Saturday, March 20, 2010

#018 04 Tybee Pier - The Nuts & Bolts of Nuts & Bolts

Here, live in the Dixie Central Blog, two modeling geniuses explain the fine art of NBW castings...which I've got to mount hundreds of very soon.

From the legendary Jack Burgess, MMR

Regarding nut, bolt & washer castings

Plastic ones are much better than metal for most applications (metal castings are much more expensive and more difficult to bond in place.) I generally use Grandt Line N-B-W casting since they have such a large selection of sizes and washer types. (Note that wood trestles generally use
those with large washers.) However, Grandt's dies are getting worn out for some sizes and the resulting parts are sometimes mismatched. Some of the smallest HO N-B-W castings should work for N scale size a 1" nut in HO would represent a 2" nut in N scale.

Some of my tips for using them on wood trestles:

Stain the wood and assemble all of the bents first and then drill the holes.

It is much faster to use a drill press to drill the holes...while I have a precision drill press, Micro-Mark and Dremel ones should work since you are drilling into wood.

Drill all of the way through the wood; you need to represent the bolt head and washer on one side and the nut and washer on the other.

Of course, paint the castings while still on the sprue. The prototype bolts and hardware I've seen start out a dark brown/black and eventually start picking up rust. Air brush a couple packages of castings a brown/black color and then go back and add a very light dusting of rust to some of the sprues.

Measure the sprue shaft diameter and use a drill one size larger. This will
make it easier to insert the casting into the hole.

Cut the sprue on the casting so that the sprue is just short of 1/2 the thickness of the wood you are inserting them into. You can cut all of the castings off of the sprue at the same time if you are careful and don't let them shatter. This makes the work go much faster.

Put a spot of regular white glue on a scrap of paper/wood/styrene, pick up a casting with tweezers by the shaft, dap the end of the casting into the white glue, and insert the shaft in the hole. Once started, push the casting the rest of the way into the hole with the side of the tweezers. The white glue doesn't actually stick to the styrene but fills the hole enough so that the casting won't come out accidentally.


One the modelers in my club scratched a 30 inch long trestle on a 33" dia curve Double track. He claimed the only pieces of wood all the same length were the ties. 1500 pieces or so. He told me later that putting the NBW's in it weakened the structure. All redwood.

If the timber sizes were prototype and he wasn't drilling oversize holes, there shouldn't have been any weakening of the structure...the prototype timbers had holes drilled in them! Assuming he was using prototypically-sized timbers, I suspect that the problem was actually the choice of wood since redwood is not a strong wood but really a softwood. The prototype (in the West) tended to use Douglas Fir which, although not classified as a hardwood, is a very strong wood, good for house building, freight cars, etc.

Note that not all bridges used bolts and nuts for every joint. Many bridges, especially driven pile bridges, used spikes (not railroad spikes but extremely large-diameter "nails") rather than bolts and nuts for attaching the sway bracing. So, the lack of N-B-W castings should not automatically result in lost points for the Prototype score. However, you those cases, you should represent the head of the spikes. The problem is that, except for very large wood trestles, there isn't a lot of places to gain points for Detail. But there are also other details that can typically be added. For
example, most bridges use multiple stringers in pairs and those stringers should have an air gap between them. These stringers would therefore be bolted together with special large washers between the stringers to provide that air gap. The washers I have from YV bridges are in an "hourglass" shape and are 4" in diameter on the ends, 1.5" in diameter in the middle, and 4" "thick". Larger trestles also need fire protection items such as drums of sand to extinguish fires. If running coal, the tops of the bents might need to be protected from dropped cinders with tin sheets.

Jack Burgess, MMR
AP Chairman, Pacific Coast Region

And from Martin Pequod…

Pretty much the same way that I apply nbw's although a few variations and additonal tips.

When you're cutting the "bolt" free from the sprue, cut at an angle to put a bevel on the
tip -- makes them a little easier to insert into the hole.

Tichy makes a decent selction of nbw's and rivets, in a rust-brown which looks pretty decent in many uses with just some stain on them. Been buying them as much as Grandt line now for that very reason.

I prefer ACC over white glue for just about all materials; having some nbw's magically some back out at the most inconvenient time can be truly irritating.

Plastic vs. metal; plastic is far cheaper, but sometimes the brass parts are better particualrly if soldering things together, and sometimes I've used brass ones for their strength.

Small variable speed drill press is a tool worth investing in and beats a day with a pin vise for this and lots of other chores.


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