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Scratchbuilding a 60ft Turntable in HO
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 Posted: Wed Jun 29th, 2016 05:19 am
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ddonley
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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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 Posted: Wed Jun 29th, 2016 05:41 am
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ddonley
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Once again, using the computer design a printed out templates to make the sides for the TT bridge wheels. Styrene made the box and the wheels are N scale wheels facing inward (flanges out) with the axles cut flush. (I have an image but I cant seem to load it). Anyway with that finished and a pit rail installed, I could get back to the mechanism. A coworker friend is a mechanist by trade and is very skilled at using a lathe and milling machine. He helped guide me in machining a rod and bushing for the crank on the fascia. This part connects a casement window crank with RC car universal ball joints and slide connection, and this with the worm gear.



In the image above you can see the brass wipers. The wires that go to these wipers are connected to a DPDT switch that controls the polarity of the rails. Every time the TT is turned 180 degrees, the polarity needs to be reversed so that a short circuit doesn't occur when a locomotive travels onto the bridge. With that the project is completed for now.

I forgot to mention that the 3D print was done through the help of being an undergraduate student at Temple. Temple has many 3D printers on campus to use, and it was a first time experiment with 3D printing that worked very well.
I know this was a boiled down version of the build but I didn't want to bore anyone with the tiny details. If anyone wants to know more about the things I forgot to mention I'll gladly explain those parts in detail.

That's it for now. Scenery and weathering will come later, time permitting.



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 Posted: Wed Jun 29th, 2016 06:14 pm
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Herb Kephart
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Good job David! Looks very professional.

Herb



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 Posted: Thu Jun 30th, 2016 01:37 am
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Lee B
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Really good work, four moose!
:moose::moose::moose::moose:

That said, man it looks small in this photo:



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Commanding Officer, 796th Railway Operating Battalion (in On30 gauge), operating on the Stoney Creek branch of the ET&WNC RR

Photos of my layout: https://www.flickr.com/photos/53587910@N05/albums/72157668176638961
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 Posted: Thu Jun 30th, 2016 06:01 am
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Thayer
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Nicely done David, it really looks great.

For what it is worth, the link picked up a period at the end that was included as part of the html code. Once that is gone it works fine.
http://www.catskillarchive.com/rrextra/rstt02.Html

This is a nice resource as well, thanks for passing it along.

Thayer

Last edited on Thu Jun 30th, 2016 06:02 am by Thayer

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 Posted: Fri Jul 1st, 2016 03:10 am
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ddonley
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Thanks guys! I'm glad you enjoy it. I've been striving for professional looking even if the core of it is made out of plastic toys. Lee, the reason it looks s small is because... well it is. In HO 60ft translates to around 8"

Its big enough for a Bachmann modern 4-4-0 to fit, and the largest engine that I had fit on it was a friends proto2000 0-6-0.
Thanks Thayer for finding the problem with the link. It's a great resource and I'm happy you thought so as well. It really helped get the dimensions right without eyeballing and guessing from perspective images.



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 Posted: Mon Jul 4th, 2016 03:09 am
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Robert Comerford
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Nice work David.

regards
Bob

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