London's burning - can you quench the fire?

I am teaching at a college in London, with a 30w Gravograph (aka New Orleans, with just three months left of a 3 year warranty) which does a cracking job at creating flames - but doesn't cut through plywood very easily.

We have the air assist on, and we are using the recommended settings for 4 mm plywood - 3% speed, and 100% power.

There is a fair amount of dark smoke, which leaves a trail on the wood as it is being sucked up the extractor hose.

The last time I used the laser to cut wood, two months ago, to cut out a few shapes from a sheet of ply, it produced so much smoke that it clogged the filters (causing an error alarm to shut down the laser). We called out the Gravograph engineer, who couldn't find a fault with the pump - and told us that we needed new filters (only 6 months old at the time). These have been fitted, and the laser runs again.

Our supplier sent down the technical trainer, who travelled from Yorkshire to spend the day with us, today, but admitted he can't work out why our Gravograph does a good imitation of a towering inferno (flames are 30mm+ in height.

The pump (compressor?) makes a loud click-click-click noise, and has done for a year apparently, when the laser is in vector mode, but not when rastering. But it is obviously working, as the smoke is being drawn towards the extractor.

The rep tried some of his 'laser firendly' plywood and, while the flames were much smaller, they were still very visible.

Our recommended settings for cutting through 4mm plywood is speed 3, power 100%.

The rep drew a circle in Coreldraw and turned the speed to 5, then got the laser to make three vector revolutions in quick succession. On the first revolution, the laser looked like it was doing a better job. There were no flames but I could see that it was barely scoring the first ply layer. On the second revolution, the flame appeared and (once lit) then continued.

I complained that I wasn't happy with the depth of 'cut.' We tried to cut through a piece of 6mm ply on the lowest speed setting (1) and highest power (100%). After three attempts at cutting, it had only reached a depth of 4mm. According to the manual, we should be able to cut through 9mm plywood.....

It cuts acrylic okay though, when I examine the cut parts, the edges appear to be serrated - like the edge of a coin. We do have to cut everything twice though, on the recommended settings and, on 5mm acrylic, we are having to use the slowest speed and highest power (again, twice).

So is the tube on its last legs...??

Is this flaming something to do with the tube, or do we have two (or more) faults....?

I recently joined this college from a university which had a Universal laser (which was great).

The Boxford software is terrible. There is no facility to adjust the ppi, and any bitmap images (that haven't received the Photograv treatment) just produce a rastered square (as if you had printed a pure black square.

if anyone knows of other software/drivers we could use, I would also be very pleased to hear from you.....

I'm not familiar with the Gravograph, but first, if it's not cutting as it should and is on warranty they need to fix or replace it. Since the manual says 9mm then they should get it to do that. Once the warranty is up it could cost a lot to fix it.

This can be caused by several things. Yes, one is a failing tube. The tech should have a meter to measure the output wattage.

Does it still cut the thicker acrylic, say 6mm as it did before? Also, will it cut 4mm solid wood like Oak?

Other things can be a focus problem, bad mirror or lens, or the wood itself. I had that happen with some African mahogany, no way it would cut with my 45 watt, just flames. Some plywood glues will also flame up and prevent cutting.

I would check that the lens is in correctly. (upside down maybe)

Don't let them keep putting you off. They may keep "TRYING" things to fix it for 3 months and then tell you it's out of warranty.... Make them move on it quickly. Just my opinion.

Does the beam seem wide? Sounds like it might be more optic than anything else. If you focus is not right on it can cause some real problems. I believe a Gravograph is basicly a Universal built laser. At least some of the older ones were. Check your focus and optics make sure everything is perfect there.

Pete

You say you are using air assist. Can you confirm that you have a good flow of air directed onto the point of cutting? Usually when I have seen flames it is a result of inadequate air assist. The wood or adhesive may be vaporizing into a gaseous mixture and possibly it is this that is burning. If so the air assist should disperse any combustible gas. I can't imagine how you would have such flame-up if the air assist is working. What are you using for a compressor on the air assist? Maybe it is undersize for the job.

As others have said, check your lens and focus. Do you use a probe with this machine? Try a test cut "in focus" and then vary the table up and down from this in 1 or 2 mm steps. Then see if the "best cut" occurs when your machine says it is in focus. If not, determine the source of the discrepancy.

If the rep does not have the experience to solve the problem you need to escalate this and get someone in who can solve it.

If you don't get through the wood in one pass the second pass will cause flame and sparking because now you are trying to vaporize carbon which is not very laser friendly.

I don't know how they can promise 9mm plywood though as plywoods vary greatly as to suitabliity of lasering. Also moisture content will have an effect. I doubt I could cut 9mm baltic birch with my 30 watt, maybe 6mm but probably marginal.

Thanks for all the replies.

I am going to check the focus, tomorrow.

The gravograph has an auto focus; the table lifts towards the lens, and when it hits the probe, it settles itself.

The rep set up a 'height block' to confirm the lens was in focus (well at least at the right height). It was okay.

I admit I am concerned about the air assist, especially because of the noise coming from the back of the machine. Does anyone know of a test to prove/disprove that it is working.

But my 'gut feeling' is that it is (also?) down on power (or has a lens problem), due to the fact it won't cut through acrylic as well as the Universal machine I was using previously.

I know it is not the plywood, as we have lots of different types, and I took samples which cut perfectly fine on a laser in a neighbouring college.

I do agree with the point about its capability on 9mm ply (the Gravograph settings, are also suspect). But I would like to be able to cut through half the maximum recommended depth, without torching the college.

Is there a way I can field test the tube, without special tools...?? That way, if it is down on power, I can force Gravograph/Hermes to send out the engineer (again!!).

Thank you so much for all the friendly advice and suggestions. I sincerely appreciate it.

30w should cut 8mm acrylic in a single pass without a problem.
Sounds like its seriously underpowered for some reason.
Flaming and serrated edges of pex sound very much like bad air assist to me.
Surely the tech trainer guy has a power meter? Doesnt sound like hes an sort of a guy that can sort your problem out , at the very least he could have confirmed the optics were in good condition, the laser was aligned , the air assist was working and it was up to spec. Ask for someone that has the barest minimum of knowledge , cos it sounds like this guy has none. Have the machine gone over with a fine toothcomb while you can. Let em check belt tensioning , bearings , motors , motion system and so on.

Check all of your mirrors and lens for clean and marks. I don't know much about the Gravograph but if it has the laser tube seperated from the work space like so many others the window needs checked along with the hidden mirror. Then a complete refocus job done. Test the beam size before each mirror and if it is changing very much reclean or replace that mirror. Because of the way it is cutting acrylic as well as wood I am thinking that the beam is either being distorted or :eek:loosing power. Hopefully being distorted. Keep records on what it is doing, who you have talked to and when. This will keep your warranty open due to an existing problem. Make sure the company understands that you have an ongoing problem and are not accepting the warranty ending until the problem is solved to your satisfaction. Many people do not realize that an existing problem can extend the warranty for a much longer period of time if it is properly documented and being discussed with the manufacturer. But this does require excellent records of your problems and their response. Include times, dates, what said and by who in your records.

Most of this is probably redundent but might help someone down the road.:cool:

One way to check if the air assist is working, Place some baby powder on the surface and run the job with the door open. The baby powder will blow around if it is working.

Quote:

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Originally Posted by Pete Wood

I admit I am concerned about the air assist, especially because of the noise coming from the back of the machine. Does anyone know of a test to prove/disprove that it is working.

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It should be easy to tell if you have air. Does your model have a small tube like the one in the attached picture? Is there pressurized air coming from it or not? If not, trace the plumbing back to the compressor and try to determine where the fault is - it could be a plumbing problem or a compressor failure.

Just got home, having spent a few hours following all your advice and suggestions:

1 Yes we have a pipe, as shown in the photo immediately above. There is no air flowing from it.

2 I proved this by putting parting powder (we have no babies, but we like casting) onto the table. It didn't move.

3 We always use the auto focus facility, so I checked the height of the lens. It was 20mm too high...!!

4 I reset the focus, saved the setting, then tasked the machine with an engraving job. I stopped it, immediately it started rastering, and checked the lens height again. It had defaulted back to the original setting and was, again, 20mm out.

5 So we have disconnected the auto focus facility - and will only use manual focus from now on.

6 I then tried cutting through 4mm acrylic. The serrations were less pronounced but we still have to use full power - and cut twice. So the tube is also looking suspect.

7 I then tried cutting through 4mm ply, on manual focus. The flames were less pronounced, compared to the auto focus setting, but still there. Again, it took three attempts at full power and slowest speed to cut through it.

I then tried damping the wood and, while this helped enormously on the first cut, as soon as the water evaporated the flames re-appeared

So I cracked open the lid, slightly, and directed a small jet of oxygen (courtesy of the thin nozzle from our oxy-acetylene welding equipment) and the flame was extinguished. Again, the fact it requires three cuts, to burn through 4mm, suggests a duff tube (but once again confirms the lack of air assist - and the need to have it working).

8 I tried lifting/lowering the bed, to see if this helped (when cutting). It didn't make much difference.

9 I reported my findings to our supplier and, following more good advice from the Creek, insisted that our warranty be extended.

10 I directed our supplier to this website, and gave them the link to this thread.

So, my thanks to EVERYONE. I am sure that Gravograph will now do their best to rectify the faults, and give our machine a thorough testing.

Pete,
you injected pure Oxygen on the flame?:eek:
Sounds like you have a default set on the machine for
the wrong size lens to me. You NEED to get your air assist working, and I wouldn't suggest using oxygen
either or we may never see another post from you.
Why not try several focal lengths to see if it helps.
Try rastering a piece of wood that's on an incline (start by manually focusing in the middle of the height) and figure out where the thinnest part of the line is, that should be the proper focal length for your lens.
Just a rambling thought.

Quote:

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Originally Posted by Brian Robison

Try rastering a piece of wood that's on an incline (start by manually focusing in the middle of the height) and figure out where the thinnest part of the line is, that should be the proper focal length for your lens.
Just a rambling thought.

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Okay, I understand. That sounds like a clever idea. So I should make up some thin wedges and place them underneath the work. Any idea what sort of angle I should be aiming at (about 15 degrees?)...?

How thick should I draw the line, for rastering...??

Oh and the oxygen thing isn't as bad as it sounds. Anyone who has done welding will know that, if you have a small flame and add anything except for a tiny amount of oxygen, at low pressure, the flame will be blown out. Hold a match and blow oxygen on to it, and you will see what I mean. But I do take your point (and promise that I am not a pyromaniac, or trying to torch our Gravograph - to claim off the insurance)...!! :)

Pete, Do you have a spare lens in the sealed carrier? If so it should say it's focal length i.e. 1.5"; 2.0"; 2.5", put it in and see if the measurement for autofocus is the same. My conversion of " to mm stinks, sorry. What is the overall distance from the material to lens. That will give you a more acurate view than of material to focus cone. I would check my air output from my compressor and make sure that it is working, then track it one conection at a time to the laser. If you have air to the laser start checking the lines inside of it for kinks, you may have to have all of the airline replaced inside of the machine if you cannot track the problem there. Don't you have a shutoff/guage between the compressor and the laser? If not I would be putting one in so that you can control the air flow and know what PSI you are running at.