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View Full Version : Pre-marking for perfect alignment using clear PET film



John Blazy
10-26-2016, 1:42 PM
Some of you pros with more years of experience may have a better method, but this one came to me recently on this strange job, and my solution might help others. However, I think I might be missing an obvious solution, like drawing little "L"s in the top right and bottom right corner of the drawing in order to index the location of where to cut, which I have done, but in this job, I have to actually cut at exact points on the panel, but those points are totally curved - very little reference.

I have a cut file that is a flame shape - no corners or reference points besides the "flame tips". The panel to be cut has a molded texture that corresponds exactly to the cut file.

So imagine trying to place the panel in the laser bed and aligning it perfectly so the cut file cuts exactly on target (the outline of the molded graphic, seen as valleys in the 2nd pic), when the panel has no reference points to follow besides its weird shape to begin with.

Kind of like lasering out an irregular shaped knot out of the middle of a pc of wood veneer, or cutting an amoeba shape out of the middle of dried leaf, where there is no "corner" to reference.

So I mounted a double index pin stick to the side of the laser bed, drilled two corresponding holes in clear PET (mylar) film, place the film in the bed over the holes, run the cut file at 11% power at 77 mm/sec to mark the PET. Then pull out the PET, place the real panel in the bed, overlay the PET film over it indexed onto the pins, then adjust the panels location til the lines on the PET match exactly to the molded texture of the panel seen through the clear PET. Then reload the same file into the laser with the high power, slower speed to cut the 1/4" acrylic.

Had to do 15 panels, so aligning each one is easy once the PET marker had been made - just put the panel in, then lay the PET over it, align in a few seconds, pull off the PET and cut.

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What I have done in the past has been to run aluminum tape (with blue masking tape over it) over the panel to be cut, then running a test file cut to make marks, then adjusting the panel's position til the laser lines up exactly where I want to cut. But that takes wayyyy too long - time is $.

Seems like there are other ways to align panels - what say you? Maybe an easier way yet is to simply mark a clear acrylic or PET panel, then align it to marks made on the grid / honeycomb edge.

Gary Hair
10-26-2016, 1:47 PM
I have done what you did with the PET and alignment pins but not quite as nicely - I used painters tape to hold it in place and then slid the part under it.

John Blazy
10-26-2016, 2:46 PM
I have done what you did with the PET and alignment pins but not quite as nicely - I used painters tape to hold it in place and then slid the part under it.

Thats actually what I did the first time. Then, realizing that I had to place the PET in the exact same spot for each of 15 panels (which you could do with tape only, using sharpie marks rather than holes with pins), thats when I decided on the pin method.

Kev Williams
10-26-2016, 7:09 PM
That's still gotta be hard to line up by eye, unless you can look dead-straight down on it--

I might try something like some 1/16" blue plex (for the sake of my very lame graphic ;) ), and rather than just mark a visual pattern, I would try to create a "3D" pattern that the pieces to engrave would fit into..
I only had the pics to go from, and I'm very bad at quickie graphics, but hopefully it explains--
left is what to cut, the middle is the plex pattern to make, the right shows how the pattern would fit into the low spots, the peaks would go thru open holes. As long as the same job cut the pattern as will cut the parts,
alignment should be pretty easy...
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This would of course depend on how much of the pattern you could leave remaining that wouldn't fall out as a stenciled "hole"; for all I know it couldn't be done at all... but the thing is, you don't need the entire pattern or to fit the entire piece (although that would be nice), you only need 2 reference areas to fit into 2 pockets, and it should be near perfectly aligned. The pattern could be mostly hole, as long as the pattern proper has enough border to stay in one fairly rigid piece...

Another option for alignment patterns, is if you could make a 3D negative of the parts- heat or vacu-form, epoxy mold, etc... Once the initial alignment is out of the way, the rest of the parts would be easy to get into place...