Summary

My wife makes soap as a hobby, and I thought it would be fun to see how I could combine it with 3D printing. I used 3D software to design the soap and experiment with different colors, and printed the pieces I needed to make silicone molds for the soap.

Instructions

After printing the dish, give it a rough sanding on top to knock down any bumps from oozing or excess plastic, and scrape away any threads with a knife. Wash it with acetone a few times by filling it up and immediately dumping it out. This will give it a smooth glossy finish and melt any remaining dust or threads. Don't let the acetone sit in the dish. Spray it with mold release or brush on a thin coat of vaseline. There are some tight corners, and this will help keep the silicone from tearing as it comes out.

Fill the dish with silicone. I recommend Smooth-On Oomoo 25, because it cures in 75 minutes which makes it easy to make a bunch of molds in a short time. When it has set, pull the silicone out, taking care with the tight corners. I made 18 altogether.

Using a condiment bottle (like you find ketchup and mustard in) pour the melted colored soap into the channel of the mold, letting it flow naturally as much as you can without overfilling it. If you have enough molds, the first one will be ready to take out by the time the last one is filled.

The Bar print needs a lot of perimeters to keep from getting gaps in the fillet on top. The curve gets so gradual that the outer radius for one layer might be more than a thread width shorter than the layer below it. I used 5 perimeters and 4 solid layers to make sure that the surface was thick enough through the curve to prevent gaps and stand up to sanding.

I didn't want to print the entire thing with that many perimeters. Instead I sliced it at .3 layer height, 3 perimeters, 2 solids and .1 infill for the base. Then I sliced it again with .2 layer height, 3 perimeters, .1 infill for the sides, and again with .2 layer height, 5 perimeters, 4 solids and .3 infill for the top.

To merge the gcodes, I searched for "G1 Z3" in the middle gcode, and copied everything after that point. Then I pasted it over everything after the inital "G1 Z3" in the base Gcode. This made it change to the middle settings at 3mm into the print. I did the same thing with the top Gcode, starting at around "G1 Z25"

The bar print then, starts with .3 layer height for the first 3mm to give the print a chance to level out before changing to .2 layers, for a smoother surface on the sides. At 25mm it changes to 5 perimeters with a denser infill to support the solid layers on the top.

The bar print should be smoothed, by whatever method you find best to create a glossy finish. I sanded it with 150 grit to smooth out any seams or large bumps, then covered it in Aristocrat Liquid Glass, a clear resin coat that cures to a high gloss. The smoother the surface of the mold, the clearer the soap will seem.

Cut the ring down one side, with an exacto knife if you can. You want as thin a kerf as you can get. If the ring won't fit all the way around the bar, you can fill in the gap with some clay. Set the bar inside the ring and fill with silicone to the top of the ring. When it has set, peel the ring away and push the bar out of the mold.

Assemble the soap by pouring a little clear into the bottom of the bar mold, spritz with alcohol to break the surface tension, and place a swirl embed. Pour enough clear to barely cover the embed, and then place the next one, rotated a little. Repeat until there are five embeds, and then top off the mold with clear soap.

In the future I would like to pour resin or plaster into 4 of the bar molds, and then use the plaster bars with a homemade vacuform machine to create trays instead of individual bar molds.

Clear Soap with a Distinctive Triple Swirl