Improving the Jouef MT
pantograph (2)

Original page created on 24/03/2023.

Improving the pantograph’s appearance

Let’s now turn to the appearance of this pantograph, and especially of its upper frames. I’m particularly critical of two things about these frames:

• the coarseness of the crossbars welded joints;
• the insufficient inclination of the sloping crossbar.

These frames are therefore going to be rebuilt. For reasons of both strength and ease of installation, the uprights will be made of piano wire ⌀ 0.4, and the crossbars of nickel silver of the same diameter.

The templates

Since the dimensions must be precise, the construction is carried out using a template made of a 2.4 mm thick glass-epoxy plate, 30 × 40 mm in size, engraved with a conical milling bit normally used for printed circuits. Sliding plates of the same material are provided to hold the parts together.

Note: in the photo, the grooves are outlined with graphite pencil to improve visibility.

Another template is provided for bending the uprights to a defined length: it is a simple steel sheet from an HJ ballast, with a ⌀ 0.5 hole at the proper distance from an edge.

Note: the use of steel is necessary; with aluminium, the edge of the plate wears out too quickly.

Here is a finished upright, before cutting to length.

Making the assembly template

As I don’t have a CNC machine, the difficulty is to make oblique engravings. To do this, the template can be rotated on a plywood or other support, according to coordinates determined with a CAD software (AutoCAD in this case).

The machining plan is available here, as a PDF.

There is a fixed pivot point, and a mobile orientation point, whose different coordinates are indicated on the plan. The grooves are engraved by changing the orientation of the template on its support.

The machining is done on a Proxxon mini-milling machine.

Preparation of the crossbars

The 0.4 mm diameter nickel silver bars are cut approximately 3 mm longer than necessary. They are flattened by 2 mm with flat pliers. The bar ends are then rolled onto a makeshift bending tool: a glass-epoxy plate with two 0.5 mm holes spaced 0.8 mm apart, into which two 0.5 mm diameter piano wire segments are inserted.

A flattened end of the bar is inserted between the two studs and then rolled with a flat screwdriver blade. The interest is twofold: aesthetic, representing the real fasteners, and mechanical, greater strength of the soldered joints.

Result.

Assembly and soldering of the parts in the template

This is how the parts look when they are waiting to be soldered.

Scroll over the picture with the mouse to see the details.

The soldering is done with tin-silver alloy. I thought of doing it for all the joints simultaneously, with my hot air gun, but it broke down. It was a relatively inexpensive device, but it rendered itself useless after only half a dozen uses… So I use a soldering iron.

Aspect of a finished frame, before cutting the hinge pins.

Click on the picture to zoom in on a soldering joint.

It can be seen that there is a need to adjust the appearance of the joints, with a soft file, for example.

Reassembling the pantograph for checking

I would first like to draw attention to two points:

• the lifting springs have a strong tendency to escape when the pantograph is dismantled. Curiously, I noticed this on the recently purchased BB-13020, but not on the CC-14014 purchased a few years ago. These springs are too big in diameter and a bit too long;
• the lower frames are made of a Zamak-like alloy and are relatively fragile. Do not try to tighten the arms to facilitate the reassembly of the upper frames.

Once reassembled, I check that the folded pantograph is flat (this is done to the tenth of a millimetre). Note: the clamp is used to hold it in place, as this panto is not yet equipped with a magnet.

Finishing

Finishing is done in several steps:

• (light!) passing of a rotating steel brush;
• shortening of the pins to 1.2 mm (a little insufficient on the bow side, it comes out too easily, because the uprights are too flexible);
• degreasing with soda solution, rinsing;
• pickling with Decapod product, rinsing;
• burnishing with ABE product, rinsing, washing;
• a possible painting will be done later.

Result, comparison

In the following photo, each of the machines (BB-13020 and CC-14014) is equipped with an original and a modified pantograph.

Comparison with the real pantograph.

I let you appreciate the improvement. The fineness is not yet at the level of the Pennati pantographs, although on the latter the bar assembly fittings are not shown, but there is some improvement.

Here is, as a reminder, my BB-12061 Trix equipped with Pennati pantographs.