Registration, alignment and double sided printing & cutting

qa

#1

Suggestions and thoughts on this topic

One of my aims is to make board game components. I’m going to outline my specific needs, but I think they are relevant to a lot of different applications.

I want to print double sided tokens, cards and other stuff.

The problem is that printers are just rubbish at printing consistently aligned sheets, so there are always registration/alignments issues.

As a use case, think of cutting out a large number of small square tokens from a sheet of them (think old school war games if that helps).

Problem 1: Registering the first side

Best solution I could come up with is to have a printed cross hair on the printed sheet and in software a cross hair and rotate option. You firstly line up the two cross hairs, then nudge rotate around the cross hair to straighten up against the print.

There are probably other ways of doing it to, but rotate around a cross hair is so much easier than rotating and nudging up and down around the centre of the piece. With a cross hair - you don’t have to have it central to the print (which may not be possible). You can put the cross hair in one corner, line it up, then nudge rotate around that point until everything else lines up. With rotate around the centre you also have to keep nudging up/down, left/right.

Problem 2: Double sided printing.

Now here the problem is somehow gluing two sides together so they are aligned. Assume that I am printing to two sheets of card (or sticky paper) and have to glue them together.

Option 1: Use the GF to trim both sheets so they are exact same size, flip one over and glue with the edges perfectly aligned.

Then put it back in the GF to actually cut the tokens out.

Option 2: Use the GF to make a jig with prongs in top left and bottom right corners.

Use the GF to drill small holes in front and back sheets to match up.

Put one face down over the prongs, the other face up to glue them together.

Return to GF to cut the tokens out.

I’m sure there ought to be an easy way - but I don’t know what it might be.

Any other suggestions?


Something new for Maker Faire
#2

The laser head really likes to move addressable on horizontal and vertical. So particularly rastering, you don’t want too much rotation.

I’m guessing Use case 1 with a sheet of preprinted things for cutting, you’d probably want to print at least 2 dot’s on the sheet, and have the same dots in your cut file. I’d purposely put them upper right and lower left, More might be better, but then you can use the print window to align the image and the target material precisely, just expect to need to move both. (also might want to see the post about the honeycomb and rare earth magnets)

This all assumes you won’t be engrave and cut, then you don’t care so much about registration I guess.

I’d do something similar for your use case 2, only laser the dots out and use dowels or something similar to align with a spray adhesive. just as you suggested.


#3

For one-sided jobs I’m hoping that the Glowforge’s camera will allow you to place the sheet in the machine, use the head camera to register both crosshairs, and start the cut. No nudging required, I hope. Two points would be enough for a person, but a third might be necessary for a machine/software.

For two-sided jobs, I think I would take an approach similar to “option 2”…

  1. Punch a round hole at the location of each set of crosshairs (drill the hole, poke through with a tack, use the laser to cut a hole, etc.)
  2. Drop the sheets down on a fixture with accurately-positioned dowel pins and glue them together.
  3. Use the Glowforge to cut both glued-together sheets at once (a fixture on the bed of the Glowforge would be the fastest to do this part, but registration of this cut could be done with the head camera as well).

#4

@lhermit

Dots for alignment are fine - its being able use one of them as a fixed point around which you can rotate as being crucial.

Interesting point about rastering on a rotated material


#5

I would hope the same feature that allows the GF to cut through 1/2 material by flipping it over and cutting from the other side would help with double sided prints.
Maybe it will allow us to set different engravings for each side and then cutting it out last.
The alignment should be handled by the camera.


#6

@Hirudin

Auto alignment would be BRILLIANT!!!

No idea how you would make that work. Maybe on the GF interface you could point at a rough area where the crosshairs are and let the software target in??? No idea.

The “nudging” I’m talking about is at the software end, I definitely don’t want to be nudging the material.

In the software world - like photoshop - they do manage auto alignment on two images.

I could imagine maybe printing a green box and saying align to the green, (either with or without a cut)

The problem with print is that you can’t rely on the GF aligning to the edges of the material, because the register of the print on the material can be off. So you need to align to the print, not to the material.


#7

@ihermit2 is right, rastering does favor lines along the X axis. Depending on the resolution you choose to use, it might not really matter though.

Here’s a super-macro of the number “2” engraved on some plywood at 1000 lines per inch…


If you look really closely, you can see some evidence of what direction the laser was moving (parallel with the wood grain), but I don’t think it would have looked much different if the “2” had been at a different angle.

Here’s a shot showing the “2” next to a US dime coin (~18mm diameter).

Here’s a vid showing how print registration could (I dare to say “should”) work with a Glowforge…


#8

From what i remember @dan said that the double sided cuts would work by you placing the design on the camera image as normal then the GF would tell you to flip the material in a certain direction after it cut the first side. then it would use the camera to auto align the back side from the material borders.
If that part works i don’t see why double sided engraves wouldn’t work with auto alaign


#9

@Hirudin

That’s the badger - CAN WE HAVE THAT PLEASE @DAN ???


#10

Plotters, which are expensive, are what you need if you want to print something precisely. Printers are cheap and print good enough for most needs - hence the rubbish. The glowforge and its need to be precise is like a plotter. As long as it can find its registration points when the material is flipped over we should be all be good. They have said that it will, so presumably at this point it is just SMOP.