Making Reproduction NX Tread Pulleys - A Tutorial by Bruce Hansen

The 12½ set was introduced in 1948 and continued as the top set in the Erector line until 1962 (except for 1951-55 when it wasn't produced). Unique to this set were the NW Tread and NX Tread pulley. With those parts you could make models of construction equipment like tractors, bulldozers, etc.

Original treads and pulleys are available from Wagner & Sons for $266 ($100 for each tread, $16.50 per pulley). If you are restoring a 12½ set to original condition I'd encourage you to visit their link from Erector World's links page. However, if you're like me and just want to build some of those 12½ models here is a less expensive alternative.

Classic Tin Toy ( sells the treads for $40 including shipping. The treads come with a steel clip which is used to "complete the loop." However, the treads need to be cut to length first. Mine were 25 inches long - the proper length is 17 - 17½ inches. I cut mine to 17½ inches which seems a little loose, but does work fine. I imagine cutting them one tread plate smaller to 17 inches would work also.

That takes care of the tread, now for the pulleys. First, thanks to Michael VanValkenberg for the outside diameter of the pulleys (he's completing a 12½ set). I used a metal lathe to make tread pulleys out of nylon (pulley) and brass (hub/nut). Here's a sketch of the components (4 pulleys required):

Let's turn some pulleys! The first steps are to chuck up the nylon and face it off:

Next, turn the outside diameter (unless you happen to have 1 5/8" stock). I countersunk a hole on one side with a forstener bit:

The next step is to drill and tap the center hole:

Now, part the pulley blank off the lathe.

This is a simple "stub arbor" used to complete the machining. This technique required the angles for the pulley groove and side chamfer to be set once to do each side of the pulley. Screw the pulley blank on the arbor and machine one side. Then screw the pulley blank off the arbor and flip it over to do the other side:

The next steps are to countersink the other side of the pulley with a forstener bit and cut a chamfer from the outside edge of the countersunk hole to the pulley edge:

Lastly, turn the groove for the tread:

Let's tackle the hub next. The first steps are to face, center drill and drill a through hole for the model's axle (5/32"):

Next, turn the brass to the correct diameter and turn a shoulder for the threaded portion:

Now, thread the hub and part it off the lathe:

Lastly, drill and tap a 6-32 hole for the hub's set screw:

The last part is a nut made from hexagonal brass stock (round would work - I had hex on hand). Face off, center drill and drill a pilot hole first:

Next, tap the hole and part the nut off the lathe:

Here's a look at the finished components. I painted the nylon pulleys with Krylon Brass paint. Then, screw the hub into the pulley. Apply a drop of loctite to the hub and screw on the nut. Voila, here's the final product:

Here I cut the tread to length; I double checked my calculations for length by placing the tread over (2) axles spaced 6 inches apart. This is the spacing in all of the model pictures from my 1960-61 Master Builder's manual.

Lastly, here's what the treads look like on pulleys/axles.:

I realize most Erector enthusiasts won't turn their own pulleys. It took me about 3 hours to make 12. However, you can purchase the treads from Classic Tin Toy and pulleys from Wagner's for a total of around $110 and make some cool construction models! In my case, I like playing in my shop about the same as building models; a perfect win / win situation!