Instructions - Step

In this section you will engage in some basic metal forming (bending). Cut all the pieces of brass to length in the miter box using your razor saw. After you have finished cutting the various pieces to length, spend a little time with a needle file smoothing the rough edges left by the razor saw. Next, lay out the hole centers and bend lines on

the 4-1/8" long piece of 1/4" x .032" brass that will become the idler shaft support "U". Use a center punch to create a starting point for the drill at the intersection of your layout lines. Drill all four holes in the piece you just marked out with a 1/8" diameter bit. Clamp the piece in your vise (Fig. 1) with the fold line slightly above the jaw of the vise. Use a scrap of hardwood to bend the piece at the fold line. By holding the block of wood as near to the fold line as possible, you will be able to make a neat, sharp bend. Turn the piece over in the vise and repeat the procedure for the other bend.

Figure 1

Slide the spacers "T" and "S" over the idler shaft "Q" and then slide the 24-tooth sprocket "W" over these telescoping spacers (Fig. 2). Slide the 7-tooth sprocket "V1" onto the idler shaft from the opposite end, followed by the spacer "R". (The set screws on my 7-tooth sprockets were too long and fouled the chain. The set screws can be shortened by grinding a little off of both ends. The easiest way I found to do this was to hold the sprocket in my bench vise with the set screw protruding from its hole. I then ground off a little at a time, using an abrasive cutoff wheel in my Dremel tool.) After aligning the sprockets and spacers as in the drawing, use an allen wrench to tighten the set screws on the sprockets to secure the assembly. The set screw in the larger sprocket will hold itself and the two telescoping spacers without any trouble. There is no need to drill holes in the spacers for the set screw. Test fit this assembly in the u-shaped support you made earlier. The shaft should spin freely in the holes you drilled. If it does not, open out the offending hole(s) with a round jeweler's file. Use great care here, only the smallest amount of material should be removed between trial fits. Once you are satisfied with the smoothness of operation, remove the idler assembly from the bracket. Cut another section of ladder chain to a length of 33 links. This will be the primary drive chain "X", connecting the motor to the idler assembly. As before, use needle nose pliers to open the links at one end of the chain. Join the ends of the chain, and slip it over the large sprocket on the idler shaft.

The u-shaped bracket can now be passed through the secondary drive chain where it protrudes from the deck (Fig. 3) and fastened down using two 3/8" long, #2 brass wood screws. A look at the drawings and photo will make this operation clear. When driving screws into wood, it is good practice to drill a pilot hole for each screw. This helps prevent stripped holes and strengthens the joint. For the #2 screws, a #60 drill bit is appropriate. A drop of white glue placed in each hole just prior to driving in the screws will strengthen the wood fibers around the thread, and yet the screws can still be easily removed.


	You may now insert the idler assembly into the bracket (Fig. 4). Make sure that the secondary chain is on the drive wheel sprocket when you do this. If you have been careful with the work up to this point, the chain should be a good fit. If it is too loose, you can put one or more washers between the bracket and frame where the mounting screws are located. This is also the preferred method for taking up wear later on in the service life of the locomotive.

This page last updated: 12/10/03