Original page created on 07/03/2022; updated on 16/05/2022.
New model
After learning from the prototype, I designed a new version which is shown below.
The overall dimensions are 18.5 × 22; the length in the axis is 14.5 mm. For comparison, the Makette KKK-1 is 17.5 × 16 (not including the spring hooking tab at the rear).
The notches in the front of the baseplate are used to provide space for the buffer tails that sometimes protrude from the rear of the buffer crossbar. The rear fixing lugs can be cut off if they interfere with the installation. The rear is curved to allow maximum space for a bogie pivot.
The return is made by ⌀ 0,2 bronze or piano wire. This return system has been criticized on some REE wagons, but this was due to poor assembly. It has the advantage of not increasing the length.
However, there is a hole for a coil spring at the rear. It will then be necessary to provide an anchoring point under the vehicle chassis.
This drawbar is adjustable in height (yellow arrow) and length (red arrow). The locking is done by soldering. Once the height has been set, the vertical tongue must be cut back if it could interfere with the dovetail of the NEM coupling head.
Note that, unlike the Makette’s and Huet’s, there are no tabs to secure the three parts of the base. This will be done by the fixing screws, or by lightly soldering the edges.
Building and fitting the new drawbar
Fitting the vertical pole to the moving part is a little tricky because of the smallness of the reinforcement part, which also serves to hold the return spring.
The base, on the other hand, presents no difficulty: ⌀ M1.6 screws can be used to loosely assemble the three parts. After checking the sliding of the mobile part, a little soldering at the ends, where there is no risk of blocking the mechanism, and it is finished.
It remains to assemble:
- the return spring, here made of a ⌀ 0,3 nickel silver wire, too stiff and not elastic enough. I think that piano wire ⌀ 0,2 will be better, but I don’t have any at the moment;
- the NEM box, adjusting its height and horizontal position according to the application. Soldering with tin.
Click on the image for a closer view. The NEM box is held at the suitable distance from the base by a 2.5 mm thick MDF spacer.
Click on the image for a closer view.
Mounting on Jouef Dd4s van
Click on the image for a closer view.
Elongation tests
The tests are carried out with the equipped van coupled to a LS Models PA 74 mail coach. It should be noted that these two coaches have neither the same length nor the same overhang.
View in line.
The same, pulling the coaches to highlight the clearance between the drawbars.
Control test, with two PA 74s in traction: the drawbar clearance is much greater. So my drawbar is better in this respect. Low clearance was a desired feature by design.
The elongation test is carried out on the worst possible curve, namely the old Jouef R = 325!
View from outside the curve.
Click on the image for a closer view.
View from inside the curve.
Click on the image for a closer view.
The buffers do not touch each other. There are no problems of hooking.
Conclusion
The operation is satisfactory. There are however some details that can be improved:
- The removal of the rear spring tab is not a good idea: it would be enough to cut it off when needed.
- The spring at the front should be located a little further back, say 0.5 mm, as it currently has almost no effect in the central resting position.
- The notch in the pole for the spring is not deep enough: the spring can easily escape (but this does not interfere with the operation).
- The pole itself was found too weak in the narrow area where the NEM housing bracket is soldered.
Note: I have a few extra. If you are interested…