Bending Chainstays To Fit 54mm Tires & 62mm Fenders

I'm building my second allroad frame for the 54mm x 559 Rat Trap Pass tire + fenders. Bending the chainstays and modifying the BB shell spigots to the degree required, without machine tool assistance and with nothing but scrap material, saws and hand files was not a trivial exercise! Photo documentation with pertinent information is in this album: Flickr

The first frame is documented here though I deleted a bunch of process photos: Flickr

As an aside: If I could have only one bicycle, that would be it, hands down. Fast on the road, handles like a dream, soaks up bumps, comfortable and is happy on nearly any surface; on lousy city asphalt it's a revelation. Actually it's revelation on any surface.

Over the course of these two RTP frames I built a few mandrels and wrecked a half dozen pairs of chainstays while evolving the better mandrel incrementally in order to achieve the necessary radius of curvature, tube support and other details. I think I've finally gotten it and the procedures to a reliable, repeatable and not so time consuming point. Chainstays are ROR units, bending filler started out as packed and contained sand (brazed one end shut, braced a large nut on the other for a large bolt and sand compression) but ended up as paraffin + sand + hammered plugs (this week); I'm trying to avoid having to use expensive and chemically nasty fuseable metal. I managed to get a good pair of stays for the first frame but the operation was iffey; I could still wreck blades or mis-locate the bend easily. This week I managed to improve the process and tooling substantially; the results are perfect and I'm pretty sure I can reliably make more to the accuracy required.

It's been quite a journey and I hope the info is useful to others.