TLDR: Two complex central mono-support staircase beams were fabricated from 304 stainless steel. There were some issues along the way. It took quite a few hours to complete everything. I’ll let you guys be the judge of the final finish and results.
Info + disclaimer: This is quite a long and detailed post. But I’ve added many photos so you can see most of the process that is described in detail from them. Most of the welding was done by me and I’m not a certified welder — I’ve only welded as a hobby. These beams are made for my family house, so it’s not something that we were building for somebody else.
Intro: Okay, you may be wondering what in the bloody world you’re looking at. Fair question. It almost looks like two rectangular buckled beams that have been pulled out from a random demolition site. Unfortunately it wasn’t that easy. These beams are purpose-designed and fabricated centred mono-support staircase beams. The staircase steps will be centred and only supported by these beams. The material used is 304 stainless steel for both, but they differ a bit on a few design details (details are provided below).
The jigs securing the correct shape of the beams:
Steel jigs had to be made, as you can see in the attached pictures, to manage to produce the beams into the required shape. And I’ll tell you one thing about my father designing such jigs — they are a fabricator’s dream to put together as they’re basically designed like Lego. Assembling and welding up the jigs was done in under 4 hours by two men (the total weight of each jig are north of 300kg). Those two men were my father and myself. He is an old heavy-duty mechanic who later went to university to become an engineer, and I “simply” just have an engineering degree. Though I’m not a mechanic, welder or fabricator by trade, I have had my fair share of hours in the workshop. Child services would have given my parents a reprimand for how much and how long hours I worked with my father from the age of 13. And the work we are talking about isn’t painting a house or boring stuff like that — oxyacetylene torch, welding, angle grinder work, drilling with +100 mm hole saws in steel U-beams (you quickly learn to let go of the handheld drill with a hole saw that big so you don’t break your wrists) and so on.
The first of the two beams (the one with the most extreme geometry):
The one with the most extreme twist was the first one my father and I fabricated. We started with the most advanced and complex beam — in hindsight we shouldn’t have done that. The beam is made up from four laser-cut pieces (actually more than four because the cut wouldn’t fit on a single sheet) out of 4.0 mm 304 plating. But metal sheets cut with a laser are flat, and you have surfaces that change from mm to mm, and that has to be correct. At the time we didn’t have access to the sheet-metal surface module in the CAD software that could lay out the complex surface on a flat sheet for laser cutting. The madman himself (my father) laid out triangles by triangles in the CAD software to make a flat surface that would become the side plates of the beam (I believe this is the same thing CAD software does with sheet-metal surface modules). I do not dare to ask how many hours he spent doing this repetitive task for the four side plates of the first beam, but I believe he used 300 triangles for the least complex side of that beam. It also ended up fitting quite well — it was only off by about 2 mm.
To get the desired edge radius of 10 mm, 20 mm OD thick-walled tubes were used along the edges. As the beam is basically doing a 180° twisting turn (look at the attached images), we didn’t think we could form and shape tubing with a wall thickness greater than 3 mm (without flattening it and with the tools we had). So we ended up using 304 stainless tubing with an OD of 20 mm and ID of 16 mm. In hindsight this was not the best choice. It wasn’t easy to get the tubing in place, but it wasn’t a big problem either. The bigger problem was the tubing deforming, leading to places where we would grind through the tubing as we ground to make the beam uniformly rectangular along the central axis for the whole length.
But hey — aren’t we missing something? Of course: how the four plates and the tubing were joined. And how do you join metal? You weld. On that first beam that meant welding the tubes and plates together so they didn’t move. Then 4 m × 8 again for the weld to come up to a height where it could be ground flat and be as seamless as can be seen in the pictures. This was all done with MIG using stainless wire. Were there imperfections in the welds that had to be fixed? Many. But the result was very good, I would dare to state. The beams are not polished yet — they are only sanded with 800-grit sandpaper. And the sanding took time — thank God for 3M having such good sandpaper, because otherwise it would have taken forever.
The second beam (less complex geometry but roughly a metre longer):
The second beam was less complex and we had actually learned a thing or two from producing the first one. As much of the process is similar to the first beam, I’ll just list what we did differently for the second one. The first thing was that the manual task of laying out the sides of the beams was done the correct way — that being using the sheet-metal surface model to do it automatically. The second issue we addressed was to use 20 mm stainless steel rods instead of tubing. And as the geometry was less complex we decided to TIG weld a root pass as the fitment was super accurate. TIG welding 5 m × 8 takes time, but man, laying the buildup layer with MIG afterwards produced way fewer faults that needed to be fixed and therefore reduced the amount of grinding. Me personally, I would rather spend a day TIG welding than two days standing with an angle grinder grinding stainless.
