Make a Latex Rock Mold

Making your own molds for rock casting opens up possibilities beyond those available using commercial rock molds or castings. Once you have your own mold, you can cast as many rocks as needed, cutting them and rearranging into varied patterns to disguise their origins. Making a latex mold is simple and inexpensive, and the materials are readily available. Although a latex mold will not last as long as a silicone or urethane mold nor make as many castings, this is usually not an issue for an individual modeler.

For this project I used some rock castings from "Ultimate, Make-A-Mold Master Castings" rock castings by Ultimate Scenery Center (www.ultimatescenery.com). These are highly detailed, urethane foam castings that the manufacturer actually intends to be used as masters for the purchaser to use to make his own molds.

I started with #123 "Pennsylvania Shale", a large (13" x 9 ") casting exhibiting both stratified and 'blocky' rock in the same casting. Here's a photo:



Here's a detail picture:



Click on any photo to get a full-size view.

Here's a photo just before starting the process. I used 'Mold Builder' latex mold compound that I bought at Michael's.



The surface that I am building this mold upon is a 18" x 18" ceramic floor tile obtained from Home Depot. I chose the smoothest 18" x 18" tile that I could find, although this was a floor tile and not a glazed wall tile like I build smaller molds on. To make the tile's matte surface smoother, I coated it with clear gloss spray from a spray can. A smooth surface will prevent the latex from adhering and facilitate removal of the finished mold.

The latex is brushed on. The first coat of latex must be applied thin and without bubbles - unless you want bubbles to be a permanent part of the mold and of each subsequent casting; so watch your brush strokes. I extended the latex beyond the sides of the master casting to form a lip on the finished mold about 3/8" wide.

And here's the first coat of latex applied.



Allow each coat to dry before applying subsequent coats. If you are impatient, the cure of the latex can be accelerated with hot air from a hair dryer. Additional coats are applied in the same way. Resist the temptation to apply the latex in thick coats. Thick coats tend to pull away from the master and they tend to dry with voids in the rubber.

Here's a pic of the mold after a couple of coats of latex have been applied and dried.



Apply four coats of latex before the next step.

Apply a coat of latex and wait for it to get 'tacky' then layer the entire thing with gauze. Forced the gauge into all of the cracks and crevices.

After the gauze is applied, add another coat of latex. Get the gauze saturated with this topcoat of latex. Here's a picture of the mold after adding this overcoat of latex:



After the latex/gauze/latex coat as dried; at least four additional coats are added before the mold is done; more coats can be added for additional strength.

Here's what the finished mold looks like ready to be peeled from the master casting:



And here's a video of removing the mold from the master casting:

Installing a DCC Decoder in a Brass Steamer Made Easy

These videos take you step-by step through the process of installing a DCC decoder in a brass steam locomotive - a Sunset/3rd rail B&O Q4b in O Scale to be precise.

There's no reason to be hesitant to disassemble and modify a brass locomotive; and the Sunset locos seem to be well soldered and sturdy. Hopefully these videos will give you the information and confidence that you need to tackle the job yourself. In fact, getting the installation right took me a couple of attempts to find the right combination of miniature connectors and flexible wire to make the installation work - but that is all explained in the film. Be sure to view the videos in order.

There is one omission that I must mention. In hooking up the backup light I forgot to film (or mention) the necessity to include a resistor in the line going to the backup light. This resistor is necessary once the backup light is hooked up directly to the decoder. Use a value of 500 to 1000 ohms and put the resistor in either line of the LED backup light.

In viewing the videos, do not click on the "HD" unless you have high speed internet and a fast computer (dual core processor and good video card); and you still may want to allow the video to buffer before playing.

Part 1

Part 2

Fast Tracks Tips & Techniques

Like many others, I have a set of Fast Tracks turnout construction tools. The videos on the Fast Tracks website provide a good overview on how to use each of these tools and I watched them before buying.

However, the O Scale fixtures are a little different then the ones for the other scales, and are not covered by Fast Track's videos. In addition I developed some techniques for using Fast Tracks that may be helpful. So I made this video to demonstrate all that I learned.





One more tip that came up after I finished the video. I installed a bunch of these turnouts in a yard ladder and as part of the installation I checked for shorts. While I did not find any dead shorts, I found some leakage between the left and right rails. This drove me nuts for a while until I isolated it to melted flux bridging the gaps in the PC board ties. Since the Oatley flux is a tinning flux, it's mildly conductive. So if you use the Oatley tinning flux, be sure to clean it out of all of the gaps (or use less flux than I did). I found that "Goo Gone" is a good cleaner to use for this purpose.

Some Simple Switch Machine Solutions

Mounting Tortoise Switch Machines

The problem with attaching the Tortoise machines is that the built-in mounting ears are too close to the machine to reach easily with a screwdriver. Plus the machine is small and it's hard to position it critically and drive the screws without pushing the machine out of place. Some vendors sell mounting plates for the Tortoise, however there is an easier and less expensive solution. To alleviate these problems attach each Tortoise machine to a scrap of plywood. The size of the plywood is not important so long as it extends well past the machine proper. The plywood is, in turn, mounted to the underside of the layout. The plywood forms a 'handle' that makes it easy to position and screw the machine in place without movement.

These photos should be self-explanatory.











You'll notice in the pictures above that the actuation mechanism of the Tortoise machine simply extends past one edge of the plywood mounting plate. In this way it is not necessary to drill a hole for the actuation wire through the mounting plate. Also note that I have pre-drilled and countersunk holes for the mounting screws. Four holes are not really necessary, but it provides some flexibility in where the mounting screws will be driven. Depending on your track construction the combined thickness of the mounting plate, subroadbed (plywood) and roadbed can exceed 1". This would be too thick if you use the music wire actuator that comes with the Tortoise. If this is the case cut another wire actuator and make it longer; the Tortoise instructions include a template for the actuator.

Mounting Servos as Switch Machines

Mounting radio-control servos for use as switch machines presents a problem. Some manufacturers sell mounting plate for servos but, as far as I have been able to determine, only for the miniature/micro servos. If you want to use the full-size servos or you need a lot of these mounting plates they are not a solution. There is a simpler and less expensive solution, glue the servo to a right angle bracket sold in home centers for building decks.





The bracket is Simpson 'Strong Tie' A21Z, note: this is the right angle bracket with one arm longer than the other, that's the arm that the servo is glued to. I used Gorilla Glue to attach the servo. I roughed-up the bracket and servo with sandpaper before I dampened the bracket with water and applied a THIN coat of the glue to the servo, then clamped the two together. Use a thin coat, otherwise the glue will foam up all over the work.

Here's the servo switch machine installed:



The machine can be installed above the table as well which is handy in areas of hidden trackage as the machine is easy to access for adjustment or replacement.



The servo switch machine is mounted on a scrap of 1x2 lumber (actual 3/4" x 1 1/2") to provide some height and thereby additional throw for the actuator wire. Notice that the PC Tie throw bar has been extended with another length of PC tie soldered on so that the switch machine can be mounted far enough to the side to clear rolling stock. The extended throw bar is supported by a wooden tie to prevent the throw bar from sagging.

For fitting the actuator arm, made of music wire, to the servo crank I came up with what I think is a novel solution which you can see here:



I bent a length of wire into the shape above. The length of the straight section to the right should be enough to reach up through the subroadbed, roadbed and through the throw bar on your turnout. If in doubt, make it longer, any excess can be cut off after installation. The form of the wire on the other end is shown in the detail close up here:



The distance between the bends should match the hole spacing on two opposite arms of the servo crank so that it fits like this:





In case it's not obvious how to get the bent wire into the servo crank, here's a short video on how it's done:



The self-retention feature that you see in the video works because I am using relatively stiff 0.039 wire as a actuation arm. That allows the right angle bend at the end to exert enough outward pressure to hold the arm in place. If you use significantly thinner wire this might not be the case.