Bachmann Class 37/55: Bogie Bolster

These instructions describe the assembly of one of the two bogie bolsters. In practice you could build the two bolsters together.

Folded bolster centre Remove the bolster centre etch (4) from the fret. Make the single fold in the etch, as shown.

The hole in the centre of the bolster is sized to take a 10BA screw. To use the 2mm pivot screw supplied in the kit, open out the hole to 2.0mm. Make sure the hole is clean and thoroughly deburred.

Open out the hole using tapered broaches to ensure that centres are preserved. Deburr the holes using a larger drill.

Clean up the faces of one of the 2mm brass nuts to remove any machine oil and grease and prepare for soldering. Take one of the 2mm screws and apply a smear of grease to its top few threads and the lower face of its head. From the 'outside' of the folded bolster centre, insert the screw through the pivot hole and thread on the nut. Screw the nut up tight and check that it is flat to the inside face of the bolster top. Run a generous fillet of solder around the nut, taking care to keep solder away from the etched slot in the bolster centre.

Remove the screw from the nut (the grease should have been prevented it from being soldered in place).

First fold in bolster sides Remove the two bolster side etches (9) from the fret. There is one pair of handed sides for each bolster, with one pair having small half-etched triangular marks.

Fold up the traction ears as shown. Don't apply any solder to these folds just yet. Take care to avoid distortion at the narrowest part of the bolster sides.

Bolster frame fitted to first side Remove the bolster frame (6) from the fret. Make the halving joint with the slot nearer the mid length of one of the bolster sides, as shown.

Frame fitted to second bolster side Fit the frame and the second bolster side together.

Engaging bolster centre in slots Take the bolster centre, and engage it in the remaining halving slots in the bolster sides…

Bolster centre slid into place …then slide the centre fully home, engaging tabs and slots with the top of the bolster frame and at the lower ends of the vertical members of the centre.

Initial soldering of bolster top Run a little solder around the joints and folds at the top of the bolster tower to hold the components in place. Keep the lower parts of the bolster free from solder for now.

Bolster bottom flanges Remove the two bolster bottom flanges (3) from the fret and make the two folds in each one. Be careful, as they can distort easily around the slot.

Bolster bottom flanges soldered in Fit the flanges in place at the lower sides of the bolster. They are handed to slot on to the lower ends of the bolster frame. Solder them in place.

Bolster outer ribs Remove the two bolster outer ribs (7) from the fret and make the two folds in each one.

Outer ribs fitted Fit the outer ribs to the bolster sides. They are handed to fit the slots in the bolster sides and to make halving joints with the vertical members of the bolster frame and centre. Solder them in place.

Bolster traction ear folds Fold down the four traction ears.

Bolster and subframe paired up Pair up the bolster with its subframe, as designated by the presence or absence of the etched triangular marks on the bolster sides and on the underside of the subframe. Orientate the bolster, with its more open end facing the outer end of the subframe - the end with the guard irons. Rest the assembly on a flat reference surface (with the guard irons overhanging one edge of the surface) for the following checks.

Bolster restraints Check the bolster for dimensions and squareness:

The bolster should be fitted to the subframe with the lower edges of its four traction ears at the same vertical datum as the lower faces of the subframe. Suspension movement is designed to be ±0.5mm from that level at each of the four corners. A tight fit can be addressed in the first instance by light filing on the circular edges of the traction ears or lateral restraints to remove etching cusps. Other adjustments may be made by gentle tweaking of either the bolster assembly or the longitudinal restraints. Try to keep the longitudinal restraints at 90° to the subframe sides, as they also serve as supports for brake detail and the cosmetic bogie sideframes. If you do need to tweak the bolster, try to end up with the faces of the traction ears vertical; adjust the fit over the lateral restraints by adjusting the traction ear folds or, in extremis, by grasping firmly the central arch structure of the bolster.

Soldered traction ear folds Once you are happy with the fit between bolster and subframe, reinforce the folds at the tops of the traction ears with generous fillets of solder.

Secondary spring cosmetic detail Remove the secondary spring detail etches (2) from the fret. There are four for each bolster, and one spare.

Secondary detail in hand vice Clamp the detail in a vice as shown…

Secondary seat end fold …make the first fold in the end of the detail…

Secondary detail second fold …and then the second fold to form the base of the spring seat.

Secondary detail, first fold in loop Remove the component from the vice and carefully fold over the first folds of the etched loop…

First folds reinforced …then apply just a touch of flux and solder to reinforce them, being careful not to get solder into the slots for the second folds.

Also tin the back face of the detail with solder, taking care not to get solder into the slot shown here.

Check now that the tab at the top of the detail will fit into the horizontal slot towards the top of one of the traction ears.

Fold tag at top of detail Fold over the tab at the top of the detail.

Second fold in loop Make the second folds in the etched loop, again reinforcing them with a touch of flux and solder.

As well as forming part of the cosmetic detail around the cosmetic secondary coil springs, these loops form the lateral retainers for the working, transverse, wire secondary springs.

Secondary detail soldered in Insert the tab of the secondary detail into the slot of the traction ear and solder in place.

Bolster end details Remove the bolster end detail etches (5) from the fret. There are four for each bolster. Make the two folds in each etch.

Bolster end details fitted Fit and solder the end details into position in the two vertical slots at the top of each traction ear.

That concludes the construction of the bolster. Give the assembly a good clean to remove all flux residues.