12/01/202118/01/2021.

Lighting (continued)

Wheel set preparation

In order to take advantage of all contact points, we need wheel sets with no insulated wheels, the insulation being in the middle of the axle.

Whenever possible (see Rapide Nord coaches), I replace the insulated wheel with a non-insulated one borrowed from another vehicle. But here I have no extra wheel available. So I have to make the insulated wheel conductive. There are two possibilities: use conductive silver paint, which is fast and efficient but expensive, or replace the insulated ring by a turned brass ring, difficult to tighten, especially without a lathe. I have already done this by combining several sizes of brass tubes: it is very long, and there is practically no tightening.

I will therefore describe the “painting” method here.

Conductive paint

Before we start, some links for “serious” conductive paint. By this I mean a product that gives a high conductivity, if possible in a single layer, and that does not degrade quickly. Some user reviews are edifying on this point. One thing in common: all these products are expensive, around 7 € per gram!

Note: the axle should preferably have a reduced point-to-point length, from 24.7 to 24.4 mm. Indeed, on the one hand I have noticed a perfectible rotation due to the insufficient clearance in the bearings, and, on the other hand, the fact of dismantling the bearings may not make it possible to put them back perfectly in place.

Step by step operations

After removing the insulated wheel, slide a 6.5 mm long sleeve onto the axle, mount the assembly into the drill, place a blade against the sleeve and then rotate the drill to mark the middle of the axle.

Marking the centre of the axle

Remove the sleeve, then make a notch with a square file placed at 45°.

Filing of the axle

When the diameter reaches approx. 0.5 mm, break the axle.

Breaking of the axle

File or grind both cones to obtain a short chamfer.

Grinding of the first cone

Click on the picture to see the result.

The second half axle is held in a board drilled at ø 2 to facilitate the operation.

Grinding of the second cone

Reassemble the isolated wheel on its half axle and then readjust it with the Puller. Theoretically, 5.75 mm between the tip and the rear flange is required for checking. As this dimension is difficult to get, it is better to measure the distance of 18.65 from the back of the sleeve which has a length — also theoretical — of 12.9 mm.

Shift the non-insulated wheel outwards by 0.1 to 0.2 mm (0.15 theoretical) with the Puller, to obtain the same dimension of 18.65.

Dimension for checking

Here are two views of the wheel adjustment operation.

Adjustment with the Puller

Adjustment with the Puller

Checking the dimension.

Checking the dimension of 18,65

Serial work on three coaches, therefore twelve axles. As the axle cut is not very precise, I prefer to keep the half axles paired.

Half axles in a support

After cleaning the wheels with alcohol (the bearings are greased), cover the insulating ring with conductive paint, overflowing onto the axle and the wheel disc. The resistance obtained ranges from 0.2 to 3 Ω, which is very suitable for a circuit where the other resistances are of the order of ten kilo-ohms.

Silver paint

Caution: there is no longer any question of touching up the wheel position, which would immediately result in the breaking of the silver plating layer. Here are the drying wheels.

Silvered wheels

Conduction test, result taken at random.

Conduction test

Sleeving of half axles

The insulating sleeve is made from a tube with an external diameter 3, internal 2. I have tried two types of tubes, Bic recovery cartridge and ASA tube. Both have a too large inside diameter, which I would estimate at 2.02 for the first and 2.05 for the second, which, combined with the LS Models axle diameter of 1.98 mm, gives a large clearance.

Another solution would be the Evergreen tube with an outside diameter of 3.2, but this time the inside diameter is really too small: 1.8 mm. On the other hand, this larger tube is likely to rub on the brake rigging of the bogie.

The length of the tube is 13 mm, more exactly 12.9 (to be retouched by checking the length between points, which should be 24.4 instead of 24.7 originally as already mentioned, and the wheel back-to-back distance, which should be 14.5 ± 0.1 according to NEM).

Reassembly of the wheel sets with a layer of adhesive tape to compensate for the clearance between the axle and the Bic cartridge tube. The ASA tube requires two layers of tape.

Here are the twelve wheel sets reassembled. First, checking of the point-to-point distance.

Reassembled axles, checking the point-to-point distance

Then checking of the back-to-back distance, indirectly. As the wheels are 2.8 mm thick, the dimension measured here must be 14.5 + 2 × 2.8 = 20.1 (± 0.1).

Reassembled axles, checking the wheel-to-wheel distance

Busch 5900
Conductive paint, 3 g
£18.49 on Ebay, to wit £6.17 per gram

Electrolube SCP03B
Silver conductive paint, 3 g
£12.12 at Farnell, to wit £4.03 per gram

Mac silver conductive ink, 10 g
$15.99 +$8.50 on Ebay, to wit $2.45 per gram

ASA (Acrylonitrile styrene acrylate) tube
Diameter 3 mm, thickness 0,5 mm, longueur 320 mm
Ref. A 7723/33 - € 1,50 per 5 at L’Octant