Transcript for Setting The Work Table Level
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The Concise RDWorks Learning Lab with Russ Sadler. Session 15: Setting The Work Table Level.
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I’m nice and clean at the moment, but in today’s session, I think we’re going to get maybe a little bit grubby.
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We’re going to look at this thing here, the work table.
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It’s an essential part of setting this machine before you really start using it,
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that you set the table up level. Level implies maybe using one of these things.
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No, forget that. That’s not what we’re talking about when we talk about level, your machine can be totally on the wonk.
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It isn’t a problem. What we’re really interested in doing, setting the table, absolutely true to the bearing rails.
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In other words, we want this to be flat in this plane running true to that bearing
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rail. And we want it in this plane running true to the Y bearing rails.
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Before we do that, I think I really ought to explain why we need it. Now,
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one of the most complicated and misunderstood things about this machine, are these things, lenses.
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I’m not going to get into a rant of mine about lenses because that’s something that
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I’m afraid you’re going to have to suffer in the future. For four or five years,
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I was very happy with standard lens theory.
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And I’m going to go through this very briefly just to explain why we need the machines set up level.
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The uses of lenses and light, even though this is an invisible light source, is well described by standard lens theory.
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But standard lens theory is all about images, microscopes, telescopes, cameras, projectors.
Transcript for Setting The Work Table Level
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It’s not really about laser beams. Let’s just look to see what standard lens theory tells us about lenses.
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We’ve got different focal length lenses.
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Now, here’s a typical example from a company, a Chinese lens company, which explains in very simple pictorial forms what’s going on.
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We’ve got four inch lens, a two and a half inch lens, a two inch and a one and a half inch lens.
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Forget this thing on the end. OK, so they’re the lenses that you’re most likely to come across.
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And basically there are two pieces of information which are stated about a lens, apart from the focal length.
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One of them is the so-called spot size, which is the point through which all the rays of light pass.
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Now, the longer the focal length of the lens, the bigger the cut width,
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because the bigger the spot size or the beam diameter that you’re going to get at the focal point.
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The width of the cut you should be able to achieve with these lenses.
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The second piece of information is this little square here.
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Now, this little square here defines what they call the working depth of the lens.
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Now there’s another company around called Parallax Technology, which you might like to go and look at their website because they have got a very
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understandable section about lenses and how lenses work and the various things.
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This is all standard lens theory without any really complicated formulas.
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It just describes very nicely how lenses work.
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And when we look at their charts in here, what we find is that they’ve defined, again, the spot size in millimeters and in inches.
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And they’ve also giving you this thing depth of field, which is the point that I was talking about. Here’s,
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here’s the focal point where all the rays pass through one single point and then either side of that,
Transcript for Setting The Work Table Level
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you’ve got this depth of field, as they call it. Now, the depth of field is plus or minus these numbers.
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So whatever the spot size is, multiply it by one point four.
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And when we get out to that distance, that’s when we’ve got roughly half the energy density that we had at the focal point itself.
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Now, what’s energy density? This is again a very controversial subject,
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because if I put 60 Watts into an area and let’s call it an area of one, it doesn’t matter what the area is.
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That means I’ve got 60 watts per unit area. Well, if I go out to one point four, I’ve doubled the area and I will finish up with half the energy density.
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So instead of 60 watts per unit area at this point here, I’m going to finish up with 30 watts per unit area.
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That’s the way the theory runs. If we’re setting our machine up somewhere in one position and we set the focus up,
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but then we finish up somewhere else on the table and the focal point has moved to here because the table has dropped away, that’s no good to us.
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This nozzle is fixed through this lump of metal to the bearing rail.
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As I move the head backwards and forwards, it remains perfectly in line with this bearing rail and with this bearing rail.
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This nozzle represents a perfect reference because what we’re trying to do is to set the table
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so that it always remains the same distance below the nozzle because it’s below the nozzle,
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that the focal point exists and we can’t have the focal point drifting in and out of focus.
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So we want the table to be true to the end of the nozzle.
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And that is what leveling the table means. Now, when you open your machine up and look underneath the table.
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There are many things that you might find. In this instance,
Transcript for Setting The Work Table Level
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I have a stepper motor here which is driving the table up and down in a controlled manner.
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That’s what this machine does, but it does so via a toothed belt and some toothed pullys, which are driving the table up and down on a big screw thread.
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Now these screw threads are fixed relative to each other via this tool belt. As one rotates,
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so they all rotate and the table moves up and down in a nice parallel plane.
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But of course, if one of those screws is out of position, then the table is not flat.
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OK, now your machine might not look like this. It may have a cover over here,
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for example. You’ll have to take the cover off and when you take it off, you’ll find the belt.
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Some machines have got two stepper motors because it’s a big machine and they’ve got two belts.
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Now, that’s a bit of a nightmare because two stepper motors, if they get out of synchronization,
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one side of the table will be going up and down at a different height to the other side.
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Something you’ll have to keep an eye on if you have a two stepper motor system. That
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normally only applies to big machines, because you can’t get toothed belts very,
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very long. And so consequently, on some machines, you may well find that
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they don’t use tooth belts. They use a chain. That’s fine.
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A chain works just as well as a tooth belt because it keeps these screws fully synchronized.
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Now, not every system has a stepper motor on it. This machine.
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It’s completely different, but exactly the same. What we have at the back there is a DC motor, not a stepper motor,
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and I’ve got two buttons on the side of the machine that allows the motor to either drive clockwise or anticlockwise.
Transcript for Setting The Work Table Level
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It’s not stepper controlled. I’ve got no Z control on this machine.
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I’ve just got, if you like, assisted table height adjustment. But the same principle applies.
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Look, we’ve got a toothed belt. We’ve got toothed pullys and we’ve got a lead screw.
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So we shall use this machine as our example to show you how to set the table.
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OK, now it really doesn’t matter where the table is, other than the fact that it’s got to be reasonably close to the nozzle,
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because here I’ve got a little measuring gauge that I’ve made.
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This gauge is ten millimeters at this end and 12 millimeters at this end.
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And it’s divided with numbers into point one of a millimeter.
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So I’ve got a point, one of a millimeter adjustable scale here. If you use a constant amount of force till it just touches.
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It’s set to 11 millimeters. Dart to the back left hand corner, make that corner our 11 millimeter reference.
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So we’ve now got to make all other corners the same. So let’s move to the back right hand corner and check what we’ve got.
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There’s 11 mm. It’s abouta millimeter and a half out.
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Well, that is absolute rubbish. We’re going to do it on the back screw.
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But I want to show you this on that front screw. Now, we’re very lucky with this machine because the screws for fixing these are above the belt.
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On the other machine that you looked at a few seconds ago,
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fixing screws are above the belt with some, the fixing screws are actually buried in the teeth here.
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And you’ll have to hunt for them, at least with these.
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All I’ve got to do is to find the grub screws. One here and there will always be two and the other one is at ninety degrees just here.
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And then I’ll do the same with this screw at the back. Now, sadly,
Transcript for Setting The Work Table Level (Cont…)
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the screws on this back one are hidden somewhere behind here and I can’t get to it because we’ve got a micro switch bracket on the back here.
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So I haven’t got full access to that one. So what I’m going to have to do is this, bring the screws into view.
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Sounds simple enough, doesn’t it? Now I can loosen those screws and do the same to this one on the front corner here as well.
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I can access the screws here easily in any position. I can access the screws here easily in any position.
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But the screws over there in that corner are the deciding factor for me.
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Those I can only access like that. So let’s go back to the top of the table and let’s drive the head back to the starting point.
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So making that adjustment to the table height to get access to the belt has completely messed up
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our original position. Well, not really, because all we’ve got to do is undo that nozzle and let it drop down.
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And there we go, we’ve reestablished our 11 millimeter reference now. So we can now come back to this corner.
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And we shall still find we’ve got a big gap that we didn’t want.
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So what we’ve got to do now is to raise the table up in that corner.
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We did not loosen the screw in the far left hand back corner.
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So it’s not going to change.
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So the lead screw is no longer fixed to this toothed pully, so I can rotate the lead screw, as you can see, and the pully stays still.
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So all I’ve got to do now is to rotate that lead screw to get rid of the gap.
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Wrong way, it’s going to come this way. Eleven point one, little bit more.
Transcript for Setting The Work Table Level (Cont…)
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And there we go. 11 mm dead, and now Ican tighten these grub screws up nice and snug and we’ve locked that corner at 11mm
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So we now come to the front left corner of the machine and we find that it is eleven point one without touching it, it’s eleven point one.
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Do I really need to worry about point one of a millimeter? I don’t think so.
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So we shall leave that one as it is and lock the screws up.
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And the final corner is quite a long way out.
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It’s close to 12 millimeters. So that’s got to come up by a millimeter, until it touches.
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Let’s check whether or not that’s 11. It’s a bit on the snug side.
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There we go, spot on 11. So we now lock that one up as well, if we put this towards the middle of the table and it’s about eleven point one.
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So I don’t think we’re going to be too worried about that, point one of a millimeter within level all the way across the table.
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That’s pretty good. Well, my hands are not as bad as I thought they were going to be.
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So maybe I ought to put some light oil on those screw threads. They have got grease on them at the back there, if you look.
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But I think a little bit of oil would not do any harm. Now, I use this a lot around the machine.
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It’s liquid Moly, in this particular instance this is a hydraulic valve additive, but it’s a lovely, slightly sticky, thick oil.
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It really does reduce friction. So I’m going to put a little bit on here at the top where we use it most,
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and it will find its way down the threads because it’ll just work its way down the threads.
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If I put enough of it on up here. And I will just paint a little bit on the upper part of these just below the table as well.
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So that’ll be as smooth as silk. Now. And that’s it.
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Table leveling done.
Transcript for Setting The Work Table Level
