Wednesday, April 28, 2021

SP Jawbone Branch (Part 25) - Wye? - Because

I'm moving the focus of this post back to the construction of the layout itself.  Specifically the wye at Owenyo.  The original plan to drop any concept of a continuous running option results in my absolute requirement to have a working wye at the end of the branch to turn the C-class and Mk-class local engines.

The placement of my station of Owenyo was dictated by the arrangement of the wye in town.  This forced the design of my layout to put Owenyo in either the SE or NW corner of the room.  Because of the bookcases along the north wall, that option was out.  The SE corner was open and the wye could fit between the large desk in the middle of the room and the east wall. 

The new top skin of 1/4" MDF applied to the top of the wye.

Still with the need to keep the shop functional and the options to bring large pieces of material into the work area west of the large desk, I needed to make the wye removable.  Because the layout already needed to have two removable sections for the doors, what's one more removable piece?  For that matter, I just made all the sections of the layout able to be quickly dismantled, if needed.


Some of these photos have been posted before in the Owenyo #1 structural posts, but they are worth touching on again here, as this is the foundation for the wye structure.

Underside of the Owenyo #1 module, with Wye "Keel Spar" in place.

The Owenyo #1 (East) module will support the tail of the wye as a cantilever, so there's much more support built into the underside of this yard module.

Overview of the bottom of the wye support structure.

Basically all the structural load for the wye tail will be handled by this box structure and an 3/4" x 2" oak "Keel-Spar" forming the structure of the wye module.

The cantilever Keel Spar in place.

The Spar extends out from the far side of the layout about 40".  I tested the spar several times at this point to be sure that it could be easily slipped into the Owenyo #1 module and then back out again.  It is still a good tight fit, requiring both hands; one inside the staging yard and one outside under about where the wye switch will go.  I'm happy with the fit, last thing I want is a loose wye module dropping a brass Mk on the floor!

The End Plate with notch for the Keel Spar mocked up.

Additional MDF support will be added around the edges to support the 1/4" MDF top skin sheet of the wye.

Mock-up of the Keel Spar and the End Plate clamped in place.

This shot gives an idea how long the wye tail will be.  Most recently I have also added a removable 'leg' under the front of the layout, which helps support it.  I may stay with this method, or consider an additional diagonal brace down to the wall brackets to support the very front edge of the box structure. 

During construction of the wye and the switch and track spiking on the wye tail, I had a pair of 2x2s clamped together, forming a support the right height to put under the tail of the wye.  I'd rather not need something like this under the tail permanently, but it is always an option.  Alternately, I could build a folding brace to form a triangle, reaching down to the workbench.  Hinged maybe 1/3rd of the way in from the end of the tail and with a scissor brace locking over-center at the workbench end.  There are plenty of options to add that little bit of extra support.

Spanning the Joint

East curved portion of the wye, the oil tank and engine layover spot are in this area.

I planned to leave out some of the ties across the module joint to the wye.  These locations will be replaced with wood ties, and spiked in place.

Laying out the equilateral wye switch.

Roughing out the flex track coming out of the 26" radius curve.  I reworked the geometery and found that for the No.5 frog, I needed to maintain the 26" radius into the frog, then allow all of the easement between the frog and the headblock of the switch.  It turns out that I had the frog a bit too close to the main line at Owenyo.

After the fact engineering of a No.5 frog on a wye switch.

It turns out that doing the CAD calculations for the placement of the No.5 DTW frog, it should be 2-1/16" from the point of tangent (PT) of the two curves.  The 5-1/2" (40 scale feet) is the length of easement and transition to the headblock of the switch.  This headblock placement could be farther, maybe up to 45ft from the point of frog (PF).

Reworked switch with all ties installed.

I needed to move the frog about 0.300" towards the headblock to get the geometry to work out.  One can see the number of PF's that have been marked from various methods, including offsets from the spiral easements, which aren't needed on a No.5 alignment!

Wye Tail being built from second hand tie sections, threaded on to the tail of the wye.

The wye tail I made from left over flex track tie sections from thinning the tie spacing in the two sidings at Owenyo.  The piece of oak flooring, which makes up the Keel Spar allows for nearly 19" of wye tail.  As there's no other obstruction in the middle of the room, I decided to just lay the extra 5" of track beyond the 14" needed for the Mk-2/4 and -6 class 2-8-2s.

Completed wye tail flex track and wye switch roughed in.

The extreme end of the wye tails often are pretty ratty.  Usually operationally the engines are kept towards the switch end of the tail, with the tender or other cars pushed out onto the 'rickety' wye tail trackage.  I decided to simulate this with increasing tie spacings towards the end of the wye, and tighter spacing for the engine length (about 50ft) closest to the switch headblock.

Cutting the Tail Loose

Pre-stained 8ft ties are glued and slipped under the rails at the module joint.

I hand spiked each wood tie at the joint.  I'll probably end up removing at least one more plastic tie on each side of the joint and getting a little more hand-spiking in to secure both rails on each side.

Close-up of the cut rails on the 26"R curve.

I've tested the wye's 26"R curve with the SP 3203, which seems to be the most finicky of the Mk-series of models when it comes to minimum curve radius.

Separating the wye tail module from Owenyo #1 module.

Good to see that the module slips apart easily.  The long Keel-Spar still holds it in place vertically.  To keep the wye tail from rolling on the Keel-Spar's axis, I drilled 1/4" holes, like I have between the other modules, to accept the alignment pins.

In Closing

Nearly completed wye being held rotationally by the clamps as 3203 is test run on the main.

I probably will still need to do a little fine tuning on the 26" radius curves to get them smooth and consistent and a little more tuning on the module joints in the middle of the curves.

The wiring for the wye will be a fun challenge.  I'm also looking forward to building in some safety interlocks to keep any engines from diving off the ends of the wye when the tail is removed!  I'll get into covering those points in an upcoming post.

Jason Hill

Related Articles:

SP "Jawbone" Branch Index Page - Links to all my blog posts on my new Jawbone Branch layout.

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