# Two-sided laser engraving

Found this HOWTO style article on laser engraving dual-sided objects that I thought people would be interested in…
http://www.mclasercutting.com/how-to-two-sided-laser-etch-or-laser-engrave/

The opening excerpt follows:

Why etch both sides?

As part of my other job at http://marginallyclever.com, I want to make beautiful boxes for my electronics. I want to put a part numbers and helpful maker tips on each piece, for reference… but I don’t want them to show on the outside of the box when it’s done – that would be ugly. I need to etch both the inside and outside of the box parts.

Another great example would be dog tags. On the front I want logos for my club or team logo, and on the back I want something custom for that member.

The Challenge

Flipping parts creates a registration challenge: When the material is flipped it might shift out of place. The first part of the secret is to make a jig that will hold the material in the right place before and after flipping.

The second part of the secret is to make sure the jig has only one line of symmetry. A jig with two lines of symmetry is a mistake waiting to happen – You might flip your parts the wrong way and create a waste of effort.

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Ideally not needed in the Glowforge. But a good read for things to keep in mind. Even if the Forge can work without all of the tricks, each of them you employ makes life easier and provides better assurance of a quality outcome.

I think you mean “ideally not meant with uniquely shaped objects”. Expecting the Glowforge to recognize the angle of difference between the front and back of a blank wooden circular object — since “round” looks like “round” from either side — would be quite the trick.

By using a jig with an irregular square shape and taping the circular object into it, it effectively helps the GF camera decipher the rotational angle. (edit: grammar)

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True, a full proper round would confuse even the forge. Though perfect round is nearly impossible, so with sufficient Camera-Fu, even a discus could be identified appropriately. I wouldn’t expect anyone to develop that level of auto control though…

The irregular shape with only one symmetry axis is the main trick which would help the Forge. And the jig is the main thing you can avoid needing because you have the forge.

This is an interesting question, especially as I was thinking of some double-sided items. I think I’m hoping that I’ll be able to set up a row of coin (or a little bigger than coin - maybe silver dollar sized?) shaped items on the GF, etch one side, then flip it and use the positioning of the first set of etchings (IE, 5 cm from the right edge of the first etch would be 5cm from the left edge of the second side) to etch and then cut the second side.

I know alternatively I could also just etch and cut on side 1 and then flip them and etch side two and not worry about the chance that the two might not have the same ‘bottom’ image…

Still - this is a really interesting way to handle the problem, and I could see using a cutout on one edge of the material as a way to define the positioning on the flip…

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Yes, a registration mark to reference.

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Or lay them down on a strip of blue tape and then flip them over onto another strip (so you can pull off the first one. That gives the GF a line of dots to work with.

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Just create a pair of templates something like this…

That way, regardless of the rotation it’s placed in the hopper, you can’t miss.

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Of course, if you happen to have an application where you will be using the Glowforge to cut the objects out too, engrave the first side of several of them on side A of a larger rectangular piece, flip the whole thing, let the Glowforge’s registration magic figure out the new placement, and then both engrave AND cut them out from side B.

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I vaguely recall somewhere in this forum that Dan said we would be told which specific axis to flip the object when doing double-sided work.

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From back in Sept. Might still be accurate, though that far back the S/W may not have been working.

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I’m still waiting to see two-sided registration working. I do tons of two sided engraving. I build jigs and index tables so I can guarantee accuracy. If magic camera registration can save me all that that would be cool, but I’ll probably still build an index table for oft-repeated work.

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I love this kind of simple solution, @jkopel. Blue tape is the duct tape of the laser world.

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For the most part, that’d work too. But just to play Devil’s Advocate, a strip of circles can still be accidentally interpreted as orientated ‘north’ or ‘south’ when flipped over, if you’re working on a backside that’s clear of all other marking. That’s not true if you use a unique key/marking from the first cut before you flip it over.

…I’m not saying it’s likely, mind you… (well, at worst 50-50%) but it could happen.

OK, fair enough.
In that case use a longer piece of blue tape and tear off one corner.

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I’ve been working on some 2"x3" puzzle pieces/ornaments, where I am cutting out multiple at a time with a design on the front, and then engraving the back with text. Had struggled on how to have this come out right, as trying to use the camera to place the design on the reverse side WAS NOT WORKING!!!. The process that I HAVE found to work is:

1. Cut the original pieces (my design file does 20 at a time)
2. Create a copy of the design file, removing the design and just leaving the outline cut(s) of the shape(s), flipping if necessary (for my design this wasn’t necessary, as it mirrored on both the horizontal and vertical axis), so you just have the outline cut(s).
3. Add your design for the back and save the new design file (I added _back to the name)
4. Place a sheet of paper in the Glowforge (remember those magnets to hold it down)
5. Engrave the pattern on the paper (I actually used Score for the outline)
6. Now put your already cut pieces on the paper inside the outlines from step #5
7. Change your engrave settings to be correct for the material you need to engrave. Make sure you set the outline cut to IGNORE.
8. Print the design.

I see lots of references to thinking the camera would make this process unnecessary, but trying to use the camera to ensure the designs were engraved where placed has been a fail.

Any recommendations on a simpler process are welcome.

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I do this:

Thanks for the reference.

I’m not sure that qualifies for my ‘simpler’ adjective. But I agree that you DON’T always need a separate design file for the front and back. You could definitely have a single file, and just CUT/ENGRAVE/IGNORE appropriate layers. One issue is that GlowForge doesn’t hide layers you’ve IGNORED, so it looks messy in the UI (not that big a deal). And the other issue is in handling objects that are not symmetrical. In that case you would need either two separate objects (each with it’s own layers) in a single design file with more ignoring of extraneous layers, or two design files. The extra cut of the outlining square does waste material as well. Depending on your design, you may have this waste regardless.

His technique could also be applied to cutting/engraving multiple objects in a single (well, dual) pass. The challenge is the phrase - DO NOT ALLOW THE BACKING MATERIAL ON THE BED TO SHIFT. You would definitely need some mechanism to hold it in place (he mentions taping it in place). In my solution magnets hold down my stencil so it doesn’t shift when I place the items on it.

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Hers actually.

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most files that I wanted to double-side I simply mirrored the image/file horizontally, nmaking 2) in the original file and used that as my upload -that way I cut 2 and then pop them out (without moving the backing piece and swap them(flipping them over-they will obviously match)and engrave again, ignoring the cut lines on the second time (since both have been “cut through” already)