I used the Paragon Machine Works chainstay yoke for the first time on Adam’s 29+ frame last month. The yoke was created to accommodate 3″ tires and allow the use of a mtn crankset with a regular chainline on a 73mm BB shell. This is a difficult task to say the least without the use of a yoke. Possible but lots of dimpling and crankset/ring size selection is needed in my experience. There’s a reason Surly created the Krampus with a yoke when they created this new genre.
Here are some notes that I thought is share to help others use this awesome machined yoke:
- There are different ways to go about using it but in general, you fuse the two pieces together, bend then cut the 7/8″ x 0.035″ to length, mitering chainstays for the dropouts, join the yoke to the chainstays, miter the yoke for the BB, and then fixture it up and make some tacks. Then I tacked it to the BB before welding it all up outside the fixture but that’s just one way to do it.
- Be sure to draw in CAD or paper accurate chainring clearances in order to find the right length to miter the yoke’s “arms” for the BB. They needed to be longer than I thought to fit a regular chainline especially if you want to run a 2x crankset or 32t single ring on the inside position of the crank. If this is taken into account there will be plenty of room for the torch and welding to the BB.
- Once you have that settled figure out the length of the 22mm (7/8″) x 0.035″ chainstays that plug into the yoke ends. Add at least 7mm to the tire radius to clear the inside of the yoke. I’m not sure the shortest chainstay length you can get but I doubt you’d be able to get anything less than 435mm unless you sacrificed chainline and chainring size (use a 28t). Get it right as you can’t dimple this yoke!
- Bend the 7/8″ stays to allow crankarm clearance. This is necessary! The yoke is wide and with 22mm round chainstays the bend needs to go straight back and then bend out after the crankarm distance. I had to put a slight dimple in the stays to clear a 2x Shimano crankarm since I didn’t roll the tube enough.
- To properly backpurge the yoke you’ll need to take an 1/8″ endmill to the inside of the yoke at a few spots and clear a path.
- I tried both welding with 0.035″ rod and fusing without rod to attach the yoke pieces. I liked the results of fusing better and it leaves less cleanup afterwards (sanding down the bead to get a clean finish).
- I left all the pieces loose in the fixture which was difficult to keep in one place and straight while tacking. Next time I’ll likely create the full subassembly outside of the fixture (using my chainstay mitering fixture) and then miter for the BB. That way is more seamless IMO but better get the clearances worked out.
- I used 0.045 rod to weld the chainstays to the yoke ends. There was a small gap because of how the yoke ends are shaped. It’s pretty air tight but i think it’s needed to get filler in there to get a strong connection.
hmm, all i can think of for now. I’d love to hear if anyone’s got some comments on their experiences with this yoke.