Fiber image shift

This issue has been going on for a long time and I always blamed it on the Z height but now I have eliminated that so I am at a loss.

Here is the setup.

I engrave about 80 different anodized aluminum parts on two different fiber lasers, they are separated by the Z height of the engraving area - 60mm or 16mm. I use my 3D printer to create fixtures to hold the parts, some one part and others hold multiple parts, at the correct height so there is no moving of the Z axis. Some of the parts have an engravable area as small .2" x .35" so alignment is critical, .001" off and you can see it very easily. Fixing the Z height and using fixtures eliminates any possible height differences and should eliminate size/position errors by not having the Z exactly the same every time I run the part.

For the last several months I have noticed a bit of movement of the engraving area, usually no more than about .1mm, or less, every week. That doesn't sound like much but with the tolerances we need to maintain, it's a lot!

There is nothing that moves, the fixtures are solidly held in place on an aluminum plate using dowel pins that they are held against, and the parts don't move in the fixtures. Nothing with the laser is changed, it doesn't get moved, adjusted, etc. The parts are all within .0001 tolerance.

I have done everything I can imagine to stop this movement but something is moving. I'm guessing it's the mirrors because that's the only moving part, but I can't understand why they would move at all, and if they did move, why so little and fairly consistently.

Any ideas would be welcome!

I think it is inherent in the lasers. I've suspected it, as I too use fixtures and have picked up where I left off the following day and have to adjust location. I don't know if it is mirrors, or just the laser output.

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Originally Posted by John Lifer

I think it is inherent in the lasers. I've suspected it, as I too use fixtures and have picked up where I left off the following day and have to adjust location. I don't know if it is mirrors, or just the laser output.

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Have you noticed it on one axis more than the other? Mine is 90% on Y.

Interesting, as that's never happened to me, and have jobs run into 2 days quite often, never noticed any misalignment.

Is this happening with both machines? Do you 'exercise' your mirrors? Like, draw a big circle beyond the working boundaries and let the machine redlight it for a few minutes? I do it occasionally just to see where the cutoff points are if I'm needed to engrave past the limits.

In the F3 menu is an option to locate the laser/red LED home position to your own XY coordinates, maybe set and tweak it to zero to a spot where the light just barely touches the corner of the jig or something, so that if it's moved you'll either have too much red light or no red light. This probably won't fix the problem but it may be a good way to let you know that it HAS moved.

WHY it's moving? Who knows-- You could pull connectors and clean them... Maybe try a different USB port on the computer, and/or a different cable.

... I've been having stupid weird USB issues here lately, I'll have to shoot some video. USB and me have never worked well together...

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Originally Posted by Kev Williams

Interesting, as that's never happened to me, and have jobs run into 2 days quite often, never noticed any misalignment.

Is this happening with both machines? Do you 'exercise' your mirrors? Like, draw a big circle beyond the working boundaries and let the machine redlight it for a few minutes? I do it occasionally just to see where the cutoff points are if I'm needed to engrave past the limits.

In the F3 menu is an option to locate the laser/red LED home position to your own XY coordinates, maybe set and tweak it to zero to a spot where the light just barely touches the corner of the jig or something, so that if it's moved you'll either have too much red light or no red light. This probably won't fix the problem but it may be a good way to let you know that it HAS moved.

WHY it's moving? Who knows-- You could pull connectors and clean them... Maybe try a different USB port on the computer, and/or a different cable.

... I've been having stupid weird USB issues here lately, I'll have to shoot some video. USB and me have never worked well together...

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It is happening with both machines and has from day 1. 99.9% of my engraving for the last 3 years has been within about a 2-3" area directly below the lens. Unfortunately, the red dot is so big that it's useless for checking position. I have test parts I put in the fixture for checking and adjusting alignment. Most often the aligment is fractions of a single line width, so using anything but the test parts isn't very accurate.

Both are "console" type machines with a built-in computer, and since I bought them almost a year apart, they are both different computers and the component parts are likely to be different manufacturers and for sure from different batches. Cabling could be a possibility but since they both do it, and always have, then either they are both sketchy or they are not the problem.

I'm not ruling out anything, but it's almost got to be something common between the two machines and the only things that are truly common are the scanhead and laser source - but almost a year apart in manufacture...

What I'm tempted to do is cut up a slew of thin anodized aluminum sheet into 3" squares and laser cross-hairs with the intersection being 0,0 onto them all in one setting - should be all the same that way. Then I could use one every few days to check alignment and instead of adjusting the fixtures, adjust the laser back to hit the cross-hairs. I'd probably end up running out of adjustment eventually, but hopefully that would be a long ways down the road.

One thing Triumph did with my machine was they added a rotary dimmer switch for the LED's. It REALLY helps to be able to dim them down (and turn them off!)- works great with anodized test pieces, you can dim the red down to where you can barely see it against the black, but lights up big time when it hits a white engraved line. I've been able to remove engraved parts and re-align them perfectly on this machine just because of the dimmable red light. Another thing that helps with viewing redlighting is 2x and 3x loupes, they help with dim AND too bright...

Two or three pieces of smoked plex will dim the red down too, but it changes the angle of the beam. But to aim just a static dot, it works :)

So guess what-- ;)

My watch guys are custom building 35 watches for a company's execs, and I'm currently annealing the SS backs-

Last night I saved the job, shut down, this morning I start up, ran a back, and it looked off-center, too far right...I'm using a centering vice, engraving these axis swap top to left, I have a crosshair for redlight centering the backs to the center point. Sure enough, the Y axis is too far up, or right as to my engraving. I stepped it back by jogging, it was exactly .6mm off. The X was dead on.

This was my ebay2 machine. It's funny--the other day I demo'd this machine for a customer, I outlined 'TEST' at .38mm tall @ 8000mm/Sec, the distance from lens to focus point is 15-1/2", and the engraving was nearly perfect. I have to wonder, as ludicrously precise as even these 'bargain basement' galvo scanheads are, why can't they locate the same home origin consistently?

I'll be checking more closely from now on!

I still don't think it is a particular machine. I think it is just the laser. Every time I turn mine on I have to refocus and move. I've been doing a lot of the same pieces of jewelry for a customer and I've left jig in machine overnight at least 2 or 3 times.
I have to readjust when I turn it on in the morning..... Just part of it.

Just the accuracy of the motors on the mirrors. Do the math, your head is "X" from the work, trig it out and see how much the mirror has to be off to make it off .001" and you'll see the problem. On the motors themselves, it's some fraction of a second of a degree, more than likely. You won't get that level of precision out of a Chinese motor (or even many western motors).

Just my opinion, it's not going to get any better, ever, unless you drop big money.