Monday, July 8, 2013


As track laying forges ahead (currently in Eugene), I still have tasks remaining with earlier work.  I recently completed installing the manual switch linkages for Springfield—28 switches.  I use Blue Point  switch machines to throw the switches and provide sets of contacts for frog polarity and an auxiliary set.  The auxiliary set will be used with the signal system for a number of these switches.  The Blue Point switch machine essentially is a double pole-double throw switch with mechanical hardware providing for switch throws.

Blue Point sells bulk packs of the switch machine—a boon to a large operation such as mine.  They also sell connection hardware kits that include a mounting bracket, a connecting clevis for the machine and a knob, all intended to be used with a flexible tube system similar to a choke cable. 

Instead of the choke cable system, I discovered I could make a more direct linkage.  As illustrated in the photo, my system uses a small screw eye, threaded rod, a brass tube bushing and a standard cabinet knob.  Most cabinet knobs use a #8-32 thread, so that sets the threaded rod size.  The bushing is a piece of ¼” brass tube, which keeps the threaded rod from hanging up on the fascia and backing wood.  The screw eye is the small (1/2”) piece from Ace Hardware.  I found the #8-32 rod threaded into this eye easily, whereas a similar sized screw eye from True Value Hardware was too tight.  If I had an #8-32 tap, I probably could make the True Value part work.  I add a nut on the threaded rod to screw up against the Blue Point throw arm, which provides a bit of compression force relief for the screw eye. 

 Switch Linkage for Blue Point Switch Machine.

I chose to mount my manual throws such that the knobs have some relief into the fascia.  This resulted in the fascia mounting being about an inch lower than the mounting on the Blue Point machine.  I had to fashion offset height throw mountings for a pair of machines very close to the aisle in Springfield.  I have a similar issue for the wye switch at Oakridge.  For Oakridge, I’ll do without the fascia relief hole and mount the throw rod and knob at the depth below track of the Blue Point throw bar.

I have a “Plan B” for the throw bar mount to replace the screw eye, should I start suffering failures.  My back-up plan involves homemade clevises for the threaded rod to throw bar connection.  Until that time, I am happy with this simple, direct, linkage.

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