So, Chris at your service. The experiments to cast bushings in a home shop are going to be a long process, but I figured I could get started out. I'd like to begin this evening with one method for creating your "master." In casting a master is the piece from which the mold is made. You need a master in order to make a mold in order to make multiples, make sense? Good.
We will be carving our masters from a bushing "blank" (an orange Khiro barrel bushing, 79a, though color and duro don't matter,) using a drill press and abrasive based tools. The fine dust from this process is hot, fast moving, and not particularly healthy, so be sure to wear the right safety gear. I have on a welding respirator and safety goggles.
The first thing you need to do is secure the bushing blank in a way that allows you to chuck it in the drill press. I used a bolt which fit the inner diameter of the bushing (hint: it would be the same size as a kingpin,) a washer and a nut, and later two nuts because the washer was becoming irritating to work with. Using a bolt thats the right width is important because it will center the bushing making it much easier for the worker (you!) to make the piece rotationally symmetric. You chuck this setup in the drill press as you would any other bit.
Check to make sure your safety gear is on right, you aren't wearing loose clothing, no neck ties, all that pre-power tool business then switch her on.
I used rasps and files to rough out the shape of my bushing. I found that the most useful/versatile tools were my half-round files, they took a bit longer than the rasps to remove material, but they did so in an even and controllable manner. This sequence of images shows how the tooling was done and the progression of the shape of the bushing as I worked through it.
I had the though part way through to mark out the proper diameter for one end of the bushing to be able to fit in a bushing cup. So i took the assembly out of the drill and used a second bushing to mark out the shape:
I then re-assembled and re-chucked the jig and got back to work. When The bushing was getting roughly to the shape I wanted I switched from files down to sandpaper, working my way though finer and finer grits. This allowed me to be more and more precise with the amount of material I was using as the piece got closer to being finished. I worked it until I had what was essentially a rough surfaced version of the shape I wanted.
Now If you are just making yourself a custom bushing, this would be perfectly funtional and if you are tired at this point you can consider yourself finished. But if in fact you are making a master to make a mold from the rough surface left by the sand paper (I went down to about 180 grit) will make the mold have a rough surface and it will be harder to release your cast bushings from it when the time comes. So I'm going to pass along a little trick I picked up somewhere along the way. I call it "The Old Bag Trick," which is a very un-clever name because all it entails is tearing off a piece of a brown shopping bag and using it in the same manner as the sandpaper to buff the surface of your bushing.
I took the following picture with the flash on in order to highlight the finish the old bag trick gives to the abraded urethane. It is almost as smooth as the brand new mold release surface of the original bushing and it should do just fine when we get around to using it to cast our mold.
All thats left to do is to remove the finished bushing from the drill press and the holding rig. There you have it! A completely custom shiny new bushing.
Now, I'm not entirely sure where this experiment will be taking me next, but most likely the next post on this subject will be about either making the silicone mold or fashioning a vacuum chamber for degassing the mixed 'thane. I hope you all enjoyed and catch you next time!
