Rear Triangle Jig

Top Page 1  One last bit - There is variance in the angle for different triangles, and you want the 1 1/2" conduit tight against the stay to be bent.  I put a flat tab of steel on the cross-tube of the jig, this to allow the placement of a washer, a scrap, whatever it takes to adjust the jig on the tabletop properly.  Like this:

THE REAR TRIANGLE BENDING JIG

A problem I and some other builders have discussed is bending/re-forming the rear triangle for this bike.    I had been doing it by hand for years, and the advice earlier in this series suggested that you do that as well - do it twice and pick the one you like best for the finished bike!    

Two other people are using conduit benders to get nice results.   I haven't achieved that yet.  Another builder suggests unbrazing the seat stays at the rear dropouts and simply folding them down.   I've made a mess of that too, and worry about strength at that joint.   

The by-hand-with-a-torch method I have used does have faults - you can bend it crooked, you can heat unevenly, the dropouts can shift alignment, the stays can crimp or crack, etc.  I think I get about one in three, really, that I like when bending by hand.   And I do practice.

The jig below just did a dozen rear triangles very handily - only two are frame rejects. 

Start with a rear hub - this one is crudely clipped out of a stray scrap wheel.




I have brazed a small tube onto and perpendicular to the hub, and another, of 1 1/2" conduit, perpendicular to that about 4" away - this latter is parallel, obviously, to the axle.




The cure for rear dropouts altering alignment is to mount a hub IN the dropouts while you heat and bend.   This jig does that, accurately at the 135mm width, and offers a surface to use while bending as well. Prop the jig up on the table so that the large, parallel conduit piece is tight against the seat stays.   This angle will vary from different donor bikes.   Crude, but it works.  

Then heat evenly, moving a torch from one stay to the other until you can easily push down the seat stays.



Here is the adjusted rear triangle, removed from the jig.   Smooth, even, no kinks!

A lot of paint to clean off, however.......

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