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.
I finally got my 1.75mm compact hot end in for my Makerbot. The last one I had built by Rick and team. This one I assembled myself. Here is a picture of the heatcore. This is a great design where the nichrome is wrapped around a nut instead of the barrel and insulated by ceramic. It makes the piece easily removable versus the original design. It also has a tendency to hold heat much better.
Look for picture of prints to come later …
I’ve been experimenting for some time with using a CNC machine. I originally bought the V90 with the express purpose of milling PCBs as well as other small things that might come along. I’ve decided however that a vertical mill is better suited to my needs than a gantry style router. To that end, I got a Taig vertical mill from Nick Carter at http://www.cartertools.com . I’d highly recommend him if you plan on getting a Taig. He is a great help at sorting through what you need to get started.
Although the weight is much less than a Bridgeport, the Taig is quite heavy compared to the v90. I decided to reuse the steppers and electronics off of my v90 on the Taig, I installed the bright yellow motors and got it all set up.
And lastly, my new Taig setup on my bench in my maker area.
I decided to build a chucking system to hold down PCBs when I’m milling. Many other folks use superglue on aluminum with acetone to release, hold down bars, or tape. The nice part about a vacuum chuck is that it should be able to pull the entire board down flat. Hold downs will only get the outside. Its also very clean unlike superglue/acetone.
There are two key components to a vacuum chucking system. You need a pump and the chuck itself. For a pump, I decided to go with a Thomas or Gast vacuum pump. New, these pumps are very expensive. I debated on a used one, but got a good deal on a new one from eBay. A video of it running is below:
You can see that its holding 28 hg of vacuum, which is plenty for what I need to do. These pumps are made to be run continuously, so longevity should not be a problem.
The second part that you need is a chucking system. I thought about building one, but I don’t have a good way of machining metal. I found a “Smart” Chuck on ebay. Normal vacuum chucks basically provide suction through a number of holes and you are supposed to cover the holes that aren’t used. The purpose is to provide a complete vacuum. The “Smart” Chuck is supposed to only provide suction when there is an object above the hole. I’m not sure how it works yet, but it does work. I plan to build a chuck of my own eventually. The chuck that I ordered is demonstrated in this video (fraesen02_small_ot.avi) . If it can hold down a big block of aluminum and work, a PCB should be no problem.
After installation, you can see the picture of the pcb being held by the chuck.
I still have some work to do. I plan to build an EVS system from veneersupplies which would all for a vacuum reservoir. More on that to come …
Today I received my Lathe. I picked up a Sherline 4400 DRO model off of ebay. This one has a 3.5×17 inch envelope. It came with the 3.1 inch 3 jaw chuck and a few basic accessories. My primary purpose in getting it is to learn how to machine using a Lathe. I’ve already found a few potential uses, but I’m not sure how realistic those are yet. The DRO will be very useful until I CNC it.
So one of my goals in getting into CNC was to be able to prototype my own PCBs (Printed Circuit Boards). I’ve gotten some special equipment to do it, but this isn’t an easy thing to figure out how to do. Its taken me some time, but here is my first attempt. I’m using the hold downs that I put on the v90 with some steel bars to help hold it flat. This isn’t ideal. More on that to come …
Below is the etched result. I’m pretty pleased with the result.
I’ve now added a stepper extruder to my makerbot. I’ve done this for a few reasons. The DC motor that comes stock on them isn’t very reliable at any speed other than a full 255 PWM. I can slow down or speed up my feeds all day long, but not being able to impact the flow has significant implications. Also, this should go a long way to combatting ooze. Realize that right now, the motor reverses itself to try and pull back the filament when it stops extruding. This can be done in firmware or software (oozebane), but it doesn’t work very well with a DC motor. The problem is that you assume that by pulsing it so many times, you’ll get it to turn a certain number of revolutions. Unfortunately, it doesn’t work reliably that way. A stepper does a similar thing, but much more reliably. I ordered the kit from Makergear. You can see an image below.
This uses the brutstruder block along with a custom stepper from MG. I’ve also added a PSSC15 stepper controller.
I decided to try an use it with my existing MG hot end, until the 1.75mm hot end was ready. More on that later.
