Bruce Lindsay really helped me out on this project. He has an original, unrestored Curtiss, and we spent a lot of time on the phone discussing (in minute detail...) every little bit of the frame. Sometimes he would fax me sketches with dimensions. It would have been a lot easier if the original frame was in my shop, but that wasn't possible. Where best to start? With the dropouts, of course (thanks, Bruce...)
This is the bottom bracket assembly to hold the pedal cranks. It really should have had an eccentric to adjust the chain separately. As it is, you really have to hope the chain and belt both want the rear axle to be in the same position.
This seat-tube junction is the most complicated part of the frame. Gas tank meets oil tank, and the seat post must be able to slide (horizontally) into the rear of the gas tank. The seatstays attach to the lug that pinchs to fasten the seat post in position. Getting the sequence right is crucial here.
This part was first welded (fillet brazed) as an assembly. Next, the tube was honed a few thou so the seatpost could slide through, the inside end then capped to stop gas leaking out, and the tube / boss / plate slotted with a very thin slotting saw (what else?) to allow a little pinching to hold the seat post in place (make sense?)
Using two 6' lengths of cold-rolled flat bar to position the gas tank. Correct alignment is a very important part of frame building.
Here the end cap for the gas tank has been TIG-welded on and filed smooth. End caps were formed in a hydraulic press using a set of dies. The rear of the frame is now complete.
The headtube and downtube lug have been fabricated and positioned on the front of the gas tank. Everything is on blocks sitting on the surface table. With alignment checked, a little TIG-tacking was used to hold the headtube for brazing.
Quite a lot of heat was needed for the fillet brazing. The "white" you see is a paste flux applied with a brush. Flux also comes out the torch, from the automatic fluxer, situated in the acetylene line of the welding set. It's a very good setup, and definitely helps the bronze to flow nicely.
The downtube to hold the front of the engine is very similar in look to a small bicycle fork. And, being 1911, I'm sure that's what inspired it. It was easier to make the fork from several small pieces due to it's complex shape.
Not the greatest photo, but you get the idea...
I recall doing a front fork too, but can't find any pictures. This is as far as I went, and the parts were shipped to a collector in Indiana.
Looking very comfortable in the Guggenheim, Memphis, TN.