Re-Inventing the Wheel?
by
Alan Schwartz
(used with permission)
I ran into a problem today and came up with a solution. The solution is so obvious that I am certain it has been described (and perhaps even commercialized) before but - there may be other innocents out there like me so:
I was repairing a car that had chewed up and spit out its gearset (and they were Slot-It gears, not easy to do) I replaced them with a steel pinion and bronze crown gear (64 DP), shimmed them carefully for clearance and tried a gentle rotation by hand - terrible! They were rough, stiff and uneven! I checked the clearance, checked the axle for straightness and the bearing for alignment - all O.K. maybe a bad gearset - tried another - same result.
So I sat and stared - and looked carefully and finally saw that the (soldered in) motor was mis-aligned - it was square with the chassis and axle but the motor shaft was not in the same plane as the axle - i.e. the motor shaft, extended, would not pass through the center of the axle. - bad business. I whipped out my motor soldering iron (150* watt American Beauty truncheon) and made several attempts to correct matters. Critical alignment of a hot motor and a hot chassis with the one hand that is not holding the iron is dicey. After several less than successful attempts, I devised the following:
Took a small block of brass - about 3/8" X 3/8" X 1/4" and drilled it through the long dimension with a 3/32 drill and then cross drilled it through the other long dimension 0.78". I then drilled down into the two bores and tapped these holes for 1/72 set screws.
Pass an axle blank through one bearing, the block and then the second bearing. Lock with set screw. Insert motor shaft into the 0.78" bore and lock. Swing motor down into place, center it and solder. - Voila (and the gears worked)
EM
* Why such a big iron - doesn't it overheat the parts - no - quite to the contrary, the big iron and its big tip can deliver heat very rapidly so the area of interest is heated to soldering temperature before the rest of the piece gets warm.