26/01/2020.

Second realization in nickel silver sheet

Note: if you are interested in the construction of this gantry, please let me know. I can send you the parts at cost price (around €300, which can of course vary). You can also consult the making instructions available in PDF (3.7 MB). There will however be small differences with the description which follows, which concerns the prototype since then improved.

Tools used for bending sheets

These tools should not be seen as essential. Many experts do without a bending tool and use, for example, angle brackets caught in a vice. However, this tool is not overpriced and is fairly practical to use.

Tools

Caption:

  1. Protective steel plate
  2. Chisel made from a broken carbide drill bit
  3. Small hammer
  4. Soft-cut file
  5. Steel ruler
  6. Heavy steel ruler
  7. Bending tool
  8. Blade delivered with the bending tool
  9. Cutter blade
  10. Xuron scissors for photo-etching

The chisel is used to cut the part tabs on the photo-etched plate. It’s only useful for fragile parts that could be deformed by the Xuron scissors. The hammer is used to hit the chisel… or the fingers. The blades are used to lift the parts placed in the bending tool. The file is used to level off the already cut tab rests.

The main difficulty for very long pieces is to bend them evenly. The blade (8) delivered with the bending tool is far too short. So I used a big cutter blade (9), on the back of which I stuck an electrician’s tape not to ensure safety, because the edge is not protected, but only to warn me if I hold the blade on the wrong side. A distraction could be very damaging.

However, for pieces larger than 10 cm, this is still insufficient. I tried like on this photo a large spatula. It works, but the edge should be sharpened and, above all, the blade as well as the handle of this bulky tool should be shortened.

Large spatula for folding

Some modest tips for folding

I found some of this advice on model building websites. Others come from my own experience.

First question: how should the workpiece be positioned under the bending tool ruler? Answer: the fold half engraving must be completely and just visible along the ruler. Reminder: the fold engraving must, except in rare and specified exceptions, be inside the fold.

Second question: if a part has a wide wing and a narrow wing, which should be put under the bending tool ruler? Answer: the narrow one. Indeed, we will raise the wide wing, so with more leverage. It will be easier and there will be less risk of deforming the part. Below, the part is already out of the bending tool.

Folding on the narrow wing

Exception: if the wide wing has a weakness, such as a cutout, then the opposite must be done. In the example below, the wide wing will be pinched in the tool, to secure the area weakened by the cut.

Exceptional bending on the large wing

Assembling the leg sets

Little reminder: a leg set — it may have a specific technical name, but I don’t know it — consists of two legs, one end girder which holds the bridge girders, and a spacer beam which connects the legs at their bottom. We’ll build in this order, then we’ll assemble these different parts.

Construction of the legs

This construction is one of this project’s most delicate, because we must hold together four independent walls, of non-rectangular shape, and to solder them while having very little access to the inside.

So, we’ll start by assembling two contiguous walls, positioning them using the spacers. Here is the adopted provision. A heavy ruler is clamped on the workbench. Note that an epoxy plate (waste circuit board) has been inserted for thermal insulation. One of the parts is held vertically on the ruler with two clamps; the second is pressed horizontally with a spring clip.

Holding parts

Two small solder spots are made. We can then check the perpendicularity before going on.

Holding and soldering parts

Then let’s put the inside spacers whose purpose is to ensure the correct geometry of the leg. Here it’s the middle one — there are three. It is held in its positioning grooves by two pairs of tweezers.

Installation of spacers

Soldering is made in the corner. Here, is the top spacer.

Installation of spacers

After a final perpendicularity check, we make a solder fillet along the corner. Here is the external appearance obtained. The slight protrusion of a sheet is on purpose, because it conforms to reality. The tin has overflowed a bit, it is unavoidable, a cleaning job must always be done after soldering.

External appearance

Installation of the third side. This time, metal spring clips will provide holding. Same process: making light solder points…

Installation of the third wall

… Check the position, then complete soldering.

Soldering the third wall

For the outside wall which will close the box beam, things are different. Tinning of the edges, addition of a good solder pack on the fourth wall, trying not to put too much on the edges …

Tinning of the fourth wall

…… Positioning of the parts. Presence of a plumbing flame arrester because…

Installation of the fourth wall

… soldering is carried out with a torch; if all goes well, the solder will flow inside the parts. It shows when the tin starts forming in droplets in the corners. It would be difficult to achieve this result with a soldering iron.

Soldering of the fourth wall

Leg finished, cleaned.

Leg finished

Construction of the end girders

It’s a little easier than for the legs, because here there is only one main U-shaped part, which of course must first be formed.

I have provided pins for positioning the beams on the end girders, in the form of sections of ø 2 brass tube soldered in the appropriate holes. Soldering is done on a template in which the pieces of tube are inserted, so as to keep them vertical.

Template for positioning pins

Template for positioning pins

Soldering of the pins and of M2 nuts which will be used to fix the girders on the end girders. Here, these are steel nuts (not stainless steel which could not be soldered), but brass nuts would be preferable.

Soldering nuts

Result. The etched arrow indicates the orientation of the part, which is not obvious, but which must be observed. Note the presence of mortises which will receive the upper footwalk supports.

end girder seen from above

Let’s move on to the end girder closing parts, which must be bent. For this I use drills of suitable diameter, by pressing on a cork support, flexible but resilient.

Bending end girder closing parts

Result of bending.

Result of bending

For soldering, the same problem arises as for legs, namely that access to the inside is limited, and that parts of particular shape must be held together. I tried the technique of tying up with galvanized iron wire, which I checked that it can’t be soldered. Its advantage is that it allows the parts to be held over their entire length. The downside is that it is not elastic like spring clips, and it expands under the effect of heat, thus tightening the parts less effectively. The ideal would be a non-solderable, elastic, supporting about 400 °C wire. Does that exist ?

Aluminium spacers, therefore also non-solderable, are placed inside the end girder to keep the closing part in good position.

tying up the parts

Here is the uninviting appearance after soldering with the torch.

Appearance after soldering

But a simple pass of solder sucking wick improves things well.

Cleaning with solder sucking wick

It is impossible to tie up end parts, so the soldering will be manual, with iron. As before, I introduce a good amount of lead solder through the openings, while keeping the part stuck with a piece of cork.

Soldering of end parts

Soldered end part.

Soldered end part

Here are the two finished end girders.

Finished end girders

Construction of spacer beams

These parts are a little easier to assemble. Only the bending of the ends is a bit tricky.

I start by soldering the web on the lower flange, with an assembly based on spring clips. Notice the part positioning precision thanks to the etched grooves and their reflection.

Soldering of the web on the lower flange

Soldering of the ribs.

Soldering of ribs

Bending of the upper flange, using drill bits and round nose pliers for adjustment.

Bending of the upper flange

Several trials are necessary.

Blank assembly

Blank assembly showing a small gap.

Blank assembly, detail

Soldering end caps

Soldering end caps

Soldering of the upper flange by pressing the assembly with a cork plate.

Soldering the upper flange

Assembling the leg sets

The leg sets must be geometrically correct. An assembly template is therefore essential. Here it is with an installed leg set, awaiting soldering. The small parts visible at the bottom right, the spacer beam connectors, are also fitted at this time.

Leg set mounting template

The 2.0 mm and 1.2 mm dia. rods perfectly position the parts in relation to each other.

Leg set mounting template, close-up view

Then, soldering of the legs on the end girder. The picture was taken after cleaning.

Soldering the legs on the girder

Arrived here, we can say that the hardest part is — almost — done!!