Problem- Is this laser unstable ?

[Danceswithcubes]

Greetings all,, its a shame my first post here is for a problem and not to give advice.
Has anybody come up against the following problem, the first image shows engraving on glass, 80w co2, 400mm/sec 40% power,200 dpi scan gap, engraved vector, Leetro 6535 and servo drive.The image starts off great at the beginning but banding apears towards the end, can anbody enlight'en me to a cause/soultion


The second is a similar problem but the laser power seems to ramp up and burn
lines into the engraved wood, maybe due to DPI of the image not matching the DPI on the machine, Maybe ?? could anybody conferm this for me or is the problem somwhere else.Image was in BMP 1 bit grey scale


Thankyou all very much for your time.

I hope these images work

[Tweakie]

I have been plagued with banding, although not quite as severe as you have shown there, for some time now and there are a number of different causes each creating a similar but slightly different result.

What type of laser are you using and is it DC (glass tube) or RF (metal tube) excited ?

Tweakie.

[Danceswithcubes]

Thanks for your reply, it is a glass tube and has only about 20 to 30 hours use from new, water temp is a constant 21 deg so doesn't look like the changing cooling water temp is the cause.I have had some perfect results from time to time,some images upto 700mmx700mm in size with no problems.

Rgds
Terry

[Tweakie]

Hi Terry,

Looking closely at your pics I would guess at power variation. Leave your machine disconnected from the mains overnight (to discharge any residual voltages at the tube) then in the morning check thoroughly both connections to the tube itself and all the associated wiring to make sure nothing is loose or making bad connection. Also check your incoming mains to the machine - cables, plugs etc looking for a poor connection. Check thoroughly.
Also check all the earth bonding for high resistance, right back to the earth stake if necessary.
There is a good chance it is something simple like this rather than faulty tube or power supply.

Tweakie.

[Danceswithcubes]

I am using the mains earth, you could possibly be correct when you say residual voltage, maybe the earth isn't as good as it could be in this setup, I am worried about adding a earth stake at the machine , might proberly have to disconnect earth on mains plug and use a staked earth, ill check that out with a Sparkie here.
Ill double check power supply earth and all earth points and see if it helps but I suspect you would be correct as the problem seems to get worse the longer the laser is running.

Ill get back to you on Friday and let you know what I have found

Thanks for your input

Terry

[Tweakie]

Terry,

The Chinese machine makers are notorious for fitting earth tags on top of painted metal surfaces - another thing to look for.

Tweakie.

[Danceswithcubes]

Are They ,, thanks for the heads up about that one,, this machine is from JQ and the build quality is exelent, not perfect but there is not much to complain about, worked straight away from out of the box with no problems with setup at all, nothing like the horror stories I have heard about on here, its 1.2m x 1.3 m and bult like a brick outhouse.
Ill add my own earth strap to the case and see what happens.
Thanks again

Terry

[Danceswithcubes]

Well here is an update, I checked the resistance of all connections and found that all earth points were 100% in the machine, all earth points were clean and atached direct to chassis with good quality conectors,, so,, now we move to the Garage wiring, it is a little aged so checked the resistance to the garage main board from the plug i was using, 2.5 ohm hmm should be under 0.5 ohm thats problem #1 problem #2 is the distance to the House main board, I suspect the resistance of this cable will be high as well, I need to get a long cable to creat a loop to check the resistance, Ill do that over the next 2 weeks, in off to Canadafor work so can't do anything this week.
I cannot use a second earth stake due to the difference in potential between the two earth stake's, there is one on the house, thats under stern advice from a sparkie.

I did notice a patterning in the paint around the general area at the HT end of the tube, I see what you mean about large static build up.

Might need to move the machine to another location with better earthing I think.

[zax15uk]

Originally Posted by Danceswithcubes I cannot use a second earth stake due to the difference in potential between the two earth stake's, there is one on the house, thats under stern advice from a sparkie. I did notice a patterning in the paint around the general area at the HT end of the tube, I see what you mean about large static build up.

Your sparkie is correct, you could create a dangerous situation unless the 2 sites are totally independent.

Regarding the patterning around the HV connection, that is an indicator of poor insulation and arcing rather than static. The difference is static has no current, the arcing certainly does and is lethal.

I would allow the machine to discharge, perhaps leave it overnight unplugged and then carefully check the insulation. You may find some carbon buildup from degradation of the insulator, this indicates the wiring/soldering under the insulator may have sharp points that promote arcing.

Zax.

[Danceswithcubes]

Zax Thanks for your input,
maybe I should have been a bit more descriptive, the patterning on the paint is only a shadow, barely visible in the correct light, the panel with the shadow is part of the machine body and is 80 to 100 mm from the tube itself, the tube is fine with no evedence of arcing but has a very light dust coating due to dust being attracted to the general area, a bit like the HT in an old TV tube.

I suspect the problems are coming from the power suply/tube being unstable at low outputs or the earth is not the best, the tube is an 80w and it will strike an output at 14% ( have not calabrated software to set 0% as no output and 100% as full) we are proberly running the tube at 5% or so at a guess and there is a chance that the tube is to large for a stable output.

Its all a learning curve , and we are getting good results at most of what we do

Terry

[Tweakie]

Totally confused here. You said in your first post that you were running the tube at 40%.

Tweakie.

[Danceswithcubes]

again I should have clarified my self , sorry my fault, the top image is glass at 40%, but if we put an image on wood it is lower and we have the burning problem where as on glass we have the fading problem and the banding as seen in the top image, sorry should have clarified if I was refering to wood or glass.
On the bottom image we get the burning as seen even though we use the lower power, I work night shift so at times my brain is like a -->