I have always been a leg man, and somehow that may have played an unconscious role in me taking lead to come up with the perfect module leg design. I’m not saying what we came up with was perfect, but that was what I felt our task was to accomplish.
Most of us had come from a 90’s era modular railroad with 2″x2″ wood legs that formed a double stacked “H” shape. These always made it feel like you were carrying around high school football field goal posts. With no way to collapse them, a few sets of legs quickly took up more room in the car than another module would have. We wanted something different.
Some of the goals were (in random order since we never actually set any priorities):
- to take up as little room as possible (see paragraph above)
- to be inexpensive (hard to compete with 2×2’s and scrap plywood)
- to be universal so that any module in the group could use any leg (hate looking for matching numbers on modules and legs)
- to provide two inches of height flexibility (might setup on non-level floors, i.e. any basement floor)
- to have soft feet so as not to mare wood floors (old group always setup on a gym floor where scratches were verboten)
- to be sturdy (seems obvious)
So here is what we came up with – 3/4″ Electric Metallic Tube (EMT) Conduit, a threaded star insert, two inch threaded feet with plastic bottoms, 1″ schedule 80 PVC leg pockets with 3/16″ acrylic spacer, a thumb screw, various screws, glue and some strapping material. It may seem obvious how this all works out, but I suggest you read on to be sure.
If you are not interested in the journey of how we settled on this design then skip over to the HowTo – Module Legs page.
Tube, Pipe, Conduit and Schedule
Maybe its just me, but I feel like I have often over looked the nuances in a lot of the words that are considered synonyms. Thus is my problem with tube, pipe and conduit – I often use them interchangeably (same with wire, conductor and cable but we can talk about that in the electrical section). Once you start looking at the details you see discussions like…
Pipes are used to transport something, and tubes to construct something; hence, tubes are defined by the outside diameter and wall thickness (for construction stability), and pipes are measured by inside diameter to allow a calculation for transportation
But when you get into the nitty-gritty details you start wondering if anyone really knows what they are doing when it comes to naming and sizing hollow, cylindrically shaped objects. Due to schedule (wall thickness) and the word “nominal”, it becomes somewhat of a nightmare to find two cylindrical thingies that will fit inside each other. The only solution I found was to dig until I found charts that had specific inside and outside dimensions, and even there I kept running into the word “nominal”.
I liked the idea of a simple pipe/tube as the leg, but most tube that had a nice round number for an outside diameter (OD) also came with a higher price tag. Piping on the other hand could be be found at a somewhat reasonable price, but the OD was always some wacky number that made it hard to fit into something else. At some point navigating my way through the rabbit-hole I ran into electrical conduit – EMT. It seemed like it would meet some of the goals, like inexpensive and sturdy, so I started searching for ways to make it work. It does not have a nice round number for the outer diameter – 3/4″ thin wall EMT has an OD of 0.922″ [23.4mm] and an inside diameter (ID) of 0.824″ [20.9mm]. God knows why you would call it 0.75″ conduit when both the ID and OD are larger that that. I haven’t figured out the details of why, but it appears if you use the word “nominal” in the sizes it it supposed to make up for these inexplicable dimensional anomalies.
A quick search showed that there are a reasonable selection of screw-in feet with different thread sizes, lengths and materials. But first I needed to get a thread in the bottom of the EMT. Ideas of welding or gluing nuts were thrown away for various reasons including zinc fumes, rust, epoxy not holding up to the stresses, etc… Somewhere along the way I stumbled across tube inserts that had the appearance of an upside-down, star shaped, bowl that you press into the end of a tube and the concave star points keep it from being pulling back out. It then took more hours to find one that seemed like it might fit the ID of the EMT and had a thread size that fit the feet I liked. Leg plan in place! Now to figure out what to stick them it.
The Leg Pockets
Playskool taught me about square pegs in round holes, but yet left me unprepared for trying to fit “nominal” EMT conduit into another cylindrical pocket. Copper pipe, aluminum tube, and plastic conduit all seemed to have inner diameters that would not fit EMT or would let EMT fit real loosely. When I was about to give up on the EMT I ran across schedule 80 PVC conduit with an “average” ID of 0.957″ [24.3mm]. Seemed like it was a perfect fit (0.035″ [0.88mm] clearance) . Lastly I found a spring-button mechanism like they used on old tent poles. These were inserted into the EMT and caught on a hole in the PVC to hold the legs in place.
With orders received, conduits cut, and legless modules waiting for leg approval, I began putting it all together. The first issue I ran into was that the threaded stars I bought were for 1″ tubing and were not going into the 3/4″ EMT. Luckily, in this case, a bigger hammer worked. With the star on the concrete floor, the EMT set on top centered, a block of wood on the top of the EMT to protect the edge, and a 5lb sledge hammer I was able to drive the inserts into the EMT. They are not coming back out. Ever.
Not too many moments later, I ran into the second problem when I tried to insert the leg into the PVC pocket. Did not fit. Too small. I had anticipated this, knowing that 4 hundredths of an inch was not a lot of clearance, so I pulled out the pipe reamer I had purchased and went at the PVC. It was much tougher than it looked. It took me over a half hour to get to a point where the leg could barely slide into the pocket. With upwards of 50 pockets needed, this amount of time was not going to be feasible. It also turns out that the specified diameter dimensions for the EMT and PVC were more like guidelines, and my EMT OD was larger than spec and the PVC ID was smaller – the perfect storm.
For weeks I mulled over ideas, but finally one of the other guys came up with the solution. He cut the pocket lengthwise on the table saw with a thin blade and inserted a piece of 3/16″ acrylic into the gap. This essentially increased the circumference of the pocket by 0.125″ and the diameter by 4 hundredths. The leg fit.
The leg fit and the spring-button popped into place to hold it secure. Too secure. The schedule 80 wall thickness made it near impossible to push the button in to release the leg. I found that a screw driver in the hole worked, but that wouldn’t fly once the pocket was mounted into the corner of a module.
Again the group mustered and came up with the solution. Because the PVC wall was so thick, we could drill and tap it for a spade-head thumb screw.
We had thought that between the Gorilla glue we used to mount the pocket in the corner of the module, along with the screw we had driven through the top of the PVC and into the end plate, that we had them mounted securely. It did not take long before the torque of a 51″ long leg easily broke the bonds of the glue. At this point we had most of the pockets mounted in most of the modules. We needed an in-place fix, otherwise it was going to be a lot of work. We turned to “flexible” metal strapping material and more glue. We put two bands (near top and bottom) across the face of the pockets to pull and hold them into the corner of the module. Since then we have not broken a leg pocket loose.
At this point we had separate modules standing on four legs and when you bumped them they shimmied like a San Francisco earthquake. When we clamped a few together, especially with a curved module, the movement was reduced, but still looked like it would be enough to derail an entire train. To be honest, I was kind of deflated. I had set out to build the perfect module leg and ended up with a leg that seemed to function substantially worse than the wood monstrosities I had shunned.
At that point we went a few different routes to try and fix the problem. One guy made clip on brackets that went between the 14″ leg gap at the module ends. These provided more stability in one direction. I had dreams of bent metal rods that fit through holes on the EMT to form the classic “X” supporting shape, or went diagonally to the module to give the structural triangle shape, but never made it through to a prototype. Another guy used thin wall PVC and “T” fittings to make some supports between the far legs on his 5′ modules. But by show time we did not have a proven stable design to fix the issue. All we had was hope that no one would really bump the module hard – at least not the yard modules.
With this in the back of my mind leading up to the show, I took the first opportunity after the modules were setup and someone starting loading cars onto the track, to whack the module. Half expecting the cars to flip onto their sides, I was pleasantly surprised to see them rock a bit and then settle down quickly. I checked that they were metal wheel sets (usually roll really well) , and they were. Holly suspension bridge Batman, the modules were finally reasonable stable when all were clamped together in an “L” shape. A combination of the curve, the mass, the shear length and whatever other mechanical miracles came together in one stable layout.
The Perfect Module Leg
Probably not, but it met most of the goals, and is working. How do I feel it stacks up?
- take up little room – for this show all 46 legs for the entire layout fit into an old WWII duffel bag. This would have been the size two sets of the old wood goal posts would have taken up. They even fit cross-ways in the back-seat, foot-well of a Prius.
- inexpensive – EMT and PVC are pennies-a-foot. The star threads and feet are more pricey, but no different than the hardware needed for wood legs. There is some man-hours in cutting and modifying the PVC, but we dealt with that by making a lot at one time – good old production line tactics.
- to be universal – the only leg that has a marking on it the first one I cut, and it is labeled as “master”. All the other legs are exactly the same height and interchangeable with every module. Due to the “stop screw” in the pocket being mounted at slightly different heights there is some need to use the adjustable feet, but we have 1.5″ of threading to compensate and only need at most a 1/4″ for this.
- to provide 2″ height flexibility – to be honest we only have 1.5″ of thread on the foot so that means we have less than that in flexibility. Hopefully we will never setup on a really unlevel floor, but if we do we will just need to bring a box of 3/4″ blocks to setup on in the really low spots.
- soft feet – The feet are not sponge cake, but they definitely are not likely to scratch a wood floor. Besides, if they are too soft of a plastic then debris just gets embedded in the plastic and it becomes sand paper.
- to be sturdy – Since this is kind of the definition of the purpose of a leg, you can see where I was really sweating Problem 5. In the end it looks like it is stable enough. I suspect as we grow, add more curves, add a branch and add other towns that it will become even more stable with the shear mass and number of legs on the floor.
Post date: Oct 2018