Scratch Building a Gas Mechanical Critter Part 2

In the first installment of this series, I discussed how I built the brass underframe for my "critter" to serve as a base for the engine frame and the decking.  The cab, motor housing and other details will be constructed from styrene and will rest on the deck.

With the brass underframe complete, my next task was to build up the side frames and end beams from styrene sheet, channel, angle and other styrene strips.   The parts were cut to fit around the underframe and test fit before gluing the assembly together with Plastruct cement.

Clearly the frame needed more detail to resemble the prototype model I found on the internet.  A quick glance at the photo I was using for inspiration reveals some interesting journal boxes, an access door of some kind, coupler pockets and ladders.

For journal boxes, I chose Grandt Line C&S caboose boxes and lids.  They were as close as I could come to the ones in the photo.  After allowing for the height and location of the Stanton Drive wheels, I cemented the journal boxes in place.  Almost immediately, the frame began to look more interesting.

For the end beam, I cut holes for the couplers in the styrene, and used tin snips to cut out the brass underframe where the couplers would go. The coupler pockets and the front and rear pilot steps were constructed from Evergreen angle stock in various sizes.  I used Evergreen V Groove .100" sheet for the decking, and painted it with Rust-Oleum weathered wood brown to see how it would look.

To my delight, it was beginning to look like a locomotive frame!  To get an idea how the finished locomotive might look, I cut up an old industrial diesel shell I from my junk box, and placed it on the deck.  The proportions were about what I was looking for.

The photo I was working from had an access hatch on the side frame between the journal boxes.  I cut a rectangle of styrene to fit, then added NBW castings and thin strips of styrene to suggest hinges.  A service ladder was added at the front.  Then I added strips of 5/8" scale rivet decals from Archer along the front and rear steps, around the coupler pockets and elsewhere.  I cannibalised stanchions from an old plastic locomotive and used piano wire to form the coupler lift bars.  Here are pictures of the finished beam and side frame after spraying the frame with Tamiya TS-63 NATO Black.

With the engine frame complete (minus couplers) I then turned my attention to the superstructure.  I drew up plans for the cab, motor housing, and the battery box on the back of the deck.  Dimensions for the cab were based roughly on the cut up industrial switcher cab.

Working from the plans, I cut out the walls of the cab from Evergreen V Groove .080 sheet and placed them on the drawing for comparison.  I made windows to approximate those in the photo using Grandt Line 6 light single sash (#5280) which I cut and sanded to make double windows without sills.

The cab was assembled with Plastruct cement.   The motor housing was built the same way, with additional detail (ladders, stack, access panel).  A radiator grill will be added in front after painting made from Scale Scenics aluminum micro-mesh.

 

Thin styrene sheet was cut to size and pre-bent to the curved shape of the roof by rolling it around a fat pencil.  The battery box and lid on the rear deck was cut from .080" V Groove sheet.  Bolts were added strategically using small NBW castings.  Cal Scale PRR style brass headlights (190-477) were installed on the cab roof.  By now the critter was beginning to take shape.

At this point, the realization dawned on me that with the roof glued in place, I had no idea how I was going to secure the cab on the deck so that it could be easily removed to reach the decoder.  A few days of mulling the problem over led to a solution.  I built up an open box from styrene that would be glued to the deck and sit over the motor.  The cab and motor housing would slip snugly over the box for operation, but they could be removed when necessary.  Here you can see the box mounted on the deck. 

There are still a few details needed at this point, such as the air tanks on the roof, the rear railing and various grab irons.  But the structure is finished enough to see how it might look on the layout, pulling a reefer on my Altoona Brewery spur.

This concludes part 2 of my series on scratch building a critter for the AP certificate in motive power. In the third and last installment I will discuss replacing the styrene deck with lead sheet for weight, installing the roof detail, railings, lights and decoder, painting and test operations on the layout.

Scratch Building a Gas Mechanical "Critter"

Over the last several years I have been slowly working my way through the Achievement Program of the National Model Railroad Association.  The AP provides incentives to learn and master the various crafts and skills necessary in the hobby of model railroading.  For each category (scenery, structures, track work, wiring, etc.) there are requirements demonstrating your skills.  Successful completion of the requirements earns a certificate of achievement.  Earning seven or more certificates is recognized by the title Master Model Railroader.    I currently hold five certificates: author, electrical, scenery, structures and prototype modeling.  This year I have started on the Motive Power requirements.

This AP category has only three requirements: Build a superdedailed locomotive from scratch and build two other engines that can be from kits, but must also be superdetailed.  Motive power is not as intimidating as you might imagine.  It isn't necessary to scratch build a brass steam engine with all the valve gear and rods.  You can choose to build a diesel locomotive, a street car, or just about any other kind of motive power you can imagine.  I have chosen to scratch build a gas mechanical "critter" based on a photo of an S scale engine I found several years ago on the internet.

I was immediately smitten by this little engine, apparently some kind of gas mechanical switcher.   Here is another view from the rear.

Since I model in HO scale, I decided to design my critter as an HO gauge locomotive.  But I wanted to keep the quaint character of the photo, with its wood decking and cab, the odd windows, the lights and air tanks on the roof, etc.

I am building my critter around a Stanton Drive from NWSL.  The Stanton is a self contained power truck unit that can run on either DC or DCC.  The drive is small enough to fit beneath the deck of the critter, with a 10 foot wheelbase that was just about right for the model.

I have an old Lifelike Plymouth industrial switcher that looked to be about the right size for a Stanton Drive, so I used that to estimate sizes for the side frames and beams, as well as overall length and width.  The superstructure of my critter will be made of Evergreen styrene, which is easy to work with.  The problem, of course, is that such a small engine made entirely of styrene would be very light and have power pickup issues, so I decided that the styrene frame would have to fit over a brass underframe to give weight and strength to the critter.

 I cut a piece of thin sheet brass to the estimated size of the deck, plus the height of the side frames and end beams.  Then I cut out the corners so that the entire sheet could be folded, using a small bending brake from Micromark.  The result was a rectangular box open on the bottom.

The next step was to solder the corners of the brass underframe. I clamped the sides using popsicle sticks to press the corners together.

I applied a liberal coat of TIX flux, and soldered the corners.  The final result was a brass box around which I would form the styrene side frames and end beams.

In order for the Stanton Drive to fit properly inside the underframe, I had to cut out a rectanglar opening in the top of the box.  The raised center portion of the drive mechanism fits in the opening, while the lower parts are secured to the inside of the box with double sided carpet tape.

Here is the motor mounted inside the underframe.  The side frames and end beams will be cut to fit around the box, then glued together using the underframe to keep the assembly square.  At this point I was able to do a test run of the motor and underframe assembly using standard DC power.  The drive ran well enough, but it was evident that even more weight would have to be added for good pick-up.

Notice that there are four wires coming from the Stanton Drive, colored red, black, orange and gray. The red and black leads are for track power, the orange and gray are the motor leads.  If one connects black to gray and red to orange (as shown) the motor will run on DC.  I plan to connect the red and black power leads to a Soundtraxx model MC2H1040P mobile decoder.  The decoder orange and gray leads will then be connected to the drive 's orange and gray wires, for DCC conrol.  The MC2H1040P decoder will run on either DC or DCC, which is an added convenience.

In the next installment I will discuss how I built the frame, decking and superstructure for my little "critter".