Hot spots in raster engraving

[rgall0]

As you can see from the picture the are lines from left to right that are lighter then the rest of the engraving. If I run my finger over the engraving the light areas are a little deeper. This was engraved in cast 5mm acrylic at 300mm/s with laser at 16%. I've tried 18% and 20% with the same results but just deeper.

I've checked the laser alignment and it's good.

The mirrors and lens are all clean.

I have a chiller keeping the tube at 70F so the tube warming is not an issue.

I have air assist from my 33gal compressor set at 15psi flowing pressure. Is the moisture from the compressor cycling causing this? The compressor has an auto air bleed that removes water after cycle so the tanks not full of water.

[waltfl]

hi there
try turn off the air assist I never use airassist with engraving just for cutting.
greetings
waltfl

As you can see from the picture the are lines from left to right that are lighter then the rest of the engraving. If I run my finger over the engraving the light areas are a little deeper. This was engraved in cast 5mm acrylic at 300mm/s with laser at 16%. I've tried 18% and 20% with the same results but just deeper.

I've checked the laser alignment and it's good.

The mirrors and lens are all clean.

I have a chiller keeping the tube at 70F so the tube warming is not an issue.

I have air assist from my 33gal compressor set at 15psi flowing pressure. Is the moisture from the compressor cycling causing this? The compressor has an auto air bleed that removes water after cycle so the tanks not full of water.

[rgall0]

Thanks for your quick reply waltfl

I never considered turning off the air assist because I didn't want the lens to soot up but I'll give it a try.

[Tech_Marco]

What power supply do you have? It seems that it is some sort of "leaking" light beam from the power supply that caused the problem.

Try engrave a vertical rectangle see if you still get the similar result. Doing that we can eliminate the possibility of having "bad image" from the original file
If it happen again on a new drew rectangle, chance is that you have a bad power supply with low current leaking.

Try change the output frequency from 25,000Hz to 20,000Hz or to 15,000Hz see if it help. Or, do it opposite by raising frequency to higher. Use the Options under LaserCad to do it


Marco

[rgall0]

I have the better 40w PWM power supply like the ones one ebay for $179. Well it's been doing this since I installed the DSP so it must be the power supply leaking. This machine burnt out the original moshi board in 10 minutes and a replacement moshi board in 1 minute. Could the supply leaking cause that? When I installed the DSPI had to ground everything in the machine including the panel or I couldn't test fire the laser without it staying on and the panel going blank until power off. Lasercad frequency was already at 22000. I've also had to decrease cut speed the past few days to get a clean cut and it can't be the tube because I bought it from lightobject in july.

[Tech_Marco]

It look like it is power supply issue or connection. Did you use "TL" or "TH"?
If you see blank screen on the LCD, the problem is 99% "grounding" issue
Make sure you have good grounding on each devbice; DC power supply, laser power supply, machine casing... I can't emphasis enough about this!

Also, make sure the "HV" cable stay away from the signal path. I'll insulate it with a silicon tube to avoid electric spart caused by bad cable skin. Like this one: http://www.lightobject.com/6X9-Silicon- ... -P756.aspx


Marco

[rgall0]

I went over all grounds, the lead wires to the tube and dsp connects and everything was good.

I decided to open the laser power supply and take a look and found a lot of cold solder joints and a cracked cold solder joint that I believe was part of the return circuit for the blue tube lead. I went over all pads with flux and good old leaded solder and the machine works perfectly now.

I believe this might have been what killed my laser tube after only 200 hours or so of use. I never ran the tube over 16ma the whole time it was installed. The machine was probably putting in more current because it wasn't registering the right about coming out from the blue wire.