Day 9- Tuesday

On a completely unrelated note, I saw this disturbing article on velonews today about their editor in chief succumbing to the so called "fixed" Mavic R-Sys wheel design:

http://www.velonews.com/article/93054/a-shattering-experience---a-post-recall-r-sys-wheel-failure

These were the wheels that initially came on my Super Six that I sold as instantly as I got the bike. Something about carbon spokes and collegiate racing just didn't seem to make sense to me. While I've always been a big Mavic fan and love my Kysrium SL's, carbon spokes just seem like a bad idea. Even after supposedly "fixing the problem" with carbon weave in different directions, looks like I made the right choice.

Today I designed and welded on the chainstays. While the bike looks mostly done, Jim said this marks the 50% point. While UBI claims no prior welding experience is necessary, I've found everyone who didnt have prior welding experience (including myself) is running about a day late of where Jim is at, which is alright as long as we don't fall any further behind. If I fall any further behind a day's teaching, Jim has said he'll have to hop in to help catch us up. While I wish they planned in just a little more time, I fully agree that I'd rather have a bike 90% done by me thats rideable, than an expensive wind chime that was completely done by me.

I drew out the chainstays last night in CAD, and moved them over to full scale hand drawing this morning (step by step instructions given in longer technical section).  

Tube was oriented to provide maximal tire clearance (In my case to fit 35mm tires and a little mud in worst case scenario). Chainstays were then mitered by the dropouts with outside face facing up:

After mitered tube sides were prepped and tiny breather holes were drilled into the dropouts, chainstays were then situated in the jig and the outside measurement of the chainstays were taken at the point they would be welded to the BB. The jig was slid up and down until desire distance that was previously calculated was reached.

Tubes by dropouts were then tacked in jig, removed and then welded.

Chainstays were reinstalled in 132 mm axle and installed on the horizontal drill press, where the BB shell miter length- 1/1000th of mm was taken off to allow the miter to slightly wrap around the bottom of the miter. 132 mm axle is used as welding has a tendency to pull chainstays inward to desired 130 mm.

These tubes were then prepped, holes in the BB were drilled, and the entire frame was again tacked on the frame jig, this time along with the chainstays, where they were tacked. Frame was then removed from jig and chainstay welding was then completed.

The requisite "crotch shot":

At this point various tools were used to check for frame alignment. Amazingly, distance was found to be perfectly centered and at 130 mm. BOOYAH!

Another tool was used to measure the relation of the chainstays in relation to each other. It looks like this:

Initial reading showed right chainstay slightly above left chainstay, which would make wheel lean to the left. 

Right chainstay was yanked down pretty hard, stretching it past its yield point. Thankfully, frame was just barely off. Many bike frames meet their death on the frame alignment table at bike companies where your bending tubes to within 15% of their breakage point. This is one obvious advantage of custom built frames where there is much greater precision.

All done:

Long Technical Section: Designing Chainstays

1. Draw Rear Axle Spacing. This distance will measure the distance from the inside of your dropouts. Find the midpoint of this line and draw a perpendicular line. Chainstay length is measured off of this vertical line. This measures center of BB to axle. I have temporarily used a chainstay length of 415 mm.

2. BB is drawn. We are using a BB diameter of 40 mm and a BB shell width of 68 mm. Back of BB edge to axle distance is calculated (415-20 mm= 395 mm). This will be your miter distance.

3. Wheel radius is calculated. 700 cc wheels= 622 mm diameter, so 311 mm radius + largest tire you imagine using (35 mm) for a grand total of 346 mm. Tire width is drawn in front of this line.

4. Dropout diameter were measured to be 40 mm. BB edge to chainstay needs to be 5-7 mm; I'll be going 6 mm. A second point is drawn both 19 mm to the left of that 6 mm point and 19 mm to the right of the dropout edge. These four points outline your chainstays. 

5. If this was a road bike, the tire would be closer to the axle and the tire would be alot smaller. This would usually give you enough clearance, so then the inside angle would be taken and subtracted from 90 to get your miter angle for the chainstays to drop outs. However, as you can see, for my cross bike, straight stays will not provide the clearance. I can play with the Chainstay length by moving the BB shell closer and further away from the axle. 

I can also choose to use slightly bent chainstays and after making this drawing full scale, I can lay the bent chainstays right over the drawing and position them to allow maximal tire clearance by leaving the second S curve right over the tire diameter. This leaves more than enough clearance (including mud accumulation), so I'm good to go.