Monday, July 10, 2017

Finger Treadle, Part 3

Man, this "simple" project seems like it's taking forever! Of course, it was probably designed to occupy, for example, a high school shop class for an entire semester, so it takes the time it takes. Just for consistency, here's the photo from the original plan one more time:

I started Part 3 by finishing the base - can't really do the crankshaft and connecting rod until the base is solid and stable. Last time, I created the uprights. Before I could complete them, I needed to cut the notch in the base for the treadle - the part you press with your finger. I marked it out and milled it:

I could have just milled to the lines, but I have been trying for precision when I can, just for practice. I did a drawing and some math:

Basically, you have to understand the size of the slot (in this case, 1.012 inches), the offset from one edge, and the width of the cutter. That allows you to compute where to start, and how far to move to complete the cut. Once it was done, I had a nice fit:

Next up was boring the holes for the bearings that the crankshaft turns in. I used a different bearing from the ones in the plan, so I needed a 5/8" hole. On my light equipment, you can't just drill a big hole - you have to work up to it. Here's the array of cutters needed to reach a 5/8" hole:

I didn't have a 9/16" drill so I used an end mill instead. It worked so well that I decided to use a 5/8" end mill to bore the final holes with the frame assembled.

That should have worked fine, but it turned out the nominal 5/8" shaft of the end mill was slightly large, and wouldn't pass through the hole in the top to drill the bottom hole. Oh well. I used a "Silver and Deming" bit to finish it, and all was well:

Once the frame was done, I turned my attention to the flywheels. What a trial that turned out to be! I started by turning the recess on the back side. It fought me all the way.

I eventually realized my problem was one of clearance. Once I got deep enough, the body of the cutter was dragging on the uncut portion of the flywheel, making a mess. I found a cheap, narrow carbide cutter, and got busy with the grinder to make some clearance:

Once I could cut, I made the first flywheel without too much difficulty. But now, how do I make the second one match? About that time, I stumbled across a video from Chris at Clickspring, my most reliable Internet teacher. In 10 minutes, he taught me exactly how I should have been doing it! Here's the link, well worth the time to watch:

One of the techniques I learned was to make a "centering button," which is made to precisely fit in the reamed hole in the flywheel. It has a small indentation in the dead center, which you can use to mark cut lines. I made it carefully to be a tight sliding fit in the hole:

Once made, you can use it with a pair of calipers to mark various dimensions. The cool thing is that you don't even have to measure with a ruler - just use the first piece to set the divider for the second piece:

Finally, the lathe work was done and I had a nice, matching pair of flywheels:

The plans call for six holes to be drilled in a circle in each flywheel, even spaced. I used a hex collet block to accomplish that. I made a second mandrel to fit my largest collet, attached each flywheel in turn, and drilled, rotating the block for each hole:

The last operation was to drill and tap a 6-32 hole for a setscrew to hold the flywheel in place. I've got to come up with a couple of 6-32 X 3/8" socket grub screws for that. They are drilled at a slight angle for clearance.

Once all that was done, I put the flywheels on a straight shaft and gave them a spin. So far, so good!

Making those flywheels was the first time I've worked with bronze, and I must say, it's not my favorite metal. Unlike aluminum and brass, which turns with easily manageable chips and curls, bronze seems to spray a hot, nasty grit that gets everywhere and resists being swept away. After finishing, it took me over an hour just to clean the lathe and the area around it. Here's a little of the goop:

This project is teaching me a lot, but I feel the need to finish it! In the first place, I would like to show it on July 22nd at a library demo that Phil Oles and I are doing. But beyond that, I need to clear the backlog because there's a major project coming to the Grant St. Garage very soon. In the best tradition of fine fiction, here's a little foreshadowing...

1 comment:

  1. Looking good. Keep in mind you were working with the "easy to machine" brass. Aluminum bronze is much worse.