Cheap Z Axis Drive Belt

With the four Z axis drive posts in place, I started investigating the different ways that I could hook all the drive rods together so that rotating one attached to a motor would rotate all 4 at the same speed.  The typical method for doing this is to use a toothed belt from McMaster that costs about $30 for the belt, and then on top of that the drive gears need to be printed from a rapid prototype machine.  While this works great for those who have a working machine (albeit a little pricey for the belt) I did not have such a machine, yet.  So I looked into some other methods.  I had considered using belt/gear combinations from the photocopiers I had taken apart, but to get the 5 feet or so required for the Z axis drive I would have to splice about 4 different pieces together.  On top of this I could not for the life of me find 4 gears with the same pitch and diameter.  I had about 5 sets of three similar gears but finding the fourth turned out to be near impossible.  Doing my research I came across a post from about a year ago where someone tried to use a beaded chain as a drive belt.  These are the same chains used to change the speed on fans or the chains attached to the plug in the bathtub.  I went to the hardware store and found a 12 foot chain for only $4!  That would be enough for all 3 of the axes.  The problem now was finding gears to work with the chain.  

I was tempted to destroy the blinds in my apartment to steal the gears from those, but decided against it.  The person who tried this before had printed gears from a working reprap machine so that was out.  I set out to try to machine a set of working gears.  First, I tried wooded disks.  I tried sanding out little dimples for the beads to fit in.  The problem with this is that if the dimples were not perfectly placed, the round balls on the chain would simply slip out of their holding place.  

So onto the next idea, the gears for the reprap toothed belt are made using a mold made from the actual belt.  I thought this might work for the beaded chain.  I used some hot glue for the material and tried it out.  The rig I used is below.  

The problem was getting the chain out of the mold as, unlike the toothed belt, the hot glue could actually seep behind the chain the hold the beads in place.  I used an exacto knife to cut away the portion holding the beads in place and ended up with a slightly useable gear.  The main problem again was that the rounded beads had a tendency to slip out of their holes if I didn't cut away the exactly correct amount with the exacto knife (which I didn't).  

So idea onto idea #3.  I was looking around my pile of scrap materials looking for something I could fashion into a gear.  I realized that the 5/16" nuts I was using were just the right diameter for the beads.  I tried filing ridges into the nuts and even tried drilling little dimples into it.  Both of these failed for the same reasons as above.  If the dimple placement was not PERFECT the chain would not hold.  

I had one more idea to try out.  I cut several plastic disks from a plastic rod I had, a little over 1" diameter.  I heated up the beaded chain with a heat gun until it was hot enough to melt the plastic.  Then I wrapped the chain around the plastic disk and let it melt dimples into the disk.  This way they would be perfectly spaced because they were made by the chain itself.  The end result worked fairly well and if I hadn't of gotten a tip from one of my friends about some free bike chain (see future post) I probably would have ended up using this.  A picture of all of my attempts is below