How to test is tube is broken?

Discussions on optics for laser cutter/engravers

How to test is tube is broken?

Postby StigOE » Fri Dec 02, 2011 11:14 pm

All,

Does anyone know how I can test if the laser tube is broken? My board, for amongst other things, giving power to the mA-meter, hasn't arrived yet, so I can't measure the current yet. I connected up two wires to the wires coming from the sense resistor and connected them up to a multimeter so I could get a feel for the current versus % on the pot-meter. I was testing a couple of times and suddenly I couldn't get the laser to fire. The pot was not over 50-60% and it is a 40W PSU. I still have the green light in the PSU, but whenever I try to fire the laser manually, I don't get the plasma glow. Have I managed to fry the tube already...?

Stig
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Re: How to test is tube is broken?

Postby StigOE » Sat Dec 03, 2011 12:16 am

Looks like it was a false alarm...

After I turned off the PC and laser, I remembered that the PSU had a test button and just for completeness' sake, I turned on the laser again and pressed the button and the laser fired. When I tried the manual fire again, it worked. I have no idea why it suddenly started working again.

Stig
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Re: How to test is tube is broken?

Postby Gadroc » Sat Dec 03, 2011 1:48 am

Be very careful with out a amp meter on that. 50% of the POT on my K40 machine was easily way over max amps for a 40W tube.
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Re: How to test is tube is broken?

Postby StigOE » Sat Dec 03, 2011 10:47 am

I have been careful not to set it too high. That's why I connected my multimeter to it yesterday, because I had to use about 10 passes to cut 5mm acrylic. The sense resistor is 1.1ohm and my multimeter showed about 17mA, so it shouldn't be too high. Hopefully my board for giving power to the mA-meter, controlling the laser pointer and extra fan and checking water flow is showing up soon.
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Re: How to test is tube is broken?

Postby twehr » Sat Dec 03, 2011 1:04 pm

StigOE wrote:I have been careful not to set it too high. That's why I connected my multimeter to it yesterday, because I had to use about 10 passes to cut 5mm acrylic. The sense resistor is 1.1ohm and my multimeter showed about 17mA, so it shouldn't be too high. Hopefully my board for giving power to the mA-meter, controlling the laser pointer and extra fan and checking water flow is showing up soon.


10 passes to cut 5mm acrylic?
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Re: How to test is tube is broken?

Postby Gadroc » Sat Dec 03, 2011 1:22 pm

What speed where you trying to use?

Something definitely seem wrong as I can cut 5mm acrylic on my machine using 9ma at 4mm/s in one pass. I'm on a 40W laser that came with my K40 machine.
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Re: How to test is tube is broken?

Postby StigOE » Sat Dec 03, 2011 3:11 pm

I'm amazed at the high number of needed passes as well. I'm using 50% speed with a Retina card. I don't know how many mm/s that is. I need to check once more that the beam is coming out of the air assist nozzle without hitting something, but the red laser comes out like it should. With my old China laser, I used something like 4 passes at 50% speed to cut the same thickness. Does 73mm from the top of the laser carriage plate sound about right for the distance to the material? I did try a a test with a slanted peice of wood, and about 73mm looked to make the thinnest line.
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Re: How to test is tube is broken?

Postby StigOE » Sat Dec 03, 2011 4:16 pm

I think the laser is adjusted good enough. The beam couldn't have come out more in the middle... :)
Scan-111203-0002.jpg
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Re: How to test is tube is broken?

Postby bluewave65 » Mon Apr 02, 2012 7:37 pm

I can cut 5mm acrylic on my machine using 9ma at 4mm/s in one pass
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9mA ??????? - Unbelivable

I can cut 3mm at 100% ( 18mA ) @ 5mm / Sec ....
I got a 40w tube too.
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