Saturday, November 21, 2009

Bicycle Project 2, day 5

Fork building. This takes serious effort and time. On top of that the sun set a little early today so there's going to be more work to do tomorrow. And may be we shot the breeze a little more on all sorts of interesting tangents.

The first thing is to set the fork rake (43mm with a 73 degree head angle for those that are interested). The measurements are quite precise then we use a big mandrel, add some weight at the end of the lever, and the fork tangs bend into shape. Just how much weight to lean into the lever takes a special art (made even more mystical given that there is some over-bending required to set the curve).

Measure the rake to the millimeter then use this big (uncalibrated as different fork tangs have different plasticity) to set the curve...

Yeah ok, she looks pretty well matched (note fork ends not yet removed).

Next step is to prepare the tangs to accept the dropouts. And henceforth I enter the world of the slotted dropout. These little buggers are slotted into the tube ends. Yeah? So cut a slot into the tube end, then prepare the tube end and the dropout to fit, then braze and fill, then finish by refining the join.

A word of advice: if you are going to build a bike go for the "shot-in" or "plug-in" dropouts. Sure they're not as customizable but you just braze the lil' suckers on (even I could do it). If you want real pain then go for the slotted dropouts in stainless steel. You have to braze in silver and that stuff goes from a solid wire in your hand to molten slag burning a hole in your shoe in seconds.

Slotting the fork tang.

Machining the steerer tube to fit the fork crown.

Fork is then built up and set in alignment jig.

Slotted dropouts in place.

She's so pretty and she ain't even brazed yet.

David Bohm brazes the right fork leg.

Dave cleans up after letting me braze the left fork leg (not quite sure how the silver got all the way down there gov'ner...)


The fork crown also needs some refinement. Not happy with the curves we decide to refine them just that extra bit more. Again I have to supervise Dave...

Bit more to the left there Dave.

Lovely curve back there.

Refinement still needed on this front curl.

At the end of the day we still have to finish the crown, cut the fork legs to length and braze the whole thing together. I guess it beats going to the LBS and buying a carbon fork. Or does it? More tomorrow.

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