Tag: casting

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Casting Wax using Silicone Molds

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I’ve been experimenting with casting for the last year or so and typically my “experiments” come out terrible, mainly because I try weird things, but sometimes I sort of get it right…

This time I made a silicone mold of a model of a glue stick for a hot glue gun and it mostly worked fine. I modeled a glue stick and tall cylindrical container for it using OpenSCAD and then 3D printed the two pieces. The idea being I’d place the “stick” into the container and then pour silicone in to create the mold.

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I had a small amount of silicone we were going to throw out at work because it wasn’t enough to do anything useful with, and it was just enough after scraping everything out of the two containers and mixing it together.

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Once again I had to destroy the original mold master to get the mold out, but since it was printed using PLA I just smacked it with a hammer a few times and peeled away the plastic to get the silicone mold out in good condition.

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I could not find the cheap little cooking pot I bought at Goodwill a few years ago for melting things so I grabbed an old metal can, made a makeshift gaff tape handle, and melted down some old candle wax to pour into the mold.

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Hey, it worked! A wax stick the same size as a glue stick you would use in a hot glue gun. ;)

Oh, see those rubber bands? They hold the mold together because I split it down the side to allow for getting the wax out of the mold. I may have wrapped the mold too tight or not aligned properly because the first stick wasn’t totally straight.

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Here’s the second one… much better. You can see the split in the mold. I just ran an X-ACTO blade down the sides to split it.

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Now, to ramp up production I may need to make a lot more molds, or come up with an alternative. Here’s a method using a metal tube and parchment paper that might work. Honestly I think I prefer silicone molds but this might be a good way to get really long sticks.

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The next part of this experiment requires a hot glue gun, and most likely, disassembling it for the heating element. Stay Tuned!

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A Concrete Bolt

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When last you saw my cast bolt it was made from plaster and an ABS 3D print which served as a mold. It sort of worked. As mentioned, it was more “art object” than “functional thing” and that was what I was going for…

Well, I made another ABS mold from the first experiment and even though I had worked with a flexible filament mold I thought I would give the ABS version one more try, this time with concrete instead of plaster.

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I really liked the way this one turned out. Yes, I had to destroy the mold again, and in the process the part got damaged and broken, and then I pulled out the hot glue gun and put it back together, and now I like it even more!

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It’s one of those situations where things go wrong so you just do something and it turns out (possibly) better than you thought it would. I joked that this was the modern maker equivalent to Kintsugi, using hot glue instead of gold.

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I really like how it has this feel of being an ancient relic. In a strange twist of fate, I was at first annoyed with all the tiny pebbles in the concrete, so much so that I made a sifter to remove them, but now I’m thinking up a list of things I can mix into the concrete besides pebbles (and, probably pebbles too.)

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Water Bottle Repair

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I bought a water bottle about two years ago after my old one was stolen (I know, who steals a water bottle!?) While the new bottle was much better, since it was insulated and could keep water cold for more than a day (with ice added in) one of the things I didn’t like about it was a small rubber ring used to seal the cap. The rubber ring had a split in it (maybe to assist with the seal?) and it was difficult to clean, and eventually it broke from attempts to vigorously clean it.

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I replaced the sealing ring by 3D printing a small mold and then casting a replacement using Smooth-Sil™ 940 silicone. The silicone is a two part mold, with a volume of 100:1 for part B to part A, which is why you get a giant tub of silicone along with a small bottle of whatever the red stuff is.

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This was my first silicone casting at home for a personal project. I’ve done casting at work for prop making, but this time I didn’t have a vacuum chamber, and I was doing a tiny part all by myself.

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So how did it turn out? Pretty good! I used a digital scale and filled a cup with 10 grams of part B, then added 1 gram of part A and mixed it all up with a popsicle stick and smeared it into the cavity of the 3D printed PLA mold. I let it sit overnight then used a sharp knife tip to pry it out. There was a thin skin around the piece but it peeled right off.

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So how does it fit? It’s good but not perfect. If I make another one I may decrease both the inside diameter and outside diameter. It could fit a bit more snug, and it could have just a wee bit more clearance when inserting into the bottle. (I’m guessing between 0.1mm and 0.2mm, maybe)

I’ve got plenty more silicone, and it is food-safe, so I want to experiment with making some food molds, and yeah, I’ll probably 3D print the objects to create the molds from, taking a page from Anna Kaziunas France.

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More Mold Making

My last mold making experiment was a good experiment, and if I learned one thing, it’s that the mold should be flexible to allow for the removal of the piece you are casting without destroying the mold or the casting. (Duh!) Instead of ABS I decided to print a mold using flexible filament. Now, to print flexible filament I had to do a small modification to my extruder lever to allow the insertion of a piece of PTFE tubing so that the filament wouldn’t bend over before it fed into the feed gear. Once I did that, I was printing flexible filament (very slowly.)

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I decided to start with something less complex, and used a 2.5D object instead of a 3D object. I had an illustration of a hammer, which seemed to be a simple shape, with no weird inside parts or sharp corners. I started by opening the vector file in Inkscape.

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Once I had the file open I used Inkscape’s dynamic offset feature to extend the shape into a larger piece so I’d have “walls” for my mold.

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I did a Boolean difference between the original and the scaled part to get the wall piece, with the wall pieces being approximately 4mm wide.

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I also created a bottom plate that the wall piece would attach to. I did not make it fit with pins or any other alignment method, I just ended up using tape to hold the pieces together.

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Here are the modeled pieces. The wall piece was easy enough to flex around, but seemed strong enough to hold up for the casting.

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And here are the printed pieces. The flexible filament did not print as well as PLA does, and there were some rough parts on the top of the walls, but it wasn’t going to matter for these purposes.

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I put the two pieces together and applied some masking tape to hold them. Since I was going to use plaster I knew that it didn’t have to be too water-tight to hold the plaster in place.

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I then filled the vessel with the plaster. (Yeah, I have a big bag of plaster on hand for weird reasons, so I occasionally use it, though eventually I want to use concrete for these experiments.)

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After letting the plaster dry for a few days I removed the tape and then pulled off the bottom…

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…and then was able to flex the wall piece enough to get the plaster out of the mold, so that worked pretty well. Again, this was not a complex shape, which really helped as I just had to push the piece straight down through the mold.

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And here’s my (tiny) plaster hammer. I like how it turned out. The edges are not perfect, but then, what is, Right?

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I ended up making two of them, and with one I found that it was fairly easy to shape the edges using tools, so my 2.5D hammer (sort of) became a 3D hammer.

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Bolt Casting via 3D Printing

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I made a plaster bolt and painted it red. Sometimes I do things in the “wrong” way so I can see why it’s the wrong way and to see if it might work doing it the “wrong” way. Also, I like a challenge.

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I started by using OpenSCAD and the thread-drawing modules for OpenSCAD and created a Metric bolt. I added the bolt head and rounded the edges just a bit.

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Once I had my bolt I used it to create the two part mold by doing a difference into a block, and then cutting the block into two pieces. I also added some alignment holes and pegs. (And I managed to forget to make the holes a bit larger than the pegs, but a drill bit fixed that easily enough.)

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Here’s what my mold looked like printed in ABS plastic. Yes, I should have used a flexible filament for this so I could demold the cast, but I didn’t. Again, wrong, experimenting, etc. (I’ve got some flexible filament on order, so we’ll see how that goes.)

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I taped up the mold and added some rubber bands to hold it all together. Somehow I missed getting a photo of the wet plaster, but I just poured/shoved it into the top and leveled it off…

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Here’s the result after letting it dry for a few days. Oh, I didn’t have any proper mold release, or any good substitutes so I used some silicone spray. I don’t know if it worked that well. You can see some of the threads broke off. To be honest I was expecting much worse! It was totally stuck in the other half of the mold though, and I didn’t want to force it…

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…so I ended up putting the mold into a bench vise and crushing it until it released the bolt. I know, in theory you should be able to use a mold more than once. But maybe part of the beauty of 3D printing it is that it’s low cost compared to silicone molds. I’m also thinking that a 3 or 4 part mold might be the way to go, rather than just two parts. At least for something like this.

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I think I could still use one side of the mold, so it wasn’t a total loss. (More like a 50% loss, which isn’t too bad for this experiment.) Enjoy the photos below. This is, of course, and art object, and not a functional bolt. I like the way it turned out, and I plan on doing more weird experiments like this. (By the way, it’s about 60mm long.)

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See Also: Fail Of The Week: Casting A Bolt In A 3D-Printed Mold