Got the metal I ordered for my swing arm last friday. My original plan was to narrow the CR80 swing arm I had, but it ended up seeming like more of a pain in the arse than just starting with new tubes and getting on with it.
Was off today, so i decided to dig in before my Valentine gets home from work.....
Cut all of the swing arm sections to length.
The BB shell at the front of the swing arm will actually set about 14mm rearward into the two parallel swing arm beams. Should be visible in the pic based on my sharpie marked CAD template..... The actual swing arm pivot will be located about 50 mm above the top of the arms, and about 25.4 mm behind the BB shell. This will all be welded and tie into the beams for strength. I am going to get all of this sorted and square before determining the lower shock mount position and configuration.
Another time consuming step coming up is going to be the dropouts - I plan on using 10-12 mm thick steel plate for my dropouts. Right now, the plan is to section out the inner portion of the tubing on the axle end to accept the dropouts, and then weld those mo fo's in. I wonder if mild plate steel, rather than hardened plate steel, will be acceptable for use as dropouts?
Anyways, with this configuration, I have plenty of crank arm clearance, chain clearance, and a nice straight chain line. I was a bit worried that this swing arm would be too long (and laterally flexy ) end to end, but the reality is that the actual length of the swing arm from pivot point to axle is what counts. The BB shell will just be welded on to the front of the swing arm, and really has no impact on the overall stiffness of the design. I hope.