Hello all, I would like some advice on a plate dropout I would like to make. I am making another rear triangle for my first bike with the intent of making it convertible from 27.5 to 29 wheels at will. My current setup is 29 only and I want to be trendy. I am doing my best impression of the banshee dropouts that have aluminum axle holders that bolt to different plate holes. (see pics)
The c-shaped plate with holes I am planning on 5mm thick 316 stainless and the tubes will be .9mm wall 19mm OD 4130. I have welded these together before and had success with ER312 filler and I plan to cap the open ends, I just didn’t do it in CAD because I didn’t feel like it. My questions are:
Is cutting out only one side of the tube bad? Is slitting better? It makes clearances (tire, crank, ankle) a lot harder if I have to slit.
Should I have more landing pad on the 5mm plate for the weld bead? I don’t have that much space but that is such thick material I figured it will work out but I have had that attitude before and been waaaay wrong.
If one sided attachments are ok, is there a guideline for how long they should be? I picked 12mm long because 12 seems like a nice number to guess.
I know it’s not what you are asking about, but I would suggest adding 2x ~1/4" dowel pins in-line with your bolts on each side. As-is, your skewer will be hard to align because each insert will have movement the amount of your bolt clearance hole. If you put 2 dowel pins in line (press fit into the insert and .001-.002" diametric slip fit into frame piece) then the 2 inserts will stay perfectly in-line with each other no matter how many times you take them in and out. This will also re-distribute some of the sliding/twisting forces away from the bolts. As the design is currently, ALL of the pressure from riding will be put on the bolts, and every bump and jump will be trying to shear that bolt in half like a guillotine. Ideally you would want some kind of boss or feature that locates and conjoins the insert to the framepeice, the bolts should exist JUST to hold the 2 pieces together, not to actually hold the whole weight of the bike. Dowel pins would be an easy way to kill 2 stones with one bird.
That’s some good advice. My plan was to ream those holes in the plate and use some high strength shoulder bolts, but the dowel pin idea is a good move. Thanks!
That’s a good idea, shoulder bolts with a precision fit should do the trick too. But if you locate on dowel pins instead then you can use standard off-the-shelf hardware. That way if you strip or lose a bolt you can go to any hardware store anywhere you are and get a replacement.
I did exactly this with a set of Banshee bikes dropouts. It worked…till it didn’t but I think that was my crappy braze that eventually failed and not the concept. I had a chainstay to C braze let go on me, but brazing thin to really thick seems to be my nemisis as it’s how I’ve had several things fail on me. On this one I didn’t have any fixturing options to braze it up without leaving the aluminium inserts in and I think they kept sucking out heat. If I did it again I’d make up something to hold the C’s in alignment where I wasn’t worried about cooking the aluminium inserts.
It might be hard to tell from the pictures but I have taken some bits of everyone’s feedback and combined it into something that I hope will work. I will ream out the holes in the c-plates and they should dock nicely with the male pockets on the 7075 dropouts I added around the threaded holes. The FEA is very promising. The 3D printed pieces all seem to have plenty of clearance. And taking @earle.b advice I will fixture the c-plates as well as I can while welding.
