I modified the original carriage to accept the timing belt approach. To do this I had to rotate the drive motor 90 degrees and mount a timing pulley on the shaft. The belt needs to thread through the carriage sides, and since it forms a loop, there are two holes on each side. The belt needs to be attached to the drill platform and loops over the timing pulley on the drive motor. The other end needs to wrap around a free turning idler bearing (or a very smooth/no-friction surface). For that I had a bearing left over from a carter bandsaw guide replacement. (it was running rough, but it is still smooth enough for this project 🙂 ). Turns out this bearing is the same one used in skate board construction, so it should be easy to be find.

The timing belt get gets cut, and connected to create a fairly snug loop over and under the platform. For the intial exercise I simply hot glued the belt together, but for the actual implementation, I plan to create a splice using a small 1″ section of the belt with the teeth up, and overlay both ends of the looped belt 1/2″ (approx) with the teeth facing down, and meshing with the patch piece. And rather than glueing this, we will have a small cap piece that is screwed to the platform to pinch the splice together.

The other discoveries with this experiment were:

1. the servo we had used to raise and lower the drill platform was not really strong enough for a Dremel drill shaft head attachment. We’ll update that to a bigger motor.
2. the drill platform was too close to the mandrel, and we really want the platform near level when the bit is engaged. (accepting variation for various diameters of course).
3. we want to mount the mandrel motor directly to the side, so the coupler will be inside the carriage – and to do that the carriage housing will need to be about an inch or two wider.
4. we don’t like the mandrel mounting setup – removing 4 screws to load and unload the mandrel is going to be too much. We are going to try a “flip up” door on that side, with a single pivot screw and a locking screw.

To make those changes the drive bar and the pivot bar will need to be moved up and back relative to the mandrel. Up by nearly an inch (to  make sure the collet and bit length are included).

We’ve not yet figured out the actual mounting mechanism for the drill head. We have our eye on a battery operated Dremel tool (7000 or 8000 series) – with the battery contacts used as connections for wires to an off drill power supply (to keep that weight low).

Next I will need to update the parts page, and rework the sketchup drawing…