Friday, March 15, 2019

Beneath the Turntable

The turntable drive with worm and worm gear above. The Mercotac connector and its adapter are below.
After my posting on the new turntable, one the followers of this blog inquired as to what the drive mechanism for the table looked like. It is fairly simple with no indexing other than your eyesight (it lines up every time unless you're crosseyed!). The table itself has a 1/4-inch tube running from the center down through a brass bushing in the center of the pit. Below the benchwork, there is a brass worm gear driven by a steel worm. I use a 30-tooth gear but there is nothing critical about that. It's just what I chose. Both of these parts are from Boston gear. These gears tend to get fairly expensive so I searched ebay until I found some which met my requirements. I was going to use a plastic gear but they were not in stock and I would have to have ordered about 10 of them to meet their minimums.
    The shaft for the worm is just 3/16" steel rod I bought from the local hardware store. It runs through two brass bushings which are installed in 2-inch corner braces. The shaft is held in place by two shaft collars. Both the collars and bushing were obtained from McMaster-
Carr is a great supplier of hardware and other items used by industrial folks. They do sell to individuals and ship the same day. I can order a part on Sunday and have it by Wednesday. I suggest that they be checked out for the odd item which might be needed.
The Boston Gear U-joint connecting the drive with the rotating
The shaft is connected to a Boston Gear universal joint. I use these just in case my alignment is not dead on. You can change the position of the crank a bit by doing this. The shaft goes through a plastic bushing glued in the fascia and is driven by a crank wheel. My wheel was made on my lathe simply because I did not like the ones I could get commercially. If you are less fussy than I, a suitable handle can be purchased at the hardware store or through McMaster-Carr. I should mention that my hardware store had the brass bushings as well as the plastic ones in their normal stock. They just did not have the quantity I needed (I have two more turntables to build).
The complete Mercotac unit at the left with the components
at the right. The top part on the right will have wires soldered
to it for the rails and will press into the adapter in the middle.
Power still has to be routed to the turntable track. I did not use a pit rail because I found a rotating connector made by Mercotac in Carlsbad, California. It is designed for rotating electrical connections and works very well. I used their Model 205 unit. It is a two-pole unit to which you solder two wires. These go up through the central turntable shaft and solder to the rails on the table. At the bottom end, the connector snaps on to the main body of the Mercotac unit and track power can be soldered to its leads. I did have to turn another parts which has a hole to fit the 1/4-inch turntable shaft on one end and another to fit the press-in connector unit on the other. It attaches to the shaft with a set screw.
    I should mention that both the brass worm gear and steel worm had to be tapped for a set screw to hold them to their respective shafts. This was not a big deal as the brass was easy to drill and the steel worm already had a pilot hole which just needed to be slightly enlarged.
Turned rotating wheel with nylon crank handle.
  I use a reversing unit to change the track polarity on the table. I have used units made by DCC Specialties and Tam Valley Depot and both work well.

1 comment:

  1. Don,
    This is fantastic info! I was intrigued by your turntable mechanism when I saw them during the NNGC a few years ago. I have two manual turntables on my On30 layout that are waiting for such a cool mechanism! Thanks for sharing the details!