Figure 2: Throwbar mechanism attached to a Tortoise switch machine. The moving parts are shaded. Both the throwbar and fulcrum can be adjusted by sliding along the rails that are moulded into the Tortoise's shell.
of plastic provides electrical isolation between the points. This isolation is necessary because each point is electrically connected to its adjacent stock rail. However, the plastic tube that was available (Evergreen) is not especially robust. Consequently, the posts actually pass through 3/32" inside diameter brass tube that is cemented into holes in the throw bar. These tubes are approximately 30 mm long, which allows an even stiffer connection to the points.
Now because the posts are filed by hand, we don't know how far apart they need to be when they connect with the throw bar. We could hold the points in a correct position, and then attempt to measure the distance, however, this procedure is error-prone as the points can twist giving inaccurate measurements.
I decided it was best to make the throw bar's length adjustable. The throw bar was cut in two parts and joined by a section of telescoping styrene tube. To obtain the correct switch throw, the two halves of this assembly were threaded onto their respective posts, and with the points held the correct distance apart, the halves were then glued. The throw bar was then removed once the glue has set hard.
The throw bar slides in a pair of guides made again from telescoping styrene tube. These guides need to be mounted beneath the roadbed accurately to throw the switch properly. As I was already mounting the switch motor accurately beneath the roadbed, I decided it was easiest to simply mount the guides on the Tortoise.
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Fortunately, the Tortoise comes with those handy rails for adjusting the fulcrum. To mount the guides, I simply copied the part of the fulcrum that slides between these rails, and mounted my guides to the copy (See Figure 2). Note the throw bar needs to be inserted into the guides before they are fixed to their base! Do not glue the throw bar to the Tortoise as it is useful to be able to slide it off. With the throw bar attached to the Tortoise, it seemed logical to install the Tortoise and test the operational aspect of this mechanism. To do this, I slid the throw bar onto the Tortoise, and then threaded the posts back through the throw bar. With the throw bar in the middle of its travel between the two guides, and the switch in the middle of its throw, the Tortoise was in perfect position. Moving the throw bar back and forth ensured the points closed properly before I screwed the Tortoise home. Figure 4 shows an exploded view of the entire assembly, and here we can see that the fulcrum needs to slide onto the rails next. However, as it comes from the manufacturer, the fulcrum is too wide and interferes with the posts. Fortunately it is easily fixed by sawing away the offending parts. The throw bar also needs a hole for the switch throw wire. To locate this hole, I slid the fulcrum up against the throw bar, and moved the switch to the middle of its travel. The position of the middle hole of the fulcrum could then be marked on the throw bar. Next I removed both the throwbar and the fulcrum from the Tortoise, and drilled the hole for the switch throw wire. This wire is formed exactly as specified in the directions for the Tortoise, except that it is naturally shorter as it no longer needs to reach through the roadbed. With the throwbar and fulrum installed once more, 
Figure 4: Exploded view of throwbar and switch stand mechanisms. |
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