I have reported on this thread before on my slow and painful progress as a trainee metal-mangler.
As some of you have seen, I have been trying to make a mid-drive gearbox out of an 8-Speed bicycle hub where the input comes in on the hub's normal sprocket, but instead of the hub having a rim and a tyre affixed to it I am adding an "output sprocket" to drive 2 rear-wheels via a secondary chain. 8-Speed gearbox? That'll do nicely sir.
There are commercial trikes in the USA doing exactly this, but I am trying to make my own in my very modestly equipped little workshop.
Here's what happened today......
I am delighted to report that the first "trial fit" of all of the parts together has been achieved.
However, like a Spacex launch it may all fly to pieces on its first outing.
Today I drilled the bolt-circle for the output sprocket. 9 Bolts! (who is this madman?).
Actually, I just transferred the pre-drilled bolt-holes that were already in the sprocket onto the top plate with a transfer punch (new toy I got yesterday).
I used the little mini mill to drill all the 9 holes to be tapped for M4 bolts, and TBH I found it remarkably easy with the hold-down clamp and some backing Aluminium plate (to prevent drilling into the mill table).
I then tapped all the holes for M4 thread.
It was an absolute nightmare to assemble as the M5 bolts that pass up through the hub-flange are over length and so they start off trying to get through the flange and the bottom plate at and angle.
At one point I just could NOT get the bolts to pass through the flange, lower-plate and the spacer blocks and into the threaded holes in the upper plate; my heart sank and I thought perhaps I had got it wrong somehow.
But, I had put index markings on the hub and the two plates so I knew that they had been put together ok before and I just persevered.
I did get the two plates and the spacers all bolted onto the hub-flange successfully in the end.
I then attached the output sprocket to the upper plate with 9 M4 bolts, it is standing off from the upper plate
by a truly ridiculous amount as the sprocket is sitting on the ends of the 6 M5 bolts.
Now I can either cut the M5 bolts off more or less flush with the top plate's upper surface and rely on threadlock to prevent the bolts from undoing, OR, put M5 Nyloc nuts on the bolts and then cut ant remaining bolt off beyond that. What do you guys & gal's think?
While this is All of the bits bolted up together, there are still things yet to be done.
When the M5 bolts are cut down I will use M4 washers to stand the sprocket off from the upper plate only by a sufficient amount to ensure that the chain's side-plates are not trapped.
As you can see below the sprocket is quite high but still inside the OLD anyway and cutting the M5 bolts down will allow the sprocket to be placed close to the upper plate.
In closing this update I would say that it has been a hoot to make these things from raw steel plate and to such tight tolerances and have them actually all line-up and work. Yay! Go me!
