Mid-tier alcove bridge

Not much new to report. I've started building the plywood subroadbed for the rest of the middle tier of staging. Just one picture to add:


Previously I mentioned that there is a 3' 9" wide alcove that the staging tracks have to span without supports because I will later want to be able to crawl under the track to get into the alcove. In that previous post I had a side picture of the upper tier alcove bridge. This picture above shows the underneath of the middle tier alcove bridge before it has been installed, so provides a better view of the bridge construction. (Note that the bridge is temporarily resting upside down on another part of staging -- this is not where it will be installed.)

There's not much to this construction. Two L-girders are attached together with nuts and bolts to provide a level surface, then the L-girders are attached to the underside of the plywood with #8 metal screws and washers. The plywood is strong enough to hold a whole slew of N-scale trains but it will tend to warp/bow unless something keeps it flat and level -- the L-girders provide that service and also provide some vertical strength in case some doofus like me stumbles and lands on the bridge.

Next step is to finish the subroadbed and add the blue roadbed -- I can complete both tomorrow if I can get a free hour to work on it.

Diamond rail cutting

Ever since I completed the upper tier bridge structure I've had a "to-do" item of cutting the rails on both sides of the bridge in order to make it removable.

The challenge is that the rail gap must be wide enough to prevent electricity from passing across it, but narrow enough to allow the trains to pass smoothly across the gap. It is especially challenging in N scale to get a small enough gap because our wheels are so tiny. We can't use insulation to pad the bridge gaps, as we do the other rail gaps on the layout, because the bridge rails need to come up easily when the bridge is removed.

I tested a couple of thin-blade manual saws on some left over track and found them wanting: in part because it was hard to keep the saw from wandering off course and damaging the track surface; and in part because the back-and-forth saw motion created a lot of strain on the rest of the track.

Then I tested a rotary tool, commonly called by the name brand "Dremel", and it worked great. The only problem was that the resulting gap was too wide due to the width of the blade.

Today, while I was in Denver for other reasons, I dropped by Caboose Hobbies and found a thin Dremel diamond blade that looked to be perfect. It was $19 (yikes) but as no other solution is apparent, I bought it. After testing on a piece of scrap track I tried it on the track on the right side of the bridge:


The rail gap is so small in this picture that it is almost impossible to see. Look at the upper track, immediately to the right of the wooden bridge side. Below that track you can see the tools used -- the rotary tool with diamond blade, safety glasses (the blade really kicks up a lot of fine dust), and a simple box cutter I used to cut the plastic ties after the rail was cut.

The only problem was that after cutting it turned out that the track itself wasn't sufficently glued down on the right side of the cut. So, I added some glue (the white stuff at the bottom of the track in the photo) and used a pin to hold the track in place until dry.

Once dry I'll gently file the rail edges and test with a locomotive. If this works I will add the diamond blade to the track laying arsenal for special situations like this.

First Alcove bridge

As I mentioned yesterday I need to build bridges across the west alcove. Three, in fact (one per tier). The first one, for the upper tier, is complete:



1/2" plywood is sufficiently strong to hold N scale trains, the problem is that it will tend to bend and warp without supports (piers) every 12" or so. But the alcove span is 3'9" and I didn't want to build a support grid underneath because I wanted to permit maintenance access to the helix that will later be built in the alcove.

The solution is to use steel L-girders to force the plywood to stay stiff and level. Two L-girders are attached together using nut/bolt/washers and short (1/2") screws with a very wide head are used to attach the L-girders to the plywood. The plywood is supported at both ends by wooden piers. Once constructed test that it is level and adjust as needed (thin plastic shims may prove useful here).

This particular segment of plywood subroadbed was more interesting than usual because on the left side you can (sort of) see that the subroadbed divides into three parts, each with its own grade. I've mentioned this design element briefly in previous posts, but after this section is complete I'll add better photos and describe it in detail.

Upper Tier Bridge complete

So, track is in place, wired, cleaned, tuned and tested:


I changed the bridge curve slightly from what I'd planned to better align it with the track on the left. But it's still no tighter than 24" radius at the apex, which is plenty wide.

I haven't cut the rails yet to allow the bridge to be removed. I use a Xuron rail cutter (see figure 13 at the link) for rail cutting, but as good as that is for cutting rail before it is set in place, it makes a large gap if you are cutting in place rail. Better to use a thin saw for the purpose. I think I have one in my old HO equipment box -- if not I'll have to buy one. I'll target completing that task this week.

Otherwise there is a feeling of "downhill from here". It's been 10 weeks since I started dismantling the old staging, but now I've got the triple deck loop and the custom staging bridges in place. From this point I'll complete the upper tier nearest the wall and move forward until staging is complete. I will pre-wire the north end switches, but won't hook them up for remote control yet as they will be reachable by hand. All in all the rest of staging should be just about implementing a known solution -- no more big problems to solve along the way.

So, I've started thinking ahead to the problems post-staging. More on that in a future post.

Upper tier bridge (part 3)

The support piers on the other side of the bridge follow the same principle as described in the last post, but were easier to build because the bridge is only one-track wide at this point and the necessary joists are already in place. This photo shows the piers in place with C-clamps, a beam resting on top, and two levels used to verify that this end of the bridge is level with the other end.

It turns out that drill access to those piers was also problematic, and in fact I had to trim the leftmost pier to work around the middle tier subroadbed. I again used wood glue to hold the piers in place, this time snug against the adjacent piers, until the glue dried and I could put in the screws without C-clamps in the way.

In the next photo a quite a bit more has happened, and the bridge is starting to take shape:


In this photo the bridge beam on the right side is in place and the bridge itself has been positioned. Screws (#4, 1/2") have been added to the bridge floor to affix it to the beams. The end of the bridge on the right side has been trimmed to where the 1/2" plywood subroadbed will meet the lauan plywood, and the beam has had a notch cut in for where it will be supporting the 1/2" plywood.

In addition, the bridge "walls" have been attached to the edges of the bridge floor. These walls are 1 1/2" tall -- which is enough to add the lateral strength needed. They are attached with #4 1/2" screws, as was done with the middle tier bridge.

Unfortunately, the leftmost bolt is too close to the edge to allow a washer to be placed on it, now that the wall is in place. Minor oops -- I'll just trim some of the wall to make room.

One change not quite as visible is that the subroadbed for the upper tier entry track (adjacent to the back wall) is in place. I put this in when the bridge was removed. I was holding off on this task only because I wanted to verify that the subroadbed would not be in the way of the bridge.

In this next photo the bridge is ready for track:


The obvious changes from the last photo are that the blue roadbed is in place and the track path has been drawn with a marker -- the 30" radius curve I discussed in the first Upper Bridge post is the path used. Some changes from the previous photo are:

1. The roadbed and track have been laid for the upper tier entry track in the back. I did this now because it will be harder to access that area after the bridge is in place. You may also note that feeder wires are attached. If you look very closely you may also detect the upper tier auto reverse (AR) bus in yellow and blue, which has now been routed along the back of staging, where unfortunately it won't be very accessible after all three tiers are in place. I really hope I never need to get to this later. I did make sure that the places where the feeder wires attach to the bus are accessible.


2. The bridge has been leveled in all directions at all points. Interestingly, when the leveling was done at the nut/bolt/washer support piers I found that the pier tops were not level with each other, although I thought I'd leveled them by eye. It doesn't affect anything, except to show that leveling by eye doesn't cut it.


3. The last few inches on either side of the bridge have been separated from the main bridge by manual saw. These end sections will be permanently affixed to the support beams underneath, while the main bridge will be removable. The reason for doing this was to assure a very level transition from the bridge floor to these end sections.


4. Because the bridge is meant to be removed occasionally, not frequently, the bridge is attached with screws on the beams and of course the nuts on the middle piers. In order to access the screws the blue roadbed has had holes cut where the screws are.

The next post will cover the track placement (and will end the topic of this bridge). My intent is to use sectional track with railjoiners on each side. This will make the operation of replacing the bridge a little more challenging, but should greatly decrease the chance of derailments. Of course, if that approach doesn't work out I can remove and replace the track without changing the rest of the bridge.

Upper tier bridge (part 2)

So, here's the bolt/nut/washer support piers in place:


Construction is pretty straightforward. Use a 1/4" drill bit. It helps, once the bit is through the wood, to hold the drill in place and run it in reverse to clean out the hole. Then run a bolt through by hand a couple times to finish cleaning the hole.

Next, put the bridge floor onto the bolts:


There is a bit of a challenge aligning the drill holes exactly with the bolts. We (Daniel and I) accomplished this by first setting the bridge floor exactly in place, then using a hammer against a block of wood that was placed on the bridge floor directly over the rightmost bolt. The block of wood protected the top side of the bridge floor from dents, but the hammer (only one hit) caused the bolt to put minor indent in the bottom of the bridge floor. This indent was our guide for the 1/4" drill bit. Repeat 4 times, cleaning the hole each time, and voila!

We didn't set the levels of the support washers yet. Instead, I started on the supports for the loop end of the bridge. I cut and measured the pieces then started assembly. First, we need a cross joist. I reused a piece of 1/2" plywood from the first staging attempt. This works except plywood is susceptible to splitting, as this photo shows:


Fortunately, the split is minor so replacement was not needed. Next, I set up the bridge beams on top of the floor to figure out best placement. This is needed to calculate where the support tiers below should be placed:


Next, piers are cut based on the measurements taken in the photo above. Then the task is to get everything to hold together in place before attaching them permanently. This photo below shows the support tiers held in place with C-clamps. The beams are resting on top, unattached, and resting on top of them is a small piece of scrap lauan plywood (not the bridge floor, but the same material). In this photo everything is in an approximate position, prior to measuring and adjusting:


In the next step everything is in place and level in all directions:


Now to fix the support piers in place, starting with the support pier near the middle tier tracks (on the right). This is the standard procedure of drilling pilot holes then 1/4" dry wall screws. Access is difficult, so the drill holes are at an angle but still effective. Alas, there was a slight slippage down on the right side of the pier when I was drilling the right screw hole. Rather than redo it with another drill hole I added a single plastic shim under the right end of the joist, and by raising the joist on that side the pier tops were returned to level:


For the other support pier I found it impossible to position a drill for setting up a pilot hole given the crowded surroundings. However, the rest of the structure was, at this point, very rigid. So, I took the C-clamp off, applied wood glue between the pier and the lower joist, then re-clamped and re-leveled. A few hours later it was strong enough to take the clamp off and drill a pilot hole and a single screw.

The next post will pick up with the support on the other side of the bridge.

Upper tier bridge (part 1)

The upper tier bridge construction has gone well. I ended up using several new (for me) techiques but I think in the end it's worked out.

First, the planning. I held off on coming up with a final design until I could see how the rest of the staging layout turned out. This has the advantages that 1) you can see everything in 3-D when completing the design and 2) you can employ lessons learned while constructing the rest of the layout. But, it has the disadvantage that you may have unintentionally created difficult or impossible constraints while building the rest of the layout. I tried to avoid this by thinking through the likely upper tier bridge designs as I made progress on the other tiers, and by deferring any tasks that might impede the upper tier bridge construction as long as possible. In this instance, the process worked without the disadvantages.

The first step was to build cardboard cutouts of two possible routes for the upper tier bridge track to take, as shown in this photo:

The outer route utilized an 18" radius curve (my staging minimum for curves) and thus allowed for longer straight sections. I thought the longer straight sections might ease construction and also make hand access to the switches easier since it put the bridge back as far as possible from the aisleway. The other route was shorter utilizing a 30" radius curve to connect the two end points. This route was close to the original design and had a few advantages. First, the wider radius curve would tend to help operations: long trains on the upper tier will have to go around the 18" radius loop -- about 5/8 of a circle -- then reverse direction after a 7" straight section. This shouldn't be a problem, but a wider radius further improves the chances of smooth operation. Second, the 30" radius route only crossed one switch directly, although the other switches were behind it so access to them would be slightly impeded.

What to do, what to do? (as Dana Carvey once said on SNL). Neither was an ideal solution, as both would make switch maintenance a problem. And I'm sure switches will need maintenance, even if only once per year (assuming regular track cleaning runs with the track cleaning cars). So, eventually I concluded that no route was acceptable for a fixed position bridge. The only acceptable solution was to make the bridge removable for occasional maintenance. A lot more work up front, yes, but likely to save tons of time and frustration in the long run.

So, now that I have experience using 5.2mm lauan plywood for a bridge (the middle tier bridge), I concluded the most reliable, stable design for this curved bridge is as follows:

1. The bridge would have a triangular form, allowing for straight edges on the sides. Each side would have straight edge, similar to the middle tier bridge, but taller for the additional strength the larger bridge would require.


2. The bridge would extend over the end points to allow it to be fixed in, adding stability. Both endpoints would be supported by level blocks of wood, set on end (similar principle to the spline roadbed mentioned earlier).


3. The center of the bridge would be supported by nuts and washers attached to long bolts that are anchored to the center of the middle tier.


4. I'm not sure yet on how the track connections will be set up to allow for the bridge to be removable -- this is usually the trickest part of removable track due to the lack of rail joiners to keep the rails in line -- but there are a number of methods people have used for this so I'll figure this out later.

The first step in construction was to get another 4x2 section of lauan plywood. I have some sizable scraps left, but none was big enough to cut out the whole bridge in one piece. One 4x2 sheet is just $4.24 after tax -- very reasonable.

Once bought, I put the cardboard cutouts onto the plywood for use in drawing the lines for the bridge floor:


Once cutout the bridge floor is put in place on the layout for sizing and trimming (I intentionally allowed more space than needed along some edges to permit later adjustments):


Fortunately it fit nicely with little adjustment. Next step was to build the nut/bolt/washer supports for the middle of the bridge. These are the materials and tools used:


1/4" coarse thread bolts (12" length) and bulk packages of 1/4" coarse thread nuts and washers. The saw has a blade intended for metal cutting. The two bolts shown on the right side are what is left after the cutting has been complete. The picture should also have included a metal file, which is needed to get rid of the excess metal around where the bolt is cut. Ironically, once filed the cut side of the bolt is easier to fit a nut on than the non-cut side.

Here my 13 year old son, Daniel, is busily assembling the bolt support tiers:




Meanwhile, my 8 year old daughter, Emma, is helping out by cutting insulated rail joiners:


In the next post I'll show the results of what Daniel was assembling.

Mid tier bridge complete

The mid tier bridge is now in place, track is down and wired, and testing was completed this morning, as shown in this photo:


The SD90/43MAC engine being tested in this photo has not been converted to DCC yet (a little more than half of my 50+ locos have had decoders installed). The power back being used for testing on the right is a DC power pack. I bought 2 of these packs for about $25 each in 2002 when I first got into N scale and thought I'd try DC cab control.

Now I use DCC on the layout, but the DC power packs are still useful. Being modern packs they function a lot better than the old DC power packs I'd been hauling around previously (and have since given away). In addition, you want at least one DC power pack to test new locomotives before installing a DCC decoder. And the other power pack is useful for powering accessories like lighting or switch motors/machines, unless you want to control switches with DCC.

The yellow and green wires you see running from the power pack to the track are alligator clip wires that you can get in a bundle at an electronics store. These are, IMHO, pretty much a must-have for model railroader as they are so darn useful.

Finally, some discussion about the middle tier bridge. This is a useful bridge technique if you have the need to span a long distance with minimal clearance over the level below. This is, of course, appropriate only in an off-layout area where you aren't trying to model a real bridge. The base of the bridge is thin lauan plywood that is strong enough to hold comfortably the weight of the heaviest train, and has good properties with regard to gluing and retaining screws. The width should be enough for the train and some space on either side for finger access. Too wide, however, may cause the floor to bow inwards. The sides can be made out of any stiff material that attaches easily to the floor -- typically the floor material can be used for the sides, as I've done. the sides should be cut so that the bottom will be a straight edge, because that will define the roadbed level for the bridge. The top-to-bottom width of the sides needs to be sufficient to provide enough strength to hold the trains and prevent sagging.

Support for the bridge comes primarily from the plywood at either end of the bridge. To keep the surface level a notch is cut in the 1/2" plywood so that the last inch or so of the bridge floor rests on the plywood. You can see the notch area in the picture below. In order to fix the bridge in place I first verified all was level (two thin plastic shims helped here) then used Elmer's Wood Glue, which creates a very strong bond with two pieces of wood.

This photo shows the underside of the bridge and the notch area where the right side of the bridge will rest:


When constructing the bridge I was anticipating having to use the wood glue to attach the sides to the floor, but it turned out that the wood held #4 1/2" screws very well -- these are the smallest wood screws you can get in bulk at my Home Depot.

The only real challenge was holding the side and floor in place for the drill hole and the screw. For that I found these very useful:



A small table vise, and an example of the large and small C-Clamps I use. I don't suggest these are the best available. Rather, they are what I've acquired over the years. The red-handled clamps were bought to assist with my German layout almost two decades ago. If I were buying new now I'd go to Micro-Mark, where they have a lot of very slick looking clamp and vise tools.

The next step will be to revive the CMX Track Cleaning car. At each stage so far I've cleaned tracks using the tried-and-true method of isopropyl alcohol (70%) and a paper towel, with a Bright Boy eraser only to get rid of stuff like glue drops. Once clean though, the best thing to do is to keep it clean with regular runs with a track cleaning car. So, I'm going to start that process now before the staging loops get dirty again.