Session 38 – How To Combine Laser Cutting and Engraving

Transcript for How To Combine Laser Cutting and Engraving

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The Concise RDWorks Learning Lab with Russ Sadler.

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Session 38, How to combine laser cutting and engraving. Well for change, we’ve got a little bit of peace and quiet in this workshop.

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We haven’t got the machine turned on today yet. Up to now, I’ve made it very clear to you that there are two distinct uses for this machine.

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One of them is laser engraving and the other is laser cutting. They’ve both got very distinct properties.

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For example, if you want to engrave, we’re only trying to damage the surface of the material.

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And what happens is, first of all, we’re using fairly low power.

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As I’ve already mentioned to you, all lenses are cutting lenses, potentially,

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and that means that if you set them with their focal point onto the surface, you will get a cut. Now,

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when you’re trying to engrave. You don’t necessarily want a cut. What you want is a scorch, a shallow scorch mark.

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So we tend to put the focus a little bit above the surface.

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And when you burn this material, you don’t get a huge transformation of solid material into gaseous material.

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You get a little bit of an explosion like a volcano, which is what I’ve tried to imply here with my dodgy diagram.

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Now, this stuff that’s flying up in the air is full of brown,

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I’m going to say crap, but basically it’s resins and tars and oils which are appearing when you convert wood or whatever it is, into something else.

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And if you have air coming out of your nozzle and that’s what this black thing is. If you have air coming out of here in a jet,

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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you’ll finish up blowing this crud back onto the surface of your job and you will paint the surface of your job brown.

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So in general, we use low air assist, a big nozzle, a long way away from the work, and we’re using lowish power out of focus.

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Everything, everything about that set of parameters is different to what we need

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when we cut. When we cut, we need high power.

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We need to put the focus right onto the surface. Some people will say, you’ve got to put it somewhere else, but in general,

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put it onto the surface. You need a small orifice nozzle, set close to the work so that when you put your air assist into the nozzle,

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it will jet out of that nozzle at fairly high velocity.

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It doesn’t have to be high pressure, it just has to be high velocity and the hole is small and you’re close to

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the work, so you can get efficient airflow through the cut that you’re making.

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The idea of cutting is that you burn through your work and you try and produce a parallel cut

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through the work. So that you’ve got a nice even air flow running right through the work.

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And then what happens is your air flow comes out underneath the work with the fumes, and you don’t get any damage to the top surface of your work.

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But in essence, what you’ve got to do is make sure that there is a fairly free flow of air out from underneath your job.

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This appears to be perfect for the job.

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If we go back and look at the session where I talk about air flow and this the dangers of this stuff,

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but in essence, you need to sit your work above the surface.

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Now I’ve shown you a solid surface here and I’ve demonstrated what a solid surface will do for you.

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It reduced reduce the risk of fire. It means you can carry these fumes away

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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well. If you’ve got managed airflow through your machine. Everything about the parameters here is the opposite of what they are here.

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How, if we’ve got a job to do, which involves laser cutting and engraving?

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What decisions do we make?

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With this one, ideally, we could be looking at a fairly long focal length lens to get the softest cut that we can possibly get. With this one,

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does that mean to say a short focal length lens is the right thing to use, or maybe a longer focal length lens?

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To be honest, it really isn’t that important.

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If you want a very thin kerf here, then provided you don’t have very thick material, then you can use a short focus lens.

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But if you want if you want to cut thicker material, then you need to make your focal length a little bit longer, 2 inch,

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maybe two and a half inch focal length lens, to cut through something that may be 10 or 15 millimetres thick.

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Whereas for just maybe three millimetre thick material,

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you’ll be able to get away with a one and a half inch focal length lens, or even a one inch focal length lens or even

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a compound lens. Because despite the compound lens being very, very short focal length, it will still cut.

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So how do we compromise between these two conditions to satisfy a job where we’ve

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got to do maybe engrave a logo and then we’ve going to cut the whole shape out?

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Well, obviously if you’ve got lots of air assist and very close to the work and you’re trying to do laser engraving with this,

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you are guaranteed to paint your work brown because, hey,

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we’re not going to cut through the work, we’re going to be sitting on the surface of the work.

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So everything that comes up is going to get blown down immediately and you’re going to get a very brown looking job.

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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So that would appear to be totally the wrong approach, if you want to do engraving. You can on these machines,

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if you’ve got the machine set up properly and you’ve got the right equipment on there, you can switch this air assist on or off.

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Now, you certainly don’t ever want to switch your air assist off because otherwise fumes will go back up and they will coat the face of your lens.

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Bad, bad news. So you need at least some air assist. Software for running these machines generally has the opportunity to turn air flow on or off.

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Now I’ve designed something that fits in this machine and other machines whereby you

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can choose to have air assist on – in which case you’ve got this flow here or off.

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But off really means I’ve got a little teeny weeny bypass, low flow through here.

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So even when the air assist is off, I’ve still got air flow through here, but it is very, very low flow.

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Well, that’s no good here because you’re still going to paint the surface brown.

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Here is where we use low air assist, which basically means we turn the air assist off.

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But the air assist off means we’ve got a little bypass of air which is coming into here for a gentle flow.

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Now not only have we got a gentle flow of air coming through here. Look, we’ve got a large orifice in the nozzle and a large gap to our work.

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So a low air flow in here is not going to cause a jet effect and blow this stuff back down onto the work.

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Let’s just say you’re doing a coaster or something like that.

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Most of the work will be done engraving and then all you’ll want to do is just cut the outside shape out.

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So the compromise really is, that you probably want something like this.

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Which will be able to cut. You can still cut with this configuration,

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it’s just that it won’t be as efficient because you are not blowing air through the cut, but the cut will still proceed.

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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It may well be that you have to slow down a little bit.

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I’m going to give you a quick I’m going to give you a quick demonstration of this compromise situation.

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OK, now I’ve got a combination of nozzles and I’ve got an inch and a half lens here.

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It’s a Chinese PVD plano convex.

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Now, the normal way that you’d use this is with the flat side down.

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So first of all, we’re going to put it flat side down in this nozzle here because this nozzle

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has got a big hole in the bottom, so it will allow like this,

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it’ll allow this very wide beam high up to come out and then go down to a small beam like that.

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This has got air assist in here and the air assist is going to come out the bottom, exactly

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like that picture there? I want to put that one aside for a minute.

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I could either spend time trying to find out where the focal distance for this lens is with my line test, or some people use a ramp test or there are

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various other things. But hey, here’s a fairly simple way of doing it.

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I’ve got a very soft plastic. It’s out of a ballpoint pen, OK?

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And I’ve got a small piece of plastic on the outside there.

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What I’m going to do is poke that inside there and check how far – 10.2. So our lens is ten point two inside the nozzle.

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Focal distance is supposedly – Thirty eight point one.

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Let’s not just get too concerned about that 0.2, let’s call that 0.1.

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It isn’t going to make a lot of difference. So thirty eight point one minus ten point one, gives me

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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28 mm. So that’s the distance I’ve got to set my nozzle above the work.

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Now remember what I’ve said here? Ideally, we need this at least 12 to 15 millimetres gap.

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Yeah, well, we’ve well and truly exceeded that look 28 mm. Whereas here we said that we only wanted it

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maybe three, four millimetre gap. Hmm.

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So we’ve made the compromise this way. Not that way. We’ve got a separate ball valve here so I can control

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the air assist so that you can see and hear me playing with the air assist.

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Now, this machine has got an automatic air assist control system on it, but I’m bypassing that at the moment and I’m using this completely.

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I’ve got a piece of scrap cast clear acrylic here,

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and I’ve taken the protective film off the top surface because that’s what I’m going to work with and engrave. I’m going to set my gap to 28mm.

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So there’s a 20mm block and then an 8mm step on there.

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So that should be, nominal focus. I’ve got some air coming out of there, but not, not a lot,

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as you can hear. I’m running that at 400mm/s with quite a lot of power on it.

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I’m running it at about nearly 70 watts. So as you can see, it’s cutting, perfectly OK.

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Let’s just take the back off. Because what I want you to see is what the front looks like.

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As you can see, this is somewhat of a mess, even though I’ve only got a very small amount of air flow on there.

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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Those fumes are blowing down to start with, plus the fact that I’ve got a very deep cut in there and if you remember back a few sessions ago.

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When I’m trying to convert a lot of material quickly, the fumes do not get a chance to come up.

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They explode sideways, and what you’re seeing on the side here is recondensed acrylic.

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This is not dust, this is condensation. Some of it will be dust, but

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not a lot of it. It doesn’t want to come off.

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And this is all white in here, because we’ve painted the inside of the letters white as well.

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But this stuff that won’t come off, it’s vaporized acrylic, which has gone back from liquid to solid, and it’s actually stuck to the surface.

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So this is a nightmare, and as I get closer, look, it won’t even come off.

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It’s a nightmare to get it off. One way to overcome that problem is to leave the protective film on the surface.

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When we peel this off. If we’re careful about it.

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The little spaces between the E and the T. Well, I’ve got far too much power on there.

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Now when I take that blue film off there. You can clearly see where it’s stuck to the front there.

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So I’ve solved one problem and created another, because we started this from the top, if you remember, and it worked its way down. As it got towards the bottom,

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the fumes were blowing back across here and we were painting this white.

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I mean, that’s quite a nice effect, if you want it like that. Film on the surface is not a good idea.

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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So let’s remove the film. One of the things I really ought to do is reduce the power because hey, I’ve got far too much power,

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I’m creating too much smoke and it was just painting the rest of the job. So

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I’ve put the power right down now to 20 per cent, which is probably somewhere in the region of about maybe 25 watts.

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And now you’ll see the smoke is now just drifting off gently. The text looks a bit blue at this moment in time.

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That’s because we still got the backing on. Providing we don’t have too much air,and providing we don’t have too much power.

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We’ve got enough of a cup there that it looks good. We turn it over and it’s a bit lined. But that’s only because of the way in which this light is catching it.

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It’s also got a bit of a grey to it because this is extruded.

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And So we will try exactly the same parameters, but this time we use a piece of cast acrylic.

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For a start, can you see all that stuff on the surface there?

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Let’s take the backing off. Now look, before I even clean that, can you see the difference in the quality, the brightness of the text?

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This one is white, this one is sort of grey. And yes, look, we’ve got some splatter on here, but I anticipate.

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Because it’s only dust and that’s the difference between laser engraving with cast acrylic and extruded acrylic. So there’s a compromise that works.

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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Little or no airflow, long distance, but we can still cut, because the beam is still powerful enough to cut.

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It might not be as efficient because we haven’t got the airflow there, but hey, that’s one of the compromises

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you’ve got to make. You get good engraving, but slow ish cutting.

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What we’ve got in here is a two inch lens, and we’re going to use that with a cutting nozzle.

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Now this two inch lens is actually pushed a bit further forward than it would normally be

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because this is an 18 millimetre diameter lens mounted in a 20mm diameter housing.

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And I’ve got that sitting in a small recess at the back, which pulls the lens forward.

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So a normal two inch setting will leave us something in the region of about maybe four or five millimetres

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proud of the work for the focal point.

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I’ve now pushed this lens forward and so the focal point will be out here at 10 mm. I’ve left my air at the same as it was before.

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Just enough. So this is a two inch lens, which technically is blunter,

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it should be softer on the cut. The question is, will it cut through because it might not be quite as sharp?

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Maybe I’ve got the speed set wrongly, no it’s cutting through.

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We know it’s cutting through, with a wider kerf, but it doesn’t really matter because this is an outside shape. Taking the back off,

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let’s just see. Yeah, that rubs off nice and clean.

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Not a lot of difference. From here,

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I can see that I would say that that one is very slightly whiter than that one. Because this is softer and actually surprisingly enough,

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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I can feel more indentation in there than I can in there. It’s actually cut [engraved] deeper with both of these conditions. Using a cutting lens.

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But the cutting lens is quite a long way away, remember?

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So it’s 9.6. It’s not right up against the work.

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So the small amount of airflow that we’ve got on there has not blown it back down onto the work in a violent way.

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Now this time. I’m going to turn the air assist on fully.

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Now, I think before we even try and clean this, you can probably see what the air assist has done.

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Look, it’s painted all the letters white. Yeah, I know these are white, but these are coated with crud.

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This is just a disrupted surface,

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which is giving the white effect. Here the white effect is the condensation blown back down on the job because I’ve put the air assist on too high.

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So let’s just rub it off. As it happens, we take a look around the outside of these here,

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for example. You can’t see any marks, because the air assist was not blowing the fumes back down onto this part of the job.

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Whereas now that we have air assist on the cutting.

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Can you see how all these fumes around here have bonded themselves to the outside of the job. We are blowing the fumes on top of the work here.

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So the cutting nozzle with high air assist is a bad combination. If we turn, turn the air assist right down, just enough to protect the lens.

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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We get a reasonable result. And if we use an engraving system which uses little or no air, we also get a good result.

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So there are two compromises that work, but they do require slightly different setups.

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So finally, we put, we’ve put our inch and a half lens in here,

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and I’ve got this, sort of fishtail nozzle, which is blowing air across the face of this nozzle.

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But it’s also helping to blow away the fumes from this work.

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Now this setup required 28mm, and I’ve got full air assist on there.

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But of course, it’s not blowing down at the job is blowing away from the job.

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So we’ll just take the back off. So look, without doing anything to that at all.

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I haven’t even wiped the surface, because it doesn’t need it. All the fumes have gone up and have been blown away.

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There’s nothing at all gone down onto the surface. There’s a compromise that works extremely well, for laser cutting and engraving.

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OK, so now we’ll swap over to a piece of Baltic birch plywood. We’ll use this cutting setting.

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But this is a compromised cutting setting because remember, I pushed the lens further forward.

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So we’ve got a big ten millimetre gap here, which would not be normal for cutting.

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I’m going to leave the engraving speed at 400,

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but I’m able to increase the cutting speed because this is wood and not acrylic and wood cut roughly twice the speed of acrylic.

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Now, I think you can see already, the laser engraving is quite faint, and that’s because we’ve got this lens set to a cutting focus.

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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And if you remember back to our laser engraving sessions, we really need the lens out of focus to get a nice burn.

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We don’t want a cut, we want a scorch, and this is set for cutting.

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So we’ve got a very nice cut, but it’s far too faint. By slowing it down,

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I might be able to get a slightly darker cut. But if you remember, slowing it down is only going to make the cut deeper.

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It’s not going to change the cut. We don’t want a cut.

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We want to scorch and to get a scorch. We have to move out of focus. Well on this machine,

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I can do that because I’ve got a controllable Z. But most people don’t have that facility.

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So here you’ve got a problem, when it comes to cutting wood. Acrylic is different, but wood has got completely different properties.

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So what are our options? We could compromise on the cut.

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And if we compromise on the cut, it means we’ve got to go slower.

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If we’re out of focus, it means we’re going to get a bigger cut, a slightly messier cut.

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So let’s move this two millimetres focus, one two.

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So we’ve slowed the cut [engrave] down from 400 to 300.

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We’ve increased the distance here by two millimetres, which is going to compromise the cutting.

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So I’ve reduced the cutting on this from 25 down to 15.

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OK, so it’s already darker, as you can see. So yes, we’ve got quite a thick cut now, because we’re cutting

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out of focus. It’s just about cut through.

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So yes, we found a reasonable compromise there.

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We’ve got a cutting nozzle, which has got a 12 millimetre gap because we’ve increased the focus by two millimetres and increasing the focus by

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two millimetres has changed this from a light cut to a slightly darker cut. I’ve slowed it down as well from 400 to 300.

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And I’ve changed the outside, cutting speed from 25 down to 15.

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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So there’s a lot of compromises there and that’s using the two inch lens.

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So now we’ve got our one and a half inch lens in there, running at the same speeds 300 as we had before.

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We’ve got a very small amount of air assist coming through there just to protect the lens.

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And already, as you can see, this is not very dark at all.

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This is actually even fainter than that one.

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So as you can see, the cut is quite nice. So the question is what sort of cutting compromise

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can we make if we push the focal distance a little bit further off. Now because is an inch and a half lens, it’s going to go out of focus fairly quickly.

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So we’ll put this up by two millimetres to 30 and we’ve immediately got a big difference in our colour.

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Just by pushing the focus out. Now if we were to go out of focus a little bit more, we’d get a slightly dark color.

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But if we go out of focus too much, we’re going to screw up our cutting.

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Have we screwed up our cutting at the moment by going 2mm out of focus? Well it’s definitely wider.

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But I think we may well have cut through and it’s not a bad cut.

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We can go for a cutting lens 2 inch out of focus, or we can go for one and a half inch lens out of focus.

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I like this one better. What I’ve been showing you throughout this session is valid for this and it’s valid for cutting.

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You can’t have both at the same time, unless you make compromises on both the lens type and the lens setting,

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the focus and the speeds that you run at. It’s the whole purpose of this series of videos to show you that there’s a big difference between laser cutting and

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engraving and that you can’t do them both together unless you’re prepared to make a compromise or you understand why you’re making those compromises.

Transcript for How To Combine Laser Cutting and Engraving (Cont…)

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And that’s the most important part that I hope that I’ve shown you in these sessions.

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So there are some good examples of how you can actually achieve this laser cutting and engraving at the same time.

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So I hope this session has clarified for you, how you’re going to have to go about thinking this problem through if you want to do both things at once.

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OK, now there is a different option that you can adopt. Rather than doing mixed cutting and engraving at the same time,

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separate the two operations out. If you’ve got 50 of these to do, cut 50 blanks out at optimum cutting speed and optimum focus with the correct lens.

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Don’t make any compromises. OK, and then. Put yourself a piece of material down like this, a piece of scrap material and cut out a template.

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Make sure your template is securely fixed to the table. And then drop your blanks in.

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Choose the right lens, choose the right focus, out of focus, the right speed and do all your laser engraving as a separate operation.

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One at a time. That’s by far and away the most efficient way to do it if you’ve got a lot to do.

Transcript for How To Combine Laser Cutting and Engraving