Machinable wax is something that occasionally I could use in my shop but when I look at the price of a piece of it I decide to use another approach. The other day however while browsing the web for information on 3D printers I ran across an article on making machinable wax. Now that got my attention as I am always interested in making things especially if it can be done inexpensively. So I switched my web searching to DIY machinable wax and homemade machinable wax an came up with several articles on how to make machinable wax. Most of the recipes for the wax involve combining paraffin wax with low density polyethylene plastic.
There was a rather large decorative candle sitting in my workshop that I use pieces of for various things in the shop. The most recent was making some rocket nozzle mixture with wax, grog and bentonite clay. Also there are any number of plastic items laying around waiting to be taken to the recycling center. Here was an opportunity to make something useful from stuff that would otherwise be recycled. In other words with free stuff. The temptation was too great. A number of the recipes call for a ratio of 4 parts wax to 1 part plastic. So I weighed out 2 pounds of wax and cut up 6 ounces of plastic milk jugs and added 2 ounces of some plastic from a tote lid that had lost its tote. A lot of the web recipes suggested using very thing plastic such as grocery bags or plastic sheeting presumably because it would dissolve faster. I added the red tote lid plastic because I ran out of milk jugs and I wanted to add some color and see how easily the thicker plastic dissolved.
There were a lot of suggestions on how to heat the mixture. The problem here is the wax needs to be heated much hotter than its melting temperature but not hot enough to start fire. Now I can tell you from direct experience that hot wax burns just like gasoline so you don’t want it to catch fire. Although not mentioned in any of the web articles an electric skillet is ideal for this project. The temperature can be set with the thermostatic control and the large open area makes it easy to stir and add material. The wax melts around 160F and its flash point is 395F. Based on this and the melting point of the plastic the temperature needs to be set somewhere between 250F and a safe amount below 395F. I use a picnic table outside in front of the workshop for my potentially dangerous or smelly experiments so I set up the skillet on the picnic table.
I melted the wax first by placing it in its plastic bag in the skillet. The thin plastic bag dissolved almost immediately in the melted wax. Then I added some of the milk jug plastic and some of the tote lid plastic. I could see that the thicker tote lid plastic was taking longer to melt as expected. But after adding plastic and stirring occasionally for several hours all of the tote plastic had dissolved but some of the milk jug plastic stubbornly remained as clear blobs in the melt. Also not all of the recommended amount plastic had been added to the batch. So I decided strain out the blobs and pour the melt into a bread pan. There was one expense in this project and that was the strainer I used. It is now totally clogged with wax and the plastic blobs. If I make some more machinable wax the strainer can probably be reused by melting the residue out of it in the new melt before pouring. I now have a 2 pound blushing pink block of machinable wax.
It is a little brittle so the cut broke just before the end.
It looks good except for the chip that broke off an the end of the facing cut.
All in all it looks like this was a success. There could probably be more plastic in the mix. That might make it less likely to break and smear when cutting. Next time I make some machinable wax I will probably use all tote plastic and try and get the recommended 1 part plastic to 4 parts wax.