Hi everyone:
This is my first post to the forums after lurking for some time, and finally deciding to start my own CNC machine build.
Like many people it seems, I decided to use 'skate' bearings for my leadscrew support bearings. Ideally, i'd like to use three per axis, two pre-loaded against each other on one end ( poor man's matched AC set ), and one on the other end.
This meant that I'd need to do a lot of hole cutting for 22mm ( odd here in the states ) bearings.
Over the past two weeks, I set about to make some bearing blocks that I can use to fix the bearings. My goals were:
- make lots of them quickly
- accomodate several mounting schemes
- cheap to make
After lots of deliberation, I decided to use RTV silicon to accomplish the "lots quickly and cheaply parts". I also wanted to experiment with the casting process.
I ended up making two different kinds of block-- one that has normal 1/4" holes, and another one that is a bit more compact, and has counterbored holes for socket head cap screws.
I have posted some pictures-- hopefully i've not messed that up
The process was:
I first made a master using a drill press and forstner bits, out of machinable wax. The RTV rubber holds amazing detail, so i polished the master and squared it up as best as I could. This took more than one try
Then, I made an RTV mold. This took more than one try also. Making a mold box is a pain, I ended up using Lego bricks to minimize the amount of mold rubber used.
Then i used urethane resin to make several ones. each one needs to be sanded on the back, since the mold is a 1-part mold.
I was fairly pleased with the results. The blocks are plastic, but they do not need to have high radial stiffness anyway. My idea is to 'sandwich' a piece of angle-aluminum between two of these to make a double bearing block, like shown.
I have ended this phase encouraged-- i guess my goal with this post is that someone else might find this technique useful. I was really pleased with the accuracy of the parts that i have ended up with!