Session 23 – 3D Engraving With A CO2 Laser

Transcript for 3D Engraving With A CO2 Laser

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The Concise RDWorks Learning Lab with the Russ Sadler. Session 23: 3D Engraving.

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Now, these might be cheap Chinese machines that you have, but there are some amazing things that it can do.

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One of the amazing things we’re going to tackle today is called 3D engraving. Look, put your hand up to your face,

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touch your nose, feel your eyes, it’s 3D. That’s what we’re going to get in a piece of soft organic material like wood, acrylic,

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maybe MDF, anything that will cut, you will be able to produce a 3D image on.

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You won’t be able to do it on things like slate, stone, glass because you can’t cut those.

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You can only scratch the surface. This is a very complex subject.

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We’re going to bring many of the things that we’ve already talked about into play today,

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and I will reinforce some of the things that we’ve already learnt. Go to Google, as I’ve got shown on the screen here, and just type in 3D bitmap images.

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Now, these weird looking pictures. It’s difficult to describe some of them, waxy, ghostly?

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They’re a bit unreal, this one here has got lots of contrast in it and is ideal for me describing exactly how things work today.

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So we’re going to take this picture and I’m going to open it up in Photoshop.

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Let’s just take a look at this picture and we’ll see that it is only 72 pixels per inch.

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Now, 72 pixels per inches, is quite a coarse picture, but remember the relationship between pixels, size,

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the detail that you want in a picture. For example, if you’ve got somebody’s eye you can’t clearly define in a picture, somebody’s eye with only two pixels.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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You might need 200 or 300 pixels to clearly show the detail in somebody’s eye.

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So don’t forget some of the lessons that we’ve already learned in previous sessions.

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I’m going to change this from 72 pixels per inch, which is the standard resolution that most images are transmitted over big WWW with,

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and I can convert that to 127 pixels per each.

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Now that I happen to know is a pixel size of 0.2 millimetres.

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And I’ll tell you all about that number when we come to set up the parameters for engraving this picture.

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Now, when you look at that picture, your brain intuitively can see that as a 3D image.

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The clues in that picture somehow tell you that it is not a flat 2D drawing, even though it is.

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How does that happen? Well, this will help to explain how your brain deals with that problem.

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What we have here is something called a topographical map.

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Now the top there you see an amazing picture of my wonderful desert island home.

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I’ve got a big villa right on the top of that mountain, fantastic views. No roads,

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so I can’t drive my car there. But hey, we can all dream.

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The guy that did this map, I think, made a little bit of a mistake.

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If we look at the bottom there, it says eleven hundred and then go twelve hundred, thirteen hundred, fourteen and those are rubbish numbers.

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Let’s just assume that that bottom line there should say one hundred and then 200, 300, 400.

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Now those are meters above sea level, which is the black stuff.

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If I was to do slices through my island and that’s what the slices would look like if they were laid down onto a 2D image.

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Put it another way.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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If I had a path all the way round the island at 100 meters above sea level, the line which says one hundred is the shape of the path.

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What we’ve done is to convert a 3D image into a 2D mapping, and that’s what we see here.

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The black is the sea level, the background and the white here, is the tops of the mountains, the foreground.

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And so consequently, what we see in that picture appears to be 3D.

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Even though it’s not and that’s how our brain interprets it sees the shadows,

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the shades of grey, and it puts them into some sort of perspective view that isn’t really there.

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As I said, our brain is stupid in some ways, and incredibly clever and others. You can easily fool it.

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And here we are fooling your brain into creating a 3D image from a 2D picture.

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It is this basis of shades of grey. And remember the grayscale that we spoke about in the previous session?

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Those shades of grey are going to be used now to create a 3D image with our laser machine.

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So let’s move on to how that actually happens. And now that I’ve brought it onto full screen.

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If you take a look where my cursor is, you can see the pixels around the edge of this image.

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Let me zoom in as far as I can. Remember, those squares are 0.2mm and they are pixels.

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So every pixel on that screen has got its own coordinates. In addition to those coordinates,

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there’s another piece of information that’s stored and that is the colour of the pixel.

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Now, if we take a look around that screen, you’ll see that pixels go from black.

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If you remember the grayscale code, black equals zero to white and white equals 255.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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Every single pixel and it’s information, it’s colour information is stored in the controller, the next bit almost incomprehensible.

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You start scanning across and as it scans across like this one pixel at a time,

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it says, okay, that colour there is, I don’t know, maybe one five five 1/2 power.

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So turn the laser beam on to half power and do a burn.

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And then it moves on to the next pixel and says, well, this is a bit lighter, we’ll turn the power down a little bit, we won’t burn quite as deep.

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Now we turn the power down again and again and again. And now we start turning the power up so that it’s heavy and black, OK?

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And then we get to hear where it’s nearly white. That will turn the power off.

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We don’t want any burning at this point because it’s white.

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It does that all the way across here for every single pixel at the scan speed of maybe two or three hundred millimetres a second.

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Now, that sounds absolutely unbelievable,

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but it’s not that unbelievable when you think that the electronics is capable of responding at something like nanosecond speeds.

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Once the change of current has been decided in nanoseconds, it takes even less than that,

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almost instantaneous that the change of current to occur and the Watts output to happen.

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So it’s possible to scan very fast and get rapid, instantaneous changes of current or burn.

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There are two other problems with this process. The first one is this line here is 0.2mm wide.

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It’s scanning across one line of pixels. After it’s done its scan, it has to move down exactly one pixel.

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To the next line of pixels, so that it can come back and and do the burning on the next line of pixels, and so it goes.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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So we must ensure that when we set the parameters for this image,

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we make sure that the scanline interval or the line interval matches perfectly the resolution of the picture,

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because if we don’t, we should get a distorted image. OK, now there’s another problem.

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We’re making the assumption here that we’ve got a 0.2mm wide burn line.

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Maybe your machine can’t produce a 0.2mm burn line.

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Maybe it’s only capable of producing a 0.4mm burn line.

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In which case, you will find that you’ve got half a pixel above and half a pixel below the scanline, which is being burned.

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So when I move down a scanline, I’ve already got half a pixel burnt on that next scanline.

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And when I move down again, I should leave half a pixel burnt behind.

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So the pixel trailing behind the burn line will have a double burn,

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half a pixel from leading and half a pixel from trailing. extra burn so that pixel will get double burnt.

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And that’s going to cause a distortion in your image, it’s going to make it black, it’s going to make it deeper.

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So you must really make sure that you understand what the width of your burn line is before you attempt to do any of this sort of work.

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Now, if you remember, the width of the burn line changes rapidly with speed.

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So you need to fix the speed and determine what the width of your burn line is.

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Sadly, there’s another little problem that comes in. Although the major control of line width is speed.

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As you change the power, so the burn width changes as well. A black pixel is going to create a wider burn line than a white pixel.

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No way around that, I’m afraid you’re stuck with that one.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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OK, so I’ve imported my bitmap into the free software that comes with the Ruida controller, a program called RDWorks.

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And I shall be using this program throughout this series.

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And there are other programs that you can buy, one in particular called Lightburn,

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which is in some ways a significantly better program than RDWorks.

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But you won’t need it at the moment, when you get seriously involved with this,

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you might want to go and really investigate Lightburn, because it is an amazing piece of software, but it only does the same as this.

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Plus hundreds of extra things with knobs on. We’re going to stick to the basics and we’re Going to use RDWorks.

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Now, we’ve imported this file. If you look at the top right hand corner, you’ll notice we’ve got bitmap BMP.

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If I click on that, you’ll find that this piece of software has intelligently decided that this is a bitmap and not a vector file.

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You can’t cut or draw lines with it. You can only scan it.

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When we come down to the parameter box here and look at the processing mode, we’ve got a dropdown box which would normally give us lots of options.

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Not in this case. It says you can only scan this job.

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We’re going to play with speed when we get onto the machine itself. But for the moment, I’m just going to set that to two hundred.

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Now, there are other things that we’re going to talk about in here in a moment as well. But before we do that, I’m just going to close this box again,

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OK. Click on the picture and come up here to handle and in handle,

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we’ve got bitmap handle. OK, now we get this silly box up here, which says “Do you want to process the picture?”

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Basically, that means do you want to do any Photoshop work on it? You adjust the lightness, the colour, whatever.

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But just say no, because we’re not interested in that at the moment.

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What we’re interested in, is the simple specification to make sure that what we’ve got coming in here, matches what we thought we got coming in.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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And if we take a look at the top here, we shall see that we’ve got a resolution of 127 pixels per inch.

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We’re happy. Now, it’s important that we check that.

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Now, remember a few minutes ago, I talked about the line interval to make sure that it matches the resolution of the picture.

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This is a very important piece of information that you really ought to write down somewhere, that the line interval is in millimetres,

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but the resolution of the picture is in pixels per inch.

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PPI. Just remember this one number here, twenty five point four. Now, twenty five point four is the number of millimetres in an inch.

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So effectively what we’ve got here is one inch in millimetres divided by pixels per inch,

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twenty five point four divided by 127 seven pixels per inch.

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Do that calculation and the answer will come out to 0.2mm and

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it’s 0.2mm that you’re going to have to put into here.

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Now, we’ve talked about this before, scan mode. You’re going to leave that set to X-swing.

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And basically what that means is that you will be able to scan the picture across,

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from left to right, and it will burn a line of pixels. It will then drop down one line interval and scan back the other direction.

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Now very conveniently, I’ve set the speed here to 200 millimetres a second.

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And I’ll go back and I’ll just remind you that we did set,

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the reverse scanning interval, to match two hundred millimetres a second and I said to you, if you choose any other scanning speed,

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you will need to go back and recalibrate for the speed that you are using.

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Remember how I said to you, the machine has the ability to change its power to match the colour of the pixels.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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This is how we make it perform that trick. We tick the output direct box.

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Now, we’re going to come onto a rather difficult and complex subject. Now, in the previous line drawing section.

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We used minimum power. To limit the power against velocity as we drove the line into a sharp corner.

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To stop it from over burning in the corners. Now I’ve set Max and Min power to 05 and 80 per cent for this particular application.

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But because I have got this output direct box up here ticked.

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The way in which it operated previously in line drawing is no longer valid.

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These two numbers have got completely different meanings for 3D engraving.

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What I’d like you to imagine is, that, that box there is white and that box there, Max, is black.

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When we scan across here, we come across a white pixel.

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The controller will send a five percent power requirement to the tube.

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And it will draw a very light pixel, and when it comes across a black pixel,

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it says, OK, wind the power up to 80 percent because I want a lot of burning.

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The grayscale code is zero to two five five, two hundred fifty six steps.

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This five represents white, which is two five five.

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And this 80 represents black, which is zero.

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So between eighty and five. The controller is dividing this interval into two hundred and fifty six discrete steps of power.

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If I change this down to 60 percent, it’ll change that range to two hundred and fifty six steps of power.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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That’s the way in which the machine uses these two numbers.

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If you just use the Max / Min, as I’ve specified, you’ll be absolutely amazed at the 3D ness of the image that you can produce.

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But I’ll ask you to go and look at my other channel, RDWorks learning Lab, number 126 &127,

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which deal with this subject in a slightly more analytical way. And one of the things

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that you’ll find out is this; the output from the laser in terms of Watts is not linear.

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So when you specify that you’d like five percent power and here we are down at the bottom of this graph here where my cursor is, at five per cent power.

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We’re not probably going to get anything out of the tube at all. When we get to 80 percent,

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you can see there is not a straight line between that point there where my cursor is,

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and zero. So we’ve got a very non-linear type of burning

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that’s going to take place. Because the Watts output is not related to the percent power, it’s not linear.

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You’re going to get a distorted image, unless you do something like that.

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And then what we do, we completely rework the system to find out how much distortion is required to keep the power at a constant level.

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Now, we can’t change the power of the machine. Within Photoshop,

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we have the ability in something called Curve’s to reset the relationship for these colours, if

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the mid-greys are going to over burn, because we’ve got a lot more power in the mid-greys.

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What we can do, we can make the mid-greys slightly lighter, so that they do not burn as much.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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Taking the data that I’ve just constructed in that graph, as you can see, look, I have input eight percent and I’m expecting five percent output.

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And what that will do eventually, it’ll produce a distorted image.

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So I’m going to step back and look at the way in which the white changes when I remove this colour offset.

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Do you see what I mean? What I’ve done, I have artificially lightened parts of the picture.

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So that it doesn’t burn as deeply and this offsets the non-linear power that I’m getting from the tube.

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This is why I’m saying, I’m not going to touch this in this video.

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You need to go and look at RDWorks Learning Lab 126 & 127 for a lot more data on this subject.

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Now we’ve got yet another and I hope, final level of complexity that you need to understand about 3D

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engraving. And that’s the way in which your tube works, how it switches on and off.

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As I mentioned to you when we talked about the power supply and I talked about it a little bit earlier in this session.

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Switching the tube on could take a millisecond. Once the tube is switched on,

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the control of the electronics, which is making the current flow, is happening at a billionth of a second speeds.

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So switching between different pixels to different colours is not a problem for the electronics.

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It’s not a problem either for the light speed changes that happen within the tube.

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So go back to the beginning of that sentence and let’s just restate it takes maybe up to a millisecond to switch the tube on.

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We can’t have a millisecond switch on, after we’ve reached a white pixel.

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By that time, we may well have missed another eight or 10 or 15 or 20 pixels.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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It’s taking that long to switch the tube back on after it has switched off.

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And it switches off when it sees white two five five, if we take a look at this levels picture,

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you’ll see that it runs output levels zero to two five five.

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OK, so there’s something here which is black, lots of it, as you can see,

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and quite a lot of fairly light and a little bit of white right up at this top end here. At certain points in here,

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white is going to switch the tube off and causes a problem.

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But what we can do, we can again distort this picture very slightly, very slightly by changing this number from, say, 255 output levels,

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To 250 and 250 is not white. 250 is very, very nearly white.

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So much so that you won’t notice the difference, but what it does mean is, the tube will never get an instruction to turn off.

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So that’s our goal by setting 250.

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We do not want the tube to switch off because as soon as it switches off, it loses its performance, its speed just for the hell of it.

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I’m going to set the numbers to 10 and 50.

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Any two numbers will work. It’s just that they might not be the best numbers.

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So we’ve basically now got our parameters set. So we’ve got a range of burning for our grayscale.

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We’ve got speed, which is constant. We’ve got a step which matches the bitmap resolution and we’ve ticked our output

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direct box. So we’ve now spoken about all the principles and problems associated with 3D engraving.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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I’m going to give you a quick demonstration on this material, which is Bamboo. One of the worst possible materials you could ever use for 3D engraving.

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I did say that all these colored strips in this material represent a different type of wood. The molecular structure

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of all these strips is completely different, which means they will have completely different cutting characteristics.

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Now I’ve change the parameters away from what we spoke about in the office very slightly, five millimetres, a second minimum.

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So we get virtually zero cut because this beam will hardly fire at five millimetres a second.

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But remember, it’s not the firing of the beam that causes

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the problem. It’s the switching on and off, the switching on and off of the beam is controlled by white.

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And there is no white in this picture because we’ve changed away all the white to nearly white at colour 250.

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So I’m going to do two things. Remember the lessons that we learned from previous engraving?

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We don’t want to cut. We want to mark the surface.

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We want a little bit of depth. But we don’t want serious burning. All right.

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So I’m going to set this up for 25mm.

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Remember the manufacturers gap here, specification that we’ve been using is 20mm.

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I’ve raised the focus up by five millimetres. We’ve got an extra window here which allows me to select the number of passes.

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This is not a one hit job. I suspect it’s going to take at least six passes probably to do, to get some 3D ness into this, some moderate 3D ness into this.

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It might require eight or even ten, but we’ll carry on with six. 5.0 and 95, 0.2mm increment.

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First of all, I’ve got my engraving nozzle in here, so I’ve got plenty of gap between the work to allow the smoke to come upwards.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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And I’ve got just a small amount of, hmm too much,

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just a small amount of air assist on there to protect the lens, because I want

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the smoke to come up and be drawn away before it gets blown down onto the job.

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Bamboo material is very sticky with its debris, very sticky.

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OK, now I’m going to put the extraction on. What we really want to see, is cutting without burning. I would estimate

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we’ve got probably half to three quarters of a mill cut going into that job.

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So six cuts will get us to four millimetres. There’s our 3D engraving. Not bad,

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as you can see. Let’s take a little bit of a closer look and you’ll see that,

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just here. This black wood, that all the joints look, can you see all these joints? They just haven’t machined away.

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That’s the glue and this dark wood here. Has machined away a lot more than this wood. This would here is quite hard.

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The darker the wood, the more it’s machined away. It’s a pretty abysmal wood for this sort of work. You can see the 3D

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ness, it’s worked perfectly well. Let’s try another wood. Now here

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I’ve got a piece of Poplar plywood. We’ll use the same settings.

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But before we use the settings who just test to make sure that we’re not getting too much burn, we want to remove material without burning.

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So sentenced to 25 mm. We’ll go over to one corner squares a softer wood.

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I’m going to set the parameters this time to 90 percent power and 400 millimetres a second.

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Again, we’ve got 0.2mm because remember we’re set to 127 ppi.

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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That’s not bad, we’ve removed about a millimetre in one pass, six passes is going to take us about six millimetres deep. That’s a

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more even 3D replication. We’ll try it on one more wood, which is a uniform wood, but it has got a grain in it.

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And we’ll see the effect that, that has on a slightly harder wood than this. I’m led to believe that this is a piece of maple.

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We’ll try the same sort of settings again, 25mm gap, so we’re 5mm above the focal point.

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Four hundred millimeters a second. Ninety five per cent power.

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Oh, that’s not bad at all. We’ll drop down to three hundred maybe and see if we get a little bit more depth without changing the colour. You can see

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it’s still not badly burnt. It’s a little bit darker, but that’s not bad at all.

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I think as you see this go on, you’ll see that the grain that’s in this Maple,

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will stand out in the same way that the glue lines stood out in the bamboo. Now,

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there is no point in me going on with that because, look, you can clearly see how the grain is doing exactly as I said it would.

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So you’ve got to choose the right material to do this job with.

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This is a piece of acrylic. And I purposely left the film on the surface so that you can see those areas which are not being engraved.

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I suspect after several passes, most of that white will have disappeared. So in the background there you can see the beam, the pink

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beam and you’ll see it switching on and off just at the end of the stroke.

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And now it’s starting to run across the shape.

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And as it runs across the shape, you can see the intensity of the beam changing rapidly as it’s trying to keep,

Transcript for 3D Engraving With A CO2 Laser (Cont…)

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as it’s trying to change power as it runs across every single pixel.

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For this last cut, what I’m going to do.

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I’m going to take the take the beam up by at least 10 mill, like that, out of focus and I’ve also dropped the power (SPEED) to 200 millimetres a second.

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So it’s out of focus. It’s adding more heat slowly.

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I’m trying to exploit one of the properties of acrylic, and that is that it has a melt phase at one hundred and sixty degrees C, it turns to liquid.

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So what I’m trying to do is just heat and melt the surface of the material rather than vaporize it.

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I’m attempting to put a polish on the job for the final pass.

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Obviously, acrylic is a nice uniform material that’s absolutely ideal for doing this sort of 3D work.

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Well, here we are at the end of a very, very complex subject,

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which I hope, we’ve managed to cram into just over half an hour with the aid of additional learning from my RDWorks Learning Labs.

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You’ve been through the problems with the materials now. I’ve got here the nozzle, it’s nicely caked with all sorts of stuff.

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The fumes that have shot up. You’ll need to clean that from time to time with acetone. Look,

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we’ve only had a very small amount of air, passing through here all the time and assure you that Lens is as clean now as it was when it started.

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It doesn’t require too much airflow to keep that lens clean. Even though there’s a small amount of debris that’s gone up inside the nozzle there.

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It hasn’t gone up as far as the lens and caked the lens.

Transcript for 3D Engraving With A CO2 Laser