Sorry for a long post here, just recording my thoughts and notes before I forget and hopefully they are helpful to some.
As usual I decided to try something way over my head and it was a struggle. My girlfriend wanted a hardtail with plus tires, so I drew up a small hardtail sliders and 3" tire clearance. I’ve been working with 3d printed yokes whenever I can to speed up my process, so I used them on the chainstay and seatstay. The designs are my own, and they were printed by RAM3D in new zealand. Great customer service, really good pricing and the lead times aren’t horrible. I asked them to be printed with an internal support lattice, but I’m not convinced this was the right move, at least with the type of lattice they use and since I didn’t have any internal hollow geometries to support. My thought was that it may add strength and stiffness but that’s probably wishful thinking. The lattice actually slightly interfered with the miter since it terminated at the miter surface. I’m sure I could have sent a model with an offset surface to fix that mistake. Technically it was flush but things warped. The seatstay yoke turned out great, both were printed in wall thicknesses slightly thicker than steel. The chainstay yoke was another story, it warped so bad I had to re-miter the BB cut on my mill. I think this was a fault of my design. The way it gets printed ends with a thin unsupported surface that I could see pulling out of line very easily (which it did). I also think that the lattice contributed significantly in pulling this area around, another reason to not use it or specify an offset termination surface.
Everything mitering wise went well, I didn’t have any major issues cutting or filing the Ti, and I kept my miters as tight as possible which helped a lot during welding. I was able to bend .047 wall .875" diameter chainstays on the famous vevor chinese bender with really nice results, I really took a gamble on that one. Wouldn’t be possible without a follow bar and clamp like others have done
Fusion welding went surprisingly well, didn’t have any keyholes only small spots of color on the dropouts and I had better venting for back purge so there wasn’t as much disturbance in flow once the frame was sealed up. The biggest pain was the tiny acute angle between the top and downtube, it was near impossible for me to get in there. Better welders out there make it seem like no sweat but I really was struggling to get that closed up. I really could have gone with a longer headtube to save myself the trouble but I wanted to be sure the stack wouldn’t be too high. I’ll hopefully never do that miter again.
On the filler pass is where I got completely wrecked, a number of areas went worse than expected. I tried to make a good tinfoil argon dam for the slider hoods but it wasn’t enough to keep them from getting color. I also learned very quickly that the yoke lap/butt joints need a healthy amount of tinfoil shielding to prevent the gas from rolling off too quickly. Once I got that dialed the prints welded just like the rest of it. Overall my welding was sub par and I’m really not proud of it, I learned a lot but the whole process was incredibly stressful.
Luckily my back purge worked well, no color inside the BB HT or ST. I used the super thick 1.625 OD BSA BB and had minimal distortion, didn’t have to chase the threads which was a relief. My girlfriend wanted a fully anodized frame so I decided to give it a shot, took way longer than expected and the finish wasn’t nearly as even as I was hoping. But she likes it and its definitely unique so I’ll take it. One thing I didn’t account for with regards to clearance was the additional thickness of shimano chainrings. The stock two piece chainring interfered with the yoke where the outer ring bolts to the spider due to the fasteners. This was definitely oversight on my part but it seems silly to have a two piece ring when it adds that much thickness. I can’t find anywhere that sells the outer ring alone to replace for wear but someone can probably educate me about that one. I swapped for a one piece oval and had plenty of room.
Probably won’t attempt another Ti frame for a long time, the added time, cost, and stress wasn’t worth it for me. Although when I picked the bike up it certainly made me want one.
