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Friday, April 12, 2013

Marble Machine Goes Modular - The Crank

If you've been keeping up, we are just about ready to start building the actual pieces to make a marble run. The only thing we have left is a crank handle to operate the pump assembly.
To attach a shaft to the pump, running to the outside of the base box, we are using a half inch dowel. That dowel has a hole drilled the same size as the metal shaft. Then the dowel is split with a band saw down the middle of that hole. This slips over the shaft.
Next we have to pinch the dowel down onto the shaft. To do that we take a block of wood and drill a half inch hole through it. Then we drill and countersink four holes for screws. Then we split the block right down the middle of the half inch hole. Next, drill the hole larger on the countersunk side, just large enough for the four screws to pass through cleanly without catching threads. We want the screws to pull this top piece to the other one. So the threads do not need to catch that piece at all or it won't tighten.
After all that is done, and the screws are in the block to hold it together, slip the block onto the metal shaft. Put the wooden dowel through the side of the box and slip it over the metal shaft. Now pull the block back over the wooden dowel and tighten it down, pinching the dowel down onto the metal shaft.
This all creates a good enough fit to turn the pump rod. Now, if something jams up enough to completely stop the pump, this clamping system will slip. That is on purpose. You'd rather the rod connection slip than for a jam to destroy some part of the pump, or anything else. A jam is unlikely as long as we do everything else correctly, but you never know. It's better to be safe than sorry.
Now this part is not actually necessary, but I thought the outside of the box looked too plain. So I decided to add a dress up piece with an arrow cut out with the scroll saw. I made this out of a piece of walnut for a nice contrast to the color of the box.
Next, in my opinion, there was just too much play in the wooden dowel shaft as it came through the side of the box, so I added a block to the inside to give it more stability.
Then I made the crank from a piece of sapelle. The crank handle is made out of mystery wood. It is a piece of wood that a friend sent me for pen blanks that I have yet to properly identify, so I'm calling it mystery wood for now.
The reason I used a pen blank for that part is that I just needed a small piece of wood to turn for a crank handle, and this piece looked good to me next to the walnut and sapelle. All the dowels I have are softwood, mostly pine. I did not want to use pine for the crank handle, so I turned a piece for it on the lathe.
Now everything for a functioning feed system and base is finally complete. We can now start on actually building pieces.

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