I’ve been working to assemble the two side trusses in my Central Valley 150’ truss bridge kit. It’s a nice kit that goes together much more easily than one might imagine at first blush - the fact that I’m struggling with it just betrays how much my model building skills have atrophied (and how much fatter my fingers have gotten!) in the past few years.
But I digress…
They’ve provided some monofilament line to use as tension diagonals in the center two bays of the truss.
My problem is that by the time I was able to get the line tied off on one truss, there wasn’t enough left to tie off in the other truss. I have about 1/8" total excess line available with which to tie a knot in this fairly stiff line. So my question to those who’ve built these kits before is twofold:
Is there a suitable alternate material out there that I could substitute for the monofilament line? Heavy black thread seems like it would be too “frizzy.”
The truss still looks structurally plausible without the monofilament line diagonals, though it’s certainly more visually interesting with them included. Has anybody else just omitted these lines from their finished models?
I looked at that stuff and tried to figure out how to get it to hang straight. Decided that it never would and threw it away.
Replaced it with some lengths of brass wire, I think probably Detail Associates 0.010 inch or so. Cut it to length and went from top to bottom, and then put in a parallel piece. Uses 4 pieces per side of bridge. Painted it black. Far as I’m concerned it looks a lot better than that line ever will.
You can probably do without the line unless you allow the nitpickers to get a close look. The line, or cable, on the real bridge is a tension member and the bridge would probably collapse without.
Edit: I said “cable”, but I don’t believe that is what it really is supposed to represent. I believe that it is really a round steel rod, not a cable.
That monofilament represents a metal tension rod. Since I prefer to use metal to represent metal, I’d use some fine wire that has brown or black insulation, or some slightly heavier wire painted brown or black.
On the prototype, there’s a big, fat nut and washer on each end, resting on a drilled, angle-cut piece of wood above the top chord and below the bottom chord. The washer is, or should be, perpendicular to the tension rod.
DON’T leave the tension rods off. The bridge can’t carry its designed load without them.
Thanks for the suggestions, one and all. Time to go rummaging for some wire.
Being a structural engineer by trade, I know a thing or two about how trusses behave, and could point out rivet counter-level deficiencies at all of the connections. But I still maintain that the bridge produces an excellent and well-proportioned overall look.
Not only are the rods in question tension-only members, but all of the diagonals are tension-only (thus they may be thin double bars) and the verticals are all in compression (thus the solid pieces of steel with all of the lacing). Our Structural Mechanics 101 class for the day.
That’s very interesting–the original CV truss kit (at least the one I remember) had thin plastic struts to represent the monofiliant line. If this newer kit doesn’t, I’d go with the other modelers on this thread and substitute brass wire.
Skip the brass wire and go with music wire. Most of the brass wire available nowadays is soft, and therefore very easily bent, which wouldn’t look believable on a tension rod. [swg]
Well, yes and no. Certainly the music wire will be more durable if you can find a small suitable diameter. But since the “tension rod” is really just a non-functional detail item on the model, the brass rod will work just as well unless the bridge is a location where big hands will be coming out of the sky to bash it frequently.
Brass wire: Hobby shop. Actually, I’ve found thin brass wire that isn’t that ‘bendable’. A company makes wire that is ‘tempered’, but I’ll be darned if I remember what the company is. I know my LHS carries it. I think it’s actually steel with a brass coating.
Piano wire: Check a music store, or better yet, your local piano tuner in the Yellow Pages. VERY thin piano wire, possibly what is called a C-8’, the highest key on the piano. NOT inexpensive, BTW, because it has to be tempered to about 2500 lbs of pressure!
Starts at 229-2501. Even gives you the equivalent HO scale diameters. Probably the 1 inch scale diameter material would look appealing, but if you have a micrometer, you can see what the diameter of the monofiliment line is before you throw it away.
My LHS sells piano wire in various useful sizes. I used .015" on my bridge and, if I recall correctly, fastened it only at the top ends. My comment about the soft brass being easily bent was more in reference to mishaps that could occur during construction - anything bending the wire after the bridge was installed on the layout would probably damage the bridge, too.
Hobbyshops at one time did carry half-hard brass wire, but I haven’t been able to find any for some years.
The kit I had was old and had the monofiliment. I think that was what it always had, but I could be wrong. There were some thin plastic struts however. Take at look at doctorwayne’s photo above. The plastic struts are to the left in the photo, and you can see the thinner line material sloping down from the top right to the bottom left on the right side of the photo. Are these the struts you remember?
