ITP Entry - 1938 ERA E-Type GP1 May 14, 2019 9:15:54 GMT -5
Post by Aurora on May 14, 2019 9:15:54 GMT -5
Hi John, I feel the same. The seemingly endless number of problems can be frustrating but it is certainly enjoyable to solve them.
....solving small problems in as elegant way as possible as they come up during the build process.
For example...here is my motor mount. Can you see the problem? Not a big problem, maybe not a problem at all, but an interesting situation.
A decision is required here about how best to accommodate the pinion (I don't have a removable pinion; if I did this problem wouldn't exist). On my drawing of this part, I made the hole diameter large enough for the pinion to pass through, about 5.8mm. I drilled out all the holes, the screw holes also, before cutting the part out from the brass sheet stock.
However, I was trying to think ahead, which can be dangerous! I didn't drill the pinion hole to the final diameter of 5.8mm, but stopped at 4.7mm, which is the outer diameter of the boss on the motor. I wanted to take advantage of the fact that the motor shaft boss could be used as an additional locating feature for the motor. The two screws of course locate the motor, but the boss can be used as an additional, third locating feature. I felt this would be helpful because of the way the rear end is designed. Instead of making a one-piece axle/motor mount, this motor mount is a separate piece from the axle pillars. It will all be soldered together at the end, on top of an underlying support plate, after all the parts have been made. The problem with this design is that each separate work piece must be made to very small tolerances and each piece must fit precisely. So having an additional locating point, and a fixed, immutable point at that, would help maintain alignment of all the various parts as they are being fitted together.
After everything has been sized and fitted together, I will be able to drill the hole for the pinion to the final dimension of 5.8mm. But the snug fit over the motor boss is satisfying and is giving me pause. It all clicks into place and feels very precise and sturdy. Drilling the hole to a larger diameter would result in the loss of that extra locating feature, and I'm hesitant to give it up, if only due to the mechanical satisfaction.
But still, the pinion must be accommodated. So, how to accommodate the trouble-making pinion?
Do I simply drill the hole out to 5.8mm, (red circle) which would allow the pinion to pass through, was the original design, and how I've always done it before? Or do I cut a channel (red lines) for the motor shaft and keep the 4.7mm hole, which is a nice snug fit for the motor boss? Would it be worth it, to cut the upper web of material to create the channel, with the loss of some structural integrity? Would the motor mount weaken significantly, perhaps distort over time from vibration and metal fatigue if the top web is cut? Cutting a channel and keeping that tight fit feels "elegant"; making the hole bigger does not. But simply enlarging the hole is probably the better mechanical solution. KISS rarely fails.
What else could be done? How else to solve this problem?
And those are the kind of goofball things I think about...