"Overshoot" spots during engrave

[SWMS]

I've just purchased a shim to isolate the motor from the frame. I will test out the steps and current when I go and look at my machine and let you know. I bought mine second hand but the AWC08 is from lightobject, so thats why I am on the forums and I am not sure of my stepper driver settings and current settings.

this will either be this weekend or next.

[Toasty]

Please keep us updated if you find a solution to the extra dots. I have the exact issue on certain materials. Here is a link to my recent post:

viewtopic.php?f=70&t=3117

I engrave a lot of black plastic. If it's laser scatter I imagine the black absorbs more of the light making it more noticeable. I should try some anodized aluminum, I know anodizing is very sensitive to laser light so the scattered beam would show up very easily. On most other materials I don't have the problem, perhaps because you just can't see it on lighter colors.

Like you, I don't think I have any loose mirrors and I know for sure my lens isn't loose since it's glued into it's holder and the holder is tight.

I've had some luck increasing my power a little and raising the speed a bit. My original theory was that hot splatter was landing back on the plastic causing the problem. I'm not so sure now that I've seen your pictures. I would sure like to find a solution though.

[DonL]

Because the laser fires with high voltage, I would make sure that your grounds are A1 if you have not tried that... And if you are not using the chassis ground, consider using it. House mains have a ground but I have seen them less than perfect. If your chassis is not well grounded, you can end up charging the water like a capacitor and when the laser stops firing, the water gives up some voltage and you can get spotting as your laser is not picky on where the HV comes from

[Toasty]

Because the laser fires with high voltage, I would make sure that your grounds are A1 if you have not tried that... And if you are not using the chassis ground, consider using it. House mains have a ground but I have seen them less than perfect. If your chassis is not well grounded, you can end up charging the water like a capacitor and when the laser stops firing, the water gives up some voltage and you can get spotting as your laser is not picky on where the HV comes from

Thanks for the reply! That makes a lot of sense. My machine is grounded very well but is there a good way to ground the cooling water?

[DonL]

Because the laser fires with high voltage, I would make sure that your grounds are A1 if you have not tried that... And if you are not using the chassis ground, consider using it. House mains have a ground but I have seen them less than perfect. If your chassis is not well grounded, you can end up charging the water like a capacitor and when the laser stops firing, the water gives up some voltage and you can get spotting as your laser is not picky on where the HV comes from

Thanks for the reply! That makes a lot of sense. My machine is grounded very well but is there a good way to ground the cooling water?

You could clamp a 12 or 14 guage wire to a nearby cold water pipe and strip off 12" and stick that in the water or run the wire from the grounding post on the laser so the water is grounded to the same potential as the case.

You could also check that the laser tube ground is good, Jump a wire across the amp meter to make sure the meter is not the source of a bad ground...

Or run a jumper from the wire that retiurns from the tube, ground, and attach it to the ground stud. Maybe the power supply ground is not perfect.

I have burned a fair bit of plastic and never had an issue of spotting. I have heard of people getting shocks from the cooling water when the laser is running and other strange issues that are always attributed to poor grounds. Don't trust the ground in your electrical outlet

[Toasty]

Well, I tried grounding the water with no change in the random dots. It's possible I'm missing something but I've gone over this machine with a fine tooth comb and I just don't see any other grounding issues. I really think my original theory of splatter might be what's causing this on black plastic. As I said, I've never seen it on anything else. I really should try to engrave some anodized aluminum and see if I get the dots. That would pretty much tell me if it's scatter or splatter. lol

Again, if the op finds a solution please post it!

[Tech_Marco]

Do you have spare mirrors/lens to try.
May be the coating on the optics damaged.
Also, try to engrave without the laser tip on and no air assisted


Marco

[Toasty]

Do you have spare mirrors/lens to try.
May be the coating on the optics damaged.
Also, try to engrave without the laser tip on and no air assisted


Marco

Marco,

I'm using a high quality lens and mirrors that are like brand new. Like I mentioned in my thread about the same problem, this machine has done this since I purchased it around 3 years ago and that was before I switched to the good lens and mirrors. Rollers are tight and I just don't see anything obvious that's causing it.

I also never engrave with air assist since it makes a huge mess out of the plastic. I did, however, try it with air assist but it didn't change the dot issue. I also don't run a laser tip, my lens is open but I have a very good exhaust system so it stays very clean. But, I see where you're going with that and no, the beam isn't scattering off of the lens holder.

I've always engraved plastic at a VERY low power setting, maybe too low. Is it possible that my power supply can't handle my low settings? After raising the power and speed a bit I can almost get rid of the dots. Again, my dots only show up on black plastic, I don't have the problem on other materials so maybe my problem is different. Again, I keep going back to a splattering issue perhaps.

[Tech_Marco]

I don't recommend anyone doing engraving with 130W or higher power laser tube. Bigger tube require higher current to enter stable zone or the beam will not be solid and fluctuated a lot. If you put a piece of paper to the laser head inlet hole and fire laser at lower current, you will see that tje beam spot is very big and not in good shape. I think that is the cause.

Soluation: increase laser current and increase engraving speed( not the best solution), or replace the tube with a 100W or a 80w(better result)


Marco

[Toasty]

I don't recommend anyone doing engraving with 130W or higher power laser tube. Bigger tube require higher current to enter stable zone or the beam will not be solid and fluctuated a lot. If you put a piece of paper to the laser head inlet hole and fire laser at lower current, you will see that tje beam spot is very big and not in good shape. I think that is the cause.

Soluation: increase laser current and increase engraving speed( not the best solution), or replace the tube with a 100W or a 80w(better result)


Marco

I have a dsp modified k40 laser engraver so nowhere near that kind of power. I do, however, generally engrave at only 12% power so perhaps the same issue just on a smaller scale? If I move up to around 13.5% power it goes away, so maybe...

[omegait]

Ok, had a long adventure with a wiring failure to the Y-axis motor and a web browser that was a couple of months overdue for a reboot...

One new data point: the dots only happen on the trailing edge. I tested this by switching from x_swing to x_unilateral: all the dots were on the trailing edge.

I upgraded my tests with a 4X stereo microscope so I could see exactly what was going on at the surface of the aluminum. That made all the difference in the world as I scientifically went through a lot of combinations of speed and power.
The microscope also allowed me to see, in detail, that the dots are all teardrop shaped with the narrowing ends trailing away from the main pattern. Definitely a misfire situation, and it could be caused by many things: electrostatic, resonance, whathaveyou. However I did get a chance to look at a 3rd party's part and I saw the same effect there: it wasn't visible with the naked eye because it was so close to the real pattern.

From those observations, and Marcos' very helpful advice about the 150W being way too powerful, and DonL's example with power levels and speeds, I was able to find a set of settings where the machine is happy and produces acceptable parts:

Basic-Anodized Aluminum Engrave:
* 400mm/s. Faster speed results in needing more power, slower speeds results in needing less power.
* 15-19% power on our 150W tube, depending on lens focal length and quality. Going lower power results in an inconsistent finish, just what Marcos was talking about above, going higher increases the overshoot spots beyond what I consider acceptable. I also found that too high of power, in the upper end of the range I gave, starts melting the aluminum and results in a light grey pattern that scrubs off easily exposing bare metal. Getting the power level Just Right results in a nice white finish that takes a heavy amount of abuse. It's real obvious in the microscope too: just watch the surface patterns.
* 0.03mm line spacing. Very heavily depends on your optics. My optics, including my F38.1, leave lines 3x the width of the other guy's laser.

Basic-Anodized Aluminum Marking Cut:
* 10mm/s. Slower is pointless, faster results in wobbling lines.
* Power Min 15%, Max 23%. Determined after finding the fastest speed that left no wobble in the lines.

This means that our parts are now taking about 2x longer to produce than previously, but the results are far and above what I started out with!

During my observations with the microscope I did notice what seems to be a minor control issue, and it may again have to do with being too powerful of a laser. When the two edges get close together along the line of the engrave, ie the "off" time gets short, the engrave pattern's ends will start exceeding the pattern space, closing the gap faster than they should. It's like as if the laser isn't being turned off in time and being started back up too early when it has only a short span to skip over. Only a minor cosmetic detail, just was a surprising find.

And yes, the initial beam pattern is not a nice clean circle at the emitter.

[DonL]

I generally never cut after engrave, I find my edges even at 400mm/s are very clean, it does tend to give a bit of dimension to the lettering I must admit and so it is a matter of taste. Having said that, I tried the cut after engrave several times and I set the speed to 300mm/s with 40% Power, (I only have a rebuilt 200x300 35w with original X-Y Frame and Steppers)) and it was fine, no wavy lines,

I would love to see what you get when you run the test pattern just as it is on say a small sheet of scrap plywood.

viewtopic.php?f=16&t=2698

I will do the same tonight and post it, If you don't get at least as good a result as I do, some more troubleshooting will be in order Or you can send me a laserCAD file of what you are engraving and I will run it on some Anodized Aluminum and post the result, I will use a macro lens on my 24mp camera to get a good close look....

Don

[DonL]

Well... looks like I have to eat some crow....
I am getting wavy lines too, looks like vibration issues, but like I said, I seldome use CUT unless I am cutting and then it is at low speed like 10mm/s so not a concern for me. when engraving the head movement is more fluid so much less vibration

[omegait]

It is done. Definitely has wobbles, but not bad. I took the shot using a 600dpi scanner, then scaled down until the website allowed the upload.

Marco do you have any links showing what and how to tune for acceleration?

[seeigecannon]

It is done. Definitely has wobbles, but not bad.

MX-2600N_20160413_165209_001.jpg

This is a problem I am working on with my laser. If I put a finger on the bottom of my laser head I can get it to wobble a bit. Well under a millimeter, but it is too much for me now that I am working on optimizing my carriage accelerations. I have a new pillow bearing on order, but it is being shipped from China, so it will be here sometime between Monday and June. When I get it I will try to get creative with springs or something to pre-load the bearings and keep them from being able to vibrate. If I manage to pull something interesting off I will make a post about it.