The Base, New Hot Wire Tools and Foam Features
The Upper Level Base
While most of the upper level Is built on shelf brackets attached to the walls of the train building, the center peninsula is a free standing “blob” 24 feet long. Traditional benchwork techniques would use a 2x4 stub wall as the base of the peninsula. Usually the wall is connected to the ceiling for strength and acts a a view block. The wall also adds some extra width to the peninsula, depending on the design.
I chose a different route. I wanted the top of the peninsula to represent Johnstown, Colorado and to be operated from both sides. One side leads to the Welty Branch beet dumps and the other side leads to the Johnstown sugar factory and the town of Milliken, as does the prototype. I will use two-story buildings in downtown Johnstown to create a virtual view block – the room is still open but operators on each side of the peninsula mostly can’t see each other because of the buildings.
On my previous layout I used a non-traditional way to create a free-standing, two-level peninsula. The lower level was a 2’x8’ flat sheet of 3/4” plywood. This plywood connected to the main layout benchwork at one end. The other end was supported by a 2’x6’ vertical sheet of ½” plywood forming a T-shaped section seen from the side. This was obviously not very strong or structurally stable. To complete the design, another piece of ¾” plywood was used to create a center “spine” on the top side of the T. The spine ran the length of the peninsula and acted as a backdrop on both sides of the lower level and a support for the upper level made from 2” extruded polystyrene insulation foam. A Masonite backdrop was added to the top to make a mushroom-like upper level. I thought of this as “monocoque” construction as used race cars – the base, end and backdrop acted as both structural members and scenic elements.
Not having legs under the peninsula allowed me to put an old sofa under the area to add seating to the “crew lounge”, albeit with a low ceiling.
The new center peninsula draws upon this design. It has narrow sections of open grid benchwork screwed to 24” high pieces of ¾” plywood. The open grid benchwork provides the base for the lower level as well as supporting the plywood spine. The spine provides great vertical rigidity, reducing the number of legs needed. The top of the spine will support the upper level foam benchwork.
That much was constructed early on without much thought to the actual support of the upper level foam. Being a frugal person (in some respects), the plywood I purchased was a lower grade and not the straightest pieces of lumber I have ever seen. Because of this, the spine had a definite curve on the top (the open grid benchwork kept the bottom nice and straight). To correct this, I screwed a stiffener made of 1x4 plywood across the top edge. One problem solved. An afterthought was to add some stamped metal shelf brackets to temporarily support some 2x8 sheets of foam to provide more storage for odds and ends (I have a lot of odds and ends). As things tend to happen, the temporary shelf brackets became permanent when the lower lever backdrop was added. (I’m on the left).
The initial pipe dream was to use shelf brackets on each side of the spine to simply support the foam. The 1x4 across the top threw a wrench into this idea. After some thought, I decided to use plywood 1x2 ribs connected to the shelf brackets on one side and cantilevered across to support the other side. The stamped metal shelf brackets are plenty rigid and do the job nicely. The 1x2s will be embedded in the foam to provide the correct height of the upper level. The final schematic of the structure is shown below.
The overall design creates a center “support wall” only 1 3/4” thick including the backdrop on both sides. That extra 2-4” of aisle width is always a good thing.
New Hot Wire Tools
As mentioned in previous blog entries, I was not very happy with the first versions of the hot wire tools. They were dead simple – 0.047” piano wire stuck in holes drilled in plywood pieces. The problem was the hot wire used to cut the foam also singed the wood, making the holes sloppy after a short time. This allowed the nicely shaped wire to lean over and distort, making the cuts dimensionally inaccurate. I tried stapling the wire to the back of the tool but that only helped a little bit. The end result was having to rebuild the tools every so often.
I thought about searching for a more heat tolerant material – Bakelite might be good – but how to find something like that in my backwoods little town? A random thought came to me – how about using some kind of metal support for the wire? A further thought took me back to my days working in a hobby shop. Model airplanes use metal “wheel collars” to hold stuff in position on piano wire. A visit to the local hobby shop produced some 1/16” wheel collars – a smidge too big but the set screw holds them tightly in place. The collar is recessed on the foam side and another collar on the other side clamps against a small piece of brass. Shown below are the new and old tools after a lot of foam cutting (two different types of tools).
The new tool worked beautifully. I was even able to turn up the current on the Variac to speed up the cutting (now 1/2” per second). I cut a lot of foam with the new tools and they show no sign of distorting. I guess the metal collars spread the heat just enough to avoid singeing the wood. I am careful to not cut too much at once – I cut about 12” then let the tool cool down for a few seconds.
Foam Features
The new sections called for 4’x8’ sheets of 2” foam. Only one lumber yard in town carried this size and it was a Dow Corning product called “Foamular”. It had one odd characteristic – it was scored ½” deep on both sides, presumably to aid insulation installers in trimming it to fit between studs. This obviously compromises the strength of the sheets so I have been careful when carrying them around. The sheets are well supported when installed on the layout so I am not very concerned about the strength. With some luck, the latex paint will seep into the scores and seal them up.
The only difference between the previous foam structure on simple shelf brackets and the new structure is the need to embed the 1x2 ribs in the foam to keep the height correct. The new tool shown above is used to route a 2 ¼” wide by 5/8” deep channel in the foam. The 3/4” thick 1x2 is not flush with the foam – I wanted a 1/8” space between the foam and center spine to run DCC feeder wires through.
Everything else is the same as before with the exception of the vertical rear notch for shelf standards and rear horizontal groove DCC buss wires. Here is a photo of the bottom of the center peninsula foam pieces after the features were carved, the fascia supports were glued on and they were painted “Sky Blue”.
What Would I Do Differently?
A lot of extra work was involved in working around the warped plywood spine. I would spend a little extra money to get good quality, straight plywood for the spine next time. This would allow simple shelf brackets to be used on both sides and avoid the whole “cantilevered rib” thing.
However, the stamped metal shelf brackets do cause extra work when adding the backdrop. The backdrop needs to be notched to clear the upper part of the brackets unless you waste extra space between the spine and the backdrop. These notches are extra work on straight sections of the backdrop and are real bears on curved sections (like the backdrop around the helix). The backdrop on the other side of the spine is simply screwed directly to the spine.
So I would also probably avoid stamped metal shelf brackets and go with simple “standard and bracket” type systems like I used around the outside walls. The thin notches to clear the brackets are easy to cut, even if the backdrop is already in place.
