How to get smoother edges on acrylic cuts

Hi,

I have a Chinese 100w co2 laser with Ruida controller, size 100 x 60 cm. Using Lightburn software ofcourse and love it so far.
New to lasers so have a lot to learn. One of the first things I am looking for is a way to improve the smoothness of the cut edges on acrylic. They are a bit textured from the laser pulse I think.

Tried with air assist and without, maybe slightly better without but still not perfectly smooth. Using the small fish tank air pump that came with the machine.

Settings used were I think 20 mm/s and 50% power.

Also, I don’t know what is better to use for settings.
Do you always use max power for the machine, say 80% (about 35 mA on my machine) and pick the correct speed which is as fast as possible and still cuts through the material. Or do you use less power and less speed? I did cut a few of the test square patterns/matrix which are available on here.

Thanks for reading!

Smooth edges are all about heat which in turn is all about the combination of speed, laser power, and air assist.
First of all, you don’t want to use more than about 3psi of air pressure for acrylic, otherwise it’ll cool too quickly making for opaque edges. Granted, you have an aquarium compressor so that’s probably about where you are at. Just noting it. Wood needs high pressure, but acrylic should always been JUST enough to prevent flame ups.

Otherwise basically either use higher power or, honestly the better option, cut slower. I know, you want to get things cut ASAP but if you cut quickly the acrylic cools too quickly to be “flame polished”. Just using higher laser power will only get you so far.

I pulled my hair out over this as well at first and the only thing (aside from low pressure air) that really made a difference was to just go slower. Which is so painful for 1/4" acrylic since you have to cut at ~10mm/s to get a nice edge. So it just comes down to if you care. If so, go slow.

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We have a saying around here, “Go slow to go fast.”
If the meaning isn’t obvious, think about the extra work you have to do if you go fast…

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I’ve been working on this very issue lately. I’ve found that my best results are from using 5mm/s and 30% power from a 90W CO2 laser on 5.6mm/0.22" acrylic. Now having read this I’ll have to do more experiments because I’ve been using air at 30psi - just didn’t think of changing this.

Now “30%” doesn’t mean a lot if you ask me because power isn’t linear, so it’s just a setting that I can refer back to on my machine. I’m not sure of the actual mA reading but I know it’s more than 30% of the 25mA maximum I have my tube set at. If I recall I started at about 50mm/s and 50% power, lowered the speed until I got smooth edges and then lowered the power to find the lowest setting where I could cut through in one pass. Not only was I getting an edge like you show but the top or the bottom of the edge would just be completely rough when I first started.

I’ve cut a lot of 1" square pieces with a 1/2" hole in them as tests! Now tomorrow I’m going to run with less air pressure to see what that does for it.

Also… Acrylic aint acrylic.

There’s a ton of different types.

Most cheaper stuff is extruded PMMA (polymethyl methacrylate ). It’s the Volkswagen of the signage / display world. Scratches easily, but cuts easily too. Lightweight, strong, easy to glue, doesn’t get a polished edge as easily. The next is MMA (methyl methacrylate monomer) - the good stuff. If your supplier can’t tell you what the polymer its made from is, move on.

Cast sheet is usually MMA, is optically clear, strong but not as strong as extruded, not uniformly thick - it can be out a mm or so across the sheet, so you need more power than for extruded, works well for everything from display cases to windows.

Continuous cast is MMA, uniformly thick, has the best optical clarity, is very strong and withstands scratching. It’s an extrusion-type process, which gives the uniform thickness. It’s ‘The Best’ - IMO, but you pay for what you get. ~30%-50%-100%-200% more expensive than extruded PMMA of similar spec. Engraves the best of all sheets, cuts consistently, get that flame-polished edge.

Sign grade is another MMA continuous extruded sheet, made of some secret squirrel formula. It doesn’t break down under UV, is stable outside in weather and sun for 10 years or so, the dyes don’t fade and it cuts brilliantly. It’s about 10x as strong as extruded PMMA sheet. It’s not great at engraving, though (tough surface, de-stressed), but you get the best polished edge of any product and the best scratch resistance. Depending where you buy it, the price can be wildly different. I’m a sign guy, so buy it from signage wholesalers - the same place I buy my wide-format rolls, vinyl, etc. and it’s about the same as basic cast. I would find a sign wholesaler or large signage company and get it from them.

There’s a bunch of other types, speciality sheets for particular needs - temperature stable, marine, impact, but probably outside your need. Marine is good if you are making something for outside that is in an adverse climate - made for boat and caravan windows, it’s face-hardened and de-stressed. If you’ve ever seen an old boat screen with the millions of tiny fractures, that’s because they didn’t use marine grade. Not particularly expensive, and you can get it in clear and smoked and that’s about it.

Then there’s brands… Chinese no-name is ok for general use. 3M and Plaskolite are the gold standard. Astariglas is at the better end of the sign acrylic range. Mostly those three are MMA, but who knows - it’s all secret herbs and recipe at that end of the market.

For my money, and not living in the US, Astariglas is what I use for anything arty or that needs a quality finish.

If you’re going to do a lot of acrylic work, it’s worth investing in an oxygen/hydrogen edge polisher - they aren’t expensive - and investing the time to learn to use one properly. you can sand using wet and dry paper, wet. Start at 240grit and work up. We pay $200-300 in NZ for one, so I imagine in the US they are $100-200. They ‘crack’ water for the hydrogen and oxygen and then burn it as fuel. I’ve used this one, it’s a good basic unit for a small shop: https://www.amazon.com/Portable-Hydrogen-Generator-Polishing-Polisher/dp/B01DNAU33W

The advantage to a flame polisher is that you can edge, relieve stress in the sheet and remove scratches in the face, as well as weld the sheets, without glue (although that’s a skill I’ve never acquired).

Often the polisher is sold as just the unit, you will need a couple of different handsets, depending - a fan jet for stress relief, scratch removal, edge polishing, and a point jet for welding. They are basically oxy welding tips/handsets, but lighter.

handset

The Amazon one does come with a basic handset, but just check when shopping around.

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Thank you guys very much for the detailed information about materials, settings and the flame polisher! Will do some tests today with slower speed and power.

I only used extruded cheaper acrylic until now (PMMA). So stepping up to cast MMA will improve the edges and future engraving work. Sounds good! Price wise it’s only a couple Euro’s pricier then PMMA, just checked online.

About the oxygen/hydrogen edge polisher, great piece of kit so it seems! I just looked up some videos on YouTube about it. Didn’t know these excisted. Already found some affordable ones on my local Amazon website (Netherlands, Europe). I have a Map gas torch, bought for this application really (used it for thicker acrylic) but that flame is pretty huge. Warps the acrylic pretty easily no matter how carefull or small i adjust the flame.

Really appreciate all the help guys, this Lighburn community is great.

This is the Map gas torch i have now, but don’t really use it for flame polishing since it’s a bit too rough for fine edges in my experience.

I cut 1/4" acrylic (on either of my Chinese 80W CO2) at a painfully slow 3mm/second, I think about 40% power if memory serves. I could go a little higher power and a little faster, but I keep my max power down to extend tube life.

I get acrylic from a few places on Amazon and from Mcmaster-Carr. The stuff from Mcmaster-Carr is a little more expensive and no free shipping, but it does engrave more clear than the Amazon stuff I get which engraves slightly frosted which doesn’t matter for some projects.

Also, dont forget to raise your acrylic off the bed so the heat reflecting off the honeycomb can’t distort the face of the acrylic conacting it.

One more thing I have done is increase the PWM setting in the cut parameters for the layer/line color you are using to cut from the default of 20 I believe up to 60. Not sure if this helps, but o believe it does.

I am sure there are other, better sources, but these are mine for now.

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Calibrating your upper limit on the psu is more effective. For 80W, take 2-3mA off the rated operating max and you can use the full range of power with no appreciable loss of life.

For a W2, for example: max power at 28mA, recommended power is 24mA, long life continuous running at 22mA

Taking 2mA off a W2 can add 2000 hours.

Running at 40% on a calibrated tube is likely running at ~10mA but won’t give you much more, if anything, as you are running the tube much longer in elapsed time than you need to.

Unsure where you are changing ‘pwm’ to effect pulse timing. Can you explain?

A follow up to my earlier post. I just cut some pieces at 5mm/s / 30% but this time without air and the results were fantastic. A big thank you to Adam for that suggestion! Now I have a good result I’ll play around with speed and power settings for various thicknesses, but these come down to individual machines and tubes.

Edit: I just noticed this was under the Ruida Controllers category. I don’t have a Ruida but was experiencing the same issue. Just want to clear that up - I didn’t do anything specific to a Ruida.

If you want air, but not too much, a small bulldog clamp on the line will cut it down so you still have flow, but not too much. My lens tube has a screw valve to adjust flow - they’re about $3 on aliexpress

Hi
I see you have a nice laser machine with Ruida 6445G.
I’m trying to buy one soon but finding very hard organising shipping from china to here in UK London.
Did you used any forwarder that you can share it with me please so I can use it.
Thanks for your support.

Hi,
As you mention that you are in the UK as I am I thought I would mention this. I purchased this Laser in December 2020.

with (Ruida RDC6442G controller).

It was already located in Czech Republic which is part of Europe so no worries about importing, duties, VAT etc. Shipping was free and was just like ordering from another UK city. No complications and shipping took 7-days.

I had no idea at the time if a Brexit trade deal would happen so purchased before the end of December. no Brexit is complete an the UK has a trade deal so you should still be able to buy in Europe and ship it here with no issues. This needs checking out but with luck will still be the same.

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I bought mine off from China (Aliexpress). A French guy I know did it before me, went really well. Delivered to your door, don’t have to arrange transport and papers yourself. They have warehouses in Europe (France and Poland I think). So they can ship pretty fast and without custom Tax and shipping cost. My machine, end 2020 model, was little over €3100 including S&A CW-5000 cooler. Here is the link to the one i have: https://tinyurl.com/yxq6jk9k

Thank you very much Barry and David.
I’ll check this machines and probably contact seller’s for import to UK now.
Thanks for your time answering me.

I got mine from Amazon it shipped from Poland and no issues at all however since Brexit you have to pay UK VAT rather than the EU VAT and if they don’t collect it at source then the courier has to collect it and they then charge a handling fee.

HTH

Doug

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