The first steps are to determine the size of the plate from frame measurements and computation. The length can be anything up to the maximum flat surface on the frame top minus about an 1/8" for adjustment. The minimum should handle the motor mount plate with ample allowance for the bushing mounting method chosen. The width should be less then that of the frame to allow for adjustment.
Since most HO standard gauge frames are about .5", a good starting point is K & S .5" bar stock. Two or more strips may be fastened together to attain THICKNESS. These should be sweat soldered, ACC'ed, riveted or screwed together before final shaping with the thicker one on top for a later reason. Narrow to suit frame width with a file or power tool.
If the shaft length is cut to match plate width, the wormwheel can be easily centered on it. Before mounting the pinion, add about .020" spacer washer(s), smaller than the pinion root diameter to prevent the properly aligned driver gear from rubbing the wormwheel. Next add a couple of .010" thrust washers, then the bushings to each side. Measure over the washers, or if present, the bushing flanges, to determine fork slot width. Add about .010" for clearance. Errors can be corrected to within .005" using .005" thrust washers.
Before the next step, the bushing mounting method must be decided. Using ACC or solder works, but does not permit easy repair or adjustments. Care must be taken not to solder or glue the shaft to the bushing. In haste I soldered them once during an early try. Straps similar to pipe or conduit types can be made, from 1/64" brass, freehand or in a die and fastened with screws.
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Since almost every case is different, no dimensions are shown and only general guidelines can be given.
The slot length should equal the the wormwheel OR + allowance for straps, if used, + .040" clearance. Mark the shaft centerline at the wormwheel OR + .040" from the slot rear and mill or round file a bearing alignment groove across the plate. This only needs to be from .005-.010" deep, just enough to keep alignment while fastening. This may be omitted, if you have calibrated eyeballs.
Next mount the gears to the plate and the geared driver in the frame. Try the plate fit and trim to clear obstructions. Then locate MOTOR MOUNTING screw centers and drill over sized clearance holes to permit adjustments. Most open frame and can motors have bottom mounting holes, but some have only end holes requiring angle brackets, while others have none.
The Sagami 10153-9 square open frame, mounting plate, which must be cut to fit and glued to the motor, is shown above as a dashed rectangle. Using the motor with worm, determine and mark the leading edge on the pillowblock plate. Align and clamp the motor plate and mark the forward end. Then drill two pilot holes on the center line clear through both plates. Re-drill up to the screw tap bit size the separate. Tap the holes in the motor plate, and re-drill pillowblock plate holes for clearance and countersink the bottom for flush mounted flathead screws. Screw plates together with marked side up and grind off screws flush. Thoroughly clean gluing surfaces and glue marked side to motor avoiding screw holes. When completely set, try assembly and shim as necessary for proper mesh.
Last locate frame mounting holes. These are shown a paired circles. The dotted ones are alternate locations to avoid obstructions. The ones at the right may be added if the plate is thin and flexible. Mark the holes on a longitudinal line at a distance just over the clearance bit diameter. (ie: 2-56 = .090". separate .100".) This separation is more important in deep holes to prevent bit wandering due to wall break through. Drill small pilot holes then align and clamp plate to frame. Transfer centers with very light drilling into frame. Separate, drill and tap hole at the midpoint of line connecting marks on frame. Enlarge hole pairs, break through wall and file to form slot.
If top slot is not accessible, start with the two pilot holes drilled through the frame and cover plate, then transfer centers to bottom of pillowblock plate to locate center for tapped hole. To allow cover plate removal without disturbing alignment, its slot may be enlarged to clear screw head.
Mount, test and adjust.
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