Bearing Carriers: Co1 Bogies

This stage of the assembly is fixing the subframe bearings into the bearing carriers and folding up the carriers around the bearings. The carriers are located on the fret in four frames, each of which folds up into a jig to help to fix the bearings in the correct place. The carriers are a little fiddly, but worth spending time to get right as they are one of the main functional parts of the suspension.

We find it useful to use two containers to store separately the components of each bogie; 1kg margarine tubs are suitable. Within them we have 35mm film cannisters, one for each axle, to keep the components for each wheelset together. We mark the containers and cannisters to match the id marks etched on to the subframes, bolsters and bearing carriers as explained below.

Separate the two Subframe:Mainframe (S4) etches from the fret. Remove the other components contained within each subframe etch and put them safely to one side.

Note that one of the subframes is marked with small triangular dimples. You will find that one of the bolsters, and one set of bearing carriers, are similarly marked. You can use the marks, through all subsequent work, to distinguish the components of each bogie.

Take one of the axle bearings and test it in one of the subframe axle slots. It should be a free sliding fit but if it's a bit loose don't worry. It will more likely be a little tight in which case gently file the vertical sides of the bearing slot - take off a little at a time equally from each side and try to keep the two sides vertical - until the free sliding fit is achieved for the entire depth of the slot.

Now select eleven more bearings and test them for fit in the same slot. You should find that they are all about the same size. If there is a variation, then you may wish to individually fit the bearings to the slots. You will then need to preserve the identity of each bearing through subsequent operations (there are marks etched on the bearing carriers and the subframes to assist with that - see below). But do bear in mind that, as we have no coupling rods, the accuracy of this fit is by no means as critical as it would be if we were building a steam locomotive. Whatever you choose to do, dress the remaining eleven bearing slots to get the free sliding fit for each of the bearings.

Put the subframes in their containers safely to one side for now.

Test fit the axle bearings on the 2mm replacement axles. They should be a free running fit. Remove any burrs or swarf from the front and rear faces of the bearings.

Remove the Bearing Carrier frames (C1) from the main etch. DO NOT at this stage separate the bearing carriers from the frames.

The photographs in this section show a similar set of bearing carrier etches which have minor differences to those supplied with the Co1 bogie kits.

The individual bearing carriers each have small half-etched identification marks. Use these in conjunction with corresponding marks on the subframes to ensure that each carrier is always mated with the same subframe slot (The diagram shows a three-axle subframe and its carriers: the same principle is used on the 1Co bogies).

It is essential that the 'two-spot' (outer) axles are fitted with the matching bearing carriers, on the correct sides. The remaining four carriers, on the centre and inner axles, are interchangeable.

Test fit the bearings in the large central holes in the carriers. The body of the bearing (excluding the flange) should pass through the hole. If necessary, gently relieve the holes with a round needle file, working evenly around the edges, until the bearings pass through.

The folds in the bearing carrier frames are best made in bending bars, or between any two trued and parallel surfaces clamped together. Use a rigid piece of flat material to make each bend simultaneously along its whole length. This will help minimise any unwanted distortion in the fret.

Note that Fold 3 is a jig fold, made along the tags at the base of the carriers.

Make Fold 1, check that all sections of it are at 90°, and reinforce it with solder. Be sparing with the solder; you don't really want to get any on the carrier faces to the inside of the fold. Apply a small amount of liquid flux to the slots on the outside of the fold, then get a small amount of solder on the iron and touch it against the central slot on the outside of the fold on each bearing carrier. You will see the solder flash along the joint to the other slots. Repeat for the two sections of fold on the carrier frame.

Make Fold 2. You will need a thin, firm, flat piece of material to drive this fold; a robust steel rule (not a thin springy one!) works OK. If anything, overfold beyond 90° just slightly.

Make Fold 3, to approximately 45°. Note that this fold is along the line of the tags at the base of each carrier, forming part of the frame assembly jig, and is not a part of the finished carriers.

This is a view of the folded carrier frames. Fold 3 has been made to 90° in this case, but anything over about 45° will do.

Stick a length of double-sided tape, large enough to take one of the carrier frames, onto a clean, flat, heatproof working surface. Ensure the tape is firmly smoothed down on the surface, with no air bubbles or foreign bodies trapped underneath.

Remove the backing paper from the tape, take it to one side and place on it three of the axle bearings, flanged face down. Place the carrier frame, inverted as shown, over the three bearings with the bearings passing through the three holes. Use the backing paper to carry the three bearings and frame on to the double sided tape, then slide the backing paper away, leaving the three bearings in contact with the tape and held in position by the carrier frame. Press the bearings firmly into place on the tape and remove the carrier frame. Repeat for the other three carrier frames.

Using a cocktail stick, place a thin fillet of multipurpose grease around the flange root of each bearing. This will ensure that the area is kept free of solder when the bearings are fixed into the carriers. An alternative is to use a permanent marker: the ink should resist the flow of solder.

Place the carrier frame, the correct way up, over the bearings and press down firmly the back of the frame and carriers, above Fold 2, on to the tape, as shown here. The unflanged end of each bearing should protrude from the face of its carrier by a very small amount (not quite as much as in the sketch), and the faces of the carriers should be parallel with the end faces of the bearings.

Using a cocktail stick, apply a small amount of flux around the join between the protruding part of each bearing and the face of its carrier. Holding a bearing in place with a heat insulating instrument, to make sure it doesn't move, bring the iron with a small amount of solder to the join between bearing and carrier, and let the solder flash round the joint. Repeat for the other bearings. A small amount of solder may appear on the bearing outer surface under the inner face of the carrier but most of the bearing outer surface, in particular within about 0.5mm of the flange, should be free of solder.

Remove any excess solder from the front faces of the bearings.

Free the fret from the working surface.

Weaken the bond of the double sided tape with a soak in methylated spirits and slide a Stanley knife blade or a similar thin strip of metal under the fret and bearings to break the bond of the tape without causing too much distortion.

Unfold Fold 3 and separate the individual bearing carrier assemblies from the frame. Take care, as the top parts of the carriers are quite fragile at this stage: it may be best to leave cleaning up the tags until after the folding and soldering stages below.

Taking each carrier in turn, clamp it firmly into a vice (a hand-held vice is ideal for this) across the ends of the bearing with the bottom of the bearing carrier protruding. File away any remnants of the tag from the lower edge of the carrier.

Working against a hard, flat surface, make the fold to form the bottom flange of the bearing carrier.

Then, invert the carrier in the vice so that the carrier top is projecting. Fold in the ears at the top of the carrier. You may find that the ear catches against the top flange: do not apply brute force, but adjust Fold 2 and/or the direction of the applied force, and you will find that it folds easily. Folding against a block, as shown, gives a good, tight fold.

Pass a piece of the 0.9mm nickel-silver wire through the hole in the back of each carrier and across the top, parallel to the line of the axle. With a small amount of flux, solder the wire in place, at the same time reinforcing the folds and butt joints around the top of the carrier. Keep the bearing clamped in the vice while soldering; this will act as a heat sink and prevent melting of the joint between the bearing and carrier.

We hold the 0.9mm wire in the correct alignment with the bearing as shown here. Clamp the wire horizontally in the 'helping hands' at a distance above the bench that allows the hand vice, holding the bearing, also to rest on the bench. Using one hand to steady the vice, the other is free to wield the soldering iron. Snip off the wire, close to the bearing, when done, and it's ready for the next one.

Trim the wire and file it flush with the front edges of the ears and with the back of the bearing. Clean off any solder which adheres to the outer faces of the ears. Ensure the holes in the ears remain clear of solder.

Taking each subframe etch in turn, check that the carrier assemblies can slide freely in their respective subframe slots (see the next paragraph for a solution to bearing misalignment). File away any burrs from the outer edges of the carrier tops. The fit along the line of the axle, i.e. of the subframe plate between the bearing flange on one side and the inner facing edges of the carrier on the other, should be quite loose to accommodate tilting of the axle. Check that all traces of the tag are removed from the edge of the bottom face of the carrier, as otherwise it can bind with the lower edge of the subframe slot.

Although the aim is to have the bearing flange parallel with the front face of the carrier, a certain amount of misalignment can be tolerated. If, however, you find that the subframe side is 'pinched' between the two, then an individual carrier assembly can be corrected by clamping the back of the top of the carrier against a flat working surface. The soldering iron can then be applied to the bearing to melt the joint between bearing and carrier and allow the back of the bearing to be held down against the same surface. This should set the correct alignment.

That completes the bearing carriers. Clean them up to remove any flux and grease residues and put them, and the subframes, away in their respective containers.