unusual dot shape when test firing

[Ian Stewart-Koster]

Hi Folks,
after realigning the mirrors on the Chinese Goldenlaser, after we had the broken/burned lens last month, I have a bit of a peculiar thing happening.
Changing the broken lens for a new lens has not changed it either.

The beam makes the burn mark on tape fairly well dead centre on M1 & M2 all over the bed, and it sems to hit M3 in the same place too.
A nice oval or circle.

With the lens removed, the burn shape on the bed isn't the nice circle though-it's like a circle with a bit of a banana or a fingernail clipping sliver at one edge. Not much of a sliver, but noticable.

With the lens in and the air nozzle on, and the beam aligned dead centre through the air nozzle, when I do a test burn, the resulting dot is like Saturn - a blob, with a skinny mark off each end. Changing the focus doesn't change the shape- a short line with the main hole in the centre.
Rotating the mirror or lens made no difference.The direction of the line is left-right in line with the X axis.

For the most part the fatter aspect is not significant, but it means that a rectangular hole is going to be a whisker wider in one dimention than the other.

I was wondering if anyone might have any ideas on what could be contributing to this extra piece of beam?

[Jerome Stanek]

Is the beam actually straight up and down. Test by placing a piece of wood on the bed with the lens close to it and fire and test shot then without moving the wood lower the bed and fire another test dot they should be exactly the same spot

[Doug Fisher]

My first thought, which I think is what Jerome is suggesting too, is that your beam might hitting the inside edge of the nozzle and reflecting off of it.

[Jerome Stanek]

My first thought, which I think is what Jerome is suggesting too, is that your beam might hitting the inside edge of the nozzle and reflecting off of it.

Yes that is what I was getting at. I do know that on mine I have the beam enter the final mirror a little high so the beam hits the lens dead center for some reason the mirror is a little to far back for the beam to hit the lens dead center when I center the beam entering the last mirror.

[Doug Fisher]

>>I have the beam enter the final mirror a little high so the beam hits the lens dead center<<

From what I have read, the is as intended/correct for most heads on Chinese lasers.

[Dave Sheldrake]

opposite way round

Aim around 2mm low on the last mirror

[Kev Williams]

take the nozzle off, then there's nothing for the beam to hit :)

If you need air, fab something up-- this is just a scrap of laserbrass bent to go round the lens tube and hold some old tubing in place. Works just dandy. I just use the diaphragm pump that came with the laser with no air valve. If I just need a poof of air to move leather or wood smoke away, I remove the smaller end piece. As shown works for most anything. If I ever need more power, I have a smaller hose that'll fit inside this one. But I've never needed it...
366481366482

My old ULS never had a cone nozzle, my LS900 never had one, and the GCC never had one. The Triumph came with one, and even with the beam hitting the hole dead to rights center, in testing I found I had noticeably more power without the cone, and especially with a 3" lens. Another reason I don't like cones is because I use shims and steel bars and stuff that are too tall, the cone will hit them.

At the least, remove your cone and re-test, that'll tell you if the cone is at fault... :)

[Jerome Stanek]

opposite way round

Aim around 2mm low on the last mirror

If I go lower it gives me an angle cut

[Dave Sheldrake]

Then the rest of the optical train is off, you should be able to set the beam perpendicular using the last mirror alone

[Jerome Stanek]

Then the rest of the optical train is off, you should be able to set the beam perpendicular using the last mirror alone

I have it perpendicular I test fired with the bed as high as it would go then lowered the bed all the way down and the holes lined up perfectly

[Ian Stewart-Koster]

Thanks again for the advice.

I looked at umpteen options, and ended up blasting the bed with the lens out, then trying it again with the elns in, so see if the pin burn was central to the big splotch - it wasn't. It would hit on the outer edge.
Trying to move the mirror on the head to bring the pin prick into the centre of the big dot worked in reverse - the more thought I shifted it in, the further out it actually went.
When they were finally aligned nicely, I pyut the air nozzle back on - I like it, Kev. It works without it, but I need a decent airblast to get keep the smoke from diffusing the beam when marching through 20mm thick acrylic.
Amyhow, putting the air nozzle back, made it tweeible, and I got comet-shaped blasts on the substrate, mewaning the beam was bouncing off the inside of the air nozzle.
I must have tweaked it for 2 hours, going back and forth.
It turns out that the lens itself must not lie dead flat or perpendiculat in the lens holder, because when I rotated it, I could shift where the pin-prick blast landed, compared with the unfocused blob. Nearly 2.5mm variation in a circular path.

I took the lens out, cleaned everythng agajn, replaced it, and still got the variations, so twisted it to get it nicely centred, marked the centreline with a white paint pen, and re-tuned it with the air nozzle back on, and it's suddenly all lined up again and cutting nicely & finely, with or without the air nozzle.

Now the nozzle is locked into alignment, I don't want to shift it, to refigure the focus, so had to do ramp tests to get to figure the ideal nozzle height above substrate for optimum focus, with the 4" lens. 8mm was the answer, so I made a spacer block of 6mm + 2mm acrylic stuck together.
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Problem #2 (or is it 12?) A job I did 2 weeks ago involved lasering some letter-backs to fit behind some cnc routed letters.
For some reason I could not fathom, the lasered backs were out by 1/4" in size on the bigger letters (24" high & wide)>
So I set it to laser a 600 x 500 rectangle in cardboard, and measured it - it was 604 and a bit x 503 and a bit mm. No wonder!

That means going into the paramater settings of stepper counts per mm, and resetting the laser, from 32mm per 18200steps per revolution, to 31.918 from memory, after a bit of mathematics & tweaking, and now two dots 1200 mm apart, ARE 1200 mm apart, not 1208.5 mm apart like they were!

So I can breathe again! (briefly!...heading offf to fix the HP latex printer now after a media jam broke a feeding sensor) ;)

Thanks!

[Ian Stewart-Koster]

P.S. with this machine, I can't raise or lower the bed- only raise or lower the lens and air nozzle.