Page created on 03/09/2024; updated on 04/09/2024.
Straightening the chassis
There is a defect particularly noticeable on the non-braked end of the high extension hopper coupling: the end screwed to the body, which I’ll call the end piece, is tilted upwards. The other ends are affected by the same defect, but to a much lesser extent.
I’m going to try to understand and correct this problem, taking different hypotheses one after the other.
Metal chassis
To check whether the chassis would be warped, I dismantle the end piece…
… and then I fit a HDF plate of similar thickness in its place.
This plate is correctly aligned with the body. That’s not where the problem lies. Before continuing, I lightly deburr the tapped fixing holes with a 45° milling bit, as there are a few small burrs that could play a role.
The end piece
So we need to look at the plastic end piece. To get a better look at the fixing, I remove the decorative inserts.
The decorative parts are marked ⓐ and ⓑ; this will be useful later.
I suspect that the problem lies with the sloping rear part, which I think is a little too long, bearing on the sloping part of the hopper body.
Another possibility is that the axis of the screw holes is a little too close to the centre, say 0.5 mm. But it’s impossible to move the holes! There’s only one option left: shorten the oblique part of the end piece.
Note: the defect has been deliberately accentuated.
- contact point
- axis of fixing screws
Shortening by sanding
The hand-held part is rubbed on a sheet of 180-grit sandpaper (fairly aggressive). I stop from time to time to check the length obtained. In reality, I’ve taken off almost a millimetre.
Watch out! I nearly lost an axle box, which is an attachment!
After putting the part back in place and checking it, it’s obviously not enough. So I tried tilting the bearing surface in the opposite direction.
Tilting the bearing surface
To do this, I scrape the surface from left to right with the blade of an X-Acto knife at a slight angle.
I reassemble the part once more, and there’s a miracle! The result is good and even a little inverted! Now, the lower part of the hopper is parallel to the rail.
Final reassembly?
All I have to do now is dismantle again to replace the ⓐ and ⓑ decor pieces and reassemble the whole thing. And then, disappointment: the problem reappears, albeit less accentuated, and, as a corollary, the bottom of the hopper is no longer parallel to the rail.
Fixing the inserted parts
So these decorative parts would be the cause of the defect? Proceeding by successive tests, I put the part ⓐ out of the question. Let’s look at part ⓑ. There are indeed these little tenons protruding because of the shortening carried out earlier. I level them off.
Unfortunately, this doesn’t change anything.
The last and only cause I can think of is the horizontal bar of the part ⓑ, which is 1 mm thick. I reduce it to 0.8 mm with a diamond file, carefully, as this part is visible from the outside…
This last modification improves the situation just a little. I don’t know what else I could do, even though the decorative parts are obviously involved. The result isn’t perfect, but I’ll be happy with it.
If at first you don’t succeed, try, try again…
The result isn’t perfect, but I’ll be happy with it. That was yesterday! Taking an idea from a member of the Loco-Revue forum, François M., I stuck a small strip of paper, in fact from a self-adhesive label, on the outer edge of the metal chassis, flush with the screw holes. I did this on the second coupling, the one with the small extension.
Measured with a micrometer the thickness of this paper strip is 9/100 mm. The good news is that this completely corrects the defect, with even a slight over-correction.
This simple solution is very easy to apply, and gives a very good result, at least when the defect is not very pronounced. In the case I’ve described in detail, I don’t know if it would have been enough, but applying the same solution also solved the problem.