The first step in actual construction was to build the wood core.
The two images above show the patterns I made to transfer the design to the plywood. I made a detailed drawing of the frame using TurboCad and printed out full scale copies. Then I glued the drawings to poster board and then cut them out. In both images the lower pattern was for marking off the outer perimeter, while the upper one was used to indicate the location of the lightening channels in the core layers.
This image show the three center layers (3/4 inch 13 ply Russian birch plywood) after all the lightening channels were cut. Getting to this point was a lot of work! I first rough cut the outside perimeter of each piece using a band saw (borrowed from my neighbor), then brought each piece close to the final shape by sanding with a drum sander attachment on a drill press (borrowed from my brother-in-law). Then I temporarily screwed the three pieces together to sand all three to the final shape at the same time.
I cut the channels by first cutting out a circle at each end using a hole saw, and rough cutting the channels with a jigsaw (my own!). I used the drum sander again to clean up the cuts. For the two side layers of the core, I cut the channels narrower than that in the core, and then used a router (also my own!) with a quarter round bit to round off the inside corner.
A close-up of the lightening channels.
This image shows the three core layers stacked on top of each other. The 1/8" thick skin layers (3 ply Russian birch) can be seen just above.
This image shows the skin layers in place. At this point nothing was actually glued together, but just stacked on top of each other to check the fit. Note the swingarm in the background.
Here I've clamped the layers together while the glue sets. First, I glued the three core layers together. After applying the glue I screwed the three layers together using the same screw holes that I used for alignment during the final sanding process, and then clamped them together as shown. The next day, I removed the screws (excess weight!), and glued the skin layers in place using the same clamping arrangement. To avoid putting screw holes in the skin layer, I cut them both a bit large, so that they did not need to be positioned exactly. After the glue set, I took off the excess with the sanding drum. Notice poor Woodie (sans swingarm and wheels) on the floor to the left.
Here's the wood core after laminating, rounding off the corners with the router and drilling holes for the bottom bracket shell, front derailleur tube, head tube, and swingarm attachment points. Notice Woodie in the background, now reassembled (if only temporarily). Also visible in the background just behind the pin pong net is evidence that I had been starting to do some practice working with carbon fiber.
A closer view of the front end. At the tip you can where I cut into the frame a bit to make sure there was clearance for the front derailleur to swing in all the way.
I cut all the holes using "Forstener" bits, which worked very well. I can say that now, but truth be told, drilling the holes was nerve wracking to say the least. As noted earlier, I did not use any sort of jig for alignment. Rather, I was depending on the flat sides of the frame to use as clamping surfaces to make sure the headtube, bottom bracket and swingarm were all properly oriented. All the holes were to be drilled for a tight fit, so if they were not oriented properly from the start, there would be no good way of fixing it later. If any one of the holes was messed up, all my work to this point would be wasted. So I spent a lot of time setting up to drill each hole, making sure the frame was clamped firmly and squarely to the table of the drill press. When it was finally done, and I had verified that the alignment was good, I was relieved beyond description.
Preparation for installation of the idler was almost as nerve wracking. For attachment of the idler wheel, I used a threaded furniture insert from the local hardware store. The insert has threads on the outside to allow it to be screwed into the the wooden frame of a couch (or recumbent bicycle) and threads on the inside to accommodate a machine screw. I clamped the frame to the drill press and drilled a pilot hole. Then I clamped a threaded rod into the chuck, screwed the insert onto the rod, and used the drillpress to guide the insert into the frame. I figured this was the best way to ensure the insert was screwed in square relative to the frame. Later, I unscrewed the insert and epoxied it back in place. Finally, I screwed in the shoulder bolt that would serve as the axle for the idler. I was again relieved to find that the alignment was good.
Just behind the clamp you can barely make out the threaded insert for the idler axle and the shallow semicircular indentation around it. The indentation was to allow the idler to get a bit closer to the frame and keep the chainline as direct as possible when using the inner cogs and/or chainrings.
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