Molding a Hacker Passport Stamp With Sugru, a Laser Engraver, and a 3D Printer

We need a passport-style stamp for Tampa Hackerspace for stamping Hacker Passports. We could carve one by hand but instead I thought I’d apply some high-tech tooling. So here is how to use a laser engraver, 3D printer, and Sugru to make a passport stamp.

First we need to engrave a mold for the stamp. To do this, we will use the raster engraving mode of a laser engraver. This takes a bitmap image and uses a laser to burn away material.

I used fairly thin 0.093” (3/32”) acrylic sheet which was more than thick enough for this project. Note: remove any protective cover from the acrylic before engraving.

When engraving the mold, you want to engrave a normal (not mirrored) copy of the design that you are going to stamp. The molding process will create a stamp that is mirrored, resulting in stamp prints that match what you engrave.

Laser engravers differ so consult your machine’s manual for recommended settings for etching acrylic. The suggested settings for "deep raster engraving" settings warmed the acrylic too much and lost the detail I needed for the stamp. I recommend engraving several versions, starting with a light engraving and working towards higher-powered deeper engraving settings. Find one that is deep enough to really feel the engraving but still has good detail. With our laser engraver, my best engraving was at 50 power, 100 speed, and 500 pulses-per-inch.

You could use a block of wood or scrap of acrylic sheet as a base for the stamp, but I 3D-printed one from ABS.

I posted the model I used here. I updated it to be closer to the size that I actually printed (44mm diameter) and to have a thicker base so it will flex a little less.

Use your 3D printer’s software and slicer to print the model. I used 10% infill, two shells, and did not print using a raft or any support material, but I don't think any settings are that critical, as long as you get a sturdy print with a mostly flat base.

I would recommend printing two stamp handles and molding two copies of the stamp since a small packet of Sugru has enough material for two typical stamps and it isn’t easy to save leftover Sugru.

You may want to lightly sand the base of the print to flatten it and roughen the surface a bit for the Sugru to adhere better.

Clean the etchings to get rid of any plastic residue. I used a watercolor brush to sweep the mold. I wouldn’t recommend using anything like a paper towel that might shed paper into the etching.

The Sugru is too sticky to go directly onto the acrylic mold, so we need a release agent. Take a small amount of water with a drop or two of dish soap and brush the water all over the etched mold, inside and around it. If you don’t use enough dish soap, the water will bead up in only a couple of spots. Add a little dish soap and the water will coat the acrylic. If you brush it a bit too much, bubbles and foam will form. You can always rinse the acrylic and start over.

There should be a thin, even layer of water over the mold area.

Read the directions on the Sugru. If you prefer, wear gloves to protect your hands. One small packet of Sugru was enough to make two 1.5” stamps. If your stamps are a little smaller or you press them harder, you may be able to get three stamps out of one packet.

Open the Sugru and knead it. Be careful when folding it that you don’t create air pockets or bubbles. Separate the Sugru into two equal portions.

[Note: I molded two copies of the stamp, one with the stamp handle and one on a scrap of clear acrylic so you can see the process better.]

Make sure the mold is on a flat, stable surface that you can press down on quite hard.

Apply the Sugru to the stamp handle and shape it into a rough disc shape approximately the size of your stamp’s mold. Align the stamp to the mold, making sure to use the “this way is ‘up’” marker if you use one.

Press the stamp into the mold. Do not wiggle or twist the stamp or the design will be warped. Do not press down around the perimeter of the stamp base or you will get a curved rubber stamp. Press down as hard as you comfortably can.

Carefully pull the stamp up, keeping it as straight as you can.

Inspect the Sugru and see how the stamp impression looks. If it is twisted, warped, didn’t cover the whole mold, is curved, has a bubble, etc. you can remold it.

If you need to remold the stamp, first gently blot the stamp with a wet paper towel to remove any soap, then blot it as dry as you can, making sure to get into any details.

Re-wet the mold with soap and water, making sure it’s a smooth, thin layer of water.

Reshape the Sugru on the stamp handle, pushing it back to the center a bit and smoothing out the surface. Be careful not to trap any air or water bubbles.

Repeat the molding until you are happy with the results.

The stamp needs to cure 24 hours or at least overnight.

After curing, the Sugru is a little too smooth to use as a stamp and still has a layer of soap. Clean the surface of the Sugru with a damp paper towel to remove any soap. Then roughen the Sugru a bit by setting the stamp on a sheet of paper on a flat surface and carefully "sanding" the surface of the stamp with the paper. The Sugru will wear down a bit like an eraser, giving you a good stamping surface.

[Note: I misplaced my stamp pads and will update soon.]

You can stamp using stamp pads or I tested with both alcohol-based art markers and water-based markers swiped from my kids.

When I molded using the stamp handle, I pressed down around the base of the stamp handle. This squeezed the Sugru more around the outer parts of the stamp handle, resulting in a stamp that’s slightly rounded (thicker in the middle). I was able to flatten the stamp by "sanding" it on a flat sheet of paper for a bit.