Making Plaster Casting Molds

I hadn't made plaster molds in over 30 years so it was like learning new tricks all over again.  I bought some liquid latex called "Mold Builder" (32 oz, $22) from Castin' Craft and a box of 24 1" chip brushes through Amazon and borrowed some gauze pads from our 1st aid box.  I used one of the extra walls I had gotten ten years ago to practice on in case I screwed something up.  My first attempt was usable but with only five coats of latex it came out too flimsy.  I did confirm that I could spread the latex directly on the bare plaster without creating problems.

Here's my technique.  I laid a sheet of parchment paper on my workbench.  My wife uses this for baking and it prevents food from sticking to cookie sheets.  Waxed paper works well too.  I use inexpensive "chip" brushes because the latex builds up in them and they only last for two or three coats.  I trim the bristles with scissors so I'll get a nice even coat on the mold.  To start I spread a thin layer of latex on the plaster wall section.  This first layer is critical and will define the quality of your castings.  Make sure the latex is spread evenly in a thin layer and then go back with your brush and gently work it into all the joints, cracks and crevices.  I use the brush this second time to make sure the coat is spread evenly over the entire surface and to remove any bubbles that may have formed.  If the first coat is applied too heavily it might hide bubbles so it's more important to ensure full and even coverage.  The first three or four coats should be kept thin and bubble free.   With each layer I also build up a 1/2" wide flange around the outside edge.  I lay on four coats before adding a thicker layer with the gauze.  The gauze pads I use come folded over in three sections and when I unfold that it's still three layers thick so I use it like that without separating it any more.  I lay the gauze on the casting and am careful not to overlap it to prevent unnecessary lumps in the mold.  In the picture below you can see where I overlapped the gauze and then had to cut recesses in the support frame to account for the unwanted lump.  The gauze gets held down with a heavy layer of latex that's been worked into the fabric with the brush.   I then add three more layers of latex over that for a total of eight.  In between each coat I let it dry until all the latex has turned a light yellow color and no longer shows any white which would indicate it hasn't fully cured yet.

When I was cleaning up the original wall castings I realized that the walls were not exactly straight and tended to bow out in the middle a bit.  I suspect the molds weren't properly supported when the plaster was poured.  This caused me to think long and hard about a better way to go about this.  Back when I did this 30 years ago I was creating molds of rocks to be used on mountain sides and it didn't really matter if they were cast to lay flat.  Making walls is a different story.  They have to be straight and flat or they don't look realistic.  I decided to make a wood frame to hold everything flat and square during a pour.  I built the frames on a backing panel of 1/2" plywood.  Each wall section has windows or doors and cap stones running along the top edge.  They also have stone buttresses and heavy stone frames around the windows.This made making the support frame complicated because all these details are at different levels.  I glued wood shims of various thicknesses in places where they were needed and the end result provides a good flat support for the mold (see picture above).  With that done I decided to go ahead and make molds for six other wall sections just so I'd have them if I ever needed them.  It's a pretty quick process to make the molds so why not?

OK, here's a good reason why not.  Of the six extra molds I made only three came out perfect on the first try.  I suspect I was rushing things.  Because of all the detail in the rock walls the molds were very difficult to release from the original castings and parts of the first layer separated and smeared, ruining the details of the stone wall.  Bummer.  For my second effort I really took my time and allowed plenty of drying time between coats.  To get eight coats of latex takes at least two days of work so it's worth while not to rush the process.

Once I had a good mold cured and released from it's original casting it had quite a bit of flashing that needed to be trimmed off.  For the outside flanges I trimmed them with scissors.  For any flashing inside the mold I carefully trimmed it off using wire cutters that have a good sharp cutting edge.  I stretch out the flashing while cutting to help prevent cutting too deeply into the mold.

For a really excellent explanation of mixing and pouring plaster check out New England Brownstone's web site (click here).  They also have some great painting techniques for plaster cast stone walls (click here).

Another problem I ran into showed me the necessity for applying thin, even first coats.  When I started pouring plaster it took several tries before I found a good consistency.  My first pour was too thin and the casting came out pock marked with bubbles and grainy looking.  My second try used a thicker mix, like a thin milkshake, and the casting came out perfect.  For these first two tries I used a smaller wall section but now I felt ready to take on the larger roundhouse side walls.  I used the same thicker mix but when I removed the casting from the mold I found it was full of air pockets again.  ???  A closer look at the mold revealed small air bubbles had formed in the first layers of latex and I suspect this created air pockets during the pour.  I realized these two molds had been the first ones I made and I wasn't careful enough to get thin, bubble free coats.  I had to throw out my two largest molds and re-do them, this time with thinner first coats.

Another problem that was revealed after pouring the larger wall sections was an uneven wall surface.  I thought I had created enough support for the molds but the areas around the windows looked wavy.  I needed to add about an extra 1/8" of support in this area.  On some of my molds the outside edge is built up too much in some areas and the mold won't sit squarely in the frame.  The inside edges of the frame need to be rounded off to allow the mold to sit down flat on the bottom.  The best way to verify the fit of the mold in the frame is to press your finger around the inside edge and see where the mold doesn't sit flat.  Re-work the frame to allow the mold to sit firmly flat on the bottom of the frame.  This will ensure a good square and flat casting.

I now use a spray-on mold release and this makes the whole casting operation much easier with less chance of damaging the mold when it's removed.  I also found that when I pour the wet plaster into the mold I should only fill it about 1/3 of the way.  Then I take a ball peen hammer and tap the wood frame from underneath and on the sides to drive out air bubbles.  When this is done I'll pour in the rest of the plaster and repeat the tapping.  This will cure most of the problems with air bubbles.

I also found out that you can buy high quality latex for making molds.  Make a water tight 5 sided box (no lid) and place your wall section in the bottom.  There should be about a 1/2" gap on all sides to form a thick side wall on the mold.  Then pour in the Latex to fill the box to the top.  I think tapping the box with a hammer or using a mechanical shaker will drive out any air bubbles from the mold.  I haven't tried this yet but it's the way all professional Latex molds are made.  More expensive but better molds.

Building a Doodlebug

On the layout my main goal was point-to-point operation but I added a return loop on the lower level between the stamp mill and the roundhouse.  The purpose of this was to run a railbus on autopilot to create interference for yard and switching operations.  I found a "Doodlebug" kit on eBay  that fit the era, 1920's, but would need some modifications to suit my eye.  The running gear for this kit was supposed to be an HO scale Bachmann trolley car but I felt it looked kinda wimpy and the overall profile was too high above the tracks.

The first thing I did was to carve out the frame and floor to allow use of an HO SD40 diesel switcher. The power trucks from this switcher looked much better than the puny wheels of the trolley and the drive motor from the switcher was already set up for DCC.  The wheelbase measurement was spot on too.  I used a Dremel to carve out the base of the Doodlebug and did it in stages so I wouldn't go too far too fast.  My first attempt looked good but the body sat too high.  I lowered it an additional 12 scale inches and then added running boards to visually lower it even more.

The cow catchers that came with the model was small and clunky so I made my own.  I used scale 1" square and L plastic shapes and formed them up using tape to hold the rounded shape while I glued it together.  I added grab irons next to the doors made from brass rod.  I used thin clear plastic sheets made for my printer and fogged with flat clear spray paint for the windows.  I plan to use most of the interior for electronics so fogged window panes allowed light to pass but didn't provide a clear view of the interior.

I couldn't find suitable headlights so I made my own using plastic straws and 0.010" styrene shapes.  I placed LEDs inside the new housings and wired them up to the diesel switchers control board.  I also added a brass bell above the windows at one end of the Doodlebug.

I painted the body Pennsylvania RR maroon with black trim to give it a sharp, early 1900's look.  The prototype for this model was an awkward looking homemade affair with a center control cab and a small steam engine for propulsion.  My modified version has the cab at one end sharing space with the baggage compartment and using gas/electric propulsion.  I installed a bulkhead at midpoint to separate the driver from the passenger compartment and to add some needed bracing to the car body.

This came out pretty sweet.  The SD40 mechanism runs quiet and smooth and can do creepy-crawly very well.  I'm pleased with the final paint colors and I think it gives it the right look for the 1920's.  The cowcatchers also give it the right look, at least to my eye.  I'm sure someone out there will point out that this combination isn't correct but I don't even care.  It gives me what I wanted for my layout and it runs great.  I still need to convert it over to deadrail operation and add sound but for now it's complete.  Fun project.

Turntable Pt 4 - Installation and Final Adjustments

With all the bugs worked out of the program and the model completed it was time to get the thing off the bench and onto the layout.  This should be a simple matter of dropping the module into place and plugging in the power.  It turned out to be sooooo much more.

The physical positioning was the first thing.  I had recently added the final top layer of Homasote for the yard section of the layout.  When I went to drop in the turntable module I found two problems.  The biggest was that the framework for the layout was in the way and had to be modified.  The second was that I wanted to rotate the module to fit the gear hanging under it for the easiest access for maintenance.  When I rotated the module it wouldn't fit in the hole.  I ended up running the base through the table saw again to square it up.  I also had to clean up the edges of the hole where the Homasote didn't match well.

With that completed I got the module in place and the turntable bridge reassembled.  I now had to deal with several inaccuracies I had ignored during construction.  One end of the bridge was 1/16" higher than the other.  I thought this might be caused by the dolly truck installation where I had added some shims to get the rail up to the right height.  I ran the wood buck that the bridge is built around through the table saw and squared that up as accurately as I could.  The I used my digital calipers to measure the thickness of the bridge ends and found a 0.030" difference there.  It turned out that the dolly trucks had a large variation in the thickness of the castings.  Rather than trying to correct this I used a hand file on my shims to make up for the difference.  The bridge now sits flat and is square with the world.

My next problem was that the pit wall isn't perfectly round in one spot and one end of the bridge is too close when driving past this area.  I want to have 1/16" clearance all around.  I took another look at the bridge and found that the wood framework extends just a hair further on one end.  I filed and sanded that and now have those problems taken care of.

My next issue was getting the bridge to go through a full rotation smoothly.  I wanted to have as little weight as possible on the dolly trucks to prevent unnecessary loads on the stepper motor due to small variations in the ring track height.  I added a second bearing at the base of the turntable shaft and this solved the problem by removing any side-to-side movement.

Now the turntable operates smoothly and the module can be taken out and replaced easily.  My next problem was with repeat-ability when going from one track to another.  I found there was an error of about 0.030" in alignment when reversing direction of rotation.  The drive belt had too much slop in it but if I tightened the idler too much it would load down the stepper motor.  I found that I could add two more idler pulleys between the stepper motor and the turntable shaft pulley.  These can be adjusted to add just enough tension to remove any slop in the belt.

To finish off the turntable I painted the pit walls a concrete color and used Bragdon weathering powders to add streaks and stains to the concrete.  In the floor of the pit I added a layer of dirt and then a layer of cinders that will also be used on the rest of the yard area.  The dirt I got from my sister's back yard in Pennsylvania.  I couldn't use local dirt around my home because I live in Florida and what they call dirt is mostly sand.  The cinders I got from the Arizona Rock and Mineral Company (click here).  These guys have a great selection of scenery material.  I used HO and O scale cinders because I wanted both fines and granular.  To finish it off I added small clumps of weeds here and there.

With these these things taken care of the operation of the turntable is reliable, repeatable and really enjoyable.

Laying Track By Hand

I've built several layouts in the past using kits for structures and flex track and pre-made turnouts to run the trains on.  For this layout I'm planning to build things from scratch as much as possible.  I have a good start with structures for the engine service terminal and the turntable already completed.  It's time now to start laying some track.

For rail I'm using Micro-Engineering O scale code 70 rail and white pine On30 ties from Mt Albert.  The dead rail layout uses 17 #5 turnouts (10 left and 7 right), 14 #6 30-21 curved turnouts (6 left and 8 right) and 1 #5 wye.  The 30-21 refers to the curve radius for the two legs of the curved turnouts.  The test track/switching puzzle in the shop uses 5 #5 straight and 3 #5 wye turnouts.  I'm using assembly fixtures to build the turnouts.  When I went to order them from Fast Tracks (click here) my original track plan called for a variety of turnouts, six different styles, and had a minimum curve radius of 18".  The assembly fixtures (jigs) are not inexpensive and this caused me to re-think my layout plan.  The 18" radius is pretty tight for some of the larger engines so I re-drew it using a minimum radius of 21".  I also re-drew the turnouts to reduce the variety as much as possible.  With a total of 44 turnouts to build using just three styles (#5 straight, #5 wye and #6 curved)  I'm saving several hundred dollars by building my own rather than buying them ready-made.  Building your own straight and curved track is more expensive than using flex track (about $3 versus $2.50 per foot) but it looks sooooo much better.  I think the total cost for track, including turnouts, is less expensive if you lay your own.  My layout uses about 210' of track with 36 turnouts.  The puzzle track uses 8 turnouts and about 35' of track.  Using ready-made track would have cost me about $1680, plus shipping.  I've spent $985 in materials, tools and jigs from Fast Tracks.  Yikes!  That alone makes it worthwhile to lay your own track but the finished product is way better too, in both looks and operation.

So I went ahead and built all the turnouts for the existing benchwork.  That includes both the layout and the test track/puzzle track in the office.  Altogether I have 16 #5, 4 wye, and 4 #6 curves.  I'm getting ready now to lay all the track in between the turnouts to tie everything together.  To do this I had to weather and stain the wood ties prior to gluing them down.  I have a bag of 1000 precut cross ties made of white pine from Mt Albert.  I also have a bag of their turnout ties but these need to be cut to length.  This is a bear of a job.

I started out with about 300 cross ties just to get me going.  In On30 scale there are 28 ties per foot.  That gives me about 10' of track to lay.  I also cut the ties for the 24 turnouts and placed them in bags by turnout style.  I'm scribing fine wood grain on the upper surface only using an old Xacto saw blade and then going back and scribing deeper grain with a hack saw blade.  Then I sand it lightly with 220 grit paper to take off the sharp edges and fluff left over from scribing.

I made up a batch of stain using a formula I got from Rusty Stumps (click here).  Basically I double his recipe to get enough stain for large quantities of wood:

40 oz water
4 tsp raw umber acrylic artists paint
2 tsp burnt umber acrylic
1 tsp black acrylic
2 tsp water soluble black drawing ink

The last time I did this (two years ago) was to get ready to build the coaling tower.  I had enough stain left over to build the water tank, sand house and turntable and still had plenty more.  I decided to make up a new batch for this project because the old batch was getting kinda ripe.

I pour enough stain into each bag to cover all the wood and let it sit for 24 hours, pinching and turning the wood through the bag occasionally to make sure everything gets stained.  For my other projects 24 hours was enough time.  For the ties I decided to go an extra 24 hours thinking they would come out darker.  I don't think it made any difference.  After soaking in stain for 48 hours I drained the stain back into my stain jug and laid out the individual ties on newspaper to dry.  It's really important to completely separate each tie or they'll stick together permanently when they dry.  For every step of this project the word "tedious" comes to mind.  This is highly repetitive work but it's also the kind of brainless work that can be done while doing other things.  I'm recording digital copies of a gigantic CD collection for my music server and writing this blog while doing my ties.  When everything dries it has a very realistic silvery grey aged wood look with slight variations of color from tie to tie.  In the end it's all worth the effort.  The picture below is what I'm striving for, maybe a little less aged.  This was done by Bob R., a cohort on the Free Rails Forum (click here).

After staining and gluing down over 500 ties I decided I didn’t need the level of detail shown in the picture above.  For me, that might be the way to go for any track that is right under your nose but most of mine is set back and wouldn’t merit the time needed to achieve that look.

My modeling shop is in the next room down the hall from the layout.  I have a desk and workbench in one corner of the room and decided to build a test track on a shelf above the workbench.  I wanted a simple piece of track that I could test locos and rolling stock before taking it to the layout.    I decided it would be a good idea to add 18” and 21” curves in the corner to mimic the curves on the layout.  Then I decided to add a few turnouts.  Uhm, can you say snowball?  In the end I added a version of John Allen’s Timesaver switching game at the left end and a UK switching game called Inglenook at the other.  I’m using the new test track to develop track laying techniques instead of experimenting on the layout.

New Digs For The Shop

The railroad had some additional real estate donated to it.  After my sister-in-law moved out my wife relocated her art studio upstairs to the room over the garage.  The space she left behind was right across the hall from the train room so I negotiated for it.  This is another small bedroom, 12' x 12', with a large walk-in closet.  I moved in my desk and added a nice workbench beside it.  Also installed some shelving in the closet for all my railroad stuff.  Very organized.

Originally I was going to have just two parallel tracks on a shelf-style layout above the workbench and use that as a test and programming track.  When I sat down to design it using AnyRail I decided it would make more sense to design it as a switching puzzle.  I set up one end as a Timesaver, designed by John Allen probably 50 or 60 years ago.  The other end is a European design called an Inglenook.  The track will be hand-laid code 70 On30, the same as the layout in the other room.  This will be a DCC layout with power on the tracks.  The control is a DCS51 from Digitraxx and it can run DC or DCC.  The layout is "L" shaped with a switching puzzle at each end and the two tracks running through the curve in between will be 18" and 21" radius curves.  This will give me enough options to put engines and cars through their paces and when I'm not testing or working on the layout I can play with the trains on the puzzles.

The idea behind the puzzles is that each leg services an industry and can hold anywhere from one to three cars.  A program on the laptop generates random car shuffling orders for eight cars and it's up to the operator to perform this task in as few moves as possible.  Time can also be factored in.

Lighting in this room is pretty poor so I installed some LED rope light beneath the shelf layout.  I probably should add some track lighting on the ceiling too.  This will be a great space for building models.  I also set up my stereo system in there for a little music while I'm slaving away.

Turntable (Pt 3) - Control

For the actual operation of the turntable I originally wanted to use an Arduino Uno with a motor control board driving a stepper motor (if you're not familiar with Arduino here's a quick explanation).  Three good sources for Arduino stuff are Arduino, Adafruit and Sparkfun.  This is probably the cheapest way to go but I'm new to the programming so there's a learning curve involved.  I waffled on just using manual control with a gear or belt and pulley driven by a hand crank.  Still pretty cheap but the operation of the turntable will be from 2.5' away and I'm concerned about getting the tracks lined up properly.  So now I'm back to the Arduino control because you can program it to do very accurate indexing and with a stepper motor it would be repeatable.

I ended up going to the Yahoo group "Arduino for Model Railroading" (click here) to ask for help.  Several folks there were very helpful and stuck with the project for a few weeks to develop a working sketch (program).  This required a lot of going back and forth because they had the programming knowledge but I had the gear to run it on.  Suggestions would be made and then I would modify the sketch and run the program.  In the end we came up with a very cool control system for the turntable.

The system consists of an Arduino microprocessor, the Mega 2560, running a 4x4 matrix keypad, a Nokia LCD display and an EasyDriver board running a NEMA 17 stepper motor.  This is a stand-alone system and won't need to be connected to a computer to run.  The Mega and the EasyDriver both run on 5VDC and the stepper motor runs on 12VDC through the EasyDriver.  The Mega provides power for the Keypad and the LCD.

If you're not familiar with some of this stuff I'll give a quick explanation.  The Arduino Mega ($17 - $25) is a larger version of the Uno, mentioned earlier.  It's a small microprocessor that can be programmed through a USB connection to your computer.  Once it's programmed it can run independently on power from a wall-wart style power supply or even a battery.  The board has numerous pins around its perimeter for input and output connections.  The EasyDriver ($8) is a stepper motor control board that uses a "library" of commands to provide custom control of the motor.  The 4x4 matrix keypad (5 for $7.50) has 16 keys set up in 4 rows and 4 columns.  The keys are 0 - 9 and A,B, C and D.  The keys can be programmed to be anything you want; symbols, numbers, letters, anything.  The LCD ($5) is actually a display from an older style cell phone.  It doesn't do color but can display low resolution images.  You can use Photoshop to make your display as a GIF file and then use an app to change it into code that the display understands.  The NEMA 17 stepper motor ($17) is a medium size (NEMA 17 is the size) motor that has a bunch of coils mounted around the output shaft that causes it to rotate in steps.  This one uses 400 steps to make a full rotation.  I'm mounting a 20 tooth pulley on the motor and a 60 tooth pulley on the turntable shaft to give me a 3:1 ratio so it takes 1200 steps to make one full rotation.  The EasyDriver can operate in 1/8 steps so I'll be running 9600 steps per revolution to give very smooth operation.  The total investment for this control system is about $75 and that includes everything mentioned above.

The program, called a sketch, is pretty cool.  When it's first initiated the stepper begins homing in full step mode.  I've mounted an Infra-Red Beam Break detector under the turntable platform.  As the turntable bridge rotates it also rotates a small metal flag attached to the shaft beneath the layout.  When the flag interrupts the IR beam it sends a signal to the Mega board which stops the stepper and sets that point as zero.  Everything the stepper does from that point on is referenced to that point.  There are 16 tracks around the turntable pit and each track is a certain number of steps from the zero point.  They're listed in the program and that's how the stepper knows where to find a specific track.  I can punch in a "2" on the keypad, hit the # key to enter it and the bridge/stepper knows to turn 90 steps to get to that point.  If I enter 15 it'll go 975 steps.  That's full steps though.  The program knows that after the zero point is established it needs to multiply everything by 8 so that 975 steps now becomes 7800.  That's how you get the smooth operation.  The EasyDriver also uses code that automatically starts and ends every motion by slowly ramping up speed at the beginning and then ramping down to a stop.  This creates a very realistic motion for the turntable bridge, especially since my turntable will be representing an Armstrong turntable, one that was totally positioned by man power.

Prototype turntables were used to position locomotives, to turn them so they'd be headed in the right direction for whatever job they had next.  Sometimes an engine would come onto the turntable so it could be swung around 180 degrees and head back out.  To simulate this I can enter the track number on the keypad and then enter "A" and the program knows to add 600 full steps or 4800 1/8 steps to the track value.  If an engine comes onto the turntable bridge at track # 15 I can enter 15A on the keypad and the engine will be turned 180 degrees and it can go back out track #15 in the opposite direction.  Using the * key you can erase an entry for a track number if you make a mistake.  There are still 3 other keys not used yet; B, C and D.  I'm planning to use a thumbstick (small joystick) to manually drive the turntable and one of those keys will be used to initiate that.

The LCD screen is set up to display current track #, next track # and it also displays "mvng" (moving) when the bridge is in motion.

Anyone interested in using the turntable sketch for their own project can find it at the Yahoo group mentioned before, "Arduino for Model Railroading".  It's located in the "Files" section in a folder called "Turntable Indexing".  Here's a link to the folder (click here).

Update (2-23-18):

Over the last three weeks I made some changes to the Arduino software.  The biggest one was adding the use of a joystick for manual control.  It's set up so you hit "C" on the keypad to run the turntable manually and "D" to return to keypad control.  The joystick is only connected for operation on the X axis so pushing it to the right drives the turntable CW and to the left CCW.  There are four speeds for the stepper motor in this mode so the further you push the control the faster it will go.  The speeds are 1, 2, 7 and 38 steps per second.  This is using full steps so the motion is course but the main purpose is for setting up track locations around the turntable pit.  You would drive the bridge at a faster speed and slow down as you approach the spot you want.  The display shows the actual full step distance from zero, which speed setting you're in (1 - 4) and says "stick" to indicate joystick control.

There is quite a bit of math involved in setting up a turntable using a stepper motor.  To start, you have to find equivalents for metric and fractional parts.  The stepper motor shaft is 5mm and we need a 20 tooth pulley for that.  The pulleys turn a metric GT2 belt that has teeth spaced 2mm apart.  The stepper motor uses 400 steps to make one full turn.  The turntable shaft is 5/16", or 0.315" in diameter.  This is equivalent to 8mm which is also a common size for GT2 pulleys.  I chose one with 60 teeth which gives me a ratio of 3:1, or three turns of the stepper to rotate the turntable one full turn.  That means it takes 1200 full steps for one rotation.  It's important to make calculations for track locations in full steps because if the motor stops on a partial step it will relax to a full step position when the power is turned off and this will cause a track misalignment.  So, we have 1200 steps per revolution.  We need to calculate the circumference of the turntable pit so we can figure out where to put the tracks in full step locations.  My pit is 13.75" in diameter.  To get circumference you multiply diameter times pi or 13.75 x 3.14 = 43.175".  Now we divide that by 1200 to get 0.036" per step.  Since I'm using On30 track my rails are 11/16" apart so I can safely separate the tracks by just over 1" center-to-center which works out to 30 full steps.  Perfect.  With a circumference of 43" I have 42 possible track locations around the pit.

My track plan only calls for 16 tracks and most of those are storage or dummy tracks, too short for cars or locomotives.  If you view the picture above as a clock then the 12 o'clock position is the return lead coming in across the ashpit.  This is track #0 and is the zero location for the stepper motor.  The tracks are listed below and follow a CW rotation around the pit.

Track #         Name             Degrees    Full Steps      Micro Steps
___________________________________________________

   0           Return Lead           0                 0                     0 
   1           Storage #1            20               60                  480
   2           Storage #2            30               90                  720
   3           Ready Track         40             120                  960
   4           Shop Track           55             180                1440
   5           Stall #1                 70             240                1920
   6           Stall #2                 80             270                2160
   7           Stall #3                 90             300                2400
   8           Stall #4               120             330                2640
   9           Plow Storage      135             375                3000
  10          Crane Storage     165             405                3240
  11          Storage #3           195             435                3440
  12          Storage #4           205             465                3720
  13          Storage #5           220             600                4800
  14          Outbound N.       295             765                6120
  15          Outbound S.        325             975                7800

When I start laying track I'll use these numbers to manually drive the turntable bridge to the right location, mark center-of-track and position the ties and rail for best alignment.

On the underside of the pit floor I've mounted an IR beam-break detector and attached a flag to the turntable shaft.  I found that the best material for my flag was a short section of an old hack saw blade.  I tried several other materials but they didn't interrupt the beam.  Not sure why.  Anyway, the flag gets positioned so that the detector sends an interrupt when the bridge is aligned to the zero track.  This gives the stepper motor a way to keep track of it's location and it references everything to this zero position.

I also added easy disconnect plugs to the stepper motor and detector wires.  Being able to separate the control panel from the turntable makes installation and removal easier.