View single post by ddonley
 Posted: Wed Jun 29th, 2016 05:19 am
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ddonley



Joined: Tue Aug 30th, 2011
Location: New Jersey USA
Posts: 167
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Long story short, I stopped modeling for a year or so. With recent inspiration for a practical layout I started modeling again. The turntable project was a good way to start and to try scratchbuilding.

So first things first was to find a prototype. I wanted a small turntable that would fit a 1900's era so with research I found plans from the Catskill Archives http://www.catskillarchive.com/rrextra/rstt02.Html.(for some reason the link won't work, google wrought iron turntable and look for the link to the archive) Using these plans I was able to make a 3d model in Trimble Sketchup

Using the virtual model as reference for all the measurements, I started construction. I printed out the girder plates to build from and made them out of styrene bits and painted them black.


Next I cut out of solid pine a block that I could adhere the sides to and the ties and rails. As a note the atlas track in the photo is not what was used, it is there to show the TT's size in relation to an Atlas 9" track section.

Using another template I made the ties for the top of the turntable.

I mounted this to the block with girders, soldered feeder wires, and added decking.


Later I"ll get to the lower half of the bridge and how the rod and pickups work, but first I'll show how I made the pit. Gluing 2 or 3 1/4" MDF panels together was the start of the pit. I made a curvature guide for the router with different holes so that each radius could be made.

Using a nail as the axle, the plate could pivot around, and changing the depth of the cutter created the desired shape of the pit.

The center hole for the rod from the TT bridge was fitted with brass bushing. Once I was happy with the contours I spray painted the pit with a gray color. On reflection I should have used a more yellow color.
The next part was to make the mechanism that could turn the turntable. I wanted it to be manual, that way the operator can rotate the bridge using a crank from the fascia. To make this work I needed a worm gear and a radial gear. Being cheap and trying not to spend any money I used Lego and Knex toy pieces that I had laying around. I know..not the best, but they do work. I needed a housing for the two gears so using sketchup again I designed a peice to be 3d printed. (that's the red box)
Now I can describe a little bit about how this works. The brass tube has the Knex plastic rod inside of it, the Cross shape of the plastic rod allows the two pickup wires to go underneath the rod. One wire contacts the larger length of tube, while the other reaches the lower tube. Brass wipers contact each individual tube, electrifying the two rails on the bridge.

Above you can see how the brass/plastic rod is attached to a styrene block. This block can pivot within the bridge, that way if the pit rails are uneven the bridge can swivel and shift with the rod still being ridged. In the next post I'll describe the wheels. 
 

Last edited on Wed Jun 29th, 2016 05:53 am by ddonley



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David
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