After making my brother a custom retro digital photo frame for Christmas last year I wanted to create something just as meaningful to him while learning some new skills along the way. I saw the skill of at home metal casting and was hoping to be able to apply that. While browsing thingiverse.com I found a user who created multiple functional 3d printed scale size car engines and a jack stand as well. My brother is a petrolhead so I decided to take on this task and make him a cast metal copy of the 1/3 size jack stand.
I started with downloaded the files and printed them out at home on my FDM (lower quality) 3D printer to see if I was happy with the design, size, and function. I redesigned the lifting handle to better match production versions of the product. Focusing on the final goal with these designs being cast in an alloy metal I couldn't just think of how the models were 3d printed but also how they would fit as a mold and how the metal would fill that in as they're cast. To make for an easier build process I split the main body of the stand in half. With the design finalized I had the pieces professionally printed from an online site. These pieces would be the first step in creating a negative mold. By using the online service to have the parts printed I could get a much higher quality print done on an SLA printer.
With the 3d parts in hand I could begin making the molds; 2 part silicone molds. To make the molds I started with a chunk of modeling clay encasing half of a 3d printed piece vertically. A watertight box was built around this clay encased mold and registration marks were put in, these marks would be used when putting the 2 parts of the mold together as this verified they always fit together. A quick release spray was applied to the clay/model so the silicone would not stick to the pieces. With the box built the silicone can be poured in.
The silicone is made from a 2 part liquid that, when mixed in a specific ratio, cures to a solid mold over a in 24 hours period. Because I was going to be pouring hot metal into this mold it was recommended that the silicone be "degassed" before pouring into the mold. Degassing removed all air bubbles created from hand mixing the 2 part silicone together, these air holes can cause issues when hot metal is poured into the mold, possibly causing the air trapped inside to expand deforming the final product. Using a vacuum chamber I evacuated all the air from the mixed silicone and then poured it into the created mold box. 24 hours later I removed the silicone from the mold box but was careful to keep the 3d print inside the silicone mold as the second part needed to be made. I created another mold box around the silicone, sprayed more mold release, and poured another mix of degassed silicone into it. Another 24 hours later I had a 2 halves of a full negative mold of the original 3d print. After a quick clean up on the sides the final preparation step was to cut out air holes and pouring spouts for the mold. I had to visualize how the metal will fill up the mold as it pours it in and make sure that no trapped air would prevent the metal from filling out the piece.
With the air holes planned and cut I could start the casting. I used a pewter alloy based on others recommendations of its low melting point (~466F) so as to not destroy the silicone molds too fast. The molds were lined with baby powder, to help the release, and preheated in the oven so the hot metal wouldn't be too drastic of a temperature change. Once the metal ingots were melted down they were poured into the molds and left to cool down for about 10 minutes. They could then be removed and another pour could be done in the same molds.
After pouring all the pieces the next step is cleanup. The pour spouts and air vent sprues were cut off and sanded down. With the parts all clean painting could begin. I started with a grey primer and, after that dried, covered the base and level mechanism gloss black finishing with a gloss clear coat. The teeth jack got painted gloss red and the same clear coat. I did most of the painting before assembling the 2 base pieces so that I could more easily reach into the inside crevasses of the base. After everything dried the edges of the half bases were sanded and epoxied together. I didn't bother with making a perfectly clean edge since the epoxy, when applied properly and painted, gave the look of a welded join which helps to sell a proper manufacturing process similar to full size production units. Once that was glued up and painted over with the gloss black I could begin final assembly of the pieces. The jack stand has just 1 moving part that I used with a machine screw going through the small lever that catches the teeth jack and ends at the release handle. Those pieces were epoxied together and the model was complete, ready for boxing up and gifting.
For building the box I learned more about cardboard than I ever thought I would. For instance the type of non-corrugated cardboard that makes up cereal boxes is called, “chipboard” and that’s just the material I wanted to use to build the boxes for holding these jack stands. Searching online I found a few websites for building different types of product boxes and template generations. Entering in the jack stand dimensions I had a snug box that was ready to be made.
The total template laid out flat took up a pretty big space so it was printed in multiple pieces and attached together. Once taped together the entire template could be taped down to the chipboard and cut out. Once cut the fold lines could be made. Using a bone folder score lines were made in all the required place and the template was removed. The score lines were bent to their full angles and the box was dry fit together. Ensuring a complete product I used hot glue to secure the box folds. The measurements for the inside dimension were a little too tight as I did not compensate for the thickness of the material or of the fold thickness taking up available space inside. I cut out a little slot that the jack teeth could slide into, this also helped secure the jack stand from rocking back and forth inside the container.
By this point the project was completed but I had a little extra time and wanted to go the extra mile, first by designing a warning sticker to match what a production jack stand would display. This can include the manufacturer’s name, weight capacity, model number, etc. With some measurements of my scale size jack stands I created a similar sized template in photoshop and began laying out everything I could include being customized for this project. A scale size weight load of .09 tons, a company name/logo of my last name, the model number being the date for Christmas 2018, and individual serial numbers for the 6 jacks I created. After I was happy with the design and fit I had them printed out on glossy paper to mimic stickers and epoxied the labels to the jack stands.
While still in photoshop I created a template for some box art. I had the general idea of the border and layout for the art but could not decide on what image to put inside it. I narrowed my choices down to 3 patters of car engine schematics and to make the final pick I modeled how they would look on the box. Using Blender I mocked up 3D designs of the boxes, duplicated them, and UV unwrapped the individual objects so that I could apply custom designs to each. Laying out the 3 choices together the choice was easy and I decided on the cross section of the Honda NSX engine for the design. Back in photoshop I printed out the box art, cut them out, and glued them to the boxes.
As the final finishing touch I used twine to secure the boxes closed for transport, using a simple, yet elegant, bakery tie to provide the strong knot but allow it to easily come undone. With the final loop in the knot I included a label for the recipient.
