Nick, I am starting to plan for a prototype build of a new bonded spindle design similar to the construction of the Red BB30 left crankarm. I hope to mold the first parts at the end of August followed by machining in early September.
Please review the model below and let me know your thoughts on machining of the molded crankarm.
44-6118-174-bonded-spd.asm
Please note I may make small adjustments to the machining geometry, but let’s start to plan for the machining fixture. We only need to machine the pedal interface and a counterbore at the spindle end of the crank. I will complete a machining drawing shortly. See the mold crank machining features highlighted in red below. They are very similar to what’s machined on the Red BB30 left.
This is only an advanced development prototype build to see if the design works. If there is a simple prototype method for machining these features lets consider that option. If not, what fixture design do you suggest?
For reference below is a picture of the Race Face machining fixture with integrated spindle. I can’t tell much from this, but maybe you can. It looks like they might be fixturing off the bottom of the crankarm at the pedal end and the B-plane. They are also holding the spindle, and maybe there is a gap at the bottom of the spindle.
Our current Red BB30 left fixture looks more like shown below. One downside of this fixturing method is the spindle axis is not established. This could lead to the pedal axis out alignment with to the spindle axis. Ideally the machining fixture indexes off the spindle axis to guarantee the pedal axis is aligned.