SP Jawbone Branch (Part 53) - Curved Spline Sub-Roadbed for Owenyo#3

Well, I've been on a break from working on the layout for the last few months, SP Jawbone Branch (Part 52) - Curved Front for Owenyo#3.  My hand injury from last year ended up finally requiring a surgery to get things straightened out.  So now a month after the surgery, I'm getting back into the construction of the Jawbone Branch layout!

Extra 2850 West leads the Owenyo local back towards Mojave from Owenyo around 1949.

In this post, I'm covering the construction of the spline sub-roadbed of the Owenyo #3 module.  Most of the construction is fairly standard process, however this is the section I've been dreading building for 2+ years, as it will require fairly complicated transition from the level yard at Owenyo to the 1.25% down grade to the Mojave staging, plus a spiral easement into the main curve for this corner of the layout, which I've not build any curved sections for the layout yet.  In addition to all that, it will also have a terrain feature requiring me to depress the transfer trestle spur down "into" the scene, so that had to be planned into the previous construction of the basic module's structure.

CAD rendering from January 2024 for the Owenyo #3 Module.

The result of this has required me to develop several renders in my computer CAD design program to help visualize how this will both look when complete, and also how to build it, plus certain critical dimensions.

Carefully transferred measurements are taken from the CAD model to construct the module.

There were several nights of transferring and making notes, then going back to the computer to change the drawing to exactly what is being built.  Of course the room that I'm building this for isn't quite square either.... so there are some minor adjustments that had to be made, and sometimes as I'm working there's an extra 1/4" here or there gap, which will eventually be covered by the backdrop, so all I really have to do at this point is not let the fact that the module doesn't fit all the way into the corner bother me.

Once the main construction of this spline is done, I'll be pulling out this module, and putting in the scenery foam sections and cleaning up the underside of any hand-ripping rough spots or edges.  Eventually, LED lighting strip for the Mojave Staging Yard, which will be under the rear section of this module will also be installed, but thankfully I don't need to deal with the wiring for this just yet.

Building the Center of the Spline Sub-Roadbed

This early phase was mostly dry-fitting and pre-cutting the first bits of spline strips, seeing how I was going to clamp them, and be sure that I wasn't going to be in too much trouble when I opened the glue bottles and started making a mess.  So we join the construction immediately after I applied the glue to a nearly 6ft long piece of spline strip and put it against the other spline strip, which will form the two-ply central spline section.  It almost immediately became strong having the two pieces bonded and in a curved shape.  

The first pair of Masonite strips are bonded together with wood-glue and clamped.

Strips of 1/8" tempered Masonite were cut on my table saw with a fence.  The strips were then marked and notched to fit around the bracing of the module.

A scrap of 3/4" plywood formed a nice wedge to keep a proper bend in the spline near the "western" end of the module.

While still having some flex, as I added the additional splines, the whole sub-roadbed spline assembly quickly stiffened up and locked itself into the shape that I wanted it to be.  I did several times adjust the exact positioning to stay aligned to the marks that I made on the cross-beams to where the center-line should be.  I also had temporary vertical pieces clamped as 'fences' to keep the spline sprung into the right shape.  One of these temporary pieces can be seen clamped to the 3/4" plywood wall-bracket, just to the right of the splines.

Unfortunately, I only cut the notch for the diagonal cross brace on the spline, which made it very weak with about 0.888" of the nearly 2" regular height left.  So as I flexed the strips into place with the test fitting, both strips broke at this point.  The result was that I had to add 1/4" MDF splines down both sides and clamp them to keep a good curve throughout the whole sub-roadbed spline.

With the clamps removed, the eastern section of the spline, with the complicated notching over the main frame of the module.

I added a cross support about 1/2" tall to keep the front straight frame beam at the right distance from the back frame, also keeping the new spline sub-roadbed from flexing the assembly in this area.  The sub-roadbed is notched to fit around the twin 1/4" MDF frame strips.

One slight oversight at this point, is that I mounted the end-block for the joint with Module #2 too far back, along the extended centerline of the center track of the Owenyo yard, which I should have pulled it about 1/4" closer to the front edge, which would account for the spiral easement entering the curve of Module #3, but I won't really figure this out until nearly the end of the construction.

Adding the Spacers & Additional Splines

First inner spline strip being added, showing the detailed notching around the front frame structure.  Basically I made the notches to ideally just clear and be close fit to the tight edges of the spline.  This does leave some air gaps in the joint, but as the spline structure is formed, it does hold pretty well.

Through this part of the build, I'm using temporary support MDF pieces to hold the broken center splines in place at this crossbeam where the break is at.  These 1/4" strips are stiffer than the Masonite, but with multiple clamps, the natural flow of the spline can be maintained.

An additional scrap of 3/4" plywood and 1/4" MDF shim are used to keep the center spline in the correct curved form between these two braces.

The first strip of the inner spline stops in the middle of the curve, between the front frame and the diagonal cross-brace.  I made longer spacer blocks to secure the shorter spline strips to, forming lapped splice joints.

I bonded in a longer space block, which extended down, below the notched section of the spline, to lock into the back corner of the front frame structure.

Back over at the left end of the module, the extra spline strips are coming together with extra temporary space blocks keeping everything in place.  A spare track-cleaning slider pad was used as a space-holder for the 2nd outer spline strip in the end-block at the top-left of the photo.  Also note the use of the heavy clamp under the end-plates to hold the spline at the correct height.  I should have placed some kitchen wrapping plastic over it before gluing this joint, as it make a mess later!

Temporary spacer blocks were placed between the main Masonite splines to support them while heavy clamping was done to bond the spline-strips were being fitted with wood-glue.

Reverse angle view of the tab at the front frame cross-over notch of the spline.

The spreader block at the front frame cross-over notch was extended down behind the frame cross-brace joint.  Eventually the laminating of the sub-roadbed spline glue worked its way down into this joint, and bonded the sub-roadbed to the main frame.  After the construction is completed, these joints would be back-filled with some expanding poly-urethane Gorilla Glue when I could flip the whole module upside down and before the foam scenery base would be installed.

Lapping of the joints in the splines was required, as I only had a couple of 8ft long strips, and in some ways shorter sections were easier to measure and notch around the cross-braces.

This area is where the original two splines broke, so very long MDF sister spacers were used to keep the curve consistent through this part of the spline.  They required multiple clamps to keep the bonding area tight until all the glue dried.

The "right" or western end-plate joint fitted with the spline strips.  Foaming of the Gorilla Glue is again showing itself after the joint dried for a day.

Clamping of the sub-roadbed spline at each spreader-block.  Several of these spreader blocks were glued in place with the Gorilla Glue to have better "grab" over smaller cross sections.  I also improved the bonding area by scratching up the smooth Masonite strips with a hard steel tool before applying the glue.

A view of the underside of the spline sub-roadbed.  Some glue-drips squeeze out the bottom and were caught on paper-towels.  Most I was able to catch with a glue-spreading strip of styrene before they became too hard.  Any remaining sharp bits will be knocked down with the orbital sander when I turn the finished module over at the end of construction.

Central two splines with spacer blocks and first of outer spline strips installed.  Note that the tops of the frame and cross-braces are kept to the same level, which will be used to support the future transfer trestle roadbed sheet.  I purposely made this offset at least 1/4" lower than needed, so that I can shim it up later as I decided exactly how low the trestle roadbed floor should be compared to the main track on the spline.  The sheet of MDF in the background is just a loose scrap of the original sheet that I cut the main line roadbed and trestle roadbed out from.

Note that the spline was allowed to stick above the module-end frames, which would allow for the future shaving down of the top surface of the sub-roadbed spline to form the vertical curve from the level Owenyo modules to the 1.25% down-grade starting in the middle of the #3 module, and will extend all the way around the layout (to the right) down to the Mojave staging yard.

The western end of the #3 Module spline joint with the notches in the end-block.  This joint eventually was just filled with wood-glue to fix it in place.

Completed splines with six strips in thee pairs and spacers between them.

Gorilla Glue expanded foam-glue can be seen at the diagonal cross-brace in the above photo, filling the notches of the spline and joining the two pieces together.

In Closing

While these photos showing flex track and equipment simulating future operations are actually just mock-ups of what I expect things to look like when construction is completed.  Basically I want to visualize the grade separation of the trestle spur and how much shimming it will need before construction proceeds too much further.

Another view of the Extra 2850 East arriving at Owenyo, passing the trestle.

In the next steps, I'll show what prototype photos I have that show how the land-form will need to fit around this area.  There's a large amount of selective compression going on in this corner, and I'm just going to have to live with the "feeling" of the place, and work around the space issues as best I can.

Jason Hill

Related Articles:

Jawbone Branch Layout Build Index - See all postings in this series from this linked page.

SP Jawbone Branch (Part 52) - Curved Front for Owenyo#3 - Previous post in the series