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I'm currently designing some tokens to be engraved onto acrylic and cut out, however I'm having trouble working out how to ensure that the designs will line up when the acrylic sheet is flipped over. I'm planning on using Inkscape to create the designs to use with the laser cutter.

Are there any tricks or methods that would help me ensure that the finished tokens have the designs centered on both faces?

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One method I've used is by creating a split jig:

  1. Fasten a large piece of material to the cutting table with screws. Only fasten it on one side. It is important that this piece not move.
  2. From that piece of material, create a pocket that will fit the token snugly. Drill a top or side mark for alignment later.
  3. Cut that pocketed piece in half, down the center so there are two equal halves. Be sure not to cut away your top or side mark.
  4. Elsewhere on the table, cut the token's first side as you normally would, but leave a small tab on the edge to align with the jig.
  5. Place the token face down between the two pocket halves, using the tab to align it properly.
  6. Clamp the two Jig halves securely.
  7. Using the same XY 0 as you used to create the pocket, and the depth of the pocket as Z 0, cut the second half of the token.
  8. Cut off the tab and complete the finish.

Be sure to use an appropriate material for the jig. It should be hard enough to hold it firmly, but soft enough to keep from damaging it. If the pressure in the clamp is not enough, the part may tend to rock, lift or spin in the pocket.

  • Im planning on engraving and then cutting a whole sheet of tokens at once, as it seemed easier than engraving them individually. I'm not sure if I could realisticly follow these steps with a large sheet of acrylic – Psycrow Nov 13 '18 at 13:44
  • It's possible to scale up this process so the jig holds several tokens at once. Unfortunately, doing precision placement on a mass scale on CNC is going to require some compromise on speed and a lot more attention to each piece. – 13ruce Nov 13 '18 at 14:35
  • @Psycrow you can do that. It all comes down to how much time you have for setup and how much tolerance you have for error. With full sheet method you risk ruining one sheet at a time. Its faster true but also riskyer. – joojaa Nov 13 '18 at 14:57
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If you are using a full sheet of acrylic, place a rail on two adjacent sides on your cutting table. It could be as simple as bolting scrap to the table, then cutting away that which is out of bounds of your cutting head. Anything placed firmly against these two rails will be in exactly the same place for each action performed on the work piece.

When you flip the material over, it will be in a known location, but you'll have to ensure that your inkscape files are properly aligned (also known as registered) with the flip.

You can create files with registration marks outside the token area to use as alignment assistance while creating the templates for the tokens.

If it's not obvious, your engraving will be done on one side, then the material flipped and engraving and cutting on the second side. One hopes you don't have such thick material that it requires dual passes to cut through.

The alignment rails need not be outside the range of your cutting head, but you will want to secure them first, then cut them for more precise alignment considerations.

One way to go about this is to create a rectangle in inkscape. This is the guide cutting rectangle. Use this rectangle to also create the token images. When you use Inkscape mirror/flip feature, you'll be able to see how well it aligns. You may have to add compensation for kerf, the material removed by the laser, which can be 0.100 to 0.200 mm depending on the thickness of your material and the power setting of the laser.

  • If the kerf is a problem then you can use the one datum edge that existed before any cut and instead measure the aligned images form that edge from a opposite datum. Its a bit tricky to set it up but it is much more accurate than relying on a kerfed surface becasue: A) you now do not have a problem with dimensions. B) Objects align just as they did on paper except the reference edge is suddenly on the other side. C) If you happen fudge with your rails then no frett it works anyway just as long as you can align yourself to the datum. But yeah taking a CNC job and flipping it is always a iffy – joojaa Nov 13 '18 at 20:43

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