Session 16 – Perfect Laser Beam Alignment Procedure

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The Concise RDWorks Learning Lab with Rudd Sadler. Session 16: Perfect Laser Beam Alignment guide.

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Now today, we’re going to look at mirrors. But we already looked at mirrors in the first session.

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Yeah, we looked at the mirrors themselves and personally, it offends me when I look in the mirror because I’m not as handsome as I think I should be.

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But in this case, what we’re trying to do is we’re trying to conduct the laser beam that we spoke about last time around the machine,

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and to do that, we have to use mirrors.

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But the problem is that most people really struggle to set their mirrors to get the laser beam aligned correctly.

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Now there are hundreds of videos out there on YouTube which purport to tell you how to set your beam.

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They go through the very simple steps and procedures, but they don’t explain why you are doing it and what you’re trying to achieve.

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Now, my goal is to try and explain to you exactly how you set your beam, why you’re doing it in the way that you’re doing it.

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There are a set of logical steps that you will follow and it guarantees that you will finish up with a perfectly set laser beam.

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This is where the dodgy diagrams come in. It’s much easier to exaggerate the situation and show you what’s going on with a diagram,

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because in reality, the errors that you are going to see me talk about are very small and you might not even notice them.

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One of the important things about mirrors is the way in which they’re mounted.

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Because the way in which they’re mounted has a significant effect on the ease with which you can adjust the beam.

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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There are basically two types of mirror holder.

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We’ve got this type here where you can see the three brass adjusting screws are set in the form of an L shape.

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And then we’ve got this weird looking arrangement here, which was on my original machine.

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I did all sorts of things to try and make this thing work.

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And it didn’t, one day it frustrated the hell out of me so much that I just ripped it off

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and replaced it with my own acrylic homemade version. With this triangular adjustment arrangement,

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you not only get X adjustment when you adjust one of these.

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You also get Z adjustment, height adjustment as well.

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With this system here, we’ve got a very simple adjustment, which is either vertical adjustment like this as we adjust that pin, which is about here.

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Or we’ve got horizontal adjustment in this plane, we adjust this screw here and we get pivoting about that plane there.

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Now we’ve gotmirror A and mirror B, I’m not going to call them one,

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two and three because these are going to change their personality as we work our way around the machine.

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Here’s our laser beam and the laser beam comes out of the tube.

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And the ideal setting for that mirror is to have the laser beam hit

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right in the center of the mirror.

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So that is the easiest mirror to set up because we’ve only got to adjust the laser beam to fire at the center of the mirror.

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Now, it does not matter whether the laser beam is like this or like this or like this or like that. Provided it strikes the middle of the mirror,

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the mirror has got full 360 degree tilt on it, so that you can adjust the error of the laser beam out before it runs down this axis here.

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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That’s the whole point of having the mirror completely adjustable and flexible.

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The very first thing you should do is to wind these locking screws back, because to be honest.

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They’re just nothing but a pain. People spend a great deal of time messing around with these locking screws,

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thinking that locking them up is going to make their beam last and be stable forever.

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Well, yeah, it would. But the problem is, as soon as you lock up, you adjust the mirror.

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These springs on the back here are automatically clamping this and acting like an anti vibration system.

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So you don’t need these locking screws.

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So what I suggest you do before you even start, is to run around your mirror and set something like a two millimeter gap everywhere.

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Right on each corner and you can see that that’s not true there, so you can adjust that until it looks about level.

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The only reason I’m saying two millimeters is because you want to float on your mirror.

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Now, the only thing that I will point out to you is: do not

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adjust that corner one. Regard this like a door. Here, we’ve got two pivot points, two hinges.

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If we adjust this one, it’s going to make the mirror adjust in this plane about these two pivot points here.

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Equally well, when you want to adjust the beam up and down. They become the pivot points and you’re only going to adjust this one,

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so there are no circumstances existing, that really means you need to adjust this one.

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Well, depending on how that beam approaches that mirror, you’ve got to compensate for it.

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Because what we’re really trying to achieve, we’re trying to achieve that laser beam running

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absolutely true to this bearing rail in both the vertical plane when you look down upon it and in the horizontal plane when you look at it sideways.

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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So we’ve got to set that up so that this beam is adjusted in this direction and this direction,

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to hit the center of this mirror here. Instead of on center I’mre going to set it off center here.

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Now, this is not the right place for it, but this is going to show you the mechanism by which we’re going to adjust the whole system.

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OK, now, just because I’ve moved it off the center doesn’t mean I’ve changed anything.

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This is still going to perform in the same way.

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So the laser beam starts off there.

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And the first adjustment that we’re going to make is to this mirror so that we can swing that mirror and get the beam onto center.

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I’ve got a special adjustable mirror B here.

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So we move this mirror as close as possible as we can to the mirror A.

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I am purposely marking this so that we can line it all up again.

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We’ve got a red mark on here on the center and we’ve got our X there.

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The first thing I must show you is that, look, we’ve moved this mirror and I purposely made it so that it runs along this bearing rail here.

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Look at the position of the red mark. So we bring these two mirrors as close as we can together.

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We put some tape on the mirror, obviously. So that we can record where the laser beam is hitting and the laser beam is hitting just here.

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When we move back to its original position here, remember here, the blue mark, is a certain distance away from this rail.

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Down here, it’s exactly the same distance away from the rail,

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and so ideally any line that struck through these blue lines is going to be what we want.

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It’s parallel to this bearing rail. OK, so let’s do that now, let’s now adjust this mirror,

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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so that we bring our laser beam into line with the blue mark.

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So we must have set the machine now. The two blue marks are truly parallel to this rail.

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But the laser beam isn’t, what we thought was the target

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has actually move. So let’s go back and relook at the situation.

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If we now move our mirror back to its closest position.

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We need to put a new piece of tape on the mirror. Now when we fire, fire the laser beam at the mirror.

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We’re going to produce a new target, which is the orange target.

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We’re going to move this mirror back to its original extreme position, which is down here.

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We’ll find that the beam is no longer pointing at that Orange Mark.

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So we’ve got to adjust the mirror again to get it onto an orange mark.

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Remember the first time we adjusted the mirror, we upset our target.

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We’re going to do the same thing again. And now we’re going to produce a red mark.

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But the red mark is going to be very, very close to the orange mark.

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This is what they call a process of iteration.

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We’re gradually, at every step that we make by going backwards and forwards, we’re going to reduce the error.

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Now, you can be as clever as you like, but you are not going to be able to set this mirror in one step.

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It’s going to take at least three steps and maybe four or five or six steps, depending on how good you are.

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But generally, it takes three steps to get a pretty reasonable coincidence between the target at this point and the target at this point here,

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because we’re looking for this laser beam to run perfectly true to this green bearing

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rail. And you do all of that by adjusting this mirror.

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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And that is the procedure for every single axis.

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And what we’ve done, we’ve actually made this position here equivalent to the position X here, X and X are now parallel to this bearing rail.

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But look, we’re way off center of the mirror. And that could be a problem! When you look at a diameter of the mirror being 25 millimeters like that.

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But now if I do this. And I set that mirror at 45 degrees.

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We’ve got lots of scope in the vertical direction, we could be two or three millimeters out in the vertical direction, and it not

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really worry. Because the beam is not going to hit the extremity of the mirror.

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And when we twist it through 45 degrees, we’ve only got about 13 or 14mm of available area.

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So in the horizontal direction, we can’t afford to be more than about a millimeter off center.

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So if we finish up with a situation like that and this happens to be

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from the laser. The only adjustment that we can make is to move the laser in this direction, so that we can allow the beam to go in

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to that position. The center of that mirror should now line up with the center of this mirror.

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And if you make an adjustment to the tube, the chances are that you will mess up your alignment and you’ll have to go through this procedure again.

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That’s an annoying procedure just to get the mirror one lined up.

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I have designed a system whereby the laser beam and the mirror are locked together.

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I’ve done lots of things to try and make the beam alignment on these machines a lot easier.

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Now, I don’t care what the Chinese supply me with, I’d throw it out and I put my own system onto it.

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If you go and have a look at RDWorks Learning Lab number 192,

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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you will see all the changes that I’ve made to my machine to make them easier to set the mirrors.

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OK, so we’ve got the beam set onto mirror two, we’re now going to stop the dodgy diagramsfor a little while, because we’re now going to add in some reality.

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Now, as I mentioned earlier on in this session,

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I take everything that the Chinese put on this machine and basically throw it awa,y because they make beam setting very, very difficult.

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I’ve spent some time trying to understand exactly how beam setting works, and I’ve modified my machine in many different ways.

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So that it’s easy to set the beam. And I’ll add one other word perfectly. Most people think that after you’ve set X and Y, you’ve got the machine set.

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And all you’ve got to do is fire the beam down this tube and twiddle these knobs here to make it come out of the nozzle.

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I was one of those people originally, but I have to say I feel rather silly now that I talk about and admit that I was like that once upon a time.

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There’s a lot more to it than that. I want to quickly explain why I changed the head design on here.

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Now, this design allows me to disconnect the nozzle and the lens tube very quickly.

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I don’t have to drop the table to pull the lens tube out of the bottom of the head.

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This has also the principle of a V block location for this lens, tube.

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Now, V block location is a very, very positive location that keeps the tube fixed in a perfectly upright and fixed position.

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You don’t want the lens wobbling around because, hey, look, this is a fairly heavy piece at the bottom here where my finger is.

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And if it wobbles around, when you start moving the machine around quickly, that’s not very good for the end result.

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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In the previous shot, you probably saw that I had this weird G clamp set up on the edge of the machine.

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And what I’ve got here is my original C series head that was fitted to this machine, now that weighed about two and a half tons.

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I exaggerate slightly, bit it was very heavy. And in addition, the clamp system on here.

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It seems like it’s a very good idea because you’ll see that it is a split collar arrangement. For this to slide in and out,

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there has to be clearance and clearance means …… Wobble.

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So, yes, I know, but when you put the clamp on, that’s going to disappear, so when I tighten this up now.

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Quite tight, snug, I’ve supposedly clamped this up and I have, it’s absolutely solid in this direction. But,

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I haven’t removed the clearance, I’ve made it, I’ve made the clearance more difficult to wobble. This nozzle can still

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move around. There are many other reasons why the head is designed like that.

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First of all, it’s got adjustment on a bracket at the back there that allows me to move the head in and out.

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We’ve got these screws here which allow me to move the head up and down.

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And then additionally, we can just clamp the nozzle in here with my butterfly clamp like that, and of course, I can easily

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adjust the nozzle up and down to anywhere Iwant. Especially when you use simple little step gauges like this.

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All you have to do is literally just drop the nozzle down onto the appropriate step gauge. And tighten it up.

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Focus set! First of all, I wanted to make you aware that I’ve got a head on here,

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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which has been specifically designed not only for lightness so I can get high accelerations out of this machine,

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but it’s been designed for setting. To make things very easy to set.

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Nothing is hidden away. Hey now to set the head, we need to make some special targets to make head setting easy.

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Now, I’ve previously cut some pieces out of three millimeter acrylic and these are an

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essential part of the final setting for your Z axis. Before you glue these together.

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What you make sure is that this piece and this do not slide.

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In other words, what you want to do is make sure that that, grips in there. Not tightly, but just enough. What we’re going to do, we’re going to

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assemble the side pieces first. So we’ll face that towards the right hand side and then we’ll put this one in the same way,

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because there’s a flat face here, you’ll notice, and there’s a face with tongues on it down the other side.

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Now, this is where you’ve got to be careful.

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This flat face has to go to this side and then we’ve got to make sure that the sharp corner goes to the bottom.

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And there are two sizes of that. The small one goes on the bottom and the larger one goes on the top and they fit into those two holes there.

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OK, now we’re going to drop this one on top here.

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That one in there and those two in there. And then with a little bit of pressure,

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to keep it all from falling apart. You’re going to stand on it’s edge and then you’re going to drop that piece.

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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I’ve always got a little bag of helpers here with me because these are essential when you’ve got so many pieces that you want to glue together.

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So I picked this up. Carefully, so that it doesn’t fly apart and we put a little helper around the end there.

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Now we’ve got my PETG, an acrylic adhesive, which is a bit like water.

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I’ve got a very, very small amount in there, as you can see. And all

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I’m going to do, is just run that, along that edge there. Along the back.

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Along that edge there, and along there. Now I’ve got this on a piece of tissue,

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because it soaks up the excess and if you keep it moving around for a few seconds, it doesn’t stick.

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And then we’ll just turn it over, and we’ll apply some pressure to that for a few seconds, and then we can run some glue down these edges here.

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We’ll put some in that edge there.

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So everything is nice and secure now. We’ll leave it for another 10 minutes or so, just for the glue to go really hard and then we can use it.

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Now, not everybody will have 3 millimeter acrylic to hand.

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I purposely made it of three millimeter because a lot of people have three millimeter material of some sort.

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And so in addition to acrylic, there is no reason at all why you can’t make this out of three millimeter MDF or three millimeter plywood.

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OK, I know my head has been set up properly, but what I’m going to do now is something that would horrify a lot of people. There we go.

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I’ve now messed up the setting on my machine, I’ve got no idea where it is.

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But let’s put it back roughly to the middle. It’s always a good point to start from.

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We’ve set the Y-axis, but we haven’t yet set the X-axis.

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Not true. I suspect that my X-axis is pretty reasonable, but we’ll go and check it anyway.

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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Technically, once you’ve set your Y-axis, you don’t have to be in a special position to set the X axis.

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But in reality, the general rule is that you always set your X axis with the beam, right at the front of the machine.

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These targets drop into mirrors one and two. When we look up at mirror three, it’s a completely different animal.

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OK, it’s round, but there’s no hole to fix it to, which is why we’ve got a special target.

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Looks like this. OK, now it’s got two holes in it which are funny shape and these screws are not a mistake on my part.

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I didn’t make them project through because I didn’t have short enough screws. They are through there so that you can plug the target into that position.

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So remember what the first action is. We’ve got to make sure the beam is at least hitting the target.

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So we put the head as far away as we can. Set my power to about 15 percent.

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I don’t want to blow the target off the mirror. I just want to put a little scorch mark on it.

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There is. Well, it’s pretty well on center this way.

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But it’s a little bit on the low side, but we’re on the target, so we’re not going to worry.

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We’ll take that out and we can just turn that round and use the other side of the target as well.

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There we are with mirror 3 close up to mirror number two, and we’ll put a mark on there.

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So that one’s out target. This is the first move, remember?

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Well, as I did say, I have got this axis set up and you’ll see that that mark is completely coincident with the one at the other end.

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All right. So we don’t need to set the X axis up because I’ve already got it set

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true in both axes. As I said, the machine is already set up.

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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All I did was mess around with the head. So the x axis is perfect, but it’s way off position, as you can see.

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So let’s just explain what we’ve got now, because this is very important.

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As we saw when we made that target, it was like that right towards the top edge of the mirror.

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So we’ve got here an exact copy of what you’ve just seen.

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The beam is hitting the mirror there, but I’m not worried, remember what I said, every axis has got to have the problem broken down into two pieces.

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The first part of the problem is to get the beam lined up.

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The second part of the problem is to get the beam into the right place on the mirror.

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Now, in this case, we’re not going to attempt to put the beam in the right place on mirror three.

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Now, we’re going to do that at the next stage. This is a mistake that I made when I was very, very naive.

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My next step was to say, OK, so now I’ve now got my beam right.

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Let me now move on to the center of this hole. To drop this beam down onto the center of this mirror, which you assume is the center of this hole.

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Means you’ve got to go right back to your tube and you’ve got to drop your tube down.

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But hang on, you’ve already set your beam into the middle of mirror one and into the middle of mirror two.

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You’re now going to compromise those positions to find a good position into the center of mirror three.

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No, no, no, that’s that’s totally wrong. You can’t do that.

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I know that’s what the Chinese allow you to do and insist you do, because that’s how they’ve designed the machine.

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But that is totally illogical. What you’ve got to do,

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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is allow the head to move up and down.

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You can’t afford to have this beam moving up and down and because you’ve already got it set on mirrors one and two,

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you’ve now got to catch the beam on mirror three, not set the beam onto mirror three.

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The problem when I had my first machine was this. I was trying to get my beam into the center of this hole.

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But that didn’t hit something called and I’ll show you this in a second.

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The sweet spot on the mirror, the sweet spot on the mirror is actually in line, aligned across there.

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I’m about, what, a quarter of an inch above center.

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This mirror holder is designed so badly, the sweet spot for the mirror is not in the center of the hole.

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Now, that’s not true for everybody’s head. Some heads will be perfectly OK and well designed.

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I’m just telling you, that mine wasn’t. And it caused me a lot of grief.

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And it’s one of those things that helped me to decide, yes, I’ve got to make my mirror adjustable.

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So my mirror is now adjustable in a vertical axis and the and the Y axis.

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And you’ll see the reason for that in a minute.

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Now, you remember in the last session we went to quite serious lengths to make sure that our table was running true to the axis.

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There is a thought that one of the first things you must do is make sure that your lens tube is true to the table in both this axis and this axis.

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Okay. Now, if you don’t have the same sort of head that I’ve got here and you haven’t got one of these toys to play with,

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then you will have to do just that. You have to make sure that your table and your head are set up

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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so that it’s completely square. Ok now, we’re hoping and this is the thing, we’re hoping that the Z axis movement, which are these things here,

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the lead screws, that are on each side of the table, are in fact all running square

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to the axis. They’re a long way away from the axis, and I think they won’t be very far out, but it is an assumption.

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And my little toy here. Overcomes that assumption, but if you haven’t got one of these systems,

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then you must make sure your head is upright before you attempt to do this. That thing there,

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which is your lens has got a curved surface and that curved surface is part of a sphere and there is a center point in a sphere.

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In other words, there is an axis, that yellow axis that passes right through the center of that lens.

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You won’t have your lens over at an angle because in the bottom of this lens tube,

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we’ve got seats and those seats ensure that the lens is both on center and 90 degrees to the axis.

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So everything is lined up inside that tube. The only thing that’s not lined up inside that tube, is the beam. Because at the moment, that beam

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is bouncing off the mirror. Here.

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And it’s coming down the inside of the lens tube. Like this.

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Now, when it hits that lens and I’m going to draw another little diagram. I told you I was no good at art. Our laser beam is coming in like this.

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The rays of the laser beam are coming in like that. And all those rays are trying to converge on this magical thing here called the focal point.

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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Having the beam off center is no different to doing this.

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Your beam will still pass through

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the focal point. Great you’ll say! So it doesn’t matter if the beam is off center.

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Well, it does. If you’ve got material that’s that thick, look what your cut is going to do.

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Your cut is going to be. Like that.

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It’s going to be off angle.

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Now, the other thing that could happen is that you’ve got this mirror set up so badly if you bring your beam in, off angle like that.

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It’s not going to go through the focal point, it’s going to bounce off further like that.

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Bear in mind what we’ve got here. We’ve got a nozzle, with a hole through it. You’re not even going to get out of the nozzle.

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OK, so that’s what we’re trying to steer clear of.

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And the way that we steer clear of that is to make sure that we put this beam, first of all, parallel to the axis.

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And I’m now going to show you how we put the beam parallel to the axis.

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First of all, I’ve got to make sure I’ve got an empty lens tube, then we’ll pop that into the corner there like that.

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Then we’ll give it a pulse. OK, now we take that and we’ll drop it into the bottom.

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Remember? This is like moving the head further away, we’ve moved the target from close in to the mirror to far away from the mirror.

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So what we should find now. It’s not bad, it’s not perfectly in line, you can see that the new mark is towards the back.

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I’ve now got to adjust the mirror to tip the beam forward.

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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Now, the way to imagine that is just here, we’ve got a pivot point. And if I want that mirror to go forward. We’ve got to pivot points here, like ahange,

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and I’m going to pivot that mirror there by adjusting this little screw here.

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So I’ve got to turn that clockwise, probably a quarter of a turn.

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It’s not far off. OK, so now all I’ve got to do is I can turn that over because I can use these twice.

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Try again. Pop it in the bottom.

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So now there we go, we’ve got it in perfect alignment. Wow I did that in two.

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Hamg on, I’m off to do my lottery ticket. In Y it’s nearly correct, in X it’s a long way out that way.

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So let’s just see what that means. There is an axis that passes right through the center

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of the lens tube. And that axis, if you project it up, will hit the mirror at this point just here.

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And that point there, is the point that we’re going to call the sweet spot.

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That’s the only place on that mirror that will reflect that beam down the axis of the lens tube and through the axis of the lens itself.

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I know the Chinese allow you to move the beam by adjusting the tube, but I don’t.

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I leave the beam where it is to get that beam to hit that spot.

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I’ve got to raise the head. I’m going to move the sweet spot onto the beam. So we will loosen these screws off.

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We’ve got to raise the head up. And in raising the head up, we should have

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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lifted that mirror onto the beam. So let’s just snug these screws up, not tight.

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Doesn’t matter whether we do it at the bottom position or the upper position, because we’ve already got this perfectly lined up remember.

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Not enough, too much! Dam the expense, lets use another target.

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I think we’re pretty happy with that. You can see it didn’t take very long at all to do this most difficult part of the process.

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I’ve got to get the beam right through that hole. If I’ve lined this up properly, it will come through the middle of the hole.

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Now, we’ve got another little laser beam alignment tool for doing that.

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It’s this little thing here, which I’ve just, I’ve got some old tape on here, but I think that will be ok. There’s a nice, clear one there.

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So we just put that on the end of the nozzle like that and we go beep.

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And there it is look, right through the middle. It’s probably taken no more than 10 minutes for me to reset that

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beam. If I was to start right from the back,

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I could reset the whole of this machine up, in about 15 minutes and make sure I’ve got it just perfect like that.

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One final check that I forgot to tell you about. That is a killer.

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It will make you tear your hair out if you’re not careful. We’ll drop our target in there and we’ll make a mark.

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Spot on! We can’t ask for better than that, can we? But now what we’re going to do is to move it to the back corner.

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If it’s not spot on, there’s an additional step that you must take. Look,

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I’m right over in the back left hand corner of the machine and I need to make a scorch mark there.

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That’s my target. So from the back left hand corner, we move to the front right hand corner.

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But if there’s an error along the way down your Y or your X-axis. If they’re not perfectly aligned,

Transcript for Perfect Laser Beam Alignment Procedure (Cont…)

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then you will generate an error here between that back corner and here.

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So you’ve got to now do a final check. You will adjust mirror one to bring the dots

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coincidental. It will require the very, very smallest amount of adjustment, on mirror one to get the two spots to line up.

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I’m happy that that machine is pretty close to perfect! I’ll metaphorically

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take a bow and see you in the next session.