Does Switching lenes cause miss alignment?

[Mike Mackenzie]

Scott,

Did you just change the lens or the entire plate? If you changed the entire plate you could try taking the lens and mount that to your existing plate to see if that corrected the offset. I still think it is important to double check your focus when changing out a lens.

[Scott Shepherd]

Yes Mike, I got the entire assembly- the plate, the lens, the mirror, all mounted. I just pull one out and put the other in.

I do agree, when you change lens, you should verify focus.

[Richard Rumancik]

. . .My swap out was a 2.0 lens for a 2.0 lens. It was off about .040-.050" left to right. Up and down was pretty close.

I don't know how easy it is for a manufacturer to "aim" a lens - for lack of a better term. In your case you have a deviation of about 1 degree of "aim" between the two lenses. So if the first lens was pointing 0.5 degrees left and the new one was 0.5 degrees right that would give you a .040" offset (1mm). It is not routine to change lenses in the middle of a job, so your situation was unusual. I expect it is just manufacturing tolerances between the lenses.

It might be more common to change from 2" to 1.5" FL lens in the middle of a job - but this thread suggests that if one tries to do that, you may not align. In other words, each lens has its unique "home" or (0,0) position. It would be nice if they could be manufactured so accurately that this did not happen, but laser engravers are not made to that level of accuracy.

In a machine tool like a mill, if you broke a milling cutter you could not just pop in a new one and resume. Each tool has it's own settings (size, length, etc) so these would have to be entered before running the new tool. This is kind of analogous as to what happens when you change a lens.

[Scott Shepherd]

Richard, I respectfully disagree again Now that I put in a new lens holder, supplied by the Manufacturer, it's screwed up every single file I've ever created. I do a ton of stuff that goes with stuff done over time. So I'm constantly adding something into a system that's full of engraved stuff. When I changed lens, it changed every file I have. Every file I create, 1000's and 1000's of them, is now off by .040". So every time I create a file or open an old file, I have to shift it .040" before I run it so I can know it'll line up with what I did last year. There should at least be an easy adjustment where I could shift my zero (there might be), and then the problem is gone.

I have a 4400 piece job sitting next to the laser right now. I made the fixtures 3 years ago. It runs 260 at a time, it's also about a 3-4 pt font. So I can't be off on them too much. So before I can even start the job, I have to figure out exactly how far I need to move my file before I scrap a batch of them.

[Richard Rumancik]

Steve, after re-reading your posts I'm starting to think that you got a misdrilled assembly. If the assembly would not mate with the carriage as you expected, what did you have to do to make it mate? Did you rework it? Maybe you should have rejected it outright as it did not fit. I'd be interested in the test Mike suggested: putting the old assembly back but using the new lens. Perhaps ULS needs to replace the badly-fitting metal bracket/plate. You might get better than .040 error, but its also possible that the error might not disappear altogether.

I do agree that countersunk screws are not good for aligning things. Each screw tries to force the plate around. To align two mechanical parts well, it would be better to use dowel pins and accurate holes, not threaded fasteners. But of course this adds cost.

[Joseph Tovar]

-Richard,

Your suggestion was exactly was I was going to do to remedy my issue. The offset seams to be consistant. It only appears that it's off on the x axis, while the y axis seams alright. I can make the fixture with the 2.0, then offset the graphic before I put in my HPDFO lens and raster.

I happen to be at the ISS show in Long Beach today and ULS has a booth. They had a tech from one of their Southern California distributors working the booth and I asked him the same question about swapping lenses. He said they should be lined up and it was a problem with my system. Then I asked him to run his demo unit with a 2.0 and HPDFO lens. He did and the results were like mine....off. His lenses were off on both the x and y. He changed his answer to "it could be off because he didn't calibrate his system before he ran the test. Then re recalibrated them both and ran again with the same result. The answer then became. "Each lens is made with the same process, but they(lens/mirrors) can slightly be off because the lens that are glued in can be misaligned, or the holes can be drilled a bit off, etc"

Anyways, I was happy to see that they had they same result as my system, but sad that they don't align as I wanted them to. Attached is a picture I took a few minutes ago of the test they ran today. They made a simple box and ran it on a piece of aluminum with each lens. You can see that the 2 rectangles are off a bit.