not by much 1/32" may improve the cut on the 1/2".

Bruce

[Ross Moshinsky]

We have slowed it down to 1.5% speed with the 1/2" acrylic. now the air assist pressure i am not sure about we have an electric fan motor that just pulls the fumes and debris out. Is there a way to test the air pressure and any way to adjust it? It seems like i just have the option of turning on the air assist but not changing any settings with it.

That's not air assist. Air assist blows air into the cut to keep flames down. It can also effect how the cut is made.

And yes, slow down more. You're barely getting through that material as is. I can see one of the edges is "chippy" which means you're just barely getting through and it's rewelding together (also shows your air assist is probably not powerful enough). You want to go slower. Probably .8% speed.

Most people cut 1/2" acrylic with 150W laser minimum. The people who specialize in that type of work have 400w+ typically. You're under powered for cutting 1/2" acrylic.

[Kev Williams]

First-- I've owned an LS900 for almost 15 years so I'm familiar with the machine in general-

- I mentioned the speed seemed slow but I also noted 'all machines are different'. If faster doesn't get thru then obviously 1.5% isn't too slow..

- I'm still confused about the pic of your machine's driver above, because your RED color is set for ENGRAVING (raster) rather than for CUTTING (vector)?
405049
If you're cutting using red, it MUST be set for VECTOR--
You also mention you're cutting at 1000 dpi, which is also noted in the photo,
but the 'Dpi Vector' setting is where the cutting Dpi setting should be entered.
But in the photo it's grayed out, this is because red is set for RASTER
so question, is this just a random photo, or of the actual settings you're using?
If they're what you're using, they need to be changed!
(and since I don't do much cutting, I'm not sure of the effect of going down in Dpi, but testing is in order)

Air assist- to the right of the control panel is a knob, that's the air-assist pressure adjustment.
I'll assume you have an air line connected to the fitting on the back of the machine..
Air assist may help with this- best advice on how much pressure to use: if you can hear the air tube hissing, turn it down until you can't :)

To Bruce- if you focus into the piece rather than on top, you lose power density at the actual point of focus because the surface of the material is absorbing unfocused laser light, subtracting that absorbed power from the focused beam spot, and the reduced power can be substantial...

That said, the point of focus IS fairly critical when cutting, and being out of focus in either direction has essentially the same effect in power loss at the beam spot.

[Dylan Hall]

I overlooked that when i took the screenshot. We do have it set to vector (was wondering if cutting was the same settings? I will attach a picture). I will also turn the air down because i do hear it hiss a bit. We are also looking into getting a hydrogen/oxygen torch with a number 2 tip (ours is very big and map gas) and some high grit paper like 600 and some polishing compound and wheel, hopefully this helps also.405052

[Dylan Hall]

So after running some tests with different dpi and speeds i took off the paper from the bottom also and i was noticing that the "chip" look on bottom was whenever it hit one of the honeycombs as it was cutting. it still gave it this slight wave look along the side above the bottom of it but it was cutting through the acrylic just fine. any ideas on that? are there better beds to use to cut the acrylic on that wont reflect the laser as much?

[Kev Williams]

You need something like a pin bed, but they can be spendy or time consuming to make...

Or you could try some of my 'bandaids' when I need to raise parts off the table... for one, I have a zillion 4/40 size SS lockwashers that I'll lay out on my flat table, they're very consistent and raise the plate off the table about .040", works great for clean edges on Rowmark and similar. You could probably get way with using large lock 1/2" lockwasher to get more air space. Just lay them about on a solid table, making sure they're not near where the beam will be cutting to prevent flashback. Cheap, temporary, and they work. Another 'thing' I use is 1/16" diameter gas welding rod, cut them to the length you need so you can make sure the beam misses them. Put a very slight bend in them, then they won't roll. These you can use on your honeycomb table :)

[Dylan Hall]

Could i just cut a few blocks that are 1/2" and screw some metal into them on the sides and butt them up into the corner of the bed that way i can still set in the sheet squarely and that will give it some space. Also after running a very quick test i noticed when it was raised up there was a constant flame underneath the sheet of acrylic and about half the time on top as well, how does one combat that issue?

[Jerome Stanek]

I made a pin bed using 1/8 pop rivets I drilled the bed with my cnc router

[Bruce Clumpner]

MAP gas works great, just be careful you don't soften the plexi too much as it will reform if you set it down hot.

[Mike Thornbury]

So after running some tests with different dpi and speeds i took off the paper from the bottom also and i was noticing that the "chip" look on bottom was whenever it hit one of the honeycombs as it was cutting. it still gave it this slight wave look along the side above the bottom of it but it was cutting through the acrylic just fine. any ideas on that? are there better beds to use to cut the acrylic on that wont reflect the laser as much?

Pin bed - make it out of 5mm mdf or acrylic and a bunch of these: https://www.aliexpress.com/item/100Pcs-P125-J-Dia-2-02mm-Length-33-35mm-180g-IC-Spring-Test-Probe-Pin/32832362694.html - 30mm x 2mm pogo pins.

They are called pogo pins because they are like a pogo stick - got a spring inside.

Cut a matrix of 2mm dia holes and push the little buggers in, then put the acrylic down on a hard surface and push them home.

Those ones have a 180gm spring, so 100 of them can hold up 18kg.