Session 26 – Photo Replication Part 1 – Making Dots

The Concise RDWorks Learning Lab Series

Welcome to Module 3 of the new Concise RDWorks Learning Lab Series with Russ Sadler. Module 3 will build on the information learned in the previous modules and will be targeted on the differing types of laser engraving methods and the techniques needed to consistently achieve great engraving results. So lets learn some new Photo Laser Engraving techniques.

In this Session, Russ continues the Photo Replication theme and explains how to make dots. Dot’s are the foundation for the whole Photo Replication process: One Pixel MUST equal one Dot. Here Russ goes through the process of how to determine your actual dot size and discusses the compound lens, a piece of kit he uses to achieve 0.1mm dots.

Release Date: 7th January 2022

Over the last 6 years, Russ has built up a formidable YouTube following for his RDWorks Learning Lab series which currently has over 200 videos.

The original RDWorks Learning Lab series on his “Sarbar Multimedia” YouTube Channel, follows Russ as he tries to make sense of his new Chinese laser machine and to sort out the truths, half truths and outright misleading information that is available on the web.

Six years later with over 3 million YouTube Views under his belt, Russ has become the go to resource for everything related to the Chinese CO2 laser machine user or wannabe user.

The Dot test for improved Photo Laser Engraving techniques
The Dot test for improved Photo Laser Engraving techniques

In this new series, Russ has condensed his knowledge and experience of the last 6 years to provide valuable information and insights into the purchasing, understanding, use, repair and maintenance of the Chinese CO2 laser machines and their key component parts.

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Podcast Session 26 – Photo Replication Part 1 – Making Dots

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Transcript for Photo Laser Engraving Techniques – Making Dots

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Photo Laser Engraving Techniques

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The Concise RDWorks Learning Lab with Russ Sadler. Session 26.

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Photo replication Part one Making dots. Now, we’ve touched on digital imagery in several sessions now, but in the last session in particular,

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I made it very clear to you that if you understand how digital imagery works, then photo replication is very, very simple.

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One Dot equals one pixel. You are in control of the DOT.

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We may get onto some pictures today, but really today’s session is all about how do you create that dot?

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Now, as I mentioned in the last session, 254 PPI pixels per inch means that each pixel is 0.1 of a millimeter square.

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0.1mm is probably four of those four hairs.

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So it’s pretty small. How on earth do you get a burn dot that small?

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Well, according to the lens industry, it is extremely simple.

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But what I can tell you is the numbers that they’re selling you, are not the numbers that you can achieve.

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Let’s take a few minutes out to look at lenses because that’s a whole subject on its own, which I’m not going to get involved in today.

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But we need to touch on lenses just so you’ve got a feeling for what it is that you’re trying to achieve.

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There is a limited range of lenses that you can get for these machines.

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Here are four typical lenses. One and a half inch focal length.

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Two inch, 2.5″ and 4″. You can get three inch can get probably five or six inch as well.

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But these are the more common lenses that you’ll find that people are using in these machines.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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I’d like just to take a look at this rather strange lens here, because it’s not a lens.

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It’s a piece of flat material and a piece of flat material allows the light to pass through completely unaffected.

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If we take a look at the way in which these lenses change, you’ll see that the top surface is very slightly curved and we get a long focal length.

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And as the top surface changes its curvature. So the focal length changes.

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These are theoretical diagrams, and they represent what you probably imagined,

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lenses to do. In other words, they focus the light down to a point.

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Each one of these is a magical point of nothing.

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Well you can’t have nothing for a focal point, you have to have something.

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So in the real world, they don’t actually go down to nothing.

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There’s something there, right in the center.

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Okay, and if we look at this larger diagram, you’ll see that we got my crossover point that I showed on the previous diagram,

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but you’ve got this funny sort of outline here, which is a magical thing which people don’t clearly describe to you.

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How is it possible for light rays to curve like this?

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But for the time being, let’s just assume that you will always see lenses described with this sort of waist effect, not a perfectly zero focal point.

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That’s a theoretical focal point, which can never be achieved, the smallest that that can ever be is the wavelength of the light.

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So we’ve got ten point six micron wavelength light for this machine,

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so that can never be smaller than about point zero one millimetres ~ 10 microns.

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Let’s just take a look at what other information the lens manufacturer tells you about their lenses.

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Well, we’ve got a focal length here of 1.5″, 2″, 2.5″ and 4″ exactly the numbers I just described to you.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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If you’ve got a very small, low powered laser, you may possibly have a four millimeter beam.

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The beam diameter is another very large and argumentative point, because on this machine that we’ve got here, which is a 70 watt machine.

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The manufacturer claims that it is a five millimeter diameter beam, but in fact, I know that this beam spreads out as far as 11 millimeters.

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Who’s right? The manufacturer or me? Because I can show you that this beam does not stop at six millimetres diameter.

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So to use these numbers here is a bit fictitious to start with.

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If you were using this lens for looking at an image, be it a microscope, a telescope.

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Well, maybe you’re using it for a projector, then these numbers would probably be right,

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but they do not work when you start putting laser beams through them, even though this material is specifically designed to work with laser beams.

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These numbers are not. Let’s take a quick look at what this diagram says.

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It says a measurement which is this dimension here.

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So if you move away from this theoretical focal point by a certain distance, you can see that the beam diameter is beginning to grow.

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This blue diameter here is what they call the spot size.

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It’s the smallest possible point where all the rays pass through.

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If we move away from this theoretical focal point by dimension “A” up here,

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which is point one five of a millimetre, if we’re using a four millimetre beam with a one and a half inch lens,

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we should be able to have a spot size, which is 0.032, three times bigger than the wavelength of the light.

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If you divide twenty five point four by point zero three two, you’ll find that you get 800 dots per inch.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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That’s what that lens claims to be able to produce, a 0.032 dot, which is the thickness of a human hair.

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I defy anybody on any material to get anywhere near that number.

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It’s not possible. The first thing we must do is ignore these silly numbers that are given by the lens manufacturer

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and the other thing that doesn’t bear any resemblance to reality is this dimension here.

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Which is the so-called working length, the working depth.

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If you’re a photographer, you will understand what depth of field is, if you move away from the focal point by a short distance.

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The photograph will start to go out of focus,

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but it won’t be anything seriously noticeable until you get to the acceptable extent of what they call the depth of field,

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and then it becomes noticeably out of focus. Again, it’s not a number that applies to us.

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We’ve got to do our own work to find out what lenses can actually do in the way of producing a burnt dot.

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There is a sort of a little bit of a rider at the bottom here that says these numbers

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are theoretical and would require a perfect beam alignment and a perfect lens.

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Well, I’ll leave you to draw your own conclusions about whether or not these manufacturers

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are making perfect lenses because it seems to me they’re admitting that they’re not.

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If you can’t get what they claim, so this is a very interesting way in which to use a lens.

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You wouldn’t.

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In most cases, because people do not recommend it, and it’s not the way that lens has been designed, as you can see, the rays go all over the place.

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The sort of lens that you’re going to come across are typically this sort of lens here.

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It’s called a plano convex lens. And as I said, the rays are designed to come in from the curved side up flat side towards the work.

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I’m sure that most people will know or have seen the effect whereby when you put a stick in water and look at it, it appears to bend.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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That’s a physics phenomenon called refraction. And that’s what basically light does.

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When it enters into a lens, it enters into the lens and it bends, because of the angle of the face.

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And then when it leaves the lens, it bends again. Okay, so there are two refractions that take place with this lens.

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Okay. And that’s how the lens is designed and why this one doesn’t work.

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Because look, we’ve got the rays coming in straight through a flat surface, so they do not bend once here and bend again here.

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They only bend once at the curved surface.

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And you can see the result of that. Now, although it is possible with CNC machines to make all sorts of shaped lenses,

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the cheapest and simplest and oldest form of lens is this form here, which is part of a sphere, a spherical surface.

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And when you have a spherical surface, there is always a strange phenomenon associated with a spherical surface.

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You’ll see the way in which the rays cross over. They do not pass through a single point.

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And therefore, what we have here, if we track round and draw the outside profile of these rays.

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You begin to see what this wasting effect is just here.

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There is no absolute focal point. There is a sort of a a nominal focal point just here somewhere.

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It is possible to put a further correction into this lens like this.

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And this type of lens here is called a meniscus lens and the meniscus lens,

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further corrects these rays to make them coincide.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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Now they do not coincide perfectly, but we probably get something like about a 90 per cent improvement in the focal point.

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We’re going to look at the performance of your two inch lens to see what it can do in the way of producing a focal point.

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And then we’re going to change over to a special lens, which I’ve designed like this,

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which is a compound lens with a specific mix of focal points to produce a close to an ideal perfect focal point.

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Okay. Well, that might be the end of lenses for the time being, but hey, we haven’t finished with the theory yet.

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We’re trying to produce this little row dots here if we can produce this little row of dots.

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We have got photo engraving mastered. Problem is, how do we do that?

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Now you remember in an earlier session how we talked about these dots and how if you have a

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machine which switches the power on and off exactly as the controller asks you to do so,

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we shall finish up with an extra pixel burn on whatever length line we choose to burn.

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So when we have a single pixel? We’re going to get a two pixel burn for one pixel signal.

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And as we illustrated before, if you have half a pixel on each one of these single pixels,

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then you are going to fill in all the gaps and we shall just produce a straight line along here.

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Now you will remember back to one of the earlier sessions when we talked about high voltage

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power supplies and the problem with the high voltage power supply is that it is pretty slow.

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It will give you 90 percent of what you require,

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in less than or equal to one millisecond.

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That’s the specification for all glass tube power supplies.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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You can’t choose to buy something better. That’s the best that anybody’s going to be able to promise you.

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We need, a dot, which is point one.

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But anything that switches on and off instantly is going to produce this problem.

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So we’re going to get a two dot pixel, as you can see, I’ve been able to reproduce this pattern of one pixel with one dot,

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and they’re nicely spaced apart exactly as that pattern there.

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So obviously I can’t do that if I’ve got instant switching on and off of the power supply, because

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otherwise I’d have sausage shaped dots and I would have no gaps between this bottom line here.

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So we know that it is possible to achieve dots with this glass tube machine and this type of power supply.

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We can achieve dots because we’ve got something to play with and the something

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that we’ve got to play with is the response time of the power supply itself.

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Let’s just have a look what one millisecond means to us.

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254 PPI (pixels per inch).

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Remember what size pixel is that twenty five point four millimetres, which basically is one inch converted into millimetres?

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Because hey, pixels are pixels per inch, not pixels per mm.

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So here’s one inch divided by 254. It doesn’t take a math genius to work out that the answer to that is 0.1mm pixel size.

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In other words, we’re going to finish up with a pixel that is that square, 0.1. So if I

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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multiply that by ten. I get one millimeter equals ten pixels.

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Now the reason I’ve done that is because I’m going to ask you the question what sort of speed do we think we want to run at?

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You can’t just choose any old speed. Let me just, let me just choose a number I know is going to work. 100 millimetres

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a second. One millimetre is ten pixels, so if I’m doing 100 mm in a second, I’m actually doing a thousand pixels per second.

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And one second, divided by a thousand, equals one millisecond.

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So hang on. They match. So one pixel is going to take one millisecond.

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And remember what we said up here,

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the response time of the power supply: you will get 90 percent of the power that you require in less than one millisecond.

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So the power supply looks as though it’s capable of doing a thousand pulses a thousand pixels per second.

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So if we try and run this machine at 200 millimetres a second.

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We either need a power supply, which is faster than its specification or we’re going to get rubbish.

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The point is you can’t just choose numbers. You have to understand what you’re trying to achieve.

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This comes back to, as I’ve said to you before, understanding what digital imagery is.

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You can’t just do photo engraving. You have to analyse it and understand all the elements that go into it.

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Both the graphics and now the machine and the machine comprises of two very important sections.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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One of them is the ability to put pulses down. And the second one is to put pulses down the right size.

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So that’s why we talked about lenses. We haven’t finished with either of these subjects yet, but I’m just showing you how all this lot relates together.

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Now I need to remind you that although this machine, we are talking about Watts, which is this blue line, the power supply is delivering milliamps.

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It’s not delivering watts. Yeah, at first glance, this might look like a fairly complicated diagram, but it’s very simple, really.

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Let me try and explain it. First of all, across the bottom here, look, we’ve got our naught point one pixels.

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This is what the controller is looking at. This blue line is actually the signal that is turning the beam on and off.

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Yeah, I know it looks like the wrong way round, but hey that’s just electronics.

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When the signal drops to zero volts, it switches the beam on and we get a pixel burn.

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This red scale here is our working scale of milliamps.

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So that’s what we are interested in because milliamps remember, turns into watts and watts turns into burning capability.

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And here we are across the bottom, look, naught point one millimetre pixel.

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But remember, we set our naught point one millimetre pixel to one millisecond, so the milliseconds and the pixels just happened to coincide.

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If this was an RF laser or a diode laser. Then what would happen is the beam would be instructed to switch on as soon as it saw a pixel.

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And of course, remember there’s half a beam that’s hanging out the end of the pixel.

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It will then proceed across the pixel.

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And when it stops at the other end, we shall have half a beam hanging out the other side of the pixel, so we get a two pixel burn for one pixel signal.

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The glass tube machine is controlled by a high voltage power supply and the high voltage power supply.

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If you think back to some of the earlier sessions I tried to explain to, it was a rather sluggish device.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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The rapid electronics says, ah yes, I’ve detected the edge of a pixel switch on, so it instantly switches on.

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The current signal does not instantly rise. What it does, it goes up something like this.

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And we get to a 90 per cent just here.

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So if we wanted five milliamps, we’ve got to tell it to aim for, say, something like 6 milliamps.

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Okay, so it’s aiming for 6 milliamps and it gets to 5 milliamps in one millisecond.

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And what happens then is at the end of the pulse, it switches off and it switches off pretty quickly, actually.

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And maybe this is only something like 100 microseconds, about 0.1 of a millisecond to switch off.

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And then it will carry on at,

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no pixel and then it will come across another pixel, and it will repeat the same thing again and again for every pixel.

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Okay, so let’s just look at this one pixel and see what happened.

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I’m going to ask you to think back again to a previous session when we started speaking about the material properties,

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the light properties, the damage threshold for a material exposure time, power.

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Remember the candle experiment where you put your hand over the candle? The faster you move your hand over the candle, the less it hurts.

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The longer you allow the candle to hurt your hand.

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It will hurt more and more and more. That’s this thing called damage threshold.

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Every material has its own damage threshold or resistance to damage.

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Okay, so in this particular instance, I’ve chosen a material that has got something like about a three milliamp damage threshold.

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In other words, if we allow the watts above that level to start affecting the material, it will affect the material. In this first example,

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what we’ve done, we’ve exceeded the material threshold with our current flow.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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So what we shall get, we shall get an exposure time and we shall get an excess of power, more power than we need to damage the material.

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We’ve got a little damage area that looks like that. What we’ve also got is a pixel burn, which is this long.

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So we’re going to get half a beam there. And we’re going to get half a beam,

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just here. So that’s what we’re going to burn.

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We’re going to burn a pixel that looks like that, still a sausage pixel.

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Let’s consider a different option. Instead of aiming for 6 milliamps, why don’t I aim for something like about 11 milliamps, which is up here somewhere like that.

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The power supply is delivering 90 percent of your demand in one millisecond, so it won’t be a repeat of this here.

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It’ll be a completely different shaped curve because it’ll go up like this.

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Here’s our exposure time. And here’s the amount of excess power that we put into the Pixel.

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That’s created a longer pixel by going for more power.

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So what happens if we go for less power? So if we aim for about, say, two and a half or two milliamps, we should finish up with that curve.

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But hang on, that curve hasn’t exceeded the damage threshold of the material, so we will not produce a dot.

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So I hope you can get the idea that we can play with this parameter here, our power parameter to get different length dots.

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Here we’ve started to get what we want. And here we are, hardly any different to an RF or a diode laser.

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So what we’ve got to find is basically this orange line here.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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It’s just long enough. To give us a certain amount of exposure and a certain amount of power, just a little teeny weeny bit.

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And now what we’ve achieved is a virtual

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dot. So the essence of this is that you have got control over the size of the dot that you produce.

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Now what goes into these high voltage power supplies is a bit of a blackart.

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Your power supply might not be able to do this exactly. So you will have to experiment with your HV power supply with time,

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the resolution, for example, the speed, the power. To try and work out how you can get the best dot out of your machine.

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So this is the mechanism by which you’re going to get a dot rather than a sausage.

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The lens manufacturer has promised you a fifty point eight focal length lens,

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and we’ve done the calculations previously to find that this lens has got to be

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20 millimeters above the work surface to be fifty point eight focal distance.

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I’ve also got a piece of very thin card here, which is about 0.3 of a millimeter thickness.

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Now I’m purposely making it very thin so that we don’t get a hole effect.

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What we shall see is a simple hole through a very thin piece of cardboard that should be the focal point because rember

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that’s the point through which all the rays are passing. You know, I’ll change the duration of the pulse to six milliseconds.

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We’ll set this to 20 mm. Now watch carefully. You might just see a little flash on the surface.

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What I’m going to do now is to change the focal distance up and down in half millimetre increments to see if we can find out where the focal point is.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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Where is the point where we can make the smallest possible dot?

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So I’m going to do those tests and let’s go and have a look at the results under the microscope.

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So I’ve purposely got this piece of paper back illuminated so you can see through the hole.

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I’ve also got my scale on here. There are three basic things that you can identify on here; a scorch,

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Let’s call it a scorch. And then we’ve got a burn, a really dark burn just around the hole.

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And then we’ve got the hole. Remember what the lens manufacturers promised you?

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There is a focal point and a focal point, as I keep stressing,

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is that point through which all the rays pass, are all the rays passing through a single point there?

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Well, obviously the answer is no, because if they were, you would only have one hole.

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So we’re looking at the very intense centre part of the beam, a slightly less intense outer part of the beam or middle part of the beam.

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And then we’ve got this not very intense, but enough to do some damage.

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Part of the beam and bear in mind, this is only six milliseconds.

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Well, there’s our nineteen point five. It’s only vaguely scorched, but we’ve got a much bigger brown scorch mark.

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And then we’ve got a distinct hole in the center, which has not got the really, really dark halo around the outside of it.

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I would say that there still point two, right over the outside of all the scorching.

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So let’s see what happens when we get to 19mm hmm.

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The diameter is actually getting bigger there’s 0.2, so I’d say that we’re now nearly up to 0.25.

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Let’s just go down and check what eighteen point five looks like.

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So we’re getting a very confusing picture here because look, we’re getting a bigger halo around the outside, it’s slightly lighter.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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So that means we don’t have quite as much power there overall, but we’re getting a secondary burn coming back in.

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We’re getting a more of a darker halo around the center. But look at the hole size about the same as it was last time.

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So let’s go one more step to 18 and see what we get. Well, we’ve still got our 0.1 hole, nearly point three five.

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This is certainly no good for our engraving. You’re not going to see the hole in the middle.

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You’re probably going to see more of this brown stuff because that’s the color that’s going to be in your picture.

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We’re now at one millimeter below the nominal focal point.

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Well I would actually say that the hole in there is slightly smaller. That’s around about 0.09. Overal,

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a smaller dot. Set the focal point to 21 millimetres.

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I’ve now changed the machine, setting away from six milliseconds to whatever I damn well like.

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I can run this for a minute by holding my finger on the pulse. Let’s just hold it on for about five seconds.

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Zero one two three four five We’ve set this onto the supposed focal point where all the rays are passing through.

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And previously, when we had six milliseconds, we had approximately 0.2

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diameter scorch mark. What have we got now?

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A millimetre. And what’s the hole in the middle?

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Point four more or less, point three five to point four.

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I don’t call that a focal point because if it was a focal point, then it would remain as it was before.

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Very small. So we don’t stand a chance do we with our lens because this is not a very good lens for doing photo engraving work.

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It very much depends on the amount of time that you allow the beam to burn in one spot.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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Remember, this is all about exposure time and power.

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We’ve got the power fixed at 20 per cent for all these tests. We haven’t introduced speed at the moment.

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Remember, this is just power. We’re not taking into account the response time of the power supply at this moment in time.

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Here we’ve got an empty lens tube, and what we’re going to do is we’re going to put the compound lens into the end of this lens tube.

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Now, what is a compound lens?

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What we’ve got here is a meniscus with a curved face there and a curved face there, lens, and that’s a two and a half inch focal length lens.

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I’m going to drop that into the bottom there, meniscus face downwards. This is a very cheap PVBD Chinese lens one and a half inch Plano Convex.

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So we’re going to put a one and a half inch lens on top of a two and a half inch lens.

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That’s going to have a very interesting effect on the beam.

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This gauge here is marked up from 10 millimeters at this end to 12 millimeters at this end.

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But it’s a very gentle slope, and it’s marked off with divisions which allow me to set this lens accurately to within about point one of a millimetre.

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OK, so we’re going to start off with the nominal setting of 11 millimetres. So we put this back to a six millisecond pulse, right?

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So this is 11 millimetres: well I’m not going to subject you to the pain of watching me doing all these tests.

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So there is a hole that I punched through at eleven point five, so that’s half a millimetre below the focal point.

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This is nothing like the two inch lens. We’ve got,

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like a little funnel that goes into here down to the hole in the centre because it is actually burning the material away here, not scorching it.

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And that’s what ten point five looks like. In other words, we’ve got half a millimeter into the material.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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We’ve lost all power. There is no hole in the centre just by half a millimetre variation in the focal point.

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So let’s go and look what the nominal focal point looks like. We’ve got a hole

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that’s 0.07 diameter. And though it looks as though we’ve got round about 0.3 diameter brown scorch mark here.

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It’s not a brown scorch mark. What I’m going to do is change the focus now, and I’m going to focus back onto the surface of the material.

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And as I change back onto the surface of the material. You’ll note it’s got those strange characteristics

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again. This is not a scorch mark. This is a conical hole. In terms of visual appearance,

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what you’ll actually see is probably only this small spot in the middle, which is the key part of this deception of your eye and your brain.

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Because this is conical, this is going to reflect the light in a completely different way to this hole in the center,

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which is non-reflective and produces something that looks like a black spot.

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But as we’ve said before, this black spot is not a spot, it’s occlusion of light because you’ve got a hole there.

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So this is a completely different sort of burn to the one that you get with your two inch lens.

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Well, I’ve now run some tests in the background with my little dot test. I’ve got 100 millimetres a second speed with the 254 pixel resolution.

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So this is the picture that we’re actually going to run.

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And I put 20 percent power in, which is probably this power here, far too much power for the dots to be just a dot.

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So let’s have a look at the result of this, and we’re expecting to see a fairly long sausage.

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They definitely black sausages. But having said that, if you look around the outside here, you’ll see there’s this, it’s not really a halo.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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As I said, this is a depression in the material where the material has actually evaporated away.

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And what we’re left with is this black slot here, but it’s black in the middle and bit brown on the ends.

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It’s not a complete sausage. If you take a look here, it’s it’s nearly round.

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But hey, it’s still not round dot.

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And because we’ve got some speed on it, if you remember a long way back how I demonstrated to you how speed affects line width.

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Well, that’s what we got in this case here. Let’s just take a quick look at the actual dimension of the line itself.

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And we’ve got a line here that is .05 wide. Okay, so that’s only half a pixel wide, even though it’s a pixel long.

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I would say that that pixel there is around about 0.12 because we’ve got fairly large gaps on either side but they are not quite equal.

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They should be equal. What we’ve actually got there is a very thin line with a very thin sausage end.

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So we’re not, we’re not actually consuming half a pixel. When we overrun the end of the pixel, we’re only overrunning by approximately a quarter of pixel.

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So we may have lost possibly half a pixel because we’ve got such a thin burn line.

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So now I’ve doubled the speed. And my line thickness has gone down to about, let’s be generous and say that it’s 0.03 by going faster.

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I’ve created an even thinner line. But what I have done is opened up the gaps between the pixels.

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So we’ve now got 0.1 gaps and 0.1 lines, so they’re don’t round dots, but they’re at least equal now.

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They’re not very dark. But when you put those on a picture, they won’t be too bad at all.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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Now, and this is the problem that you have, trying to get the colour and get the size right. Now,

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high density fibre has got a different burning threshold to the card that we’ve just seen.

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This is 100mm a second at 20 percent power. This is equivalent to the first card picture that you saw.

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The line width now is around about maybe 0.07. So it’s a slightly wider line, so it doesn’t look like such a sausage shape.

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So I’d say, I would estimate those dots to be about zero point one three because the gaps between them are about 0.07.

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Look, this brown halo that’s around here, it’s not a halo at all.

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It’s a little sloping edge in there where the material has been evaporated away.

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And then we go into this black hole, which, if you remember, is not really black.

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It’s only just occlusion of light that’s making it black.

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So in other words, increasing the speed with 20 percent power should make the dots a little bit more spacy.

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Well, they’ve certainly got thinner. But they haven’t actually got much wider apart.

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They’re still about 0.12~0.13 dots with about 0.07 gaps.

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So let’s go really fast. OK, now this is 250mm/s.

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Now at 250mm a second.

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For those dots to be drawn separately like that means that my power supply must be running at something like about point four of a millisecond.

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Otherwise, I wouldn’t be able to turn the beam on and off.

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This is another thing that I’m pointing out to you, your power supply might not be able to do this.

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I’ve got a pretty good power supply here, which has got a better than specified response time. Now running this fast.

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You can see that we’re no longer really burning a deep hole, a very faint sort of foggy bit around the outside and the dark

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bitt in the centre there is much more of a spot.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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We’ve still got slight sausage shapes. So remember, as we get faster the amount of time and the amount of power that we’ve got to do

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the burning gets less and less and less and we get closer to a burn dot. Each material will require its own detail settings.

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But if I was doing this on HDF, then this is probably the setting I’d finish up with. But I still haven’t got 0.1

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wide pixels. My pixels, my burn dots are 0.05.

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You can get thin lines to do photo engraving and you would think that well, that means my lens is capable of producing 0.05.

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Well, it’s capable of drawing 0.05 lines because you are you are using a certain part of the beam.

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This is not the whole of the beam that you’re using here. Don’t fall into the trap of thinking that this is your spot size because it isn’t.

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Lenses are not telling you the truth, it is exactly that same setting.

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But for six milliseconds. And that’s not producing a 0.05 spot.

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It’s producing a dot there, a black dot. That is something like about 0.12.

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So that’s about two and a half times wider than the line that we’ve just drawn with exactly the same lens at exactly the same focal point.

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This focal point that they keep talking about is a bit of a joke.

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And Remember what the focal point is, it’s the point through which all the rays are passing, so that technically could be the focal point.

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Okay, let’s take that same lens. And let me do this with it.

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This is actually worse than the two inch lens when I hold on for five seconds.

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That very, very small 0.05 spot or thin line or dot that we’ve just been able to draw in the pattern comes from exactly that lens.

Transcript for Photo Laser Engraving Techniques – Making Dots (Cont…)

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We’re using this lens to do something else. It’s not focusing light rays.

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It’s focusing light intensity. The most intense rays are passing through the center.

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But if you allow those rays long enough. They would do more damage.

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This is a very complicated process, understanding lenses, and it’s taken me three years to decode it.

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But now that I have decoded it, I can demonstrate to you clearly some problems that you’re going to have.

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But I’m not going to explain how lenses work until a few sessions later on.

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The lens specification is not telling you the truth because I can demonstrate something other than what the lens manufacturer tells you.

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So that’s a whole subject for another day. But I just need you to be aware that lenses are not quite what they see.

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Photo engraving depends very much on the spot that you could produce, and that spot is very much dependent upon many things the quality of your beam,

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the speed of your power supply, the power that you’re using, the speed that you’re using and the material that you’re using.

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That’s at least five factors that go into producing a DOT.

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Who said this was simple?

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This is why many people can’t do proper photo replication because they do not understand the detailed technicalities behind what they’re doing.

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They just fiddle with the numbers and they get a reasonable result. Yes, it’s a reasonable result.

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It’s a misunderstood, reasonable result. And they don’t realize that they can get better if they did a little bit more understanding.

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Now I’m going to get down off my soapbox and we’ll finish this session. Thank you very much for your time.

Transcript for Photo Laser Engraving Techniques – Making Dots

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Last updated August 26, 2021

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