View Full Version : Poor Cut and Loss Of Power

Tom Ravenscroft
11-07-2008, 12:47 AM

I am new to laser engraving and would like some help please.

I went to a trade show in Shanghai and then purchased a laser with 2 lasers. A 120W for cutting and 50w for engraving. I was told the 120W would not engave fine enough. The bed size is 1500 x 900mm

I have set up the machine and cut a few odds and ends, but i am having problems cutting 10mm acrylic. The top 2mm of the cut is rough, but the bottom 8mm is beautifully smooth. I have tried adjusting the focus up and down, but haven't had any luck, nor has speed helped. What is another possible cause for the problem.

Another thing i noticed is that when we first cut material, it would cut say 3mm acrylic at a speed of 19. Now the speed has to be 14 and all the other parameters are still the same. I have only had the machine for a short while (+- a week) and we have only had limited time to play with it, so i am at a loss as to what is causing the loss of power. The machine has a water chiller, so i don't think heat is a factor.

Any input would be much appreciated.


Tom from Perth

Margaret Turco
11-07-2008, 3:03 AM
Hi Tom! Does your machine have air assist?

David Fairfield
11-07-2008, 8:19 AM
If that were my machine, I'd be checking if the material were sitting flat and level. If the material is sitting at an angle, it leaves the focal plane of the laser and cuts become ragged. Could be the bed or the vector table is out of alignment or your material is warped.

Incorrectly seated material is the only thing I've experienced that could cause the cut quality to change as drastically as you describe. I'd also check for debris or dirt build up on the lens, since you say you've lost a lot of power in a short time.

Best advice I can give you is buy American. The stuff works and we need the help :rolleyes: :)


Tom Ravenscroft
11-07-2008, 10:43 AM
The nozzle does have air assist, but the compressor supplied with the machine is quite small and supplies air to both nozzles. Could it be that the air is insufficient.

The teble and the material is flat, so i don't think that is an issue.

I would have loved to purchase an American machine, but i only paid +-$12000 and an American one of the same size would have set me back $80 000-$100 000 and now that the Aussie dollar has fallen from $0.95 - $0.67, it would probably cost a lot more.

I will check the lens, as i tried cutting some plywood which made a lot of smoke. What should i use to clean it with?



David Fairfield
11-07-2008, 11:09 AM
Check the owners manual for cleaning instructions. (I assume you already checked the trouble shooting guide?)

Lens paper is the best material for cleaning lenses. If you don't have any, I think a Q-tip or a fine cotton cloth will work. Dampen the material with pure grain alcohol (ethyl) you can get it at a liquor store.

I hear you, the initial investment of a Chinese import is attractive. But I think over time, higher quality is less costly.


Dave Johnson29
11-07-2008, 11:43 AM
Could it be that the air is insufficient.


What should i use to clean it with?

Hi Tom,

Put small plastic valves in the air assist lines so you can direct all the air to one or the other. Look for lab-supply places they will sell 1/8" and 1/4" valves that have push to connect fittings.

To clean the lens if your manual does not say otherwise, use Isopropyl alcohol from a local pharmacy. Get the highest quality you can as the cheaper stuff may leave a fine film residue. Use lens tissues from a camera store. Try not to touch the lens with bare fingers, use the tissues to handle it.

Pay particular attention to the way "up" the lens is when you remove it. It may be convex top and and concave bottom. The concave is usually the up side. You may not be able to see the curvature, but after cleaning, rub it gently between your fingers with the tissue and you will feel which is which.

Tom Ravenscroft
11-14-2008, 5:07 PM
Hi Guys - Thanks for all the input

I have changed the laser tube and it is now back to full strength. We will have to see how long this tube lasts. I think the first one may have broken down early because the chiller was set too low. I had it set at 20-25 deg and ambient is 30+ at times. Apperently this can cause condensation to appear on the output lens of the laser tube, causing loss of power and shortening of the life of the tube? I guess I should have read the instructions first, but like all males, you take it out of the box and start using it right away. Only consult the manual when all else fails.

Changed the air flow to include a valve so I can regulate the air to the cutting nozzle.

Checked all the mirrors and lenses, found the nozzle was getting hot and realigned the morror to the lens and now it is cutting beautifully - 4mm/s through 10mm acrylic. How does that rate?

I have had quite a bit of drama with my machine. The power supply to the engraving tube stopped working and Golden Laser shipped me a spare on the basis we pay for the air freight and return the broken unit. Not happy, but what can you do.

After making more samples, the engraving laser failed again, but this time it was only a trip switch that had tripped. It is a 10A switch and is only carring a load of 0.1A, so i was puzzled.

Eventually I found that occasionally when the exhaust fan or compressor is switched on, they voltage to the laser power supply spikes from 235 to 305V, so i guess this may be the problem. The compressor and fan are wired into the Lasers cabinet. I have now put them on the mains power supply and hopefully that will be the end of those problems.

At present everything is running as it should, all I need to find out now is why the engraving head engraves skew at times. Instead of nice neat lettering it sometimes comes out wavy. I think it is a software issue because I export from Corel X4 or V12 and inport back into the Golden Laser software. I hope to sort this out in the next day or so and then we can start using it commercially.

I have tried engraing photos but the results have been poor. Does anyone know if PhotoGrav will output files that will work on a Chinese machine.

Once more, thanks for the help. I hope that through our pooled experiences we can help others make better decisions re their purchases and will keep you up to date with out sucesses and failures with this machine.

Bill Cunningham
11-15-2008, 2:46 PM
The output file from photograv is a binary file or a 'true' black and white file in .bmp for the older version, and I think the newer version outputs .tif as well.. (don't have the new version) If you can raster from a bit image file, no doubt one of those is the one you will be using.. Just don't fall into the trap of thinking a black and white .jpg is the same thing.. it is not.. There is no such thing as a binary .jpg

Mike Null
11-16-2008, 12:28 AM
I would suggest using lens cleaner from a camera store rather than isopropyl alcohol. In the absence of that use acetone but do not soak the lens in it.

Q-tips or lens paper is ok to use.

Tom Ravenscroft
11-16-2008, 4:52 AM
I have used acetone and it seems to work well.

I am still having a problem where my photos are printing out skew. I made some fountain filled black to white rectangles today in Corel and exported as a full colour TIFF.

Imported them into Photoshop and made them black and white bitmaps using various parameters.

Looks like the diffusion pattern causes my photos to print skew - out of square so I will have to try something else when I use the Gold Method

Using half tone worked OK, but I exported at 300 DPI and so when I converted to black and white is used circles, freq 300 and angle 45%. This and another using lines insted of circles printed out darker areas in the section that was supposed to be 50%white-50%black. Read the instructions for the Chines machinew againand for 300DPI they suggest freq of 50 when converting, so i tried that and got a much more even gradient and it printed out with square corners.

Is there some correaltion between DPI, frequency and angle when converting to black and white using half tones?

Hopefully I am on the right track - will try a photo tomorrow.

Rodne Gold
11-16-2008, 11:31 AM
if your engraving skews , and you have a stepper motor machine , its losing stepas somewhere.
If it skews left to right , its losing steps in the X axis. Try slowing down the engraving speed.
I think lens alignment is also part of your problem in terms of somewhat inconsistent engraving/cutting over the bed of the machine ESPECIALLY if you say your nozzle is getting hot. You need to align it so the exit beam is dead centre on the final lens all over the table. Often getting it right at one spot means it's totally out at another. Alignment is fiddly but WELL worth the effort. If for example you can increase speed 25% , thats a huge gain , 33% more than you had before. I was looking at the same laser you got , so am VERY interested in all your trials and tribunes you have with this machine.
10mm pex at 4mm per sec is a little slow , imho for a 120w machine , but getting thru 4mm pex succesfully is good.
You might have to fine tune your final focussing distance as gauges might not be correct.
Air assist pressure and direction is critical to cutting pex , it ejects the melt so prevents remelting and has to still allow the pex not to cool too much to not get a nice polished edge. Stops flaming too.
Ideally you want to adjust air pressure to the point where acrylic flames and then whack it up a bit till its stops and a bit more for safety. That should give you best edge quality.