Sunday, February 21, 2021

SP Jawbone Branch (Part 12) - Cutting Time

Here we go!  Time to make chips.... errr, sawdust.

Freshly cut materials for the Jawbone Branch!

I've started cutting apart the skin sheets which will form the top of the Owenyo sections of the layout.  The 2x4's under the layout here are providing a good flat surface to prepare the assembly of the sections on.  I maybe able to clear some of my longer workbench under Mojave Yard for the construction phase, but I'm not counting on it.


Designing the under structure for the layout started with the underside of Owenyo #2 module because it is one of the simplest of the layout's sections.  The main challenge is that with my designed 1.5% grade, the lower level staging yard of Mojave is only ~5.5" rail-to-rail below Owenyo.  I may be able to squeeze a tad more, but I'm leaving that to work out as I assemble the layout.

As with many aspects of this design, I'm including these little 'gifts' of 1/4" here and there to allow for slightly more space in case something has to move, or doesn't work out exactly as I measured for the CAD model.  For example when I had to change the wye from 24" radius to 26" radius, the west (south) switch had to move several inches.  Better to plan for some slight changes to happen during construction, than to plan yourself into a corner where you must make it work *exactly* as planned. "This track has to be exactly here.  Because it needs to go through this hole, and there's only 0.025" clearance for a cabforward's overhanging running board and cylinder next to this support column for the roof of the building... and don't forget we have to get over this reversing loop, but under that helix!"

Owenyo #2 section - Underside with bracing. - Feb 7, 2021 Design

The skin of the layout is made from the 1/4" MDF material.  The sides of the frame are also made from 1/4" MDF as well, cut to 1-3/4" wide strips.  I may laminate the long sides to 1/2" thickness if I decide it needs the strength.  The end plates are made from 1/2" solid MDF.  I'll be putting some alignment pins into the end plates later.

The middle braces and diagonals are also 1/4" MDF.  The complicated part comes from the need to scallop out the center sections where I'll prefer not catching my hand while reaching into the staging yard.

Owenyo Yard & Mojave Staging Yard with brackets. Feb 7, 2021 Design

Yes, I actually don't do everything in CAD!  This is a quick photo from my notebook where I was doodling ideas for the structural supports of Mojave and Owenyo.  The main concept here is not trusting the MDF to hold in a cantilevered condition.  The use of a simple angle bracket system isn't really an option with the Mojave Yard directly below the upper level.

The lower level will use some form of bracket to support the outer support arms up to the outer edge of Owenyo.  These vertical supports will come in directly under the support nodes of the upper benchwork, which should be strong enough to take the focused vertical weight bearing.  I want to be able to remove any sections of the layout to do work on if needed, so this design is reflecting that concept as well.

Bolts from the lower level into the wall support system probably will be a good idea to ensure that the whole thing doesn't come loose!  We also installed several inches of foam insulation and drywalled the interior, so each of the brackets will need to have a long connection into the fairly small horizontal studs to be secure.

Backdrop will be made from 1/8" Masonite, if I build the brackets after the fashion sketched out above, then I should be able to have the backdrop panel slip behind the Owenyo modules.

Owenyo #1 section - Underside with bracing.

The Owenyo #1 section is going to be a bit more complicated as it will need to support the cantilevered wye tail.  The overhanging section of the center wye area will be supported by a pair of diagonal 1/2" thick solid MDF.  The hole will be for a section of 3/4" plywood which should be strong enough to support the wye tail.  Again alignment pins and clamps will keep the wye tail in place and prevent it twisting.

The East (north) end of the #1 Owenyo panel.

The underside of the layout is marked up from an old version of my track plan that I transferred over to the MDF.  The updated version of the track plan, after some photo scaling and historic photo research is on the other side.  These lines show the shape of the structure which will be supporting this section.

The north side of the wye, center of Owenyo #1 panel.

The shot above and below show the sun-burst radial arms which will support the 23" deep base of the wye.  I could have gone with a square support system, but the triangular design will provide more twist and sheer strength.  I want to have 'strong points' where the weight of the section will be transferred to because the supports will be coming up from below or hung off the wall.

The west leg of the wye from the bottom.  To the left will be section #2.

Note in the photo above the slight change of angle in the over hanging section, which now aligns with the structural node point to the left.  I'll probably double-up this module's longitudinal frame pieces so that I can have these diagonal joints actually notch into the main frame.

I plan to assemble the structural frame for each module and get the sections mounted to the bracket system before working on mounting the track and switches.  Trying to get the track alignment within 0.5mm with the modules apart, and then trying to get it to fit is not something I'd look forward to doing.  I'll prefer to have the track in alignment and secured in place before I take the sections apart.  I plan at most joints to have rail joints already planned to be at those locations.  Most of them will be able to have rail joiners slipped in to or out of place if a section needs to be lifted out without separating it longitudinally first.

Another Pair of Plan Changes

Bookcase located under the East end of Owenyo. - Feb 2021

One last thing that I realized while I was going over the space in the shop was that the book case on the desk under the north tail of the wye has to stay about 2-3" away from the wall because there's a plug on the wall at that location.  This pushes the bookcase into the area which I planned to have for the curve between Mojave Yard and the east bridge across the doorway.

There are two options; I could simply account for the moved bookcase and shorten the bridge section a couple of inches.  However, I do have another location that I could put the bookcase in under Bartlett, which I think will be a better option.  I can still put in a custom upper case over the work table/desk custom fit around the layout's shape.

During this time, I also was looking more closely at the 60" height of the layout at Owenyo.  The bookcase under the #1 Owenyo section's top is 58.5".  Would the layout height really work for my height, reaching over it to work the switching moves, rerailing, etc.  This really dictates a layout height of 60-61".  If I do move and replace the bookcase, then I can lower the height of the layout to ~57", which makes the operations much better.  The new limiting factors become the distance to from the underside of the Mojave Staging Yard to the work bench below it, as well as the cabinet and the Lathe under Little Lake.

Mojave Staging Sections

Mojave Staging Yard, west end, the opposite end of the branch from Owenyo.

I decided to place some cars on the staging yard to double check track length.  This photo at the west end, showing the run-around crossover.  I may end up moving the crossover east a bit more than an engine length.  The run-around works out to about 22 cars long, which is well over my planned maximum train length that I expect to be able to pull up the 1.5% grade to Owenyo.

The Mojave Staging Yard height I believe can drop to 51", giving 6" rail-head to rail-head now, which should help the access into the staging.

Mojave Staging Yard, middle of the west section

I figure that the front track will be kept open as running track.  The next track is the A/D track for the Owenyo Local and any other cuts that need to be run around.  Tracks 3,4, and 5 are planned to be single-ended staging for storage 'off the active layout' or pre-staged trains ready to go onto the branch.

Mojave Staging toward the middle of the yard, west section.

Each of the rear tracks (3, 4, & 5) will end up being around 15-16ft long, at least thirty 40ft cars long (about 45ft coupled).  Note that SP in their time tables always calculated their sidings at 49ft per car during the 1940-1955 era, The lengths also included 120ft for an engine and caboose on sidings where meets would happen.

Originally my track plan called for only four tracks in the staging yard.  As I was finishing up the staging yard design in the last two weeks, I decided that it wouldn't be any more trouble to include another staging track in the yard, as I increased the width of the Owenyo Yard at the front edge for photographing.

In Closing

I'm going to close this post here, because I've been working on more research and layout construction, which will need their own posts.

Jason Hill

Related Articles:

SP Jawbone Branch (Part 2) - Researching and Changing of the Plan

SP Jawbone Branch (Part 3) - Consists and More Bartlett Research

SP Jawbone Branch (Part 4) - Freight Car Roster

SP Jawbone Branch (Part 5) - Pulling the Trigger (Buying the materials for the benchwork)

SP Jawbone Branch (Part 6) - Q&A Continuing Design Tweaks - Working out the logistics for the staging yards other details.

SP Jawbone Branch (Part 7) - Film & Construction Begins - Historic movie film clip of Owenyo Local and starting construction of the layout.

SP Jawbone Branch (Part 8) - Little Lake Grows - More research materials have surfaced for my modeling of Little Lake.

SP Jawbone Branch (Part 9) - Layout Material Changes - Shifting to MDF for the roadbed and moving the foam to secondary scenery uses.

SP Jawbone Branch (Part 10) - Track Plan Details of Owenyo - A deeper dive into the buildings and track arrangements.

Freight Symbols Over Tehachapi - Part 4 - SP Locals - Tehachapi Pass's SP Local Freights, several of which work out of Mojave.

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