Use 3D Printing For Perfect Leather Molds

Preface
Leather forming is a craft that dates back to 3000 BC when ancient civilizations began using animal hides for bags, garments, boots and sandals.  5000 years later, we continue to use animal hides for all of these purposes, though the technology available to craft this material has evolved with our culture.  For this project I created 3D Printed tools to make a custom leather press, complete with an imprint of Makey.

The Design Process
⦁ I started by designing the finished component I wanted to create out of leather.  I designed a solid body with a square profile and edge fillets, followed by an extruded detent in the shape of Makey.  After the exterior surface detail was to my liking, I shelled the model to the thickness of the leather I intended to use.  This resulted in a solid model of the leather component I wanted to create.
⦁ Once the model was complete, it was a relatively easy exercise to use the Mold Tool function in SolidWorks to craft a 2 part mold.

3DP Components
⦁ Any 3D Printer is suitable to make components for a leather press, though it is important to note that surface imperfections and build lines translate directly into the surface of the leather.  Set your printer software to the finest layer resolution, and orient your components so as to minimize build lines on finish surfaces.  Also, spend some time post processing the components to refine the details you want to translate into the leather and eliminate any raised imperfections you don’t want to appear in the leather.

Leather selection
⦁ Vegetable tanned cow hide is the industry preference for shaping leather: it tends to hold shape better than hides of other animals or those tanned with a chromium solution.
⦁ Leather is processed to a uniform thickness, and is named according to the weight of a square foot of material.  For example: a square foot  of 4 ounce leather weighs 4 ounces.  I cared more about thickness than weight, and had to consult a chart to source the 1/16″ thickness of material that I wanted for this project.
⦁ Vegetable tanned leather is the color of pale Caucasian skin, though a variety of water based dyes are available for tinting.  More on this later.

Leather preparation
⦁ The goal is to soften the leather with water, form it into a desired shape, and allow it to dry and harden such that it holds the shape of the form tool.  A few factors are important to take into consideration
⦁ If the leather is too wet or too dry, the shape won’t hold.  Make sure moisture penetrates the full thickness of the hide, but you do not want it soaking wet.
⦁ The temperature of the water can influence the outcome of the process.  Boiling leather is a technique that causes leather to shrink and harden considerably.  This may be desirable for some projects, but in this case it was important to keep the temperature below 160F.

Leather pressing
⦁ Once the leather is moistened, clamp tightly in the form for a couple hours.  I found that 2 hours was sufficient to hold the shape, though you may want to experiment if fine detail is lost in your early experiments.

Trimming
⦁ I designed the mold so that I had an edge to trim against, and left the clamps in place during the trimming to prevent any shifting of the material.  Using a #13 X-Acto blade, I was able to trim through the leather in a single pass.  Depending on the thickness and hardness of the leather, you may need to score the leather with a pass or 2 before fully trimming off the excess material.

Coloring / Conditioning Leather
⦁ A variety of colors are available to dye leather.  I used a water based dye, testing my application process with scrap material before applying tint to the finished part.  The folks at Tandy leather recommended applying dye with a cotton swab in a circular motion.  I found this worked well to eliminate evidence of brush strokes on the finished part, though to get the desired color saturation I needed to dilute the dye with water.  As a final step, a leather conditioner will helped to adjust the surface sheen and seal in the color of the dye to eliminate premature wear.

Summary
⦁ 3D Printed objects are often criticized for feeling cheap or flimsy, but using them as tools can lead to creative solutions with a variety of materials.  By marrying the versatility of digital design and fabrication with luxurious materials like leather, we can supercharge our process and generate customized artifacts worthy of handing down from generation to generation.