Blades: Bent

I headed over to Royal H Cycles in Somerville yesterday, where frame builder Bryan was able to bend my fork blades.  He actually has a bending tool similar to what I was planning to build, which was encouraging to see.  I will have to try to finish my own bender and try it out on some scrap tubing.

One piece of advice Bryan gave that I had not fully considered is the trail of the bike.  Trail is defined as the horizontal distance from the axis of rotation of the front wheel (the center of the hub) to the extended centerline of the steerer tube.  Proper trail allows the front wheel to act like a caster; hitting an obstacle that changes the direction of the front wheel won't suddenly change the direction of travel of the whole bicycle.  A shorter trail makes the bike more responsive but will lead to instabilities - track bikes will often have short trails, since there aren't things like potholes or sticks to run over on the track.

With my desired head tube angle and rake, the bike was going to have a relatively short trail; UBI apparently recommends somewhere in the vicinity of 55-65 mm, and my design was floating around the 35 mm area.  To solve the problem, I'm going to reduce the head tube angle to 72 degrees, which BikeCAD says will give me 58 mm of trail.  Since I still want the same frame size (especially the head tube, since I've already cut the steerer with that dimension in mind), this will effectively lengthen the fork blades by about 10 mm and the down tube by about 85 mm.  Convenient, since I haven't cut any of these tubes yet.

A more significant problem will be sourcing a head tube lug with a 72 degree angle.  Most of the lugs available are angled at either 73 or 74 degrees, so finding one "off the shelf" may be difficult.  One option will be to purchase a 73 degree lug and open it up a little bit by hand.

Next steps are to cut the fork blades to length, slot and dome them to accept the dropouts, and then file the fork crown tangs and braze everything together.  I'll have some photos of Royal H soon.