Metal/plastic stock can be pretty expensive when you are testing/learning how to use a CNC machine. Previously I had used Smooth-On plastic that is a two part poured plastic mixture. It works well, but its also expensive. One alternative that a lot of people use is called machinable wax. Its cheaper than the other options, but still not cheap. The kicker though is that you can make machinable wax yourself.
I found a link online that gave a good recipe that I thought I’d try. I’ll update this post with the link later. That being said, its pretty simple. You need to use 4 parts paraffin wax to 1 part polyethelene plastic. There are many sources of polyethelene bags, namely plastic grocery store bags and some garbage bags. I decided to use some regular garbage bags from Kroger.
Once you have the ingredients, you need to melt the wax, then stir in the bags one strip at a time. You can use any pot on a stove to melt the wax, but I wanted something that I could use in the garage. I went with a Presto Kitchen Kettle which came recommended for doing this. You can pick one up at Walmart for $24 (http://www.walmart.com/ip/Presto-Kitchen-Kettle-Multi-Cooker-Steamer/14321003). You can see the kettle heating up and melting the wax here. The temperature should be set to 300 degrees or so. Be careful, because wax is flammable.
After about 15 minutes of heating the wax and mixing in plastic, it should be pretty much done. You will need to strain the wax to remove any plastic pieces that didn’t melt. A kitchen strainer would work, but I wound up using the frying basket that came with the presto. Rather than get fancy and make a square mold out of wood, I to use a cake pan. I used that in the past for plastic, and it works very well. You can see the poured wax, and the strained wax in the following picture.
The wax took about an hour or so to dry. I actually waited a few, but the mold comes out like this …
So the good and the bad … I don’t think I mixed quite enough plastic bag into it. When I cut it into chunks on the band saw, it was a little softer than expected. I also found that it doesn’t like sitting in the sunlight . Instead of using garbage bags next time, I’ll use the standard grocery bags that they put your groceries in.
One of the coolest things about all this is that you can remelt and repour the molds again and again. Gathering all of the wax swarf may be difficult, but the reuse is great. In addition, what a great use of the plastic grocery bags.
And the one thing I did forget to mention was cost. To make a pound of machinable wax will cost about $4 for the bags and paraffin wax. That same volume of wax purchased would cost about $40-$50. Please look for the next iteration when I use the plastic grocery bags.