Construction of the L’Obsidienne road roller (2)

Page created on 22/02/2025; updated on 10/03/2025.

Preparing the parts

Body

Firstly, the micro-bubbles need to be filled in as far as possible, as they are located particularly in the angles, which does not help the putty to hold.

Next, the asymmetry of the cab walls needs to be corrected. Fortunately, a moderate temperature heating (120 °C) makes this operation easy.

Here, the counter-deformation is a little exaggerated. It will be rectified without difficulty.

Next comes the drilling of the various axles (wheels, pivot, bumper, etc.). But first you need to correct certain locations. The main difficulty is to position the part so that the axles are perpendicular.

Here is a general diagram of the holes to be drilled.

• Steering pivot axis

The start of the hole is not on the axis. The solution is to drill into the axis at a larger diameter (⌀ 1.6), fill in with an Evergreen round profile, then drill again into the axis at the required diameter (⌀ 0.7).

Note: the contrast in this photo has been greatly increased to make the “plug” visible.

• Location of the air tank

The cylindrical mortise provided is unnecessary and awkward; it is therefore plugged using the same principle as above. Two ⌀ 0.6 holes to 4 mm apart will replace it. Caution: they should only be made on the right-hand side of the body.

• Rear axle

The axle hole is drilled at ⌀ 3, whereas it is intended at ⌀ 1 by the manufacturer. This choice will be explained later.

Wheels

As mentioned above, drilling the wheel axles poses a problem due to the variable width of the tread, which means that when the wheel is placed on a support, its axis is not perpendicular.

The defect is minor on the front wheel. Simply drill (⌀ 1) halfway along each side. If the drillings don’t meet, just place a half-axle on each side.

For a rear wheel, it’s much more awkward if you fit it on its outer face. So I use the inner face as a reference, but it has a protruding hub that needs to be taken into account. A centring jig is needed: on a wooden board, I drill a ⌀ 15 × 2 hole with a Forstner drill bit, then a concentric ⌀ 5 × 1 hole.

After careful centring, the axle is drilled to gradually increasing diameters up to 3 mm.

Front wheel support

The arch is deburred. Blank assembly reveals a nice surprise! This part needs to be shortened by 1.2 mm to make the body horizontal.

Here is the profile view once this modification has been made.

That’s better! But it’s still a very ugly roll arch!

Cab roof

• Correcting the location of the uprights under the roof.

I’ve already mentioned the asymmetry of the upright locations under the roof. I therefore level off this relief, and replace it with a 0.2 mm thick nickel silver plate, 10 × 2 mm, with two ⌀ 1 holes 7 mm apart.

Two ⌀ 1 × 22.5 brass uprights are soldered onto it. In the photo, only the first upright is soldered. The second is waiting, with its soldering chip. The operation is carried out using Bergeon flux, with the parts held square using the mini drill.

Click on the image for a closer look at the soldering.

The cut to length is made after soldering.

All that remains is to glue this assembly to the underside of the roof, well centred this time.

Note on this photo the ⌀ 0.5 drilling for the windscreen wiper shaft and the ⌀ 0.6 one for the steering wheel. For the latter, the drilling has been extended onto the resin body, forcing the alignment of the two parts, which doesn’t happen naturally.

• Thinning the front wall.

For the windscreen and the small openings underneath, the wall is far too thick: in reality, the panes are mounted with a seal on thin sheet metal. The ideal solution would be a sheet of brass or nickel silver, but let’s be reasonable. I’ll just thin the wall, to say half its thickness.

The small difficulty is to hold the part correctly without deforming it.

Click on the image for a closer look at the milling.

Result:

There are quite a few burrs to remove from this part.