Compact 3-Speed and Reverse Gearbox
Built by Brian Leach in June 2021
From the April 1969 issue of Meccano Magazine, here is how to construct the original model:
The framework is built up from two 5½” Angle Girders (1), to each of which two 3” x 1½” Flat Plates (2) are bolted, at the same time fixing a shaped 1½”. Wiper Arm (3) (Elekrikit Part № 532) to the inside of the vertical flange of each Girder. The horizontal flanges of Girders (1) are then connected by two overlapping 3½” Flat Girders 4, the securing Bolts also fixing a 2½” x 1” Double Angle (5) to the underside of one of the Angle Girders and two 1” x 1” Angle Brackets (6), their free lugs 3” apart, to the other Girder. Note that Washers are added to the securing Bolts, not only because the Bolts pass through the elongated holes of Flat Girders (4), but also to prevent the shanks of the Bolts projecting too far into the interior of the gearbox.
Now journalled in the inside holes in the lugs of Double Angle Strip (5) is a 4” Rod (7), a 4½” (8) being journalled in the corresponding holes in Angle Brackets (6). Both Rods are free to slide in their bearings and both carry two Collars (9) outside the lugs, as well as a further Collar (10) and a Pawl with boss (11) inside the lugs. A 3/8” Bolt is screwed into one tapped bore of each Collar (10).
The head of the Bolt fixed in Collar (10) on Rod (7) engages between a Collar and a ¾” Pinion (12) on a 3½” Rod journalled in the lugs of Double Angle Strip (5) to form one of the sliding layshafts, Pawl (11) making contact with the sideplates of the gearbox so as to hold the Bolt in position. Also mounted on the Rod are a ½” Pinion (13) and a second Collar, the latter acting as a stop. The head of the 3/8” Bolt secured in Collar (10) on Rod (8) engages between two Collars on a 4” Rod journalled in Angle Brackets (6). Acting as the other layshaft, this Rod carries, in addition to the Collars, a Washer, a ¾” Pinion (14), a ½” Pinion (15) and two further Washers. Corresponding Pawl (11) again makes contact with the sideplates to hold the 3/8” Bolt in place.
Returning to the framework, two Angle Brackets, together with two fishplates (16), are bolted one to each Angle Girder (1), then the Angle Brackets are joined by a 2” Strip (17), to which two further Fishplates are bolted, using their elongated holes. The free ends of these Fishplates are brought together so that their holes coincide, then three 1” x 1” Angle Brackets (18), (19) and (20) are bolted to the underside of Flat Girders (4) in the positions shown.
Journalled in Angle Brackets (18) and (19) is the input shaft, supplied by a 3½” Rod carrying, between the lugs of the Brackets, two ½” Pinions (21) and (22) and a ¾” Pinion (23). Fixed on the Rod outside the Bracket is another ½” Pinion (24), the Rod passing only part-way into its bore. Free in the remaining part of the bore is the output shaft — another 3½”, journalled in Angle Bracket (20) and the Fishplates bolted to Strip (17). Mounted on this Rod are a ½” Pinion (25), a ¾” Pinion (26), nine Washers (27) and a loose Collar (28), held in place by a fixed Collar. A Large Fork Piece (29) is fixed to Collar (28), a Washer and Nut on the shank of each securing Bolt preventing the Bolts from fouling the output shaft. Secured in the boss of this Fork Piece is a 2” Rod serving as the gear-change lever and carrying the spider from a Universal Coupling immediately above the Fork Piece, whereas a Handrail Coupling is fixed on the end of the Rod. Tight in opposite bores of the spider are two of the special shouldered screws included in the Universal Coupling and these should engage neatly between Collars (9) on Rods (7) and (8). A Universal Coupling is fixed on the end of the shaft, while a 1” Pulley with Rubber Ring is fixed on the end of the input shaft.
Coming back again, to the framework, Flat Plates (2) are joined as shown, by three 2” Strips (30), (31) and (32) attached by Angle Brackets. Journalled in Strip (30) and in Angle Bracket bolted to Strip (31) is a 1½” Rod on which are fixed, in order, a Collar, three Washers, a ½” Pinion (33) and two more Washers. Pinion (33) is in constant mesh with Pinion (21).
Finally the “gate” is produced from a 1” x ½” Angle Bracket (34) and a ½” x ½” Angle Bracket (35). The former is bolted to Flat Girders (4) and strengthened by an Angle Bracket bolted to Angle Bracket(20), while the latter is bolted to a 1” Triangular Plate fixed to Fishplates (16).