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What to do with a 3D Printer: Make Wax Seal Stamps (plus OpenSCAD surfaces)

Posted by Alex English on

I received some sealing wax for Christmas to use with a signet ring and thought it would be a cool project to design and print some stamps to use with the wax. The approach to adding graphics to an OpenSCAD design seemed worth sharing as well.

Here's the first 3D Printed stamp I made. It is a version of an "elder sign" from the mythos in the writings of  HP Lovecraft.

3D Printed HP Lovecraft Elder Sign Wax Seal Stamp

Here's another one I made using the logo for The Gentlemen's Brotherhood. I used the logo (with permission) both because I like their mission and because I really like the logo. Using their words:

The Gentlemen’s Brotherhood Podcast seeks to inspire the modern man to continuously pursue excellence in all areas of his life. To lead by example by living life as a true gentleman. You have probably noticed that our society seems to be losing its manners and morals. We can’t surrender to these trends and must instead be courageous in our re-discovery of The Lost Art of The Gentleman.

3D Printed Gentlemen's Brotherhood Wax Seal Stamp

Let's walk through an example to see how these were made.

Surfaces From Images in OpenSCAD

I've gone over to www.publicdomainpictures.net and found this image of a smiley face.

Smiley Face for a 3D Printed Wax Seal Stamp

For a stamp, I really don't want the edges to be sharp and vertical, instead I'd like them to be tapered so there's a better chance it will let go of the wax when pulled off (and maybe a better chance of the wax filling the depression of the design). Since we'll pull this into OpenSCAD using the  surface function, a purely black and white image will only have two depths, high and low, meaning flat vertical walls. To create a taper all we have to do is blur the image to create a gradient of gray at the boundaries between black and white. I've done this in Gimp, a cross-platform, FOSS (free, open source software) photo editor. Here's the result:

Blurred Smiley Face for a 3D Printed Sealing Wax Stamp

When blurring, make sure the edges of the image are further from the content of the image than the radius of the blur. To apply a 10 pixel blur I added a 10 pixel margin to each edge. If the image you're starting with has any color you'll want to convert it to grayscale. If it is grayscale, there are a lot of options for how to process the image to get what you want in the topology once imported to OpenSCAD. Interesting operations might include invert, threshold, curves, and levels. This is also an appropriate time to reduce the resolution as far as possible while maintaining sufficient quality, since this kind of data is really system intensive in OpenSCAD.

Once you've got the image ready, go ahead and start up OpenSCAD. Here's what we get if we load up the above image as a surface:

Smiley Face Surface in OpenSCAD

This was the code to do it (assuming the file is called smiley-blurred.png, and that the OpenSCAD file has been saved in the same directory as the image):

surface(file="smiley-blurred.png", center=true, invert=true);

We've succeeded in getting a tapered edge, but it's obviously a bit much depth. Let's add some z-axis scaling.

Smiley Face Surface in OpenSCAD with z-axis scaling

Here's the code that made this image:

scale([1, 1, 0.1]) surface(file="smiley-blurred.png", center=true, invert=true);

We'll have to do a little more scaling on it to make sure it's the size we want, but we have something more or less ready to subtract from a flat surface to make our stamp. I'm omitting any sort of a handle for simplicity, but here is a 25mm diameter half-sphere with the smiley subtracted (viewed upside down):

OpenSCAD Smiley Face Wax Seal Stamp

And here's the code that did it:

difference()
{
    sphere(d=25);
    translate([-25, -25, -25]) cube([50, 50, 25]);
    translate([0, 0, 1.5]) scale([0.15, 0.15, 0.015]) surface(file="smiley-blurred.png", center=true, invert=true);
}

Finishing the design just means designing a handle or devising another way to hold the stamp, and deciding how to orient it for the print. I printed mine with the stamp up because I actually wanted some texture from the artifacts of a printed top-surface rather than the print-bed. 

Using the Stamps

There's no point 3D Printing the stamps if you don't use them. Using the stamps successfully does take a little technique. I found the best results from wiping a little bit of oil (avocado oil, if it matters) onto the stamp surface with my finger, then dripping the oil into place, waiting a moment for it to begin cooling, then pressing the stamp into it and letting it sit. After about 30 seconds with the stamp stationary in the wax I then lifted the stamp off, starting at one side and rocking it around a bit to loosen it. I had several failures before getting it right, then consistent successes. I don't know that this process would be very different with a metal stamp, other than potentially needing less time sitting on the wax since metal would pull the heat out of the wax more effectively.

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