Friday and Saturday were spent working on Eric's 650b and the belt drive project.
I also squeezed in another fork build from some of the crowns/legs that I mitered up earlier in the week. Here's a shot of the crown on a 29er fork...the miters welded up really cleanly and should look super under some glossy white finish.
Em stopped by to help me clean the shop. She does a nice job cleaning and wiping down the machines, but then gets all philosophical about it; "why bother, you're just going to get it dirty again!" How do you argue with that logic?
On to the builds... one of the first items of the frame I work on is the seat tube, as it is a key element in building everything off of. The seat tube is measured and cut to a rough length, the top cut at a 12 degree miter and then all the edges filed and cleaned so they are smooth. Next up is the binder bolt. It has to be precisely placed and then tacked, as I will use the front surface of the binder to keep the bottom bracket miter in phase.
Below, you can see how the binder is then used to orient the seat tube for the bottom bracket miter. I use parallels to shim out the binder so that the tube is straight in the fixture.
Once the seat tube cut is made, I move on to the down tube. I mentioned earlier that all the tubes are run over the alignment table. The longer the tube, the greater the probability that there will be some measure of bowing to it. These need to be positioned vertically, so that the stresses of the frame use the irregularity to it's advantage rather than it's detriment. Below, you can see the slightly raised portion in the center of the tube and the subsequent photo where I've marked the centerline on the top to orient it.The downtube is swaged/ovalized to give greater surface contact with the headtube and then prepped for mitering. I miter the bb joint first, as the cutter is already in the mill and then the headtube. As each frame is custom, I do take about three cuts to get the angle dialed in and length finalized; one to remove most of the material, a second to finalize the angle, and the third to finish length.
All fit up with 12mm of headtube extension below to allow for clearance of control knobs of sussy forks if they are eventually used.
A quick compound miter to allow the seat tube to slide into place finishes off the down tube...all nice and tight :)
The last bit is the top tube. Eric wants a frame geometry that has only a gently sloping top tube, so he may sit on top of it and wait for friends without sliding back into his saddle. I typically use an aggressive slope, as I never have the opportunity to sit and wait. Seems I'm always the one that others are looking back the trail at ;)