Turntable - Part Four

Time to install the turntable and see how it works.

I made a new shaft for turntable Mark II. The bands came out a bit nicer than the earlier version as I learned from that experience. I tinned the brass shim stock before wrapping it around the shaft, then a quick touch with the soldering iron secured it in place without melting the plastic shaft.  Note that I have not soldered the wire leads to the brass bands at this point. They are dangling from the center of the turntable.

Before attaching the shaft, I placed the turntable on the terrain surface at its intended site and carefully marked the center line of the pivot point. Then I drilled out the center with a 1/2 inch bit to create the pivot hole in the base plywood. The foam here is 3/4 inch thick.

Next I measured the center of the turntable and installed the shaft, taking care to keep it square and plumb. I epoxied the shaft and a laser cut collar on the bottom of the turntable ties. I could not laser cut everything to exact center due to the design of this turntable, so I had to measure the center by hand.

 Once the 5 minute epoxy was cured, I soldered the wires to the bands in holes that I drilled in the shaft.

The turntable pit after hogging out the foam. 

Shaft and collar before the wiper wires are installed.

I marked the perimeter of the turntable on the foam  with a pencil on the end of the turntable as it rotated. Then I hogged out the foam and removed any traces of hot glue that held the foam in place. Luckily there wasn't too much hot glue, but there was a glob right where the shaft went.

I tried two different height collars to see which one gave the proper rail height. Then I glued the appropriate collar in place. I  temporarily placed the turntable in the collar and kept it spinning while the glue on the collar set. I again used 5 minute epoxy as it sets faster than yellow glue, yet gives time to make adjustments and is very strong when dried. When that epoxy was cured, I again checked the turntable and made some minor adjustments. Then I went underneath and glued a second set of collars on the bottom of the plywood. These two collars are providing the precision placement of the turntable, not the hole drilled in the plywood.


Once everything was cured, I tested the turntable again. The spin is nicely centered and smooth. It is easy to line it up by eye, a good thing as this is a manual operated turntable.

The shaft and collars not strong enough by themselves  to prevent the turntable from rocking as the engines roll on them. These engines are quite heavy, perhaps three or fours pounds, each with the weight concentrated in the tender. In the prototype the turntable wheels control the rocking, but I am not sure the model wheels will be strong enough.  I think I will install two rub plates under the ends of the turntable that will lightly rub along the pit rail. These should prevent any excess rocking and thus the wheels will be mostly decorative. The rub plates will be almost invisible, so they will not ruin the look of the model. Unlike the prototype, I have essentially unlimited torque to spin the turntable, so the rub plates friction shouldn't be a problem.

Turntable - Part Three

I continued work on the rebuilt turntable. I removed the ties as my attempt at making the turntable look "homemade" just made it look like I was a bad builder. I trimmed all the ties to the same length and reinstalled them. Then I added the NBWs along the chord. These bolts are what hold the ties to the chord, as there is no wooden support member  under the ties other than the pivot pedestal. I did not add the NBWs on the bottom of the chord as I don't think they will be visible.

Before I added the rail, I measured the proper location and drilled two holes for the turntable feeder wires. Them I soldered the feeders to the bottom of the rail. By running the feeders through the ties I ended up with no visible solder joints. Then I spiked the rail down. The overall length of the table will be 12.5 inches, or 50 scale feet.

Next I have to build a new shaft and pedestal, as well as all the rest of the details. I'll probably laser cut the roller wheels. In careful study of the picture I note that they are not flanged. Also, look at the pit rail it rides on. It doesn't look like rail to me. I suspect that it is a wood base with a strap iron railing.

A mock up of the engine terminal at Falmouth. A wood rick, water tank and engine house are still to be built, as well as the terminal tracks.

Here is a close up of the turntable

I received a question about the bearing plates on top of the trusses from the ACWRRHS Yahoo forum. Yes, there are metal bearing plates on the tops of the posts. These prevent the truss rods from cutting into the wood. They also shed water off the end grain, though that may be a secondary concern as the whole turntable doesn't look like the builders were concerned with longevity. There also appear to be iron end plates at the ends of the chords. I plan to use my laser to cut the plates from 1/16 inch acrylic.

What thickness iron do you all think those truss rods are? The heaviest wrought iron rods specified in Haupt's bridge book is 1.5 inches. That scales to about 0.032 inches nearly perfectly. But to me they look beefier than that.

Finally, I wonder why they mortised the posts into the chords. The mortise joints don't appear to be that tight. The joints would significantly weaken the chords in bending, but not so much in compression, since the upright post would see a compressive load acoss its width. The design of the truss does put the chord into compression, but it would experience bending moments as the live load moves along the turntable. The chords are relatively massive, especially for such a small structure. They help give the turntable a "chunky" look. But I think the iron rods are providing most of the strength of this bridge.

Turntable - Part Deux

I was not happy with the look of the first turntable. The actual Manassas turntable was quite rough in construction. Mine was looking too "square and regular."

Excerpt from Railroad and Engineering Journal, Vol LXIII, No 10. 

Further research into early turntable designs revealed that gallows style turntables did not have rail stringers. In looking at the Manassas turntable, I concluded that it was very similar to a gallows style where the ties form a suspended deck. However, the Manassas turntable uses a wrought iron rod tension truss instead of a gallows.  I was concerned about racking and twisting  forces on such a design without a rail stringer, but a passage from an engineering book on early turntables explained that due to the low speed involved, those forces are minimal.



So I am rebuilding the Falmouth turntable be be a closer match to the Manassas prototype.   I did not use the laser to cut these parts as I intentionally wanted some subtle variation in dimensions that comes with hand cut parts.   I sanded the sharp corners and distrressed the wood slightly to make the parts look more "homemade." These parts form the main chords. I find it hard to believe that they mortised the main chords to accept the vertical truss supports, but the photographic evidence clearly shows this.



I am going easier on the black stain this time around as the wood should not be overly weathered. I'll have to make a new shaft and pedestal to make sure the height is correct.

Each tie has 4 visible bolts that hold it against the main chord. The bolts are in a distinctive pattern (see the prototype photo on the previous post). Adding these will be tomorrow's project. You really have to like adding NBWs to be an O Scale modeler in this period.

Falmouth Turntable in progress

I nearly finished all the wiring in the main room this weekend, but I need 3 Frog Juicers to wrap it up. I ordered two more Hex Frog Juicers (enough for 12 turnouts) so I can finish the wiring here and be ready for the yard at Aquia Landing.  Even with incomplete wiring, I ran the Engine Haupt with a short train to test track. Now that the double crossover in Falmouth is operating with auto reverse units on the frogs, I discovered that some fine tuning of the turnouts was needed.


      This turntable at Manassas served as inspiration for my
Falmouth turntable. Note the lightness of the rail, and the
crude level of  construction. It is hard to tell if there are stringer beams
under the ties and rails.  I assumed there were.


So with wiring on hold, I started construction of the Falmouth turntable.  The turntable is needed at Falmouth to turn locomotives so they can make the return trip nose first.
The turntable is loosely based on the prototype at  Manassass seen in the famous photo after Jackson's Raid in 1862.  Edwin Alexander made a set of plans based on the photo, but something about his plan didn't look right to me, so I modified the design to reflect how I think it may have been.

I used laser cut 3/16th inch basswood for the main structure and sugar pine ties from Mt Albert.  I added many Tichy NBWs to simulate the bolts holding the beans together. However, I did not simulate the laminations of the beams. I still need to add the truss rods, wheels and other details.

The pedestal separated from the shaft.
The pedestal will be glued to the pit floor. 

The shaft is a set of 1/2 inch and 7/16 inch Evergreen styrene tubes that telescope tightly together. I epoxied the tube to the center hole in the turntable bridge.

To make the conducting bands, I soldered 26 gauge wire leads to strips of 0.005 inch shim brass.  Then I drilled holes in the shaft, ran the leads into the holes. Next I wrapped the brass bands tightly around the 7/16ht inch shaft and quickly soldered them without melting the plastic.

Close up of the turntable shaft

With this design, the turntable shaft can slide into the pedestal. The pedestal will be glued to the pit floor.  If all goes to plan,  I'll be able to drop the turntable through the hole. Then add electrical wipers to the bands. I'll use a digital autoreverse unit to control the power to the rails.

This is a manual turntable, so I will not be using an indexing system. It's "armstrong" all the way.

It just occurred to me that this is the first turntable I have ever built either from scratch or kit. I had a Walthers N Scale turntable, but never installed it.

I am keeping my fingers crossed!

Overall view of the 12 inch turntable in its approximate location before I drill the shaft hole
and hog out the styrofoam.

Houston, we are DCC!

Thanks to some expert help from Paul Dolkos and Mitch Oldham, the USMRR Aquia line is  now running on DCC.  I was able to get most of the wiring done from Falmouth to Aquia Landing, but that is getting ahead of the story.

Paul installed the Easy DCC command station in a
temporary spot on the benchwork until I decide where
it should go permanently.

Paul is an owner of the Easy DCC system for his HO layout, so he was able to immediately open the boxes and begin connecting the components without any delay. Well, there was one delay. It seems I had forgotten to disconnect the DC power pack from the rails.  When Paul went to fire up the DCC system, the start-up sequence was not what he normally sees on his system. After a few perplexing moments wondering why the Easy DCC was not going through its normal start up procedure, I smelled smoke. Sure enough, the DC power pack was beginning to put out a serious amount of smoke. I disconnected the smoking power pack, and the Easy DCC system fired right up. Whew! I am glad the Easy DCC didn't fry.

Mitch at the workbench installed a decoder

In the meantime, Mitch was installing a decoder in the 4-4-0 Haupt, one of my SMR Masons in the work shop. Mitch used to run a DCC business and he came prepared with all manner of cool specialized DCC diagnostic tools. He methodically disassembled the Haupt and identified pickups, grounds etc. Then he went ahead and installed a Digitrax DH123D that I had previously purchased. This is a non-sound, economy decoder. I also had a Dallee Sound System sound chip, but we decided not to install it as it is pretty large and probably would not fit in the tender or boiler.

The Haupt crossing Potomac Creek under DCC.  Note
the bright headlight.

With the decoder installed the engine ran very well. However, I don't think this decoder features back-EMF as the engine speed varies as the loco moves across the tighter curves on the layout.

The loco's headlight light is always on when DCC power is on the track and is running quite bright. That must be addressed before it burns out by adding a resistor in line with the bulb. This will require running wires from the decoder to the headlight, but it looks easy thanks to the removable smoke box, a nice feature of the SMR Masons.

We learned a lot from Mitch's surgery on the Haupt. The removable smoke box and head light assembly will simplify many of the tasks needed to add sound and controllable headlight. We decided that on this loco the best place for the sound speaker will be in the smoke stack. Again this will require wires from the tender to the engine, but it shouldn't be too hard.  We also learned that the tender trucks have a split frame, so adding a second set of pickups on the tender axles will be relatively simple. (Note the McCallum already has these wires factory installed.) I will replace the DH123D with a Soundtraxx Tsumani decoder so that sound is integrated right in the DCC decoder. In fact I need to order five of them ASAP.

Mitch took the McCallum home with him to try to find why it is shorting on curves. He plans to get one too, so this will be win-win as he gets to study the loco before he buys it. He is making the switch from HO to O Scale ACW -  Huzzah!

The Tam Valley Hex Frog Juicer on the left lights up like a
Christmas tree.  The yellow wires run to the various frogs.
The outlet strip on the right has the bus lines to the
power districts. For now they are daisy chained into one district.

After Paul and Mitch headed home, I finished running bus lines, soldering feeders and installing the Hex Frog  Juicer. Tam Valley Depot makes the Hex Frog  Juicer and it is an absolute delight to install. No more fiddling with balky Tortoises or finicky mechanical linkages underneath the benchwork. This has to be the easiest way to power frogs. I have four frogs wired to it so far and it works as advertised. Thanks Duncan!


Terminal strip to allow smaller wires to be used on the HFJ sockets.

 Another half day of wiring and two thirds of the layout will be operational. Running with wireless throttles is really a pleasure that I had nearly forgotten.

I decided to rewire the HFJ to use smaller wires than the 18 gauge into the sockets. I added a terminal strip. This acts as an intermediate between the 18 gauge wires and 24 gauge wires. The holes on the HFJ sockets are very small. Thelast two FJs power the double crossover in Falmouth.