Session 27 – Laser Engrave Photo Replication Part 2 – Burning an Image

The Concise RDWorks Learning Lab Series

Welcome to Session 27 of the new Concise RDWorks Learning Lab Series with Russ Sadler. So lets learn some great new techniques for how to laser engrave photo replication.

In this Session, Russ continues the Photo Replication theme and explains how to burn the image based on the “One Pixel equals one dot” process. Reverse compensation settings are a vital component of this process and Russ explains what they are and how to set them up. He also introduces his home made A4 vacuum table for precise levelling of the work piece.

Release Date: 14th 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.

Laser Engrave Photo Replication: Improving the Fox Engraving
Laser Engrave Photo Replication: Improving the Fox Engraving

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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Session 27 – Photo Replication Part 2 – Burning an Image

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Session 27 – Laser Engrave Photo Replication Part 2 – Burning an Image

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Transcript for Laser Engrave Photo Replication – Burning An Image

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Transcript for Laser Engrave Photo Replication – Burning An Image

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The Concise RDworks Learning Lab with Russ Sadler Session 27.

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Photo replication Part 2 -Burning an Image.

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Now we used this image in the grayscale photo engraving.

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As you noticed, it didn’t come out very well. We lost all this detail down the side.

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We’ve got very dark nostrils and lovely, crisp eyes.

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That’s what we’re looking for. We’re trying to get photo replication, not what most people call photo engraving.

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Photo replication basically means one dot from your laser equals one pixel, as shown on the screen.

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This is a coloured image with all sorts of tones in it, which is totally unsuitable for us to use.

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Now I’m using Photoshop here, but most people won’t have Photoshop.

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There is a very good, free piece of software that’s available that you can use.

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I haven’t become an expert in it because I don’t need to. I’ve been using this stuff for so many years, and you can’t teach an old dog new tricks.

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But if you’re new to this technology, then go and find online a free program called Gimp.

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It’s equally as powerful as Photoshop, but you’ll have to learn it.

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Things will be slightly different than what I’m showing you here, but all the things that I’m showing you are available in GIMP.

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The first thing I’m going to do is take a look at this photo and look at its properties.

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So look, it’s twenty six point eight million pixels and the size is 24 centimeters by 27 centimeters.

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That’s a bit big for us, so we’re going to put this onto a piece of A4 material.

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Now that material could be card or it could be Baltic birch plywood.

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This picture is too big, and also it’s shown at a resolution of 300 pixels per inch.

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Now, we can’t deal with 300 pixels per inch.

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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It’s got to be maximum 254 pixels per inch, which is a dot size of 0.1 of a millimeter.

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Now we’ll talk more about how we achieve that size, short;y, but let’s think about preparing the picture to start with.

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When you want to create a picture of a different size, we first of all, have to go and produce a new frame.

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A new picture, 210 depth or height, 297 that’s A4.

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And we’ll make the resolution 254 and we’ll put it onto transparent pixels.

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So there’s our piece of A4 material that we’re going to put this images onto.

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So I’m now going to make sure that I go up to the top here where it says show transfer motion controls.

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We need that box ticked. First of all, choose this arrow here.

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Click, we’re going click in this original image, click.

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We’re going to drag that image across to here. Now can you see how that black box has just appeared?

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Look.

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That means I’ve pulled my picture across there, and if I let go of the mouse button now, the picture appears, I can now move this picture around.

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And as you can see, it doesn’t really fit on there. I’m going to use control minus key and what that’s going to do.

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It’s going to bring the original picture frame, as you can see here with the Corner Dots in to view.

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Hold down the shift key. Hold one of the corners. Keep the proportions correct.

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So let’s shrink it just a little bit more with the shift key on this corner.

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Well, we may as well make it a comfortable fit on A4. This is still 254 PPI pixels per inch.

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There is a very important lesson here about sizing something. So I’ve shrunk that image right down.

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It’s still a 254 PPI image, so now I’m going to expand that, control + and zoom in and we’ll look at that little white

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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Highlight in the eye. One, two, three, four, five, six, seven pixels across there.

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Right. So there’s my original picture back. Yeah, we’ll just shrink that again.

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This is a much larger picture. So what we’ll do this time is we’ll go and have a look. So instead of seven pixels defining that shape.

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We’ve now got about eighteen pixels defining that shape.

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So we’ve got, we’re using a lot more pixels to actually define each object, which means we get a better resolution.

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So the golden rule here is keep your picture as big as you can,

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because that way you’ll have the maximum number of pixels defining each element of your picture.

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So we’ll get a much better quality picture if we’ve got 18 pixels defining that

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little highlight as opposed to seven pixels defining that little highlight.

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OK, now we don’t need the original picture now, so we don’t mess around with the original picture.

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We should just get rid of that. We can’t use color. So we’ve got to go to image / mode /

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Grayscale. It says Merge. Get rid of the layers. Yeah, OK, but we still can’t work with that image.

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Go to image / mode / bitmap. Now it’s not called bitmap on gimp.

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It’s called something else.

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And I can’t remember what. If you have any doubts, just do a help and search for Floyd Steinberg because that is the algorithm, as they call it,

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that is used to decode this grayscale image and convert it into a series of dots of varying density patches that simulate this grayscale. In Photoshop,

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they call it diffusion dither, that is, in effect, the fluid Steinberg algorithm.

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Now, as I said to you before, when you saw this, it looks as though we’ve destroyed the picture.

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What’s happened here is we’ve got pixels on my monitor and pixels in the picture, which only coincide in certain places.

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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If I change the size of the picture with control minus.

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I’ve only got to step it one, but if I go this way that what we’ve produced now is a whole series of black and white pixels.

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There’s no gray in there at all. We can now print black dots on a white background.

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We’ve now brought it down to something that we can handle. But if we go control minus.

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It looks exactly the same as the grayscale image. Our eyes are totally incapable of seeing the small single dots.

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What it does, it just sees the pattern and the density of the dots, and it converts it into a pseudo grayscale.

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We can’t see any difference between this and the grayscale image.

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If we can copy every one of those dots, we don’t need to do any enhancement on that picture.

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If we can’t copy those dots, we should get over burning. And we shall get a much darker picture than that one.

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So this is what I call photo replication and not photo engraving.

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So we are now going to save this image. Here,

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you’ll see it’s currently shown as a Photoshop image. We don’t want that.

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We want to change that into a bitmap. It says the depth is one bit, i.e. just black and white.

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Now, as I mentioned earlier in this session, I’m going to be using RDWorks as my piece of base software because that’s the piece of

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software that you will receive free with your Ruida controller when you get your machine.

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Now, if you don’t have a Ruida controller, I would advise you to almost immediately go and download and pay for a piece of software called Lightburn.

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You can download it and get a 30 day free trial, this is a much more fully featured version of RDWorks.

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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For today we’re going to be using this machine.

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It’s only recently arrived, but six or seven years ago when I first, when I bought my first Chinese laser machine.

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After about six years of gradual development, I finished up with a machine that was very similar to this.

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The guys at CloudRay in China decided that they would like to be able to sell a machine already pimped up.

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It’s got many extra features on it that I didn’t have on my machine that Cloudray have included.

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So today we’re going to do two things. We’re sort of going to be testing this machine and demonstrating photo engraving at the same time.

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Now one of the problems with these machines,

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because they’re belt driven when you drive them in one direction and then turn around and drive them in the other direction,

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there is a minor offset between the two scan positions because of various mechanical problems.

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But fortunately, the software allows you to fix that problem.

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Config sys; We’ve got something called optimize scanning reverse offset.

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So this is a compensation that allows us to fix that problem.

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But you have to calibrate this for every single speed that you want to use for engraving.

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So generally, you try and use maybe 100, 200, 300, 400.

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You only use nice even numbers and then you’ve only got to build a table in here of maybe

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four values and that will cover all the engraving you ever need to do. With photo engraving,

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it is most important that you get this calibration right. Because you don’t want dots in one direction, mismatching the dots in the other direction.

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And so we do add, I think we’re going to run this around about 200mm a second.

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So we’ll set a calibration for 200 and we’ll set a reverse compensation at the moment to zero.

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What we now got to do is test with a small, and I use a 15 millimetre square. We’re going to run this at 200, scan and 25 power. For scan mode,

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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you want x swing. Now X-swing means you’re going to go, engrave, engrave, engrave. If you do x-unilateral go engrave, engrave, engrave.

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I’m going to set the interval,

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which is the gap between the scan lines at point five because I want a big gap between the scan lines and you’ll understand why

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when you see the test. Now here, I’ve got a very short nozzle, which has actually got two lenses built into it.

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You can remove this screw and there are two lenses in there. And this is called a compound lens, which you can buy from Cloudray,

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It’s a compound lens kit, and it’s specifically designed for producing very, very small dots for photo engraving.

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All we need to do is just screw that into a lens, tube.

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This has got a focal distance of around about ten point five to 11 millimeters.

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There isn’t such a thing as a fixed focal length with a lens. Mechanically,

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the lens is designed with a fixed focal length. But for performance purposes,

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the focal length can change as you change the speed or the power, or the material. We’ll come on to all that sort of stuff in a much later session.

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What we’re also going to be using here is my latest design air assist nozzle.

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In the past, I’ve said that for engraving, we don’t need any air assist.

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What we’re doing is we’re really putting a very small amount of air into a nozzle to just protect it from fumes going back and hitting the lens.

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Well, in this case, what we’re going to be using is full power air assist, which is blowing across the orifice to keep the smoke away.

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This has two effects. Not only does this keep the smoke away from the lens,

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it also makes sure that we’re not blowing any fumes back down onto the work, no matter how low the flow is.

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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We’ve still got a small airflow that’s passing back down onto the work, and this bypasses that problem.

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We just swapped this lens over. Here we go.

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That’s now fully connected up, and I can bypass the air assist on this machine and I can turn it on manually.

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You will hear what I mean. So when I turn the air assist on, it means I’m doing something.

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And so consequently, the fan also turns on at the same time as the Air Assist.

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Now I’ve turned on the air assist off, and after about 10 seconds, you’ll hear that the fan stops as well.

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So I don’t have to keep remembering to turn the fan off when I’m not using the machine. The fan goes dead.

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One of the key things about photo engraving and using a very short focal length lens is you have to be very, very accurate with the focal point.

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And so consequently, I’ve got this device here, which is basically a vacuum table.

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It’s basically a flat surface with three location feet on it one two three.

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And those three location feet means that I can adjust this to be absolutely perfectly

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level; uniform distance away from the nozzle at all points on this surface.

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These fans run off a 24 volt power supply, and they’re now working.

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And, you can see that sucks,

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a piece of card down very nicely flat. What I’ve got here is a slope gauge which runs from 10 millimetres to 12 millimetres and 11 is in the middle,

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which is norminally somewhere between 10 and a half, and 11 is the focal point for this lens.

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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So if I drive to there and set the height of that nozzle, just let it drop down onto the gauge; 11 millimetres.

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What’ll happen is now, that might be low. That might be high.

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It doesn’t matter because those two will change as I adjust the two at the front, so I can now adjust this front corner to bring it up onto the gauge.

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And that’s a little bit on the low side, so we need to drop that down little by little.

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So we did about 0.1 of a millimetre. That whole table surface is now flat, so we’ve got two tests to carry out before we can even do any photo engraving.

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The first test is this scanning offset. Ideally, what we’re looking for.

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We’re looking for the beginning of all of these lines to line up perfectly.

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But if we look down this side here, you’ll see that there are bits that are sticking out.

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So lines two and four are hanging out and line three is in. And we’ll double click on two hundred, double click and that will bring that live again.

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And we’re going to put some reverse compensation in there. Let’s put point zero five, 0.05 of a millimetre.

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Not a lot. Well, I think we’re going the right way because, look, we’ve nearly corrected the error, so maybe I ought to go 0.06.

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So we went the right way. We just didn’t quite put the right number in.

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Now I’m going to look at this through my eye glass because I think it’s looking pretty good.

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You’re not going to believe this, but that 0.01 has made it go the other way by as much as this one was this way.

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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So it’s got to go 0.055 and that is just about spot on. Something we’ve talked about a few times before.

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Those lines look nice and black. But let me just twist this. Can you see them going pale brown now?

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They’re not black lines at all. They’re brown lines that are very deep.

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So you need to be very careful when you look at colours because they can be very deceptive.

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Light plays all sorts of tricks with you. We’ve now got the machine set correctly to do photo engraving.

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Well, not quite. We’ve got another test that we’ve got to do. And that’s my little dot test. We’ve just calibrated this machine for 200mm a second.

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We can’t use 400 millimeters a second for the DOT test if we’ve calibrated the machine for 200.

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Now I’ve got to set the parameters for this test to make sure that they are at 200mm a second.

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So I’ll just run the test very quickly three times 14, 15,

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16 percent. We’ll just do one more 17 percent and see what results we get. The test takes maybe two seconds at the most.

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Normally, I’ll examine this with just an eyeglass like this,

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and I can determine whether or not my dots are roughly the right size along that bottom line. The one that looks the best,

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is around about 12 percent power.

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It is the weakest, but it’s only the weakest on this very small test here because they’re single dots. When you see the whole pattern of dots

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you’ll be surprised at how dark it can get. We’ve imported our file.

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You can see that this is the dot file black and white dots.

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OK? It’s not what it looks like a grayscale.

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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I’ve specified this to run at 200 millimetres a second, the head will run across the picture at 200 millimetres a second.

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But it can’t instantly stop at this point here and go back 200mm a second.

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It has to slow down from 200mm a second to zero.

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Turn around, accelerate back up to 200 millimetres a second.

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Do a scan, turn off, slow down, stop and come back again.

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So there is a dead time at the end of each one of these scan cycles,

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and the amount of time that’s wasted at the end is directly related to the acceleration of the head.

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Now, I’ve got no idea how they’ve set this machine up at the moment,

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but that acceleration time at the beginning and end represents wasted cycle time.

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And here we’re going to be going. Scan scans scan scan and we’re going a fixed increment on every scan – 0.1mm. Scan speed 200,

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and now we’re going to set our power to what we’ve just established, which is 14.

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OK. There’s a lot of point ones when we go down the picture this way.

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So that means we’re going to get a lot of dead times at the end of every one of those 0.1’s.

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If I grab hold of that picture and I go to here and I put 90 degrees in there, I’ll flip the picture around.

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That means I’ve got a long stroke at 200mm a second. I’ve got the same amount of dead time at each end, but I’ve got a lot less scan lines down here.

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So it’ll take a lot less time to scan the picture this way than it will when it’s turned up the other way.

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So in terms of cycle time efficiency, that’s a little trick to always remember.

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Now, another little trick that you must remember is this. If you look here,

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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the Green Dot tells you where the head is going to start and it’s going to start

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at the top here and it’s going to work its way down the picture like that. Well, when we create, when we create these dots,

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we’re going to create little puffs of smoke and that smoke is going to get drawn towards the back of the machine?

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We don’t really want to produce a nice picture like this and have smoke passing over it.

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So what we do will change the start position for the head to the bottom.

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And I like to put it in the bottom at the middle. So we’ll show you where to do that: config / system setting.

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And we can change it here, laser head. So we click that to there.

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And so now if we look, we find our Green Dot is now down here.

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So that’s where our head will start.

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And that means that we will now pass up the machine, producing smoke, going this way and leaving behind a nice, clear picture.

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One final issue to think about, is this. This machine cannot walk and talk at the same time.

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This is a very complicated picture which is going to take maybe two, one or two minutes to download into the machine.

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Now, if I press this start button here, what’ll happen is it will be downloading the program and trying to run the machine at the same time.

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Bad news. Anything that’s a complicated program like this, you’ve got two choices.

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You can either download it into the machine first and then run it from the machine and you’ll be OK, or you can still run it from

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here as a temporary file. But what you need to do is this.

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I’m just going to show you on this piece of scrap paper here. So there we are, we’re roughly in the middle of the page, OK?

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And we’ll press our origin button now, and that will be where we’re going to start.

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I’m going to press the start

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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button on the PC, and as soon as this head starts to move, I’m going to press the pause button, the green start pause button on this machine. There we go.

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At that point, what I’ve done, I’ve stopped the machine from running, and it’s busy downloading the program.

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The PC tells me when it’s there, and it’s now there. So I can now release the green button again and we can carry on.

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It might not look as though it’s doing much because there’s all sorts of very, very faint dots in the picture.

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But if you take a look here, you’ll see that we’re starting to generate part of the ear.

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OK, now that foxy picture has now downloaded temporarily into the machine as a temp file. If I

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press pause. It’ll pause the program, if I now press escape it completely stops and restarts the program.

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I don’t have to download that program again because it’s still in the temporary file.

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I can just press start again and it will run exactly the same program again.

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If you change the parameters on your PC, you’ll have to download the file again.

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You can listen in here. That we’ve got lots of air assist going on there I’ve got full air assist blowing across that jet because it’s

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not blowing down onto the work it’ss blowing across the work and taking the smoke backwards.

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And at the same time, it’s blowing right across the mouth of the nozzle, so there’s no smoke or fumes going back up into the nozzle.

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OK, with our new sheet of paper in there, we’ll just leave that cooking. That’s a classic example of what I call photo replication.

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This is not photo engraving, anybody else’s photo engraving will lose a lot of the detail that’s in there.

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Look at the subtleness here. We’ve got the shadow on the top of the nose, the shininess on the top of the nose, which we can see in the original.

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If we look carefully, we look at the dark nostrils.

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That are contrasting with the rest of the nose, which is still black, but it’s a slightly subtle shade of black.

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The eyes you can see the glaze, that glassiness in the eyes.

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You can almost count the hairs in the ears here. We are only able to achieve this because we’re copying every pixel with a dot.

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Now I’m just offering these up for comparison, because I did take the one that we did with grayscale engraving,

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and this is the one done with dithered engraving. You can see the difference immediately.

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Now the problem is, as you can see, that both of these pieces of card are sepia coloured.

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We can only produce one colour of dot and that dot is brown.

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And as I also pointed out to you at the beginning of the session,

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you mustn’t be fooled by black dots or black lines because they’re black when you hold them to the light in a certain direction.

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Because they’re so deep, there’s no light in the bottom of the groove that’s illuminating it.

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Therefore, it looks black. It’s a black hole. So don’t be fooled by that.

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I’ve recently been experimenting with a new technique which, as I said, I didn’t discover it,

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but I have done investigation into it to try and find out exactly how the system works.

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And that’s really not for this session. But what I will do is just demonstrate for you something that’s pretty amazing.

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And look at that dark brown, not black, quite, but again, look at the quality of that picture.

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You can see all the detail in the eyes. You can see the shiny marks on the nose and you can see the nostrils, the colored black on the nostrils.

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Very, very clearly. There is so much more definition in this picture.

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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What have I done to make that dark brown like that?

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So I’ve dissolved some Borax into water and painted it onto the surface of the card, that’s completely changed the characteristics of the burn.

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Now I understand what I’ve done with Borax, the chemical change that I’ve made to the surface.

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We’re not going to go into that at the moment.

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We’ll deal with that in a completely separate session at some stage in the future and down at this bottom corner here,

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you won’t really be able to see it. But remember what I said? Whenever you change the material, you’ll have to change the settings.

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I had to do a little dot test down here to make sure I got the settings of the focus right.

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It’s already a very, very nice picture,

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but I could just add maybe another one percent power to it to get a little bit of extra definition definition into it,

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a little bit of extra colour into it. But adding power, this is important.

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Adding power is not necessarily always the way to make the picture darker or lighter,

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because usually you finish up with a very dark picture and you want it lighter.

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Well, if you want it lighter, you have to ask yourself the question Why is it dark?

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It’s not dark because you’ve made the dots darker, because as I’ve just explained to you the dots are the colour they are.

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You can’t make them any darker. You can make them deeper and blacker. But as you make them deeper, they will get bigger.

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There’s the clue, bigger. Your dots are too big and therefore you’re over burning the dots one on top of the other.

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They don’t comply with the basic requirement of one dot equals one pixel.

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If you’ve got one and a half dots equals one pixel, you’ll get over burning and it means you cannot produce a picture at 254 PPI.

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You’ve got to reduce the PPI on your image to make the picture lighter.

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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So from maybe two hundred and fifty four, you might have to go back to 180 or 160.

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The other way to do it is what other people do, which is to go into Photoshop,

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make the picture lighter so that when you turn it into a dithered image, you get less, you get less dots and bigger gaps between the dots.

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That’s not photo replication. That’s cheating. This is exactly what you see one dot, one pixel.

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I didn’t modify this picture at all. Now here’s that same image done on a piece of bolted birch plywood.

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Again, I had to set the parameters down here. As you can see, there’s a little dot tests done here.

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I had to set the parameters, but it’s come out much, much better.

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Maybe a little bit on the dark side because you can’t quite see the the detail in the eyes.

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The focus is very slightly wrong and my dots are just marginally to big, marginally too big makes them blacker in the black areas.

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The whole purpose of my instructions and not to tell you exactly what to do, I’m showing you the techniques.

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I cannot give you numbers that suit your machine because your machine will be different than mine.

Transcript for Laser Engrave Photo Replication – Burning An Image (Cont…)

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Last updated August 26, 2021

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