Session 18 – Surface Laser Engraving Organic Materials

Transcript for Surface Laser Engraving Organic Materials

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The Concise RDWorks Learning Lab with Russ Sadler. Session 18: Surface Engraving Organic Materials.

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Now, remember I did this demonstration in the last session where I showed you that without a lens in here,

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you got all these different thicknesses and different colours of lines from just the raw laser beam.

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And I explain how it was possible to get thin lines lighter colour, and thick line

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very dark colour, because of the different intensity levels within the laser beam itself.

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The central part of the beam is very intense light, and intensity

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equals damage. Because when we run it 240, the exposure time is so much less that we can only, if you like,

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burn or do damage with the highest intensity part of the beam, which is the central part of the beam. Now, because the beam is sort of pointed.

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We get a thinner line just down here. Just because we out the beam through one of these things doesn’t mean to say we’re changing anything.

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We still get the same property. We’re just making it more intense by focusing the light down through this.

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Everywhere you look on big WWW, on YouTube, on lens manufacturers pamphlets.

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You see information like this. Where they will show you a lens, depending on its focal length, has got certain very definable properties.

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One of the properties is that it has a focal point. As the focal point changes, so various other properties of the lens change as well.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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One of the most important properties is this thing just in the centre here called a spot size.

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And a spot size is that point through which all the rays, here they are, pass.

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So that spot size, i.e.,

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the smallest possible burn that you can make, changes with the focal length of lens. When you get a very short focal length lens,

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look, we’re saying three thousandths of an inch or point zero seven millimetres.

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You go up to two inch and it goes to five thousandths of an inch, seven thousandths of an inch, twelve thousandths of an inch for different lengths.

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So those are supposedly the thinnest lines or the thinnest spots that you can produce with a lens.

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There’s another key feature about the lens, which is its so-called working length.

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And here it’s called depth of focus. So for a four inch lens is supposed to be plus or minus five millimetres. For a two and a half inch lens,

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it’s supposed to be plus or minus nearly four. For a two inch lens,

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it’s down here at around about roughly two and a half millimetres. For a one and 1/2 inch lens,

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it’s down here at around about two millimetres.

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I’m here with experience and two years of hunting, to tell you that what I’ve just shown you on that piece of paper is total junk.

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These are what the lens manufacturers are telling you.

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But in reality, you can work to these nominal numbers and you get round about the right results.

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But I can assure you there is no such thing as a focal point, for our lenses, on this laser machine.

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There is no such thing as the working distance as specified here, and certainly this spot size is laughable.

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I know it’s unbelievable that everybody else is getting it wrong and I’m the only person that’s getting it right.

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But hey, I can easily prove that this is wrong and that’s what we’ll do today.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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We’ll talk about how these lenses actually work and we’ll show you that there are cutting lenses and there are cutting lenses.

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There isn’t really such a thing as an engraving lens. What do I mean by that?

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Well, if you want to do normal straight engraving, all we want to really do, is what we’ve done here.

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And that’s mark the surface of a piece of wood. We don’t want to dig into the wood and cut deep.

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Sometimes you might want to try and produce relief engraving. That’s a separate problem.

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Today, we’re going to be talking just about surface marking engraving.

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In other words, putting colour into the surface of a material.

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And in this case, it’s going to be some sort of wood because there are other types of material where you can’t perform this different colour engraving,

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organic materials you can.

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So part of engraving is understanding the material that you’re trying to work with and also the lenses that you’re trying to work with.

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What they do and how they perform. I can almost certainly guarantee that when you bought your machine, you would have been supplied with

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a two inch plano convex lens, and so that’s what we’re going to start off with today,

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and we’re going to look at the performance of that lens and see how close we can get to doing this, i.e., marking the surface with a lens like that?

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We’re not trying to cut through the material. We’re just trying to make the surface brown. With the centre of the beam,

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we will actually do a lot of damage.

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OK, but if you take a look underneath, we’ve still got plain material under there, clean material, and as we get faster,

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it gets shallower and shallower, to the point where you can hardly feel anything on the surface here.

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All we’ve got is colour. Well, to me, that is what engraving is all about, this sort of stuff, colour.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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This is not really wood, this is MDF. So this is a mixture of sawdust and plastic, which is turned into manufactured wood, artificial wood.

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What I’m going to do,

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I’m going to do some experiments with some real wood, because there you’ll see some of the effects that I want to show you much clearer.

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One of the ways that people try and find this so-called magical focal point of a lens is something like this.

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It’s called a ramp test and it’s called a ramp test, as it’s a ramp.

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It’s running up and down hill. The lens tubes I use on this machine, are

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C-series lens tubes and you can get lens tubes that have got a thread in here and you can just see the bottom of the thread.

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There’s a location for the lens. This particular lens holder is designed to take a two inch lens.

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So there are two ways that you can put a lens in. You can either put it flat side towards the work or you can put it curved side towards the work.

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Convention says you always put it flat side towards the work. We’ll do that, we’ll drop an o-ring on top.

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Because I don’t like to put too much pressure on the lens itself, so when we put the clamp ring in,

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we don’t need a special tool because if you’ve got any sort of fingernails, you only need to put a small amount of pressure on it.

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And you can feel the clamp ring biting on the lens and it doesn’t rattle.

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Now, I’m going to use a short nozzle here because I want to be able to move right the way along here.

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If I put a long nozzle on, I will limit the amount of distance that I can travel up and down this slope.

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So I’ve done some measurements in this assembly and I’ve got my lens set here.

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It’s fifty point eight focal length lens. So I’m expecting the focal point to be just there.

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I’ve measured the distance, that the lenses inside the nozzle there.

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I’ve subtracted this dimension from fifty point eight and that means I should have a gap of

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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21 millimetres to my work, to put a focal point right on the surface of the job. Now my little fixture here.

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Is purposely designed so that, that point there, this surface here, lines up with the central point of this piece of wood.

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So if I set my focus just here at this level, it should be perfectly in focus when I hit this central line.

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Now, all the other lines on here are one millimetre difference in focal height. So there we go, I’ve set this gap here to 21 millimetres. Lets

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use a typical engraving speed, which could be, say, 300 millimetres a second.

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So we put the power to maybe. Eighty percent.

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OK, so let’s just reflect on those two results, should we? 300mm/s put the focal point where we expect it to be at two inches.

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Ten millimetres a second. Well, it looks as though the focal point,

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the thinnest part of the line is there. It’s changed by a millimetre, just because we’ve changed the speed, we haven’t changed the path.

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We haven’t changed the orientation of the lens. And we’re still on the same focal point.

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If this is the focal point, just here and this is the focal point just here, why aren’t the
line thicknesses exactly the same?

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Because remember what the definition of a focal point is, it is that point through which all the rays pass.

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So the promised spot size for this lens is a joke.

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It’s not the same here as it is here, because we’re working at different speeds.

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Our exposure time is different and therefore, what we’re seeing is this effect again as we get faster and faster and faster.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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Only the highest intensity part of the beam is doing any damage. I’ve set the lens up now 21 millimetres.

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And I’ve done two quick tests for you. Here we’ve got the two results for 10 millimetres a second and 300 millimetres a second, at 90 percent power.

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What I want you to see this time, is not what the thickness of the line looks like, but what the depth of the cut looks like.

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OK, so same lens, same focal distance, different power.

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Here’s the damage. It’s doing at 300 millimetres a second. Very, very shallow, it’s just about going through the first layer of that plywood.

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And here we are at 10 millimetres a second and look, we’re piercing right the way through this 10 millimetre thick piece of material,

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there is just the merest hint of a taper at the bottom here,

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as you can see. That line that we thought we had, it’s not a line.

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It’s a very deep V shaped slot because the energy at the centre of the slot is very intense.

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And that intense energy has allowed it to cut very deeply, even at 300 millimetres a second. But as we get faster and faster and faster.

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The only part of the beam which has any possibility of doing damage is this really high intensity stuff at the bottom here,

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which is why the line is thinner at the bottom. Than it is at the top, we’re filtering the intensity out with speed.

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This one has had power filtering and we’re only using part of the beam and you can see just a little tip of the beam there.

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This one, the beam has had a chance to penetrate right the way through.

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The main thing that we’re trying to do with this engraving is to use a lens in such a way that we burn the surface and not cut the surface. And here,

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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we’ve produced a very thin line, but we still cut the surface. We’ve not marked the surface. From a distance,

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that looks like a very nice, thin black line. I know we’ve got this thick black one, which is a cut right the way through.

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Fortunately, the light is catching it just right.

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So we’ve got some transparency or translucency in that groove. That is completely wood white in that groove.

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It’s not burnt at all. The colour that you’re seeing is actually occlusion of light, it’s dark because the light is not catching it in the right direction.

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That’s an interesting problem, isn’t it? We got some black scorch marks and that’s what we really want with thin lines.

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We need black thin lines, not these deep cut lines that are not black.

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OK, let’s try and analyse the problem, because this engraving that you think is simple is a very complex problem.

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I want to remind you of something we talked about a few sessions ago, when we spoke about the laser beam itself and shape of its intensity.

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The intensity is very, very high. More power, more intensity.

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So we’ve actually got a sharp beam. A sharp beam is great for cutting.

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As we’ve seen, it goes right through this material and as we increase the speed,

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what we’re really doing, is we’re cutting off more and more of this low power and we’re leaving just this little tip of high power.

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And so consequently, when we look at our thin line, what we really seeing is that little bit just there.

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Think about this for a moment. Logically, we don’t want that little bit there.

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What we really want is some burning, some stuff that we get around the bottom here.

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And the way that we do that is to reduce the power. If we reduce the power down, look what we’ve done.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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We’ve changed the shape of the Gaussian distribution. OK, so we’ve still got high intensity in the middle of the beam.

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But the relative difference between the high intensity and the low intensity is now substantially less.

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We got what I call a blunt beam now, if we turn the power down. And remember what the lens does, the lens amplifies what the beam is doing.

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So if we start off with a blunt beam, we probably finish up with a blunt line. Let’s give it a try.

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If we’re going to reduce the power, is 300 millimeters a second

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going to give us much exposure time? Because we’re going to reduce the power so much,

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we’ve got to reduce the speed as well to allow the damage to take place.

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Yeah, that’s a difficult one that, should we reduce the speed and reduce the power with a blunt beam?

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Let’s experiment with both shall we? So we take the power down to 20 percent. We still need the speed at 350.

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Well, it’s thinner, but it’s just as white as the previous one.

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It’s about half as deep. Let’s slow it down and see whether we can get some burning involved,

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should we? Lets drop the speed to 100 millimetres a second.

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Looks like a slightly thicker but blacker line. But as you can see there,

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look, we’re still leaving a lovely white edge inside the groove.

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We’re not actually creating a burn. Now, that does look like a burnt line, doesn’t it?

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Here we go, look we can see how lovely and clear and white that cut is inside. The fact that it’s black on the surface, is again just occlusion of light.

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That’s an optical illusion, that’s not burning. So I’ve now put the power down just about as low as I can get on this machine, which is 10 percent.

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And the speed is still 30 millimeters a second. I mean, that’s ridiculous.

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That’s cutting speed. Here we’ve got depth of cut and a lovely clean burn.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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So how on earth do we scorch this wood? What other mechanisms do we have for decreasing the power?

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Before I started to understand things about lenses and laser beams.

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I did something very naive like this test.

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And there we go. We’ve got something called a matrix test, what speeds and what powers I need to produce different colors.

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I was very naive when I started playing with this machine and look.

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There’s nothing there’s no color there at all. All I’ve done is produce a great big deep pit.

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It’s very simple to set up an engraving program. Look here I’ve got a very small rectangle. It’s 20 millimetres wide and 10 millimetres tall.

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It shows black because it just shows you that it’s being engraved as opposed to cut. We just go to here and set some parameters.

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Now we’re going to run it at 100 millimetres a second, and we’re going to run it at,

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in fact, I’ve got it set to 90 percent power here and we’ve got this set to scan.

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I’ve got a line interval, which is the amount by which it will move every time it’s scanned a line. For this first test,

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I’m going to set my line to 0.3. What’s all the trouble about, hey, look we’ve got a fantastically black engraving on a lovely white wood.

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How did that happen when you couldn’t get a burnt line?

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I might have got a black surface. But, I haven’t actually got a black surface.

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What I’ve got is black tips on the top of some very deep cuts.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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Can you see that? In fact that’s not a good engraving at all, because look.

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It’s just a load of teeth on a comb.

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Let me just go to something a little bit wider, 0.5. Yeah, you can see the lines and they look brownish on the surface.

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But hang on, look, if I tip that over a little bit. Can you see how white it still is in the cat?

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We’re not burning inside the cuts. All we’re doing is burning on the surface of the cuts.

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And this is still very much… a comb. That’s not what I call engraving. All organic materials have got,

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let’s call it a colour range. We can lightly scorch this or we can turn it into charcoal.

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Again, this comes back to understanding the properties of materials.

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You can’t use a laser machine without understanding the materials that you’re actually using.

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Wood is a very interesting material. First of all, there is no such thing as wood.

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Every wood is different and every part of wood is different.

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This is a poplar plywood. It’s fairly uniform in its texture.

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If we take a look across here, you’ll see that there’s a band of slightly different coloured

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wood. It’s a resin grain of some sort in the wood.

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This will cut completely differently to this basic material here.

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Some parts of it engrave deeply like this and yet half a millimetre away, it will engrave like this. Wood has got some very interesting properties.

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First of all, this stuff that you mainly see on the surface here is, the light stuff, is a cellulose material.

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OK, now cellulose could be vaporized at around about

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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200, 250 degrees C, something like that. It will just disappear. It will produce fumes and gases,

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but again, remember, we’re shaking the molecules and we are changing them into something else.

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We’re breaking up the molecular structure and creating different materials.

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But there will still be some material left behind. And that material that’s left behind will be the cell walls of material called lignin.

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And that doesn’t get destroyed till about three hundred and fifty or even four hundred degrees C.

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And when that’s vaporized, what we’re left with is this black stuff here, carbon.

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Once this wood gets degraded to just carbon, then carbon shakes very, very easily and it heats up very, very, very quickly. And it will

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almost instantly heat up to about three thousand five hundred degrees C. As the temperature goes up to about

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three hundred fifty when we lost the lignin, up to three and a half thousand degrees C. On the way up,

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the carbon will also shake itself to pieces and mix with things like oxygen.

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So you get carbon dioxide and carbon monoxide gasses forming, but eventually the carbon will disappear, it will vaporize and disappear.

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We kept on seeing that we were getting clean wood finish.

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The only reason we were getting clean wood finish, is because we were taking away the carbon and vaporizing it and we were leaving clean wood behind.

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Now we’re just going to catch the natural low power laser beam on this piece of wood.

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And I want you to watch carefully. And first of all, I’m just going to give it a quick pulse and there we go, look,

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we’ve done a little burn on the surface there and we’ve done some scorching. Some of the stuff is pretty black, so it’s on its way to carbon.

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But look, I only gave it just a little teeny weeny beep, OK?

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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And now if you notice something else is happening, did you see the red glow in the middle?

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So now we’re getting carbon in the middle, which I’m allowing to heat up.

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Oh, goodness me. Now I’m going to hold the beam.

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I’m going to hold the laser beam on now. And you just watch what happens to the middle of that spot.

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White hot, that’s a carbon arc there. That’s 3000 degrees C or more. We’ve produced carbon.

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But if I dig deep enough, look, there’s still clean wood underneath there.

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Just change the lens in here from two inch, which is your standard lens to an inch and a half meniscus lens.

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Now, I want to just point out something to you.

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First of all, this meniscus lens, which was supposedly thirty eight point one, actually sent us up with the ramp test at thirty six point one.

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So it’s already two millimeters different than the specified focal length.

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The size of the line is around about 0.1mm wide.

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Now, that’s not a spot size. That’s a line thickness.

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That’s not the same as the spot size. Now, if we take a look here, we shall see that they claim that for this lens,

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we should be able to get plus or minus roughly two millimeters, plus or minus two millimeters is the working depth of field.

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Well. If we go plus or minus two millimeters on my nominal,

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we find that we’re probably up to about 0.3mm line thickness here and about 0.25m or maybe even 0.3mm line thickness here.

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So there’s a huge difference between our line thickness,

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if we work according to this. We really have only got plus or minus around about half a millimetre at the most working depth on this lens.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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There are always compromises that have to be made. You can’t have everything perfect all the time.

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So here we are setting up to the perfect focus for this lens.

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We’ll run it at a reasonable engraving speed.

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It’s not the best engraving speed, but 100 millimetres a second is OK.

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There’s our first test as a reference. I’ve got this inch and a half meniscus CVD lens in here.

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I’ve run it at 10 percent power, 0.4mm line spacing, there’s a huge line spacing and this is set to perfect focus.

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I’m going to lift the focal point above the work surface by three millimeters and run the same test again.

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Let’s raise it by six millimeters. You see some slight gaps between the lines, so what we’ll now do is just increase the power a little.

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Was there any major colour gain, by going to 15 percent from 10 percent?No, I suspect if we look at the edge of it,

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we shall see that there’s a big difference in the depth of cut that we put into the surface.

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Is there a little bit of difference between plus six and plus nine? Well, there’s a small amount of difference, I suppose, in colour.

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So maybe we could get rid of those lines at plus six by bringing the line spacing down to 0.3mm as opposed to 0.4mm.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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You will remember that we set the beam to the lowest intensity we possibly could at 10 percent,

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and that’s the green shape at the bottom where although we’ve still got some intensity in the middle of the beam,

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it’s not a huge intensity that we experience when we turn the power up to 100 percent.

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And remember, it’s intensity that does damage to our material.

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So here is the 10 percent damage that we’re doing to the material.

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We’ve still got the intensity right at the center of the beam here,

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which is actually causing this deep cutting effect, even when we’re using 10 percent power.

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Now, at the moment, these grooves here, these cuts are point four of a millimeter apart.

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We’ve seen earlier what happens when we increase the power to try and make the cut blacker.

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We see what happens to these grooves as we close them in and they start to join up.

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We get a very weak comb, which we can easily flake off.

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That’s not engraving. What we’re trying to do is to get the softest amount of power into the surface,

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so that we scorch or damage the surface to the extent of adding some carbon,

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if you like, to the surface if we possibly can, without cutting into the surface.

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But at the moment, we’re failing badly, the manufacturer said this lens was thirty eight point one.

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With these settings, 10 percent power and 100 millimeters a second,

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we found the focal point and it’s not the light wave focal point, it’s the intensity focal point.

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We’ve set the focus onto the surface here to the specified thirty six point one.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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We’ve turned the power right down and we still can’t make a shallow cut.

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We lifted the lens up by three millimetres. And here’s the result.

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We’ve now got rid of our deep cutting. We’ve made it much shallower.

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We’ve now raised the focus by six millimetres. And if you look carefully, you can just see here, the grooves, just.

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They’re almost invisible, because they’re on the surface, and that’s exactly what we’re looking for,

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for engraving. We want surface damage, then we tried to make it darker by increasing the power.

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And increasing the power didn’t seem to make much difference to the appearance.

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It’s put some grooves back in here again, as you can see, but it really wasn’t of any benefit to increase the power.

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And then finally, we put the focus back down to six millimetres above the work surface.

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We kept speed at 100 and the power at 10 percent. But we closed up the line spacing to point three as opposed to point four.

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Now, you can’t see anything on that surface, so what we’ll do, we’ll go and have a look at those same results from above.

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So there we are focused on the surface of our material. And this is a point four millimeter spacing between the lines.

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So the lines look as though they’re roughly about zero point one wide.

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But if you look carefully, you’ll see that there’s curvature on the lines at the top here, there’s some strange markings on the edge of the groove,

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which you would expect to be brown, because that’s where the effect of the lower power is taking place on the edge of these grooves.

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But in fact, it’s not.

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There’s so much power in that beam still that it’s actually just taking away material, evaporating material and not leaving any carbon film behind.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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So without making any other changes. We lifted the focus by three millimetres.

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So here you can see the wood grain running across.

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OK, and so what we’ve got here is the cut, if you can call it a cut, it’s very, very, very shallow now.

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And what we’re seeing here is the edge of the cut here and the edge of the cut here, joining together to form a slightly carbonaceous type of band.

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It’s not brown, but it looks as though it’s leaving some little flecks of carbon in there.

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So now we’ve shifted the focus up. And the actual grooves themselves, the cut lines, the point four spacing is a lot less obvious.

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We’re getting more burning across the width of the cut.

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In other words, we’re getting a more even burning. we’re burning the surface without cutting the surface.

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And I said we can maybe get some more colour into it by adding some more power to it. By adding more power to it,

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we’ve made these marks slightly darker, but what we’ve done, we’ve separated them out again because look, we can see now the groove coming back in.

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So it’s done nothing for our coloration. It’s made the colour more intense in bands, but that’s not what we’re after, we’re after a uniform colour.

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So then we went back to 10 percent power. Point four line pitch.

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But this time, we were nine millimetres above the focal point, so we are well out of focus, we’ve got a much softer uniform distribution of power within the beam.

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And we’ve got a much more uniform distribution of these little specks of carbon and then we said, well,

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can we improve that a little bit more maybe by closing the gap back up instead of point four,

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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could we get it down to point three and take the focus back down to six millimeters?

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It might not look very dark to you.

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But that was the darkest colour that we could get on this white wood, you can see the green structure in the background,

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the cellular green structure, and we’re not having an effect on all of it.

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The point I made earlier was different parts of this grain structure burned completely differently.

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These may well be slightly at a different height, so slightly out of focus,

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but it’s more likely that these untouched sections are slightly different chemical composition to those that have actually burnt.

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This whole process of laser engraving is very complex.

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It’s not the simple process that everybody tries to explain to you.

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Yes, you can do engraving with no knowledge, no skill, and just choosing random numbers to put into your machine.

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But I’ve shown you what happens when you put random numbers into your machine.

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I mean, I can’t even get to the bottom of the groove. Well, there it is. Look, there’s the bottom of the groove.

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Look how deep it is. You know, you start engraving with lines like that.

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0.2mm apart and your whole job is just going to disappear.

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We’ll go back and see whether or not we can achieve anything similar with your two inch lens. That’s 0.3mm at 10%.

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In other words it’s 0.3mm spacing, nominal focus. And we’ll go up by another three.

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Then we’ll go up again by another three. I think we can see quite a pleasing result there, change of colour only because we’ve changed the focus.

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So it looks as though this nine millimetres above the focal point is about the best result we’re going to

Transcript for Surface Laser Engraving Organic Materials (Cont…)get.

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What you must remember is because we’re pulling the beam out of focus. We’re going to be marginally increasing this dimension here.

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So it hasn’t increased it by a huge amount, by changing the focal distance by a significant amount.

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So there’s a summary of our best result there, nine millimetres above the focal point point three line spacing,

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hundred millimetres a second at 10 percent power. Now that we’ve got something that works.

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Can we make it faster? If we make it faster? Say 200 millimeters a second.

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The line is going to get thinner and the exposure time for the power, is going to get substantially less.

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So maybe we should put the power up to 30 percent, the speed up to 200.

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And maybe see whether we can leave the spacing at point three and gradually close up the spacing to get the colour.

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The first thing that we note. Is we’ve taken material away, we haven’t got any colour.

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Oh, dear. I didn’t mean to show you that. That’s another session completely.

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Well, let’s see how that setting works on MDF, shall we?

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So that’s nine millimetres above the focal point, 0.3mm line spacing, 10 percent power and 100 millimetres a second.

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That’s a pretty good contrast. This is high density fiberboard, which is normally different than MDF.

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This is more difficult to colour up. That’s loking pretty good on there as well.

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Here’s another material that I use, which is basically the same sort of card that they make beer mats from.

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It’s an absorbent card. Basically, it is pure wood

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pulp. It’s done a very good job on that as well.

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And here’s a piece of marine plywood, very good. Here’s a very small sample here of some birch plywood, not quite such a dark colour.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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But then again, it might change. No, it didn’t.

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It’s not an optical illusion. It remains the same colour regardless of the direction that you do the engraving.

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You can do nice engraving with your two inch lens if you choose the right parameters and understand what you’re doing.

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Throwing power at the job does not make it darker. It just makes the cuts deeper.

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You’ve got to understand, that you’ve got to scratch the surface with low power, not high power.

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So you need to even out the burning as much as possible.

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So what we’ve done,

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we’ve lifted the focus to soften the intensity of the beam. There is one vital thing you need to know before you start doing your engraving.

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And that is something called reverse scanning offset.

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I have to say the MDF is a very good material for doing this, setting the reverse scanning offset.

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We need to do the reverse scanning offset calibration at the correct focal distance.

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Now, I’m going to draw a very small, simple program. It could even be this program here.

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All we need to do is change the spacing on this program to0.5mm line pitch.

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If you look at the edge of this pattern here, you’ll see that the lines do not line up with each other.

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Every other line is correct.

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But they should all be correct and perfectly lined up. This offset calibration you’re going to choose or set only works for the number that you set it for.

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You can come up here to config and then you’re going to choose system setting and then you’re going to get this window here.

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Now, depending on the version that you’ve got, you may or may not get this window.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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Yeah, maybe other windows that you’ve got to hunt for,

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but you’ll find somewhere a table that looks, it will not look like this because I’ve filled my table in.

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It’ll be an empty box over here that calls scanning reverse compensation.

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Now, the first thing that you must do is add a tick there.

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So that the compensation takes place, the next thing you must do is go to add and you add one for a hundred.

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Have I got one for 100 in there? I don’t think I have. So I’m going to have to add one for 100.

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We’re going to do this for real. So the speed millimetres

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per second is going to be 100. And the reverse scanning offset, we’ve got no idea what it should be.

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So in the first instance I’m going to put 0.2mm. I’ve got no idea whether that’s the right number or not.

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And we say OK. There is a method that you must adopt.

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And generally you look at the second line down.

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It doesn’t matter which end you’re working from, whether it’s the left or the right.

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But in this instance, what you’ll notice is let’s look at our first pattern here.

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The second line down is out this way.

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That’s also out this way. Question is it more or less than this one?

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Well, the answer is it’s more so I’m obviously going the wrong way.

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I think I might need to even go minus. So let’s try minus point two and see what happens.

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Now, I’m being aggressive with my numbers just to demonstrate. And this time if we look at the second line down.

Transcript for Surface Laser Engraving Organic Materials (Cont…)

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The second line down is now gone in and it’s come out this way, so 0.2mm plus was too much and 0.2mm minus was too much the other way.

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So let me set it to zero. I’ve just had a quick check and zero is not quite enough.

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It’s got to go something like maybe 0.02mm plus. So I think you can probably see now the lines up pretty well,

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all squared up across the ends compared to where we started from.

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And that’s what you need before you start any engraving. Let’s do a quick final demonstration to show you what surface engraving can look like.

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This is probably the most difficult type of engraving that people struggle with, that’s why I’ve tackled it

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first, it is standard engraving, but the most difficult to try and achieve.

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And I’ve told you all the tricks and all the methods by which you should be able to achieve this satisfactorily. There are so many other types of engraving,

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which we shall have to cover in future sessions.

Transcript for Surface Laser Engraving Organic Materials (Cont…)