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While building the All-Road frame, I found it difficult to miter the rear triangle evenly and accurately. There was lot to consider to get this right, so I relied heavily on the designs of Kristopher Henry from 44Bikes.
The fixture needed to:
Hold chain and seat stays rigidly enough to miter cleanly using the Bridgeport.
Space stays evenly to confirm tire clearance and dropout alignment.
Accommodate a variety of chain stay heights that club members might use.
I cleaned up some rod stock on the lathe and put offset holes so they could be tightened against stays. I couldn't use a clamp design because the centerline of chain and seat stays vary between builds.
The 3d printed tire clearance checker and a 3d printed clamp alignment tool helped keep spacing between the stays and the angles of cut equal.
There are a handful of updates I'd like to make to this design to improve rigidity and accuracy.
Planned improvements:
Machine the cross extrusion pieces so they slot onto the main extrusion.
Machine a component that checks for varied tire clearances and creates symmetric cutting angles at the clamp.
Incorporate the fixture into the frame jig so stays can be held in place while being welded.
Taller chainstays are especially difficult and put this fixture at its limit.
The fixture can be set horizontally in the vice to miter chainstays.
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