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Sidewall of my Sn3 pilot model.

Sidewall of my S-scale pilot model

! On3 Roundhouse - Constructing the Base



    The Denver & Rio Grande - DURANGO and GUNNISON Roundhouse!

   

    With the patterns and molds complete we can move on to building our pilot model. We start with a good firm base. I chose 3/4" cabinet grade birch. A full sheet costs $40.00 at a local building supply. We'll need half a sheet if doing the entire ten stalls for Durango or eleven stalls for Gunnison. And we'll pick up a sheet of 1/2" Homasote too. We'll need the whole sheet as it will become our floor, double thickness.

4x4board.jpg - considering the pieces.

I'm beginning to consider the placement of the roundhouse on my 4 x 4 plywood base.

durfp2.jpg - the plan.

I drew up the plan to see how it best fit on the plywood.

base1.jpg - the plywood base has been cut.

The 3/4" plywood base has been cut to its basic shape.

    I needed to cut my base in two down the middle in order to fit it into the car so I could take it to the Narrow Gauge Convention in Durango, and perhaps other shows later on. I really do not recommend this as it compromises the flatness of the model which is really pretty important. It's also a big pain. I probably should have simply cut it but I attempted to then route out a 1/4" slit, sort of a tongue and groove deal, however it didn't go down the middle and I ended up with a much larger off center slit and, well, I'll never do that again. A couple of holes and some dowels, maybe- Hopefully you won't ever need to do this.

ccutr1.jpg - center cut

To keep the cut straight I clamped down the straight-edge ruler and ran the circular saw along it.

ccutrc.jpg - center cut

Another view of the cut.

ccutrm.jpg - center cut

The completed center cut.

    Cutting the thing down the middle shortens it by the width of the blade, 1/32" in this case, but a 1/32" is a 1/32nd of an inch where were really want to be super accurate in the layout. I cut it along the centerline between stalls 5 and 6. The plywood was cut down the centerline but I staggered the layers of Homasote above by 1/4", one this way, the other that way, creating an interlocking joint that will keep it level.

plyj.jpg - plywood

The plywood joint is reinforced with this tongue stick and groove.

plystrap.jpg - strap

Three metal straps connect the halves.

    I found some 8" metal straps at the builders supply and used three of these to hold the base together and stabilize it some. They are fairly heavy with lots of holes for screws. Again, I hope you don't have to do this to your model. I think it took a fool day to mess with this.

strap.jpg - the strap is held with several small wood screws

Detail of the straps.

    The roundhouses will just fit on half a sheet of plywood. I am reluctant to provide a full-size template for this. The reason is they might not be accurate due to variations in printing and casting. We must be as accurate as possible and plot it out on the base ourselves. This starts with measuring the actual castings. The rear walls are pretty close to 25'-0" (6-1/4") but measure yours to be certain. The molds shrink over time (though most of this happens in the first 72 hours) so yours may be slightly different. Same for the side walls.

    The side walls were supposed to be 70 feet long but somehow the castings came out a little over a scale foot longer. I was trying to keep the brick counts even on each panel and the windows centered and this is how they came out. The real walls were 67 feet long so we are stretching it by an inch. Note that the Gunnison stone sidewall is closer to 70 feet so we will have to cheat a bit there. Or we might add to the front extension.

    Now that we know exactly how long the walls are we can start laying things out. Let's start in the middle and work our way out both directions. That way if we are a little off it won't accumulate and be way off when get to the other end. It will only be half off and hopefully that won't matter. Did I mention how important it was to be absolutely accurate? We'll try anyway. Since we are into the 40 plus inch range I suggest you buy a 4-foot metal ruler when you pick up the plywood. They'll have them in the drywall section. I also had a scale ruler, a square, good lighting and my reading glasses handy. Oh, and a couple of sharp pencils.

    Before we begin consider your layout. It might make sense to include one of more outside tracks. I debated this and finally decided to leave them off since my model is going to be a static display at least for now. I was tempted to include the one outside track that parallels the boiler house. This would be a great place to take pictures of your favorite locomotive! Instead I wanted to include a good firm base for the boiler house on this side and the foreman's office and storage shed on the other and this is about all I had room for on my half sheet of plywood. If you get a whole sheet you'll have some options to consider. I'll talk about how I laid Durango out on my half sheet. At a later date I may add that lead track onto the side. There's a coal bin that extends out the back beyond my board too. For the time being the ground under those buildings is not going to be glued to the base. Instead they will just rest on top and can be packed away separately for transportation.

base2.jpg

base2r.jpg

The lower layer of Homasote with some foundation pieces.

    I should explain we are building the cinder floor up with two 1/2" layers of Homasote. This will be skirted with 1" tall cast Hydrocal stone foundations. The backs of these will be right on the centerlines. I know, it's crazy to got to all this trouble because the ground line at Durango is above the foundation, so we won't see any of it. However, on Gunnison they are exposed and I want to illustrate that. Still, I like modeling things you don't see. I once spent hours (maybe even days) building roof trusses on a depot model only to cover them all up with shingles. Building models is fun so why not make the most of? You're looking at me kind of funny.

    No matter. Do what you want on your model. We are cutting the Homasote to fit the foundation pieces on my model. The center of the rear walls will be in from the end of our side walls end by their thickness or about 1/4" allowing for the pilaster. Then the skirt or apron under the tracks will go all the way to the turntable pit. Durango's turntable is 65 ft so that an 8-1/4" radius. But we need to allow for the concrete pit wall, which is back another 6" and is 1'-8" wide at the top, though I have not yet figured out how wide the model of this might be. I should be alright if I cut it back a strong 1/2".

    My friend Glenn's modeling Gunnison and will be offering an article to the Gazette on its construction. Gunnison's TT was 80 feet. I'll be scratch building the Durango turntable but I must do that later in order to meet the convention deadline. It seems there are currently no On3 turntables being marketed (please let me know if there are). We'll talk about this at the convention and I suppose if there's enough interest we'll consider offering a kit, but first I should complete mine to see if it is possible.

    I would definitely start with the turntable if I were you and build off of it in regards to how the roundhouse base fits and plotting the measurements as I'm about to explain. Obviously all the tracks lead back to the center of the TT. It's much easier to work from the real thing than it might be to my pencilled center but certainly not impossible to joint them later one. I think you do want to avoid having to cut the apron or base or do other such rough construction once you've built your roundhouse and/or turntable so think it out now and do all the rough cutting now.

    Okay, so let's plot the stalls out. It's really pretty simple. I started out by placing the TT center 8-1/4" in on the diagonal, a line drawn kitty-corner across the 4 x 4 sheet. This will be the track centerline of stall 5. I then measured along the track centerline and marked 24" from the TT center. This is the center of the 14'-6" wide engine door opening. Now let's measure back another 17 and some inches, the length of your side walls. This will be the back wall's furthest point, actually, the pilaster. Again, the center of the back wall will be in 1/4" and since that is what we are really measuring for, to cut the Homasote, we'll mark that. From here we want to measure out 12-1/2 scale feet, half the distance of one of our rear walls to mark the centerline between the stall on both sides. Just do a little hash mark. Now draw these centerline by aligning the ruler on the TT center and the hash mark. Measure the same distances along them. 24" for the engine doors, 17 something to the rear wall center. I put a pencil mark on my ruler so I could quickly spot this reference point.

    Now draw the rear wall centerline between the two points you've just marked on the stall centerlines. And draw another at the engine doors.

    Now we repeat these steps to plot out the remaining stalls. Keep in mind that each stall is angled. It's actually 8.65 degrees if that matters. Just measure over another 25 feet and you have the next centerline at the rear. Measure the lengths along it. Use a sharp pencil. Keep in mind we'll come back later after we add footings we'll mark and drill for 1/32" brass pins along the stall centerlines that will attach the timber truss posts. We'll also pin the walls to the foundations and one another- No, I do not glue them, preferring to be able to disassemble large models like this.

sawplung.jpg

Cutting straight lines with the circular saw.

sawplung2.jpg

Cutting the top layer's edge with circular saw.

hom1.jpg - Homasote

Here's the top layer of Homasote. I've very carefully plotted out the footprint of our roundhouse. Unfortunately I must cut it in two.

    Once the footprint of our roundhouse has been drawn we can begin cutting up the pieces. You're lucky, you really only have to worry about the top layer. You can actually cut both sheets of Homasote simultaneously. Again, I had to deal with a joint down the middle and shifted it from layer to layer.

ccutt1.jpg

Cutting the centerline joint along a straight-edge.

ccutt2.jpg

It's cut in two now.

    I first cut my base to size, trimming it tightly to the structure but with a little overhang to provide protection during transportation and display. Your main worry will be butting this up against the turntable with a nice clean level fit. I plan to construct my turntable so it fits up snug underneath the 3/4" base plywood. As I mentioned earlier, Durango has a 65 foot turntable which is an 8-1/4" radius, I allowed another 1/2" for the pit wall. This is where I cut. I really don't want to cut it again later on.

    I decided to keep the sides straight lines out from the TT center. If I cut odd angles then I would be scratching my head on how to match them later one. The plywood base includes the boiler house on the left side and the office and shed on the right. The Homasote in these areas will be separate. I trimmed the lower level of Homasote by one-quarter inch so these separate sections will slip in underneath and lock themselves in place.

    Once I had the plan thought out I began cutting the pieces starting with the base and working my way up. When I got to the top where it counted I had already made all the mistakes and did my best not to mess up. Again, the task was made more difficult for me because of that extra cut.

    You have a choice of tools. A big circular saw is not a good idea. Especially with Homasote you'll have that fuzzy gray stuff all over the place. Instead I used a little 4" battery powered Makita circular saw for the straight cuts. From time to time it kicked back and especially cutting thing pieces close to an edge it would grab chunks and shred instead of cutting cleanly. I had fewer problems with my saber saw which is great for curves and finishing up corners of the circular saw but it's difficult to get nice straight lines. So I used the circular saw for those. Surprisingly I found the Homasote was fairly easy to cut with a mat knife along a metal straightedge. Simply use repeated strokes and lots of muscle. Be real careful of course.

    Oh, a very important tool was the shop vac. Even cutting with the knife is very messy so I vacuumed after just about every cut to keep it under control.

joints.jpg

Fitting the center joint.

jointc.jpg

The center joint.

    Things are taking shape. I checked and double-checked as I went. I was finally tempted to get the glue out but remembered I needed to cut openings for the inspection pits. These are cast in Hydrocal. There are two wide pits that are 50 ft. long. And three narrow pits that are 40 ft. long. Each pit is set back 9 scale feet from the engine door so I marked those points. I then took the castings and placed them over the centerlines and squared them up, and then traced their parameter. This are the cut lines.

    Okay, now things are getting serious. After I was very sure that I had the top aligned over the bottom piece of Homasote I decided I should screw them together and to the base. Just with a couple of screws but from this point forward they needed to be aligned this way. You really don't want to cut two or three of the pits and have it shift when you do the others. So I shot two screws in each section to hold them in place for the next step which was drilling 3/32" holes in the corners of each pit thereby transferring their location to the lower panel. This also made cutting the corner a little easier.

pit-s.jpg - where to cut hole

The wide inspection pit sidewalls are 50 feet long. I cut them to 40 ft. for the narrow version.

pit-wf.jpg - mark the spot

I'm marking the location of one of the wide inspection pits.

    I could have used the saber saw to cut these but I once had a bad experience where the cuts were not straight but angled. Actually this was someone else's saber saw and it must have had cheap flexible blade or maybe it was dull on one side and made it cut this way- At any rate I decided to use the mat knife with good success. I cut one side over half way and then flipped it over to finish it from the other side. It wasn't too long until I had them all cut through both levels. You'll want to cut them slightly over-size, a little more than I allowed as mine were just a little too tight. I went to the hardware store and bought some fresh blades for the utility knife which made it a lot easier to trim these to fit the pit wall castings. I also filed the back side of the castings.

pit-f1.jpg

Marking the pit locations.

pit-wf.jpg

Cutting a wide pit.

csawx.jpg

Using the circular saw close to the edge kicked out chunks of Homasote.

bcut.jpg

It is better to cut thin areas with the utility knife using repeated strokes along a straight-edge.

drillp.jpg

I'll drill the corners of the pit openings so I'll know where to cut on the lower layer.

drillh.jpg

Drilling the corners.

bcutp1.jpg

Cutting the pits was done with a utility knife.

pit-co1.jpg

Here I've just finished cutting the top layer for one of the pits. Now we need to do the same for the lower level.

pit-s1.jpg

Narrow pit.

pit-w1.jpg

Fitting one of the wide pit.

    At this point I will note that the pits will not be flush with the top of the Homasote but rather will be shimmed up the height of our ties. In fact I recommend that you simply use some extra ties for this to assure the correct height as the rails will rest right on top of the pit walls. A simple enough trick but don't forget it!

    I think we will be doing the same for the foundations. The prototype plans I was working off of were measured off the base of the rails. The five or six scale inches (1/8") isn't that big a deal but I'm thinking we probably want as much headroom in our model as we can find, noting the center extended stall's roof rafters were "dapped" (cut away) to clear the doghouses! I don't think we really want to have our roof shoved up every time we park a locomotive.

    While we are on the subject of the extended stalls the brick walls were removed and a simple wood frame shed was added on out the back. We'll simply built the concrete foundation for these on top the Homasote.

set1.jpg

I've cut all of the pits and am refining the fit.

found-s.jpg

Let's take a look at how the foundations are going to look while we are at it.

    With the parameter cut out on both layers of Homasote and the pits cut I spent some extra time refining the fit. I dressed the edges with an angle cut and removed any chunks or fuzz. And I worked on the level of the lower sheets. Unfortunately, one section of the Homasote was a bit thicker than the rest along one edge and I did not realize it when I laid out the cuts for the lower level- resulting with a miss-match along the centerline. I should have cut the whole thing and then cut the center but I was trying to conserve material and use the factory cut edges where they joined. Wrong. The fix was simple. I shaved the hump down by carving with the long utility knife blade and a rasp. I avoided this problem on the top level by cutting it from one piece.

hom-l1.jpg

Homasote, lower level.

    Okay, we are ready to glue the Homasote down. Again, alignment is critical. I mentioned earlier that I had shot two screws through each section. I now added two 3/32" holes and inserted nails, finger tight, through all three elements: both Homasote layers and then the base.

clamp-pre.jpg

Prepare the clamps beforehand.

clamp-bd.jpg

I'll use these boards to clamp the center sections down while the glue dried.

elmers.jpg

Elmer's Carpenter's Wood Glue is my choice for wood and Hydrocal.

    We'll use Elmer's Carpenter's Wood Glue and do one section at a time. I readied some 4" C-clamps for where we could reach and clamped the areas I could not with sheet rock screws and small boards to spread the force. Glue was applied and evenly spread out avoiding an excess. I then placed the sheet and inserted those nails to insure the proper alignment, and then clamped it down.

glue-1.jpg

When everything is ready the glue is applied to the back of the first piece of Homasote.

glue-spread.jpg

The beads of glue are spread evenly.

glue-clamp.jpg

Work quickly. The Homasote is placed in the base and carefully aligned. The nails are pushed into those alignment holes I drilled earlier. Then it is clamped down firmly.

wait.jpg

Now we wait.

    It's summertime so it only took about fifteen minutes for the glue to take hold. I then moved on to the next section and top layer after that. Make certain you have your C-clamps ready, preset to the right opening and the screws are the right size. You don't want to have it all glued up and be delayed looking for more screws or twirling C-clamps.

glue-ooze.jpg

I like to see a little glue ooze out the side. This assures we have used enough but not too much. The excess is wiped off before it sets.

glue-clamp2.jpg

In about 15 minutes or so we can move on to the next piece.

glue-2.jpg

The glue is applied.

glue-spreader.jpg

The beads of glue are spread evenly with a small scrap of wood.

glue-clamp3.jpg

Next, we move on to the top layer.

clamp-cat.jpg

The top layer of Homasote is clamped down. Sugar the Cat is getting tied of all the waiting.

pit-fit1.jpg

Let's see if the pits fit. No doubt they will need a little fine tuning.

hom-done.jpg

The completed Homasote roundhouse floor.

    Wow, we're all done with this stuff. What next? Ties, we need a bag of ties. Should have thought ahead. Have to order some. Well, we can start working on fitting the foundations, coloring them and the inspection pit walls. There's lots of stuff to do. Did I mention I'm having a lot of fun? I'm really enjoying this. After months of planning, days and days of pattern work, molds and casting it's now actually coming together.

   

   

4x4board.jpg - considering the pieces.

Just a few days ago...

   

   

Link back to:     Durango Roundhouse Page    

   

   

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