How to get a perfect edge when cutting acrylic.

[Charles Gaudet]

I would like to cut acrylic and get the most perfect cristal clear smooth edge possible.

I have access to an Epilog Helix 24 and I made a few test cutting a 3/8 cast acrylic sheet. The results were acceptable. Pretty clear but not quite smooth. The edges were kinda wavy, with an effect similar to saw cuts.

Does anyone know what settings would works best?

Thanks!

[Dan Hintz]

Without a picture it's difficult to say with certainty, but your description makes it sound like you've about hit the limits of what you can expect with the laser. the laser can get you pretty darn close, but if you want that perfect edge, you may want to consider a flame polisher.

[Steve Clarkson]

Stop gloating Dan.....some of us are jealous enough!

[Dan Hintz]

Stop gloating Dan.....some of us are jealous enough!
No whining... you had the chance to get in on the group buy, and the price point was perfect. Besides, you can just steal, er, I mean borrow Frank's. :)

[Charles Gaudet]

Flame polishing is what I use now to get a perfect edge. I would like to find a solution that would eliminate the flaming step.

I think laser cutting would give adequate results. I just wanted to know what would be the best settings to use because I have limited access to a machine and I want to make the most of the time I have with it.

Should I cut 100% power, full speed? or 100% power, slower? or lower power and slow?

Thanks!

[Doug Griffith]

All machines are different. I would build some test files that you can run on the machine. Create multiple small D shapes that have different speed/power/frequency settings for each. On an Epilog, you can use color mapping. Start off with settings that are close to optimum and then vary each parameter (and parameter combinations) up and down a few percent in steps. The files take a while to create but once you have them, you can use them on each new substrate you work with. In addition to S/P/F, you can also experiment with air assist and focus.

In any case, you'll never get "perfect" with a laser.

Cheers,
Doug

[Garrett Nors]

The reason it's wavy is the frequency. Even if you turned it to 5000 frequency (which I do believe is suggested for acrylic cutting) you'd still get the squared off edge look. It's just the way the laser works.

[Peck Sidara]

Charles,

For best results I'd recommend raising the acrylic from the vector table using pins/magnets/whatever. Similar to using our vector pin table, raising the material away from the table removes unwanted "tick" marks where the laser hits both the grid and material.

Frequency of 5K is ideal, speed in the low range of 2-8%, 100%Power.

Try focusing "into" the material. Set up the focus using the manual gauge, once the bottom of the gauge barely touches the acrylic, raise the table up 2-4 clicks.

Try it with and without air-assist but keep an eye out for flaming that could lead to a fire.

From what I understand, extruded acrylic is best for vector cutting. Cast is great for raster engraving (frosting of text/graphics).

HTH,

[Rodne Gold]

You cannot emulate flame polishing with a laser, the striations are from melt ejection and heat related issues such as material expansion and localised resolidification.
You can minimise this by the correct air assist direction and pressure but if your standard or your customers is flame polishing , your best efforts here would be unnaceptable.
A diamond polisher will give you even better than flame polishing results in one operation and quickly too .. You can then router / table saw cut very cheaply.
http://www.awltech.co.uk/diamond_edge_polishers.php

[Frank Corker]

Posted this link a few weeks ago from an American company which shows how to polish acrylic and gluing it. Well worth a browse.
http://www.youtube.com/watch?v=4yp-kumgpoM&feature=channel_page

...and this one which shows how the big boys do it http://www.youtube.com/watch?v=URjOCpL5ro8

[Bill Cunningham]

Posted this link a few weeks ago from an American company which shows how to polish acrylic and gluing it. Well worth a browse.
http://www.youtube.com/watch?v=4yp-kumgpoM&feature=channel_page

...and this one which shows how the big boys do it http://www.youtube.com/watch?v=URjOCpL5ro8
The tap plastics one was interesting, but over the years, and making dozens of custom underwater camera cases, I have always found that mapp gas was too hot. Butane or hydrogen has a cooler flame, and always seemed to work better.. Perhaps just from the fact that the job is done slower, and you have the time to actually see whats happening.. I have no doubt that mapp gas works, but I have a feeling that it will work so fast because of the higher heat, that it may be hard for the occasional user to control the 'clear' flow while polishing.. Just my opinion..

[Andrea Weissenseel]

Thank you for the link, Frank - on the video with the "big boys" I would have expected that the flaming is also done by a machine

IMHO it's one of the best selling fairytales for lasers, that it creates a perfect edge like flame polished ;)

Andrea

[Frank Corker]

I agree, personally I wouldn't be without mine, if you work in acrylic a lot it really does make a difference. I just wish that diamond edge polishers weren't so damned expensive, the results from those just have to be seen to be believed.

[Dan Hintz]

I just wish that diamond edge polishers weren't so damned expensive, the results from those just have to be seen to be believed.
Is that another group buy I hear in the works? :D

[Jon Colley]

I would agree with almost all of Peck's points. Here are the critical points to getting perfect edge quality on acrylic:
1. Power - Although you can cut 1/4" with a 25W, you really need at least 60W to have enough energy at the top and bottom of the cut kerf to get smooth edges. I use 120W here to get great quality on 3/8".

2. Cutting table - The traditional honeycomb table will cause reflections and trap the acrylic gases in the cells, increasing the risk of flame ups or fire. We have a slot table on our larger machines that works perfectly or in the case of the Epilog, the pin table is your best bet.

3. Frequency and focus - Peck is correct; 5kHz and focus into the material by 0.030-0.060" depending on the thickness.

4. High air assist - There are many opinions on this, but I have my best results with high pressure. It evens out the striations and keeps the piece cool. I find with no air assist, the edges look great but the surfaces show some heat damage towards the edges.

5. CAM Software - We use a CAM package to drive the laser to give better curve quality than is possible from any printer driver.

If you search for troteccanada on YouTube you can see the edge quality that is possible on 3/8" cast acrylic. Cast is best for thicker (3/8"+) cuts because the extruded will deform at the cut kerf and you will find that the material is either bowed in or warped at the edges. Small features will also warp on extruded acrylic.

[Doug Griffith]

5. CAM Software - We use a CAM package to drive the laser to give better curve quality than is possible from any printer driver.

I know nothing about Trotec machines but I'm curious how you bypass the print driver and output(vector obviously) directly from CAM software. How is speed/power/frequency handled? Is it based off a formula applied to the z-height coordinates?

On CNCs curves output better as arcs instead of segments. Is this why you think CAM output(arcs) on the laser is better than the print driver(segments?)?

Cheers,
Doug

[David Fairfield]

I just tried Peck's suggestions on some 1/4" plexi, and got very good results. The surface isn't glass smooth, shows some minor rippling, but it is glass clear. I'm pretty sure if I had more than 35 watts to work with, it would be smoother.

Dave

[Jon Colley]

On CNCs curves output better as arcs instead of segments.

Doug is absolutely correct on this and this is why we use a CAM package.

CAM packages use post-processors to convert the toolpaths into the native language of the machine that will run the toolpaths. When the toolpaths are output to the machine, the post-processor asks for the speed, power, frequency, power correction and gas assist parameters from the user and incorporates these settings into the code going to the laser. Our new version of the post-processor has a material database as well, so it operates more like the standard interface.

Printer drivers are really easy to use and are perfect for most jobs, but for certain sensitive applications they are just not the right tool for the job.

[Doug Griffith]

So it sounds like your machine has proprietary post-processor software that also acts as an interface to the machine. A feature I'd like to have - as long as it isn't strictly a MasterCam thing. It would be nice if it is a G-code converter. Then any CAM package can process to commonly used g-code such as Fanuc prior to it being converted.

[Rob Bosworth]

Charles, if you are using air assist, and introducing the assist gas through a air assist cone rather than blowing it across your material surface, you could try trickling oxygen through your system. Most of us use compressed air for assist gas. Compressed air is something like 78% nitrogen, which is an inert gas. Nitrogen will actually retard the burn, a term we DO not use with lasers. If you use pure oxygen as your assist gas, it actually enhances the thermal process and will help to make smoother edges on your plastic cutting. I do not think it will enhance the cut when blown across the surface of the material. But if you can blow it straight down through the kerf, it will enhance the melting of the acrylic and smooth out some of the striations.

Think of using oxygen as a an assist gas being similar to using the oxygen to enhance cutting with a oxy/ acetylene torch. The acetylene keeps the flame going, and the mashing of the high pressure oxy button allows the plume to super heat. The high pressure blast of oxygen also blows the molten material down and through the cut area while it is super heating the process.

You do not necessarily have to use a lot of pressure to enhance your cutting of acrylic with a CO2 laser system. I believe most of these systems run fine using 25 to 30 psi. A lot more pressure than that, and you could distort or break your focusing lens.

[Rodne Gold]

This is what synrad have to say


Process Date: March 1999
http://www.synrad.com/search_apps/images/3-1.gif
¼" thick acrylic cut at 50ipm with 100W
When cutting material under 1/8" thick, the gas pressure will have to be systematically changed to the correct level. The edge should be consistent through the depth of the cut. With thicker material, finding the correct gas pressure is a little easier - initiate the cut with no gas pressure, and then increase the pressure until the topside flaming disappears.
It must be noted that a perfect flame polished edge is not possible. The edge will have very slight vertical striations due to the periodic ejection of the vapor. Although decreasing the cut speed can eliminate these striations, micro cracking then occurs on the cut face.
For material over 1/3" thick, defocusing into the material will help achieve the best edge squareness.
As a note: because acrylic acts as a waveguide to CO2 radiation, a 2.5" lens can be used on 1" thick acrylic with reasonable results. This gives any cutting system a great range on thickness for a single set-up if a perfect cut is not necessary. Otherwise, for thicker material a 5" lens is generally recommended.
Acrylic is an excellent material to cut with a CO2 laser. The cutting occurs as a result of material vaporization, and, with 100% laser absorption, even a 25 watt laser can cut 1" thick acrylic!
Simply cutting acrylic is straightforward enough: just select the laser power for speed required. When the thickness increases, however, and a polished square edge is required, the set-up becomes more critical.
The gas assist is key to achieving a polished edge. Air should be delivered to the material at a pressure that just enables the vaporized acrylic to be ejected through the cut, while not cooling the edge so much that frosting occurs.
As a rough guide, a pressure of approximately 1-4 psi should be used, although this is totally related to the exit nozzle diameter and the stand-off distance from the nozzle to the material. Generally a nozzle diameter of around 1/8", positioned about the same distance above the acrylic, is recommended. This offers the user good tolerance on the gas pressure setting.

and



Cutting and Marking Acrylic Signs
http://www.synrad.com/newsletter/images/60-1.jpg

Ideal for cutting and marking acrylic, sealed CO2 lasers are widely used for this application. The acrylic sign in the photos to the left was created using a Synrad laser. The circular base and attached rectangular display was cut from a sheet of 0.1"-thick cast acrylic using 25W at a speed of 40 inches per minute. Nitrogen, at low pressure, provided the gas assist to produce the clean polished edge. The laser was focused through a 5" lens that provided a 0.008" spot size with a 0.25" depth of focus.

And



Process Date: August 2002

The key to achieving a flame polished edge is to balance the power, speed, assist gas flow (pressure), and type of assist gas used. In this case Nitrogen was used because of the slow cutting speed and large amount of acrylic vapors produced. The low pressure Nitrogen removes the vaporized acrylic from the cut area and keeps it from igniting as it is blown away from the cut zone.
In the sample shown, we were able to create clear, smooth edges using our Evolution 240W laser, 2 psi Nitrogen assist gas, and our UC-2000 controller set at a PWM frequency of 20 kHz to obtain a cutting/polishing speed of 6 inches per minute.

[Jon Colley]

So it sounds like your machine has proprietary post-processor software that also acts as an interface to the machine. A feature I'd like to have - as long as it isn't strictly a MasterCam thing. It would be nice if it is a G-code converter. Then any CAM package can process to commonly used g-code such as Fanuc prior to it being converted.

The post-processor is proprietary as the laser requires special commands that don't exist in standard G-code or it's variants. Our post-processor is written for AlphaCAM. I've used about 8 other CAM packages in the past and I find this one to be amongst the easiest to work with, although the version we use is a 2D version so it's pretty simplified because of that. It's not the cheapest package out there, but this 2D version is quite reasonable. It's certainly cheaper than MasterCAM, VisualMILL or products of that level.

To my knowledge, we are the only major manufacturer that offers this second method of driving the laser unless you go up to the large class 4 systems. We can drive every Speedy series machine with this method; all the way from our small Speedy 100 to the new Speedy 1500 (59"x49").

[Doug Griffith]

That's a great feature. The drawback is that CAD/CAM programmers are not going to want to learn or invest in a new package. They've got too much invested. I'd look into developing a g-code converter (parser). 2D g-code is fairly simple. Ignore all the m-codes and anything that isn't an X/Y coordinate. Process the X/Y. Then insert the proprietary speed/power/ frequency/air/etc... settings.

Just my 2 cents.

[Jon Colley]

OK, I can see how that would work and would be pretty easy to build. I'm a bit rusty with my G-code but I think I could put this together. When I get some time, I'll take a stab at writing this and then let my colleagues in Europe port it to Windows. (I only develop in Linux these days)

Thanks for the suggestion!

[Paul Brinkmeyer]

The Vision Pro LT7 software that I use for my mech engraver can output G-code, and it can output colors. They say it can be used to drive a laser too. But I do not know which ones.
Does anyone use this software for a laser and is it any better at corners?

I did a quick test on one built in font but it out put segments for that, but when I made a circle it did use arcs in the G-code.

[Rodne Gold]

If the laser can't cut a straight edge without striations or perfectly polished , it makes little difference in terms of your curves.
In all the time I have been using lasers , outputting from corel or autocad or Signlab/profile lab , I have never had issues with curves looking bad or being "jerky"...I am using GCC lasers and have had at least 4 different models in my lifetime with lasers and have never had issues in this regard.

[Bill Cunningham]

Think of using oxygen as a an assist gas being similar to using the oxygen to enhance cutting with a oxy/ acetylene torch. The acetylene keeps the flame going, and the mashing of the high pressure oxy button allows the plume to super heat. The high pressure blast of oxygen also blows the molten material down and through the cut area while it is super heating the process.

The O2 does not really work that way Rob.. The Acet. heats the metal to a 'kindling' temperature, then the O2 actually 'burns' (oxidizes) the metal and ejects it from the kerf as a slag, and not molten steel. Heat combined with O2 will not cut anything that does not contain iron. i.e it will not cut stainless, aluminum, brass, plastic or any non ferrous metal, the oxidization process is too slow and it simply melts and blobs the metal. Oxygen itself will not burn, but it will super saturate everything in your laser cabinet, and make everything that will burn, burn much better to the point of being dangerous. Like belts, plastic, rubber,etc.. I have used oxygen fed thermic lances to 'melt' or better name is 'molten blob' through concrete pipe, re-bar, and aluminum plate underwater. but it wont cut it..

[Rob Bosworth]

Bill, many larger metal cutting lasers use O2 as an assist gas to cut many different metals. Depending on what is trying to be accomplished, O2 can greatly increase cutting speeds on many stainless steel plates. Even though it increases the processing speed of these stainless steel plates, it usually leaves the edge slightly discolored and usually embrittled. If a stainless steel part needs to have "soft" edges, or a "bright" finish, the operator will use nitrogen as a shield or assist gas. We are talking about a large volume of O2 or N2 at high pressure as an assist gas. I believe cutting of copper with a CO2 laser also requires high pressure O2 assist gas for efficient cutting speeds.

The systems that most of use, enclosed CO2 laser engraving/ cutting systems are pretty efficient at evacuating effluents and atmosphere through the cabinet. I do not think floating O2 through the plume of the laser beam will allow too much O2 to build up inside the machine. It gets sucked back and out of the machine through the exhaust system.

[Jonathan Rovner]

Hi all. I am new to this board, but certainly not new to Acrylic Fabrication. What I have found is that more powerful and better made lasers, like Coherent and Kern, will give you an edge that is far better than what you can achieve from the less expensive Epilog's or Universal Machines. Then again, the Chinese made machines that use Glass Tube Lasers also produce a nice edge, but I would not touch them, as they will not last. In my research to find out why over the years, it is multiple factors, not just one. The pulsing of the laser is one of them, the software (ie. rip) is another factor, and the laser component itself is a factor. All in all, if you dont have a laser that is capable of cutting a nice polished edge, no matter what you do, you will get that coined look. All you can do it look to minimize it by running slow and adjusting your power and air assist. Also, assisting with Nitrogen instead of CDA (Compressed Dry Air) will help.

[Bert Kemp]

What makes you say you won't touch a Chinese Laser that it won't last. I think you'll find lots of guys here who will disagree with that statement. Many are running Chinese lasers with glass tubes and have been for many years. I have one thats so far has been trouble free altho I haven't had it but going on 2 years. The machines you mention are way high priced compared to a CO2 Chinese laser and the cost to repair them and replace tubes are ridiculous .

[Dan Hintz]

Reminder: this thread is nearly 7 years old!

[Keith Downing]

No whining... you had the chance to get in on the group buy, and the price point was perfect. Besides, you can just steal, er, I mean borrow Frank's. :)

Hey Dan, newbie here. What was the flame polisher the group did the buy for, and what is the average retail price?

Also, does it have any other common applications beyond polishing acrylic edges?

[Dan Hintz]

Hey Dan, newbie here. What was the flame polisher the group did the buy for, and what is the average retail price?

Also, does it have any other common applications beyond polishing acrylic edges?

I want to say the price was around $300-350 for the unit back then? You can pick them up on eBay now for less than that, but at the time they were much harder to come by.

They can also be used for glass blowing/fusing of small parts (think of those glass animals you see them make at the stands in the middle of a typical mall).