Making Custom soap moulds - individual cavity, oval, loaf & other shapes

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Aug 5, 2014
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I've spent the last 8+ years studying manufacturing techniques of various industries and I've decided to make a setup tht will allow me to make a wide range of custom soap moulds (and hundreds of other things like custom interior car parts and a very wide array of other things like custom cell phone cases, laptop cases & more), so this will be very helpful in making moulds for my soap making hobby.

I've wanted to make a number of shapes that were just not possible without making custom moulds and none of the online companies said it was possible or the ones that did gave ridiculous costs, in the hundreds of dollars for a 6-8 cavity mold.

The only thing needed to do this is a prototype shape of the bar you want to produce, if you want raised lettering on the bar, that works, depressed lettering, should be fine as well (a little more tricky but doeable I think) and custom designs. With 3D printing being easily available, a design can be made to put on top of the bar and incorperate into your product.

Single bar moulds can be made or a grid of up to 36" long x 30" wide (possibly even larger) and a mix and match of the the bars could be put in the sheet so you could have 6 of one bar, 10 of another, 3 of another, whatever can fit on the sheet.

I've come up with a few ways to make oval shaped log moulds as well, of whatever size and shape desired and have found that making a 2 sided mould is really the best option, it gets clamped together & secured, poured & then dissassembled and it comes out much easier. It's even possible to do a squared/rectangular botton with a rounded top, to allow soap to stand up on it's flat bottom, but also have a rounded/oval side that some people like. Of course normal square/rectangular loaf moulds are possible.

I found a REALLY easy way to remove soaps from loaf moulds or from cylinder moulds w/o using lining paper. The thing you need to do is use oil on the mold and cover the entire thing with a thing layer of oil (I found a low melting point fat is the best, liquids don't work anywere near as well) then you pour as notmal and allow to cure. Now the secret to remove the soap is compressed air from an air compressor, even a $5 12v tire inflator from walmart will work.

On a loaf that I had made of ABS plastic, I glued on a piece of 3/4" plywood on the bottom with a 3/8" hole drilled in the very center of the board, up into the mould. So there now is a hole in your mould but you can plug it with a tiny piece of scotch tape, as small as you can get and I even stick it to my shirt first to make it less sticky, just enough to mot move off the mould (this is before greasing the mould). This tape holds the soap in. Once it is cured you use an air gun, place it in the hole and slowly spray some air in.

A 20" long mould that is 3.5" widr (~87mm) is 70 sq inches. An air compressor can easily put out 60-70 PSI (most can do 100-120 w/o problem). So at even 30 PSI that comes out to 2100lbs of force pushing the soap out of the mold and I'm guessing it will start to move at about 5-10psi which is about 350-700 lbs of force. I've never had a problem with the sides/corners of the mould being damaged but I guess it is possible if they are damaged.

As for a cylinder, you need to have a cap that you can either scerw on, or attach it permenantly (which is counter intuitive) with PVC glue - NOT hot melt glue. Then you drill a hole in the middle of it and you do the same thing. A 3" PVC pipe has an area of 7 sq inches so you will need higher pressure to push the log out. 60psi would be about 420 lbs of force, 90 psi is about 630 and 100psi is 700lbs - all plenty to get the soap out. if you move to 4" pipe, you have 80% more pressure for each PSI you put into the pipe, so you will need a lower PSI most likely. Also, now you know how hydraulic & pneumatic jacks work.

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