46 – Acrylic Laser Cutting and Engraving (55:08)

The Lightblade Learning Lab with Russ Sadler

The Lightblade Learning Lab is a series of videos that Russ did for Thinklaser Limited based on using the Lightblade 4060 Laser Cutting and laser Engraving Machine. Thinklasers Lightblade 4060 has a 400 x 600mm bed size and was supplied with a 60W EFR laser tube. In this session, Russ carries out some experiments to determine the best way to carry out acrylic laser cutting and engraving


  • The two problems with cutting Acrylic – the edge striations and deposits of acrylic vapour.
  • Special test apparatus to create smoothest possible X-axis movement.
  • Testing the apparatus and reviewing the results.
  • The striations under a microscope.
  • The energy density of the beam and its longitudinal profile.
  • The cutting action, the gas and liquid inside the cutting area.
  • Explanation of the energy density across the profile of the infrared laser beam.
  • Effect of a laser on Acrylic and how the erosion of material occurs.
  • Proposal that getting rid of the striations by extending the cutting time.
  • Labelling implies cast material with Acrylic.
  • Performing some test cuts with different settings on different materials.
  • Simulating a high frequency professional machine with ‘dot mode’.
  • Running a test in Special Mode.
  • Comparing the results.
  • Using Acrylic to measure the speed of the head.
  • Looking side on at the effect of a cutting action.
  • Examining ways to get a better edge finish on extruded Acrylic – running slower than necessary. Repeating the tests with cast Acrylic and comparing.
  • Diagonal angles and arcs and the effect of the stepper motors using cast and extruded Acrylic.
  • Engraving text on extruded and cast Acrylic.
  • Engraving with a protective tape on. Cast Acrylic gives the best results but the edges are never as good as with extruded.
  • Edge lighting engraved Acrylic – LED Light base can be obtained here.
  • Summary
Acrylic Laser Cutting and Engraving - Test results
Acrylic Laser Cutting and Engraving – Test Results

My thanks go out to Tom at Thinklaser for giving permission to embed these videos on this site. If you are looking for a new laser machine from a quality supplier, then I would suggest you check out their website: www.thinklaser.com.

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Transcript for Acrylic Laser Cutting and Engraving

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0:14Welcome to another Lightblade Learning Lab as you can see I’m in a fairly

0:19relaxed mood today, to start with anyway, because what I’m going to do today is to talk about acrylic. There are two

0:29big problems when you come to cut or engrave acrylic, one of them is the edge striations and the other is all the deposit of acrylic vapor that gets put

0:40down onto the surface. The reason why I am relaxed is because I’ve already done the first part of this video on my other machine, I did some experimental work

0:50over there to show you that striations are a natural phenomenon they’re not

0:58necessarily to do with the stepper motor, although I think you’ll realise that by the end of this session, that the main reason for the striations on the edge of

1:07your acrylic is the stepper motor but there are two mechanisms that cause

1:12striations and that’s where we’re going to start off we’re going to start off with the natural striations. So sit back and prepare to be bored for the next 10 minutes by one of my

1:24lectures. Now I was trying to produce absolutely step free steady motion with

1:30a small lead screw and a synchronous AC motor which runs off the mains through a

1:36very large gearbox to make sure that we get absolutely steady rotational speed

1:42and that motor is then acting through a positive acting lead screw a multi start

1:48lead screw. Now this time I’ve mounted the lead screw in a couple of bearings so that it runs absolutely true and steady and I’ve also driven it off of a

2:00motor here which is not fixed to the actual mechanism itself so the motor can

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

2:08wobble around and do what it wants but the lead screw cannot. If you look carefully here you’ll see that we’re on the end of this bearing slide there are

2:17a couple of rubber pads on the end, scraper pads and I’ve made a little shoe

2:23which fits over the rub pads and is smaller than the overall length so that there is no play in this head it’s a little bit of compression

2:32there so I’ve tried to remove every possible way that we’re going to get

2:38slop or random motion in the mechanism. I’ve just clamped it on the top here because it doesn’t need to be any more than that it’s only got to be

2:46constrained from moving in this direction so that we get good movement in the head. I have disconnected the belt for a very good reason I don’t mind this

2:54machine moving in Y, although I shan’t be moving it in Y. You’ll see my X stepper motor here and when I Drive it left and right you can see that it’s

3:05still working. Now because it’s an open-loop system it doesn’t know that

3:10it’s not connected to the head so this does allow me a little bit of flexibility I can actually send a program to the machine which I am going

3:19to be doing later and I’m going to try and fool the machine to do something that I want to test. I haven’t put the extractor on at the moment but we’ll do

3:29that in a minute I’ll run it for as long as I can and I’ll just watch the top before it crashes into the end stop there we go. Now we haven’t got a through

3:38cut here we’ve got a closed cut and a closed cut always causes plowed field

3:46effect along the bottom here but what we’re more interested in is not the roughness of the surface but the uniformity of the line itself we can see

3:54clearly we’ve got a uniform cut we got uniform power so how can I have

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

4:04striations in the background and those striations are also showing signs of

4:10drag. Now I’m using fairly low power in here so it does mean to say that I’m not

4:18generating a huge amount of heat in the cut itself so consequently the cut has

4:25not had a chance to melt and heal over the striations. Now I’ll talk about the

4:34melting process and the healing process in a few minutes but let’s go and observe what this first test has shown us. I’ve hacked away the

4:45front edge of the material here I’ve ground away the bottom and broken it so

4:51that I don’t damage this surface internally here okay so that we can see

4:56the striations. This is probably one of the most difficult things I’ve ever tried to show you there we go look at the bottom left-hand corner there you

5:04can clearly see the striations coming down and curling away at the bottom. I

5:10think the first question we have to ask is how is it possible to get these

5:17striations when we don’t have any intermittent movement we don’t have any

5:24pulsing air and we know we’ve got a steady beam because we can see the line

5:30is flat as it cuts its way into that material. I’ve got some rather nice acrylic blocks here which I’m very happy to destroy for the sake of science what I’m

5:39going to do is I’m going to fire that same 15% laser beam at that surface

5:45there and what I’d like you to do is just observe what happens now we’ve done

5:52this before but I’m going to hold the post button on now 15% probably will be enough energy to instantly turn this surface here to

6:03liquid but before you even see any liquid it’ll evaporate. Now you can see it

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

6:09still evaporating but sooner or later look you can just see around the outside here can you see that liquid forming now here’s what we’ve just produced and as

6:19you can clearly see we’ve got a point at the bottom which is where the high energy density is in the beam but as we get further and further out we get lower

6:28and lower energy density I hoped you notice that it was only when the beam was fairly well established and we’d burnt quite a long way in that the

6:38high-energy part of the beam that was doing evaporation was not the part of

6:44the beam that was causing the liquid the liquid was only happening right at the outside where the energy is very low but it happened a long time after we

6:55started the beam. We held the beam on for a long time so you have to build up heat

7:01in the cut to get a polished cut. Now we’re going to talk about this later

7:09and we’re going to demonstrate beam polishing but I want you to understand and remember this little picture here that it took a long time for the liquid

7:19to form around the outside of this cone. Now this is the low-energy side of the beam and of course we’re talking about the high-energy side of the beam but the

7:28only difference between this side of the beam and the other side of the beam is

7:34the fact that this shape is not six millimeters diameter as it is here but

7:39it’s only about point two millimeters diameter when it comes out of the nozzle.

7:45So there’s a big energy amplification difference between what you see here and

7:52what you see down there but it’s much easier to see what’s going on here slow motion but it’s no different than what happens after the lens. The beam comes

8:02out the nozzle and the focus basically sends the beam down to a focus point

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

8:12like this and at this point here which is where we’re currently focused that’s

8:19where we get the smallest possible beam after that it starts expanding quite

8:25rapidly we can demonstrate that very easily. Now here’s how the beam is growing between 20 and 26 mil quite a big difference as you can see so I’m

8:36going to fire a beam into that block with the distance the correct focal distance. Six millimeters deep does that look as though it’s bent? No well I’m

8:50going to increase the pulse time now to 50 milliseconds a twentieth of a second

8:59does that look like a parallel hole that I’ve drilled in there? Can I just point this out to you?That’s a change from eighteen to twenty six this is a change from

9:15eighteen to probably closer to thirty

9:22look at the diameter change that’s occurred between twenty and twenty six

9:28so what’s going on? We have a light beam that’s coming down and causing an

9:34interaction with the surface and causing the material to vaporize leaving a hole

9:40behind but as soon as it vapourises the first part of a hole the laser beam does not

9:47expand it internally reflects as though it was a light pipe a fiber optic and so

9:57that beam has focused at the surface and it does not lose its focus as it goes 12

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

10:04millimeters into the material look you can see that it’s the same diameter. I’m now going to try and demonstrate to you how I think that beam drag is actually

10:15occurring. Pulse, step

10:23Pulse, step

10:31pulse step Pulse

10:42step pulse

10:47step Pulse

10:54now I think it’s very important that you watch this piece of video again because after the formation of the very first cone you’ll see the way in which the

11:02erosion takes place on the leading edge of the cut and gradually folds itself

11:09backwards but more important than that what I want you to watch is the gas

11:14dynamics inside the cut. You’ll see swirling action plus you’ll find that

11:21there is what looks like a film a liquid film very thin liquid film moving around.

11:28Now it may be gas that’s condensing but whatever it is it is you can see

11:35after every cut that it leaves a striation mark. Pulse

11:43step pulse

11:51step pulse

11:59step pulse

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

12:05step, pulse

12:10step pulse

12:17to follow on from this I want you to just take a quick look at a piece of enclosed gas

12:23dynamics when the laser beam goes straight down a hole

12:44okay so there’s a demonstration of the gas dynamics that takes place around the

12:50laser beam itself in acrylic you’ve previously seen the way in which the

12:56laser beam gets deflected by the acrylic so if you add those two things together

13:01I think we’ve got a fairly reasonable explanation and logical explanation of

13:07how beam drag is occurring in my closed cut . Now this is a great demonstration of

13:15how striations can be formed with a pulsing mechanism. Now pulsing could

13:22either be a stepper motor edging forward which is basically what I’ve simulated

13:27here or if you’ve got one of the professional machines which uses an RF

13:32tube then they’ve got control of the frequency of the pulses although they

13:38may well have silky smooth DC motors their pulsing of the laser beam itself

13:44can cause exactly the same problem they’ve got the opposite problem to what I’ve got on this machine and the way that they overcome it is they change the

13:53frequency and so you can inject very high frequencies in and so your pulses

13:59basically become so high that you don’t actually see the striations. Although we’ve seen the creation of striations although we’ve seen beam drag being

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

14:08demonstrated we haven’t answered my fundamental question associated with my

14:13partial depth cut and that is why am I getting striations when I’ve got

14:20constant speed and I’ve got constant power and I’ve got no air assist. There

14:26must be some other mechanism that’s taking place so with my distance 18 millimeters that’s the correct focal distance for that particular for this

14:34nozzle I’m going to burn a pulse into the surface, 50 milliseconds, a twentieth

14:40of a second long we can see it just here and the reason why I’m punching this one hole in it’s because this is the one that’s important to me and just to

14:50confirm that our readings are right. We’ll take a plan view look at the hole the end of the hole this is the entry to the hole and sure enough the hole is

15:00about 0.5 diameter yeah so our side view and our plan view agree. But now it’s

15:09time to reflect on some of the results that we’ve just seen. Before we can

15:16really start analyzing those results I must go back and reinforce something that I’ve spoken of many times before for those people that just drop in and

15:24drop out of these sessions they’re gonna move they basically lose so much of the

15:30background data and also this is quite a difficult concept for some people to

15:36understand. Now the laser beam itself is a beam of concentrated invisible light

15:44now that’s concept number one that people seem difficult to have difficulty understanding how could here you can have light but it’s not there just

15:52accept the fact that there is something there because when you put your hand in the way it’ll get burnt if you put a piece of paper in the way it’ll get

15:59burnt there’s energy there that does something and that energy in that beam

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

16:05is not uniform like this light here it is concentrated in the middle as I’m

16:14showing you there but it gets dull towards the outside where there’s less

16:19and less light so this is a concept called energy density we’ve got much higher levels of energy in the middle here of

16:27the beam than we have on the outside of the beam. Bear with me for a few moments because I’m going to turn this picture around and I’m going to ask you to

16:36imagine that this is a rain cloud and this is the amount of rain that’s in the

16:41rain cloud it’s heavy in the middle because there’s a lot of rain in the middle of that black cloud it’s spring it’s showery and the rain is going to

16:49pass overhead now I think you can immediately see that just at this point

16:54here if you’re standing underneath at that point you’re going to get absolutely soaked because we’re going to get a mini flood just here whereas at

17:03the outside of the cloud here there’s going to be hardly any rain falling at all, not enough to even water your carrots. With

17:11that little concept in mind of rain not much rain coming down here and a lot of

17:17rain coming down here in the middle let’s turn the picture back around again

17:22and instead of rain it’s light I know they’re not the same thing one is solid

17:28and one is not, but the principle is the same. We’ve got amounts of energy amounts of water whatever you want to call it there’s a

17:37variable density of things that are happening inside this beam when that

17:42beam hits a surface two things can happen first of all it could be reflected off like a mirror and and that does happen for metals but we’re talking

17:51about acrylic which is a nonmetal and it’s a rather special type of nonmetal material which has got some interesting properties. So let’s not worry about

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

18:01other materials let’s just stay with the principle of acrylic and what will happen is this energy this rain will fall on the surface in the middle here

18:10and instead of causing a flood this light it’s a rather special light

18:17infrared which reacts with things and causes them to get excited. Now all

18:26molecules are busy just sitting there like this at room temperature if you

18:33start exciting them with extra energy they get faster and as they get faster

18:39vibrations their temperature goes up so what we’re actually doing here we’re

18:45firing light at the surface of the acrylic and we’re exciting the acrylic molecules on the surface and that is the critical word that I want you to

18:55remember “surface” on the surface we’re exciting those molecules and those

19:01molecules then raise their temperature. Now if we go back to the rain idea and

19:09the density idea we’ve got a lot more rain a lot more energy falling in the

19:16middle here than we have at the outside we’ve got just a few little bits of energy falling here and lots of energy in the middle and so what

19:26happens is there’ll be not much heating effect on the acrylic out here at the edge but a huge amount of heating taking place just in the middle where we’ve got

19:35the highest energy density I’ve drawn this shape in here as the energy profile of the beam but you mustn’t regard this energy profile as being something like a

19:44drill it doesn’t automatically produce that same shape in the material

19:50approximately approximately it does but the principle is really we’re looking at

19:55this as energy density not as an actual shape so what happened is the heating takes place on these surface molecules here and where we’ve got very high

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

20:05energy density the excitement will be great and we will instantly heat these

20:10molecules up and they will evaporate they will go through a liquid phase very

20:15very quickly and immediately turn into vapour now as they turn into vapour what

20:22will happen is we will have a piece of clean acrylic left behind and that clean

20:28acrylic is a hard surface and that hard surface will again be excited by the

20:35light that’s falling on it the molecules will heat up and they will in turn

20:40evaporate so although we’ve got very high energy in the middle here we

20:47mustn’t forget that we’ve also got energy out here as well and as time goes on this energy on the outside here we’ll have time to have an effect as well so

20:58gradually we will get a bigger and bigger erosion and this is what’s

21:06happening it’s an erosion that’s taking place on this surface

21:13and we’ve seen that erosion there it is they’re all over the place where I keep testing things and as we saw in this hole that we made here after a certain

21:25period of time. Note I’m using the word time again there was enough time to

21:33allow even this part of the low energy to start heating up the edge of the

21:41material and that was just enough temperature there to keep that part in

21:48its liquid phase whereas down here there was enough energy to push it through its

21:55liquid phase and make it disappear into a vapor because we’ve got very high energy density here. The light in itself is harmless but it has to interact with

22:04the surface to change its energy form from light to heat, it in itself does not

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

22:11heat it only stimulates the material that it hits to heat up. Okay so we’ve

22:17got that piece of science out the way. Now we’re coming back to our subject that we’re looking at which is where these striation marks come from. We burn

22:26a 0.2 diameter hole in a piece of paper now in exactly the same power

22:32exactly the same focus point and exactly the same amount of time we pushed it

22:38into a piece of acrylic and the end result was that the acrylic produced a

22:44hole which is 0.5 diameter so why the difference when I fire that beam into a

22:51piece of acrylic. We’ve previously seen the gas dynamics taking place in that tube there when we fired the laser beam into it and held the power on you could

23:01see the gases swirling around inside there and we also saw exactly the same sort of dramatic gas dynamics that were taking place when we were producing our beam

23:11drag experiment. So we have to assume that the reason why this hole has grown

23:19from 0.2, which appears to be the beam diameter to 0.5

23:24is the fact that we’ve got some sort of interaction between the acrylic and the

23:31laser beam which is causing some sort of gas cloud around the outside of it. The

23:37heating effect plus possibly and this could also be a possibility none of this

23:43is fact because all this is supposition based on what we’ve seen. We have a laser beam coming in and remember it has internal reflection because the pipe it

23:55continuously focusing down and so we’ve got complete internal reflection there. Now it’s possible that every time that we get a reflection we may well get some

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

24:04of this erosion taking place and that may well be the reason why we’re getting

24:11a bigger diameter hole so this is garage science this is not NASA Laboratory

24:18science and going from 0.2 to 0.5 leaves me with the impression that

24:23what we could assume is that there is no solid material here for this laser beam

24:31to react with. Now the laser beam itself as I said has to react with solid

24:39material a solid clean surface it has to excite atoms and if all we’ve got is a

24:44gas cloud here it might excite the gas cloud but it’s not doing

24:50anything to remove material from the edge of our solid block. So when the

24:56laser beam starts to move that way nothing happens until this high-powered

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

25:03central part of the beam at least starts to get involved with solid material

25:08again here. Now at that point we’re going to start generating another cloud like

25:16that and then it’s going to carry on jumping across this void of nothing which it

25:26can’t erode until it gets to here when again it produces a cloud of gas like

25:36this. Now this is going to continue ad infinitum while we’re carrying out the cut but look what we’ve got here these little nodes here I’m proposing that

25:51those are the nodes that are the striations. It may be exaggerated or they

25:57may be aliasing between these patterns and the pulsing of the laser beam or the

26:02frequency of the stepper motor so we may get some rather strange and random

26:09patterns but the underlying striations are produced by this mechanism here I’m

26:15proposing. So how do we get rid of these striations on a cut. Well the answer

26:23actually is quite simple, we’ve already discovered the answer and that is we allow enough time for heat to build up on the edge of the cut and heat building

26:38up on the edge of the cut means we shall get a liquid film taking place and that

26:44liquid film will naturally want to smooth out and take away the peaks but

26:54it does depend on heat being retained in the cut itself. So if you cut too fast

27:01you will probably create striations these are the sorts of things that we’re

27:07now going to investigate. We know that this is cast perspex because it’s got

27:14labeling on it as I mentioned before no labeling generally means extruded so

27:21we’re going to use this one and a half-inch lens to start with without air assist you’ll know when air assist is on because listen

27:29you can hear it but we’re running this on full power about 70 percent and nine

27:36millimeters a second this is cast acrylic.

27:47So now we’ll run the same test again but we’ll run it with air assist

27:53although the pump is a pulsing pump because it goes through so many restrictions and the flow that comes out here is nothing like that coming out of

28:01the pump or what the pump is capable of, basically what comes out here is a pretty smooth flow. I think if you listen

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

28:11you can hear that there’s no real serious indication of pulsing.

28:20Well that’s a little bit unexpected but I would say that that’s probably slightly better with air assist than without air assist. We’ll go and catch

28:30that in some sunlight in a minute and you can compare the difference for yourself. I’ve got the power set as high as I can to try and get as much heat as

28:38possible into the cut. Remember if we can keep heat in the cut

28:43we shall have a, we shall have a liquid film in there which heals the surface

28:49over and helps to cure any striations.

28:55Now that’s got a nice hot cut there I can feel it, I wouldn’t want to hold my

29:00hand on there for too long. It’s certainly I suppose, people class that as mirror-polished but I’m looking at it extremely critically and saying well I

29:08can still see a few striations in the background there. We’ve got a full set of data there cast extruded cast extruded both clear and black so we can look at

29:20the edge comparisons for those with and without air assist. |Okay now we’ve gone from one extreme to the other we’ve now got a two and a half inch lens in there

29:29two and a half inch meniscus lens and we’re going to see whether or not 70%

29:35power is enough with this huge distance here to burn through probably something

29:42like five and a half millimeter thick acrylic. With almost miraculous results.

29:49Having established that we’ve got a lovely soft cut with that lens what I

29:54want to do is something completely different now I’ve now programmed this machine to draw a line

30:03so if I press the origin button I know that I’m going to get no movement in Y

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

30:10the machine doesn’t know where X is, it’s wherever X happens to be and when I run

30:19the program the X Drive is going to run but of course I’m going to get no motion

30:25here so I should be able to switch my control on and off and whatever I programmed into the Machine will happen down here now I’m going to be using dot

30:36mode because what I want to do is to produce a series of pulses downward

30:42pulses to see if I can cut this off with pulses. Basically what I’m trying to do

30:47is to start simulating what happens with one of the professional machines where they have a pulsing laser beam now I don’t, well I’m absolutely certain I

30:57won’t be able to get up to 20 kilohertz pulse frequency that they can achieve but we might be able to get a little way into that range and see what effect it

31:07has on the cut. So at the moment what I’ve done I’ve got it set to a dot time

31:15of 0.1 which is 100 milliseconds. Now I think I might put air assist on

31:21because I suspect it’s going to flame up

31:30This produced a nail file!

31:36So those are pretty big let’s call them striations shall we?

31:46But they’re not natural they’re forced striations because they’re nice and straight, straight down but it’s lovely and polished as well so here’s the trick

31:56that I’m just trying to play on the machine the machine thinks it’s going to

32:01scan a square somewhere out here and it’s going to do it at 1 millimetre per

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

32:07second so it’s going to take a long time to do a single scan but what I’ve also asked it to do to, is run at 70% in special mode so that means technically, I suppose

32:19I’m running with 50% power it should be running with a frequency of about 20 K

32:26so if this is in any way successful it should be a fairly close simulation – what an RF tube can do.

32:41We’ve got something, didn’t burn through quite but it gives us an idea maybe of what

32:48possibly could be achieved with a Trotec, Epilogue, Universal machine those sorts

32:58of machines that use high-frequency pulsing but of course I can’t really say

33:03at the moment because we haven’t burnt all the way through the only thing that I could possibly do is to use thinner material now this looks like three

33:13millimeter clear

33:22but I have to assume that from its lovely shiny finish that it must be

33:29extruded acrylic now I can try a proper piece of extruded acrylic but even so

33:36it’s still got smooth with striations. These last four black ones are extruded

33:43acrylic, now can you tell which ones are done with air assist and which ones are

33:49done without air assist they’re all basically the same as each other as you

33:57can see there is just a hint of striations on the surface now the next

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

34:03four black ones along. Again is there any difference between them? Two of them are

34:10done at 70 percent two of them are done at 20 percent and there’s a mix of air

34:17assist and non air assist in there again you can’t tell the difference. So here we come on to these next four, they’re all different heights but if I move them in

34:26the light probably you can see they’re all shiny ish fairly polished so these

34:34are all again extruded acrylic virtually no difference between the air assistant

34:44and no air assist and then all of these here are varying speeds with cast

34:52acrylic air assist and no air assist and again I’ll guarantee that if you check

35:00those out I mean particularly all this lot here because you can see they’re they’re all just happen to be reflecting the same no difference between them at

35:09all one of these was done with the 20 kilohertz high-frequency engraving mode

35:16and one was done with just normal common mode the smoothest one which is nearly

35:23okay was 20 percent common mode and this one here which has got striations on it

35:29was in fact 70% special mode so what do we learn from this

35:34session? Well even though we’ve got a silky-smooth traverse action and we’ve

35:42got a lovely continuous power and we’ve proved that this time, we still get

35:47striations in acrylic when we tried to cut it. Those people that said that striations are induced by the stepper motor were perfectly correct but not

35:55entirely so because there’s another natural set of striations that appear to be there in the background. Well it may look as I haven’t moved and I haven’t been doing

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

36:04anything, but trust me not true. Well now you know that regardless of how we tried get rid of striations it’s a natural part of cutting acrylic. What we’re now

36:15going to do is to take a look at how we overlay those striations with machine

36:21created striations because of the stepper motor. Now at the end of that

36:26video you saw me messing around with the 20 kilohertz special mode signal and

36:33even on 20 kilohertz you were still able to detect the edge striations from the

36:39pulses of power so it was able to get better results with just ordinary common

36:46mode and smooth motion. Now you’re probably all aware of my love of

36:54acrylic, it’s a reasonably good material to work with that I do a lot of structural work with it but the thing that I really love about it is it’s a

37:02fantastic telltale material, it’s a piece of material which enables me to test all sorts of things on this machine. One of the things that it can tell me is

37:10the velocity of the head or the varying power of the beam. I’ve got a piece of acrylic little acrylic block standing on edge there

37:19because it’s much easier to see through a piece of thin acrylic than it is to see through the block now we’re going to start off at a fairly slow speed we’re

37:27going to start off at 50 millimeters a second and we’ll see what happens.

37:35Okay so that’s 50 millimeters a second okay so now we do three hundred and

37:40fifty millimeters a second now in this picture here you can see because I’m

37:46only accelerating up to fifty millimeters a second it gets up to speed

37:52very quickly and there isn’t much of a slope on the right-hand side before we

37:57get to this saw action this sawtooth look and that is the actual stepper

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

38:03motor moving along in steps as the stepper motor stops between its steps or

38:09at least slows down between these steps the power of the beam which is constant

38:14digs in deeper and then it jumps to the next step and it leaves a little sawtooth so that’s what we’re seeing there in that picture. It’s a great

38:25interpretation of the velocity of the head the or the velocity of the laser

38:30beam because they’re one in the same thing. Now when I change the speed to 350 millimeters a second all of a sudden the picture changes look it takes probably a

38:41third of the length to get up to speed and when we do get to speed we appear to

38:48have no apparent steps in the stepper motor. Basically the faster you run the

38:54less the steps show up. So how does that affect striations well it affects

39:03them quite a lot just ask yourself what speed am I going to cut six millimeter

39:08acrylic at? Five, eight, ten millimeters a second? Now this is what you cut six or

39:14eight millimeter thick acrylic at.

39:28So really the point of this exercise is to just demonstrate to you how sensitive

39:34the edge of your cut is to the speed that you’re cutting. There’s nothing that

39:39you can do about it, it will cut with striations because of the stepper motor

39:46and those striations will be mixed in with the natural striations that you’ve seen

39:53in the previous part of the video. We’re going to use five millimeter for our testing at the moment because that’s a fairly middle-of-the-road sort of thickness

40:01that many people will use. Now the first thing I must point out to you is something you will all know there are two types of acrylic one of them is

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

40:11called cast and the other is called extruded there is a big difference between the cutting and engraving performances of

40:22these two materials they are both acrylic one is good for one purpose and

40:28the other is good for another purpose and that will become clear as we get a

40:33little bit further into this test. That’s not bad we don’t have much beam drag on that it’s a fairly vertical cut and it should

40:42drop out because the smoke is going down below okay now I was using air assist on

40:48that as well. Now on the surface of it that looks quite a shiny finish there are

40:53marks on it there are striation marks on it now we’ll take the air assist off and we’ll do the same thing again. Right at

41:02the top of the cut it’s a lovely smooth finish but down at the bottom of the cut we’ve still got our striations. Something that we need for a really good polished

41:10finish is a lot of low-level energy on the edge of the cut and the way that we

41:17get low-level energy into the edge of the cut is to slow the cut down. Set the speed to five millimeters a second now, I hope you could also see something else

41:28this is hanging in here by a piece of warm molten acrylic remember what I

41:34promised you at five millimeters a second it’s a terrible cut if it doesn’t go through but here’s what happens when it does go through look. We don’t get

41:46this cut here because we’re not running at fifty millimeters a second which is

41:51what this was done out we’re running at five millimeters a second here and you

41:56can even see in this one how it’s actually produced a nice shiny burnished

42:02finish on the edge of the cut and that’s exactly what this is done here we’ve run

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

42:07it at about half the speed that we would normally want to run it at but it produces a crystal clear mirror finish there is hardly a hint of striation on

42:18there and that’s all because we’ve got this liquid phase that we kept in the cut. Let’s see if I can find a piece of 5 millimeter

42:27cast acrylic to compare it with so if we go back and repeat our previous three

42:32tests it’s got a bit of a shine you can see every single mark on the surface

42:38there so let’s run the same test without air assist now. Is there any difference

42:43nice vertical striations but as I said those striations are now induced by the

42:49stepper motor so now we’ll go to half speed now at air assist and I’ve just

42:56put that on my lip and to be honest it’s hot very hot I jumped so we’ve got

43:05plenty of heat in the job now and all of a sudden even though this is cast

43:13acrylic we’ve nearly got that mirror finish I

43:19think unless you look at it very carefully which I am being very critical there’s just a hint of striations in the background but I think anybody that

43:29wants a really clean mirror cut would get it but you have to drop the speed to

43:38get heat into the job so for the cutting war cast acrylic comes off second best.

43:47Cast acrylic no air assists half-speed

43:56same square the bottom one was done at 90 degrees now there’s lots of

44:01striations on the top one that aren’t there on the bottom one why would that be now that’s because we’ve not just got one stepper motor stepping like that

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

44:11we’ve got two stepper motors that are stepping like this to produce a compound

44:16angle and so all of a sudden even though we’ve got the potential ability to

44:22produce a mirror cut as soon as we start travelling at an angle and using compound

44:28use of the X and Y then we run into trouble and what do we get on a circle

44:37hear the stepper motors singing

44:46now I’m going to be very careful I’m gonna mark twelve o’clock

44:56and when we look around that circle we’ll see distinct patterns somewhere

45:01towards the top here where the stepper motors are nearly working on their own

45:06just here and here and here and here we get a nearly mirror finish

45:18but where we get to the 45 degree mark here I don’t know whether you can see that in the light but there are lots of striations there now bear in mind we’re

45:28talking now about cast acrylic let’s do the same last two tests with the

45:34extruded acrylic.

45:42and we have to say that wherever we look around that circle

45:48we’re getting a beautiful mirror polished page now I expect exactly the

45:54same result when we do our 45-degree cut okay I’m going to just touch this I can

46:00feel it on my hand as I touch it whoa yes that’s pretty hot but I think you

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

46:06definitely cast that as a good mirror polish we’ve started this engraving lock

46:11fast with very little power but even so look what’s happening to the

46:19surface now we’re doing a cut hopefully it’s going to be a mirror finish cut that normally when you engrave a growth

46:28acrylic you would normally reverse the image and engrave on the back so that

46:33when you turn it over you see a nice clean image now the problem here is

46:40it’s not too bad it’s not heavily caked on because we were using very small

46:45amount of power look I can actually rub and get a reasonably clean piece of text

46:54this is extruded acrylic let’s put the power up to 50% still running at 400

47:01millimeters a second even closing the lid and passing air across the surface

47:06it’s not having any significant effect on the painting effect of the vapour but

47:13this time

47:20I cannot rub some of this debris off

47:27it’s really caked on there and even if I try and wash it off it won’t come off

47:33I can try cleaning it with isopropyl alcohol and that works reasonably well

47:40but one of the problems you’ll see Hey look what’s happened to the edges the isopropyl alcohol has actually

47:50stressed cracked around the edge of my cut now the film on the underside of that is

47:58a bit tatty but the film on the topside is in reasonably good condition now I

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

48:03know that this is a piece of extruded acrylic because there is no name on it if there was a name on it it would be cast acrylic but if there’s no name on

48:13it its extruded acrylic let’s put the power back up to 50% if you really want

48:18some deep and white text on extruded acrylic then not only do you keep the

48:25tape on but you also add air assists and the air assist will drive the vapor back

48:31down into your cut and make it nice and white. Now while that’s going on in the

48:36background there let’s take the film off here and examine our results we’re also taking the crud off as well we shall have to take the center of the letters

48:47out as well because they tend to get stuck in. Now the one at the bottom with air assist is a little bit stronger this one

48:57is a little bit blotchy in places that’s our engraving and there’s our

49:05edge is a mirror polished as it clearly says on there cast acrylic name on one

49:11side film on the other so we know that this is cast acrylic but unfortunately I

49:16don’t have any five millimeter cast acrylic at the moment so we’re gonna have to live with eight millimeter and we’ll repeat this very last test here

49:26which was air assist 50% power with a film let’s put it in AIT’s a dark

49:33surface so you can see the difference the one on the left is cast acrylic the

49:40one on the right is extruded acrylic now when it comes to engraving

49:47you would choose cast acrylic every time because it gives a much cleaner crisper result. Sadly

50:00sadly the edges are clean but full of striations fairly

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

50:08fine striations as you can see. So it was a general rule whenever I do engraving I

50:17leave the plastic covering on we’re now running this at 2 millimeters a second

50:22for 8 millimeter thick if I want a polished finish on it. I think I’m gonna have to go this slow you’ll never get the high shine if you

50:29get on a piece of extruded acrylic as you can see it’s a sort of a ….

50:35it’s not a mat sheen it’s actually quite a nice clean finish free of

50:40striations which is the important thing let’s do some thin material now this is

50:46three millimeter thick and I should easily be able to cut this with 65

50:51percent power at probably 15 maybe even 20 millimeters a second

50:58this is extruded acrylic remember this is the easy stuff to cut and polish

51:03well it’s shiny they’re very distinctive striations but they’re on a shiny surface now to make life simple I’ve just suppressed the scanning because we

51:12don’t need that information we just want the cut information now.

51:17So I’ve reduced the cut to half its speed ten millimeters a

51:23second well it’s not bad

51:28we’ve still got some I’m being super critical here but we’ve still got some

51:33striations on the surface shiny so this time I’m going to take it right down to

51:39five millimeters a second I want you to watch can you see the boiling that’s

51:44taking place on the bottom of the cut there about quarter of an inch behind the cut we’re almost back to a mirror finish but

51:52we’ve had to go down by from 20 right down to 5 millimeters a second

51:59the thinner the material the more difficult it is to cut that’s always been my experience because you just can’t get the heat to stay in the cut

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

52:07what do we take away from that I suppose we could sum it up very simply by saying

52:12there are two sorts of striations one natural one motor induced and what we’ve

52:18seen is that you can get rid of most of the motor induced striations by running

52:24slowly and building heat up in the cut you start off with an advantage if you’re using extruded acrylic now the job becomes so much harder if you decide

52:36to use cast acrylic it’s that much more difficult to get a flame burnished

52:42finish you can get a nice finish and if you do it right with thick enough material you’ll be able to get a nearly striation free finish the thinner the

52:52material whether it’s cast or whether it’s extruded you’ll begin to struggle with the striations. Although cast acrylic has got its weaknesses when it

53:00comes to getting a nice finish on the edge it’s a superb material for

53:06engraving on, it produces nice white crisp images. One of the reasons I wanted you

53:13to understand that the different whiteness of engravings between cast and extruded acrylic is because here I’ve got a little

53:25pattern for a picture frame and I’ve managed to do a dot picture in

53:32there one of my dot pictures. I’ve done another one here and further one here

53:38and now we’re going to get all spooky because this is really what I wanted to show you.

53:45Here’s what you can do with those pictures

53:51we can just take that picture out

53:56and we can slip this picture in and change its color

Transcript for Acrylic Laser Cutting and Engraving (Cont…)

54:06let’s put it to white pink blow white now the horse is not so good

54:14because dots do not transfer don’t transfer the light up very well plus the

54:20fact that this is actually a piece of extruded acrylic and that didn’t work

54:26too well at all okay so here’s one of our engraved name plates and I put the light over it it comes alive now that’s not the best

54:35example because I can’t get down inside there this base which you can buy off of

54:42ebay for about ten pounds you’ll find the information about this on the Thinklaser

54:47website so I think we’ve overdosed on acrylic now and you should

54:52be moderately aware and competent of all the variations and things that you can do with acrylic and you shouldn’t do with

54:58acrylic so go forth and enjoy be creative with your machine till the next

55:05session bye

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Last updated April 25, 2024


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