Measuring laser current.

[DukeEuphoria]

Hi all.
I'm still having, what I would consider, no happiness at all with getting my cutter to do work at a decent rate.

The machine is an old school 3040, one of these. http://www.laserscript.co.uk/LS3040.html and with a shiny new 40w tube I can (mostly) cut through 3mm birch laser ply at at speed of 3, and 100% power.
Having seen another machine cutting holes out of the same sheet of ply at speed 10 at 65% power with a nominal 30w tube I think something isn't right.

I've cleaned the mirrors, checked the alignment as best I can, and am getting what I think is a well focussed spot.

So it's time to do some serious investigating as to what the trouble might be and measure the current that's being fed to the tube.

So, does anyone know of any downside to shunting a 100ma panel meter in series with the 0v end of the laser tube (black wire, closest to the output end of the laser) ?

Or indeed any other things I might want to be aware of.

Many thanks,
Duke E.

[Spooky]

Heya Duke,

I can't comment on the addition of a meter as there are safety issues with me saying so. (I'm sure you understand) but the power does sound well down.....try dropping your power to 70% and do a ramp test for the focal point. a mm up or down can make a huge difference to cutting ability.
When psu's fail they generally go in a big way...ie: dead and no fire but possible I guess, hows about we have a go at the simple things (read:free) things first then start looking at maybe big items?

Some questions if I may?

What coolant are you using?
What temperature is the cooling water?
Are there any bubbles in the mirror chamber at the end of the tube?
How well is your extraction working (any smoke in the cabinet)?
How are you storing the wood? (Damp content)
When you say alignment, how good is it set?
Do you have air assist?
When was the coolant last cleaned out?

cheers

Dave

[DukeEuphoria]

Hi Dave, many thanks for the reply.

Since I last posted on here I've hoiked the machine out of its corner and stripped it down quite extensively.
(all day job, required emptying most of the workshop to get space to do things)

The main thing I discovered was that one of the mirrors, predictably the one that's sited inside the laser chamber and a real pig to get at, was _black_ with baked on filth that looks like blow through from masking tape adhesive.

So, removed _all_ the mirrors this time and left them to soak in isporopyl for an hour, a light dunk in some acetone and then a polish with a lens cloth.
Re align using 20mm wooden disks in place of mirrors, one by one. Works v well and keeps the mirrors free of grit.

Unsurprisingly, massive difference, machine now cutting beautifully aside from one thing.

The Y axis is off true by quite a bit squares ain't square.... Going to have to work out how to re-align that now.

But to answer your questions:-
Coolant, distilled water (dehumidifier feeds laser coolant bucket)
no idea of exact temperature, water is cold to touch, not cold enough to hurt, but with a definite chill to it.
No bubbles anywhere in the tube
Extraction is sucking the smoke nicely out through the side vent
Wood is stored in a plastic box next to the dehumidifier
Alignment I'd say is ok, but not perfect, the laser hits the final mirror through the wee hole in all corners of the bed, but it does wander around the center 5mm or so. Not dead center.
Air assist is working well.
Coolant refreshed when I replaced the tube (last week or so)

[Spooky]

DON'T use Acetone Duke, it will damage the AR coating on Zinc Selenide lens's. Use Isopropanol Alcohol, it's far less destructive

The minor off-alignment could well be causing the issues on the two remaining sides.

cheers

Dave