Scratch-building chopper couplings

Ian Stock

 

 

 

This is not a quick way of providing couplings – but it does not cost £15 a pair either! If they are built as part of a larger project, then it is not too painful – what is more of a problem is finding the stamina to retro-fit my entire stock!

 

I wanted to produce something like as scale Festiniog Railway chopper for some new coaches, but the commercial offerings were either too large or too expensive. I also wanted to provide a hook on each vehicle to avoid the all-too-common uncoupling when only one is used.

 

The materials were largely bits of K&S brass I had lying around, and I chose sizes that minimise cutting and filing. The benefit of this process is that one can adjust sizes and shapes to prototype. I have also made these compatible with proprietary choppers such as the cast ones from Brandbright.

 

I don’t have anything like a fully-equipped workshop, but the following were invaluable:

 

·         Small vice for cutting/filing components

·         Mini drill in pillar drill stand – for accurate alignment of holes.

·         Small blowtorch for soldering in places where an iron won’t reach.

·         Various Swiss needle files.

·         Razor saw

·         Small point-nosed pliers

·         Tin snips

  

Method:

  

Mounting box:

 

1.Cut a length of brass square-section tube to length required, plus 1x width of section of tube used. I used ¼ inch section. Therefore add (just under) ¼ inch to the desired final length.

 

2. Place end-up in vice and cut two parallel slots into the end of the tube, adjacent to the two sides. These will create the internal void where the hook will attach. You need to add the tube-section width to the desired length of the cut.

 

3. I then used the pliers to break off the waste section created, and filed the broken edge to a slight curve; see Fig. 1 below.

 

4. Measure off the section’s width from the end of the remaining sides of the tube, and use pliers to bend inwards across the end of the tube, overlapping by 100%. This will form a mounting point for the buffing plate. File away about half the height of the overlap - you may wish to solder the two tabs together to make this easier. See shaded area on Fig 1 below.

 

Figure 1.

 

 

 

Buffing plate:

 

5. Mark out and cut the buffing plate – size as required. I used thin strip, marked my circle and cut progressively at tangents using the tin snips until a near-circle was achieved. I then filed the shape perfect.

 

6. Mark out the slot in which the hook will sit – the key dimension here is that it should be no wider than the inside measurement of the mounting box.

 

7. Make two vertical cuts and bend the tab between them – i.e. where the hook-slot will be – back by 90 degrees. Then cut off about 50% of the length of the tab - see shaded area on figure 2 below.

 

Assembly.

 

8. Offer the buffing plate to the folded end of the mounting box. When a good fit is achieved, use pliers to complete fold of buffing plate tab back into and over the ends of the mounting box, squeezing tight at 180 degree fold. The buffer plat tab should not reach the full depth of the box, so as to provide a lip over which the opposing hook will engage.

 

9. Solder the two pieces thoroughly together – both inside and outside the mounting – this needs to be strong enough to take the weight of the train.

 

Figure 2.

 

 

 

Hook:

 

10. The hook can be cut to shape from suitable strip – again I used ¼ inch. The critical points to the shape are the concave inner face of the hook so as to stop it disengaging under load, and a curved/sloping outer face to permit auto-coupling; see figure 3. The length of the hook will be dictated by the required ‘reach’ needed for it to engage over the opposing buffer lip.

 

Figure 3.

 

 

 

Mounting of hook:

 

11. Drill a 1mm hole through the rear plate of the hook, ensuring its position will permit the hook to sit horizontally along the coupling, and that its back plate will not foul the rear of the mounting box in the raised position.

 

12. Place mounting box in a vice and drill 1mm holes through both sides of the box, to correspond to the hole in the hook. It is easiest to place the hook on the top face of the box and use it as a guide.

 

13. A small spacer needs to be cut to keep the hook to one side of the mounting box – I used a small section of brass tube, inside diameter 1mm. Solder this to the desired side of the hook – I used a piece of brass rod inserted through both it and the hole in the hook to keep everything in position.

 

14. Assemble the hook inside the mounting box, using a piece of the 1mm rod as a pivot. Solder both ends to secure and trim to length. Clean up with file as necessary.

 

 

 

Draw bar:

 

The draw bar can be made to suit. I used 1/8 inch square section rod, which passes through the vehicle’s buffer beam and secures behind using a small screw or pin. Cut the bar to the required length and solder to the inner end of the mounting box. A securing pin passed through both parts may be desirable.

 

 

Conclusion.

 

This method has been proven at prototype stage, though it has not yet been deployed fleet wide. Its beauty is versatility, and batch production is not a very long job.