Session 17 Laser Engraving – An Overview

Transcript for How to Laser Engrave – An Overview

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The Concise RDWorks Learning Lab with Russ Sadler. Session 17 Engraving – An Overview.

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Well, here we are, I think we are in session 16.

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Now, we’ve done nothing with this machine up to now except trying to understand the technology and the various parts of the machine,

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because first of all, you are the only one that’s going to be responsible for servicing and looking after the machine when it goes wrong.

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But I hope what we’ve done so far by taking you through the various elements of the machine would take some of the instant fear away.

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When something goes wrong, it will hopefully make you stop,

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think, look at the various things that may have gone wrong in the chain and work your way back to find out what the problem is.

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Now, the mechanics of the machine are not really an issue because they’re just bits of metal screws, wire, etc.

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The real problem comes in doing something with the machine.

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And today we’re going to start the doing process. Now, you bought this machine for two reasons, one, to cut materials, and two, to engrave materials.

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I don’t think you really understood just how big the subject is. So, I’ve got to make a decision,

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now do I start you off with engraving or do I start you off with cutting?

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Now that’s a big decision for me because they are two completely different subjects.

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They are absolutely diametrically opposite in every respect.

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Now sometimes you’ll have to find some compromise parameters because you’re going to do some cutting and some engraving on the same job.

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That’s where your skill will come in making a judgment as to what parameters you should use,

Transcript for How to Laser Engrave – An Overview (Cont…)

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what lenses you use, how much power you should use, what material you should use. Oh dear, the problems are endless.

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Now, I’ve made the decision, after all, that you’re going to start off with engraving now, engraving is a huge subject.

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You’re going to have to go back to that first or second session and start remembering some of the science that we spoke about,

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because now that science of both the laser,

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and the material is going to be very, very important to you. Yes, you can sit down at this machine,

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you can put a few parameters into the program, chuck a bit of wood under the laser head and you’ll get a result.

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It might look like a barbecued piece of wood, but hey, it’s a result and you’ll be very,

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very pleased with it until you get a bit more proficient and you look back at it in a couple of years time and you think,

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how did I manage to produce something that bad? It is practice,

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but hopefully I’m going to teach you some of the tricks and essential lessons that I learned that will stop you making too much barbecued wood.

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I’m not sure that even this list fully covers all the opportunities for laser engraving.

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The thing that you first imagined is probably number one. That’s the only thing that you think about when you normally see engraving.

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This is the sort of thing that you’d think about doing some text burnt into a piece of wood.

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Okay, well, that is just basic laser surface engraving. Now, here is Laser deep cut engraving.

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It’s called incised text, because what we’ve done, we’ve cut deeply into this wood.

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And I don’t think it takes a genius to work out what Laser relief engraving is.

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The text has been allowed to come up to the surface and we’ve taken away all the background.

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So it’s the opposite of this incised text. This is laser line engraving.

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Now, all the lines on here are different thicknesses and I’ve achieved the different thicknesses of lines on here.

Transcript for How to Laser Engrave – An Overview (Cont…)

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By virtue of changing the distance of the focus, it’s the same lens,

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but different focal distances produce different thicknesses of lines for different parts of the job.

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So you can see these lines down here are completely different thicknesses to these very,

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very thin lines here for the cables and then here’s something that you didn’t probably know that the machine could do, laser 3-D engraving.

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Wood and acrylic.

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Was that a surprise? I’m not going to go too much into laser grayscale engraving.

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That’s a rather specialist subject, which you have actually been using laser grayscale engraving to do laser 3D engraving.

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But there is a subject of laser grayscale engraving that we can deal with separately on its own.

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Because you can actually do sort of try and do laser photo engraving with laser grayscale engraving.

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The next subject, laser photo engraving is fascinating and a huge subject on its own.

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There’s a rather handsome guy there on a piece of slate, a lovely image there on a piece of card.

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So there’s a white photographic image on a piece of black acrylic. Here

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we’ve got an amazing photograph on a ceramic white tile.

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There’s my favorite fox again on a white tile. Sometimes you come across a subject using what on earth am I going to do with laser origami?

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Sure, laser origami, is bending and folding things.

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Yes. And here I had a need recently to do some laser origami work.

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This is five millimeter thick acrylic and I put a 90 degree bend in it using the laser machine.

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Basically, I’ve used the laser engraving process to heat the material up beyond its plastic limit

Transcript for How to Laser Engrave – An Overview (Cont…)

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so that it would sag and allow me to fold it and put a 90 degree bend in it.

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If you go to YouTube and you just put laser origami into the heading, you’ll find that

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there’s quite a lot of things that people do with this, which will probably whet your appetite for trying it yourself.

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There’s something that I’ve added onto the bottom here called lacework.

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Now here I’ve got some very thin card and this looks like a very delicate laser photo engraving.

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Let me just put it up to the light. I think, as you can see, this is not quite what it appeared originally.

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This is actually full of very, very, very fine holes that’s actually allowing the light to come through.

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That’s what I call lacework. They’re just subjects.

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Now, the other thing that we haven’t talked about is what materials can we engrave?

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So you’ve only got to go back to the first science sessions. When we talked about materials and we said all materials are made up of atoms,

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but the way in which atoms combine together to make little groups called molecules, the combination of atoms to produce molecules is gazillions.

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All the gazillions of different combinations produce these different materials, and every different material has got its own properties.

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As we talked about, there are two or three special groups of materials, metals which we use for mirrors.

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These rather special transparent materials which we use for lenses and then everything else.

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Well, what we’re talking about here is everything else, because everything else will absorb or react with the ten point six micron light.

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And remember, what’s happening is we’re really stimulating the surface molecules to make them vibrate.

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And the faster they vibrate, the hotter they get.

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And they get to a certain temperature or a certain energy level where the bonds between the molecules can no longer be sustained.

Transcript for How to Laser Engrave – An Overview (Cont…)

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They break and the molecules fly off and we change from one material to another material.

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You must keep remembering that basic philosophy of how materials react.

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You cannot attack the inside of a piece of wood or any other material.

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You can only attack the surface with light. So whatever’s happening is always happening

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on the surface. It might be getting deeper and deeper and deeper, but it’s still the surface that’s being attacked, not the material inside.

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So, we will start talking about these different materials when we start doing the laser engraving process,

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but we’ve got these organic materials now, organic materials have got, they’ve got a rather special property.

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They will burn. They will chemically transform from something into nothing.

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Gas, they will vaporize. There are lots and lots of different woods which are made up of different molecular structures.

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So every wood is basically a different material. And it gets even worse than that because,

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look! This is all the same settings.

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Look at all these different structures of wood in this bamboo, and as you go across here, you can see that as we move from this basic structure.

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To a different piece of wood here, look at the different texture.

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This wood is reacting differently to exactly the same light that this wood was doing,

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because there’s something different about the molecular structure of this part of the wood than there is to this section here.

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You can see this is made up of strips that have been bonded together. Within parts of a millimetre,

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this wood is changing its material structure. This is really the point I’m trying to make.

Transcript for How to Laser Engrave – An Overview (Cont…)

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There is no such thing as wood. Wood is a continuously variable material.

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It’s just a family group. OK, stuff that burns.

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Now, card is basically just wood pulp that’s been bonded together,

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and one of the things about wood, card, leather, MDF is they have something that I would like to call a range of colour available to them.

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You can either very, very lightly scorch a piece of wood or you can make it black.

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So between black charring and light scorching, you’ve got a colour range of brown.

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And that’s what you can see in this picture here. But that range of colours looks like the old sepia photographs,

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and it’s very pleasing to the eye, even though there isn’t a white dynamic range in there.

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So that’s one of the properties of these materials, these organic materials.

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They have got a colour range that you can work with. Now, this next range of materials,

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I call them mineral materials because they are stone type materials, slate, granite, marble, glass, ceramic tile.

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I showed you an example there.

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Now, this next section here, mineral’s: slate, granite, marble, glass, ceramic tiles, they are what I call binary materials.

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There is no colour range on these materials.

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When you hit them with the laser beam, you produce a colour, whatever

Transcript for How to Laser Engrave – An Overview (Cont…)

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that colour is, and in this instance it’s a sort of a light grey. Okay.

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Now we appear to have a tonal colour range here, ranging from black to fairly light grey.

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So we’ve had to do some trickery to put a photograph on here.

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Now, Glass is another interesting material which we’ll talk about later on, along with granite and marble.

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Now we’ve got some more materials, plastics. There are a limited number of plastics that you should be working with on this machine.

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Some of them produce really nasty and dangerous fumes. So before you do any plastic work, do some research

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work on Google and find out what happens when you burn the material, what sort of toxic fumes you produce.

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The same problem exists with plastics as it does with mineral materials.

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You only have two colours

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normally. This is basically changing black acrylic into white acrylic so that we can produce a white image on a black background.

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Now, here we’ve got clear acrylic. Yeah, so what’s so fascinating about that?

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Well, of course it’s rubbish because you can’t see it unless you do something like this and you put a black background behind it.

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OK, so again, this is a binary material, it can only produce white marks on clear acrylic.

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Now, I haven’t got any Corian at the moment to show you, which is used for worktops

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normally. You can sort of do laser 3D engraving, with it even. It’s basically acrylic, which you can laser engrave, as you can see, but it’s filled with a powder.

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And so what you do, you’re basically melting or evaporating the acrylic away, leaving the powder behind.

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It’s a very messy process. Then we’ve got things like synthetic rubber, which is really a plastic, even though it’s a rubbery material.

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And here’s an example of that. And I’ve been successful in making rubber stamps with this material.

Transcript for How to Laser Engrave – An Overview (Cont…)

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OK, and this is laser relief engraving. So here’s an example of this polyester powder coating that I was talking about.

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These stainless steel flasks have been painted with an epoxy powder coat resin.

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And then what you do, you burn the resin off to leave the stainless steel finish underneath.

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And then we come to the last group, which is laser engraving metal. Now, remember, metal is very, very reflective,

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you cannot laser engrave it. In the pursuit of science and proving to you guys that you cannot laser engrave metal, I’ve done it.

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I’ve messed up lenses. What you can do, there are ways of changing aluminium, plain aluminium into a different material.

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This is a black surface, but underneath, if you look, we’ve got white.

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Now this white material here is basically aluminium oxide and aluminium oxide.

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It’s the sort of stuff that you use for grinding wheels, sandpaper.

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It’s a very hard material.

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And you can take aluminium, put it through this process called anodising, and it converts a very thin maybe two to five micron,

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maybe 10 microns thick layer on top of the material into aluminum oxide.

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Now, question: is aluminium oxide. Metal?

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No. It’s a, it’s a metallic compound, but it is not metal, and because it’s not metal,

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it comes into this everything else group of materials that will absorb energy.

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You can fire the laser at this material without it reflecting. Now.

Transcript for How to Laser Engrave – An Overview (Cont…)

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When they, when they finished the process off, before they finally seal the process, they allow dye to infiltrate the surface of the aluminium oxide.

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So this black on here is just a water based dye that’s been soaked into the surface of

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this metallic material. The structure of this aluminium oxide is a bit like grains of salt.

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They’ve got little teeny weeny pores or gaps between the grains, and that’s where the dye infiltrates.

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And that’s what you can see here, a dyed surface of white aluminum oxide.

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If you’re very careful about this process, you can heat the dye up, make it evaporate and left the aluminium oxide behind.

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So we’re not actually working with raw metal.

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We’re working with an oxide of the metal. And that allows us to do things like that.

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We can put photographs on here, we can put text on it, we can laser engrave on it.

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And then finally, we’ve got stainless steel. Now, again, stainless steel is very, very reflective.

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It’s probably in the 96, 97 percent reflective range.

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The only thing we can do is stainless steel is to chemically mark it.

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Here’s just an experimental test piece. It’s the only thing I can dig up at the moment.

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And you can see here, this is very shiny stainless steel. But I painted something on here and then I did some etching.

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When I take this grey stuff off, what’s left behind is a black mark.

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And that black mark is very, very durable. So some of the chemistry of this material has etched itself and bonded into the surface of

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the stainless steel because it’s reacted with some of the chemicals in the stainless steel.

Transcript for How to Laser Engrave – An Overview (Cont…)

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So that’s the only way you can mark stainless steel.

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You cannot laser engrave it. That’s a quick preview of what you’ve got coming up over the next many sessions.

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So each one of these materials and processes requires its own special knowledge.

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As I said, this is a very, very wide subject. Not only do you need to understand the laser beam technology,

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you need to understand something about material technology as well, because you’re trying to disrupt molecular structures

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remember, from the surface down. Never forget that fact, surface damage

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only. Now we’re going to start doing a section with a little demonstration.

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And I’ve got I’ve got the machine cover down for a good reason.

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I’d like you to observe some things that are going on. First of all, can you see the way in which the flame is blowing backwards?

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Secondly, I think you might be able to see that very, very bright light. Now at the moment.

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We put this piece of tape down here so you could see something else.

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The tape is, first of all, probably marking slightly wider than the beam.

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Certainly up here, look you can see that the tape, has burnt away a lot wider than the beam.

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We’ve got different damage. For different materials.

Transcript for How to Laser Engrave – An Overview (Cont…)

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This one is masking tape, which is so thin that it has no effect on the focus, but look what it’s done to the beam here.

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When I’ve got lots and lots of power very, very slowly. It was able to just burn through and basically hardly have an effect on the cut width.

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Here, it’s starting to have an effect on the cut width. Here it’s having a significant effect on the cut width.

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Here it’s virtually wiped out and absorbed all the power before its started to cut the wood.

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So that all the energy now, has gone into cutting the tape and nothing has gone into the wood.

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This is an interesting fact, do you remember this from a few moments ago?

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If we get the balance of power and speed right, we should be able to just remove the paint and do virtually no damage to the

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material underneath. There’s a huge amount of information in this very simple test.

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Which I want you to try and remember. Question one: Why are these lines A, changing width and B, changing colour?

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The next question is, why if we got a different level of damage here and here?

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Than we have here and here, but on this one, look, we got quite a large mark at the end and a little teeny weeny burn mark there.

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And then we’ve got a little blog here, which is bigger than the beam.

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I’m going to put my hand in that flame. How brave is that?

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Look, it even damaged me, you see, it’s even put a mark across, a black mark across my fingers.

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I could feel the heat from that flame as I move my hand across there.

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And it marked my hand. What happens if I do this?

Transcript for How to Laser Engrave – An Overview (Cont…)

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Apart from the fact that I’ve blown it out. I can hardly feel the flame.

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Why is that? I think you could answer the question the other way round.

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Would I do this? Come on, stop. Would I actually pass my hand through that plane at that speed? Ha Ha Ha

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I think you know the answer to that question and why, but try and analyse why I’m not able to run my hand through that flame slowly.

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I have got a damage threshold on my skin.

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If I move my hand through that flame very, very slowly, I shall A: exceed my pain threshold and B: I shall exceed the damage threshold

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of my skin and the molecules will start flying apart and do stupid things.

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Anybody familiar with photography will know what exposure means and that’s what I’m doing here.

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I’m exposing my hand to a certain amount of power in a certain amount of time.

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Now, if I reduce the time by going faster, I’m reducing the exposure time and reducing the exposure

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time, keeps my skin above the damage threshold for the flame.

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Now, I can pass that card through that quite quickly and it doesn’t mark the card.

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And now I go really slowly. And I’m in trouble.

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That’s a good demonstration of damage threshold.

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And exposure time,

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the material has a certain damage threshold and I’m exposing that material to a certain amount of power for a certain period of time,

Transcript for How to Laser Engrave – An Overview (Cont…)

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a certain exposure period. OK, so power and time equals exposure.

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So that begins to explain why we’re doing less and less damage as the speed increases.

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We’ve got the same power. And yet we’ve got and we’ve got the same damage thresholds on these two materials.

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But we’re exposing the material to a lower power per unit of time.

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And so consequently, the damage is less. That explains why the lines are getting lighter.

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There was less damage, so therefore we’re going to get less browning.

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Why are these lines thick and these lines thin? That’s for something completely different.

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That’s unique to the laser beam.

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We’ve talked about it before, but we’ll discuss it again because it’s an incredibly important feature of this machine.

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Now, you remember my little light here, how it’s very,

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very intense in the centre and it gets less and less intense as I move away from the centre of the light.

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And I said that was an exact simulation of the laser beam.

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Now, I’m going to start using a word that’s really very important.

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Intensity now some people technically will use the word energy density.

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I don’t think the word energy density conveys the right impression, whereas light intensity,

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you immediately know what it means, it’s brighter than anywhere else if it’s more intense.

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Well, the light at the centre of this beam is more intense than it is at the edge of the beam.

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This is just a graph of the light intensity within our laser beam.

Transcript for How to Laser Engrave – An Overview (Cont…)

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And as I said to you before, this is something called a Gaussian distribution.

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That’s the ideal shape of the intensity within a laser beam, not all laser beams conform to that pattern.

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If yours doesn’t, then it might be close to junk.

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I know that the beam on this machine is pretty close to that intensity distribution.

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Another very important factor, which I’ve mentioned before,

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but I’m going to keep stressing this because it’s, it’s just the most important thing that you can remember about this laser beam.

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The more intense the light, the faster it will do damage to the material.

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So the height of that graph represents the intensity and the more light intensity we have, the faster we can damage our material.

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How much damage are we going to be doing to the material just here?

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You’re absolutely right. Zero.

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And as we start climbing up this curve, we’re able to do a little bit more damage to the material provided we give it enough time to do the damage.

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If we want to do the same amount of damage from the power down here,

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we’ve got to allow that light to be exposed longer so that it can do the same amount of damage as that light up there.

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Can you see how down the centre here we’ve done a huge amount of damage and yet as we get to the edge here,

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look, it drops off fairly quickly to less and less damage to just a faint brown mark just here.

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We’ve allowed enough time for that,

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width of line there to do damage.

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There’s enough power here and there’s enough power here right at the edge of the beam width to do some browning just here, scorching.

Transcript for How to Laser Engrave – An Overview (Cont…)

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But in the centre here, this look, this section here. Which you can clearly see.

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On here. That farrow right down the centre, there’s so much power there that it’s able to do a huge amount of damage.

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Just there, but once we get outside that damage zone, the damage gradually creeps off like this.

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So we’ve just got lots of browning here, but we’ve got lots of damage in the centre.

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Now you can’t see in there, but that damage has gone in and done something like that. Now as we get towards this faster speed,

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only the highest amount of intensity, this bit just here.

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Will be able to deliver enough damage to the material in the time that’s available to it.

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So what we shall finish up with is a line width that

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is that wide. But look at the change of intensity across the top of that shape.

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It’s virtually a flat line.

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So we’re going to have no change of intensity. All we’re going to do is get like a paintbrush effect, just a very slight browning across that zone.

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And that’s why it is a thin line and not a

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thick line. I hope that this explanation gives you some sort of feeling for this concept of exposure time.

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This also explains why we’ve got these blobs at the end here, because the velocity of this beam starts off at zero,

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accelerate up to 240 millimetres a second, and then drops back to zero.

Transcript for How to Laser Engrave – An Overview (Cont…)

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And as it drops back to zero. So what we’re doing, we’re getting closer and closer to this situation

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again. We’re increasing the exposure time right at the end of the lines.

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Now, I’ve done this without any lens in the system because it shows this very clearly when we’re looking at a naked beam.

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This situation does not change when we put a lens in. Now, as I’ve explained to you before.

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There are two types of lens. We’ve got these which are flat on one side and curved on the other.

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They’re called Plano Convex.

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Now, this is one way that you can use a Plano convex lens, which everybody steers away from because it’s got, and this is grossly exaggerated.

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This has got something called spherical aberration.

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The actual shape of this lens as part of a sphere causes this problem here to happen to the light rays.

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We do not focus down to a sharp point. The rays that come in from the outside focus here and the rays that come down the centre focus down here.

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So we’ve got a huge range of focus. Now, if we turn the lens over, things start to change.

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The light comes in here. It’s refracted twice, once into the lens and once out of the lens.

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And we get a much smaller range of spherical aberration.

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There is still spherical aberration, because this is part of a sphere and it never comes down perfectly to a focal point.

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And that’s why you will be told this is the correct way to install a lens.

Transcript for How to Laser Engrave – An Overview (Cont…)

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And in general terms, it works for most things most of the time.

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And one of the ways that you can get rid of, nearly get rid of

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the spherical aberration. Is to put another spherical concave surface, it still doesn’t focus it to perfection,

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it only does an improvement on this situation that you can see here.

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We’re going to go for one final demonstration in this session. We’ve been using a beam full power, so we’ve been using it in sharp mode.

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It’s been doing a huge amount of damage at the centre and not much right at the edge of the beam.

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As we reduce the power in the beam, we’re changing the relativity of intensity between the edge

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and the centre. We can reduce a sharp beam to a blunt beam under control by reducing the power.

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So I’m going to run this same test, but this time we’re going to do it 20 percent power.

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He’s the imagined shape of our laser beam intensity diagram at 90 percent power.

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We’ve got a huge amount of intensity right at the centre of the beam, and we’ve still got nothing at the edge. When we reduce the power to 20 percent.

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We’ve still got nothing at the edge.

Transcript for How to Laser Engrave – An Overview (Cont…)

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But what we’ve got, is a much, much lower intensity right at the centre. So we haven’t just changed the power of the beam from 90 to 20.

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We completely changed the damage ratio of the beam itself.

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Its ability to damage has been changed because the intensity shape is completely different at 20 percent than what it is at 90 percent.

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And I hope you can see that from this diagram, when you change from 100 percent power to 50 percent power,

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you’re not really changing to 50 percent power.

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You’re changing all sorts of intensity things within the beam which are having an effect, a non-linear effect on the output.

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If you wish to have a linear change to the power of your beam.

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You don’t change the power, what you do, you change the exposure time, so if you change the speed from 120 to 240,

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you’ve actually doubled that, doubled the speed at which the beam is traveling and you halved the exposure time.

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You’ve halved, linearly halved the amount of damage you’re doing to the material.

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So I think you can clearly see here, the shape of the beam at this five millimetres a second.

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We’ve still got most of the beam width available to us here. But as we get a little bit faster, a little bit faster,

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we very quickly run out of beam width. By the time we get to our intensity just here, at 40 millimetres a second.

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We’ve run out of intensity.

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Now with this one, we may well have gone as far as 300 millimetres a second before we matched the intensity level of this one.

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And this one reached its intensity peak at 40 millimetres a second.

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So I hope this is sufficient proof to show you that this diagram is very valid.

Transcript for How to Laser Engrave – An Overview (Cont…)

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And you should imagine this diagram when you think about changing the power of

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your beam and also consider whether or not you’d do better to change the speed,

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then the power. I’ll leave you with all those complicated thoughts and the fact that we haven’t even put a lens in yet.

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Are you sure you want to keep your machine? Is this the time to send it back?

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I’ll catch up with you in the next session.

Transcript for How to Laser Engrave – An Overview