Original page created on 02/06/2018.
Let’s break everything and start again!
I recall that I modelled a 1st generation gantry, but with a 2nd generation diagram. I tried to modify this model to make up for the differences, but it resulted in too many distortions.
On the other hand, Combi24 (a participant in the Loco-Revue forum — many thanks to him) sent me a lot of documents and detail pictures.
So, I decided to start all over again for a 2nd generation gantry.
My approach this time will be less “naive”:
- I’m going to make a “modular” model, which means that I’m going to use AutoCAD’s external reference concept: a different drawing file for each subset. I already used it for the spreader; I will now generalize this method to the whole drawing. It’s much easier to modify an element. Simply, it’s necessary to often check that everything remains coherent;
- I’ll work taking into account the future making, either for the metal sheet thickness or for the minimum size of engraving details. It’s a not obvious work when you totally lack experience like me. I’ll have to do a preliminary choice of the technique used (or usable) for each element;
- I’ll also avoid combining the solids (union, subtraction, etc.) as often as possible in order to facilitate modifications during the work progress. In fact, I’ve noticed that AutoCAD 2000’s 3D editing commands, such as Move a Face, often fail even on relatively simple solids. In case of real need, I’ll do the combination, but I’ll keep an “uncombined” version to possibly go back.
After collecting some opinions on the forum, I decide that some elements (beams, legs) will be 3D printed; that others (gangways, railings) will be in nickel silver. For others (e.g. cab), it’s a lot less obvious, but I’m strongly inclined to favour 3D printing.
For sizing, I’m going to take into account the 87th reduction right from the start. For example, the gangways’ plates will be 17.4 mm thick, which will give 0.2 mm after reduction — I could have even chosen 0.16; the railings will be 26.1 mm thick to get 0.3 mm to scale. There, 0.4 would be better, but it would limit the finesse of some details.
Similarly, the axle diameters will be adapted to give commercially available values for brass, nickel silver or piano wire rods.
Choosing the subsets
I’ll create an element tree, more or less following the construction steps. Here’s what it will finally look like in the AutoCAD External Reference Manager.
Some construction details
I’ll give here some details on the choices that I had to make to simplify or facilitate the construction.
Bogies
The tricky point is the representation of the motor assembly. The motors are of the asynchronous type, and typically have external cooling fins. These fins are too thin to be rendered in 3D printing. Although I represented them in full size, I had to remove them to the 87th scale. Note also the increased thickness of some reliefs.
1:1
1:87
Cab
Choosing the technique of reproduction was delicate: the window uprights are thin and had a chance being defective in 3D printing.
By thickening them a bit, and by providing housing for rhodoïd or other transparent plastic glazing, I thought that the construction would still be easier in 3D than in nickel silver. I planned a construction in two parts, so you can access the inside to mount the windows. So, there is on the one hand the cabin itself, and on the other the floor with an evocation of control console.
The cab fastening parts under legs (shown in orange) will be made of bended nickel silver sheet.
It is not absolutely certain that the details of about 0.3 mm such as these window housings and seals will be correctly rendered in 3D printing; we’ll base judgement on evidence…
Current pickup system
There is also a wide variety of configurations here: three-phase line (380 V) in horizontal or vertical layers, cable reel in newer version, cab-side or opposite side, etc.
I chose a current pickup by trolleys on horizontal layer, cab-side. I justify this choice by considering that the most spectacular view of the gantry is facing the cab, and that it’s better that the power line is at the rear. In addition, it simplifies a little the gantry, because, otherwise, it would require an additional gangway to access the trolleys.
I don’t have very clear data on the support console of the device, which also takes quite different aspects. So I improvised a bit, being inspired by pictures and simplifying. On the other hand, I have a fairly precise diagram of the current pickups themselves.
These pickups will be photo-etched. The springs, optional, will not be functional! I did not represent insulators, too small to be rendered in 3D printing.
