Gauge 1 Model Railroad Radius 600mm Switches

Here are left and righthand track switches with spring-loaded manually switched positions.  These are for use with the Hume track system.  See https://www.printables.com/model/902291-snap-together-gauge-1-model-railroad-track

for the parent project.   These are 600mm radius switches with 30 degrees of curvature for 4 ft diameter track circles.  The straight portions are 300mm long.

Print the switch bodies with support under the bare rail portions.  Print the mechanism parts using Random Seam alignment, and supports as seen in the project file.  As necessary, use a fine file (Riffler or Swiss-pattern file) to smooth parts that slide across each other.

Improve the fit of the holes of the mechanism parts by drilling them out.  I used a 0.157in diameter drill on the lever parts,  and then a 0.302in diameter hole on the switch arm parts.  A 0.101in diameter drill can be used to open up the pass-through holes for the clearance of #3-48 screws.

I used hex head ¼" #3-48 hex head screws to attach the rails and the switch to the track (quantity 4 per switch).  Also a #3-48 round head ¼" screw to attach the rails at the pivot to the track body.  A metric user can use 2.5mm screws.

To attach the switch mechanism box to the track body, first drill out the holes in the ties (sleepers) to the tap drill size (0.070in diameter for ANSI #3-48).  Put a clamp across the tie near the hole before tapping so the force of the tapping does not cause separation of the printed layers.  I used a chip-clearing #3-48 tap for through holes (aka gun tap) which pushes the cut material forward through the hole.  Gently but steadily push the tap into the hole as you turn the tap to cut helical threads.  The rail attachment piece can be tapped more easily without clamping or pre-drilling.

The switch mechanism box top is attached with a ¼" flathead #2-56 screw.  When tapping the blind hole, use a bottoming tap, and unscrew it at least three times while tapping to remove the cut material.   A metric user can use 2.2mm screws.  A self-threading screw for plastic would work well.

It takes adult patience and strength to wind the springs using needle nose pliers and diagonal side cutters.  Wear eye protection.

I used 0.022in diameter hard stainless steel spring wire ordered from McMaster-Carr as P/N 9495K66.  I would not go smaller than 0.018in or larger than 0.022in diameter.

Use the spring bending jig held in a vise to have both hands free.  Bend the spring well beyond the desired angles so that it comes back to the desired angle when released.  As seen in the screenshot sketch and photo, start with a sharp 90 degree bend trapped in the square posts.  Wind 1-½ turns counter-clockwise on the bottom post.  Make an angled bend back through the square posts, and two counter-clockwise turns on the middle post.  Finish with 1-½ turns clockwise on the distant top post.  After bending use pliers to try to get the spring to be as close to laying in one plane as you can.  The jig will break after a few uses if you are doing things correctly with enough force for tight turns.  Just print another one, or make one using steel 2.8mm diameter drill rod.  After some practice, you can expect satisfying switching action.

For assembly refer to the photo.  The bent leg of the spring is attached to the shorter arm.  The reach arm part is reversible if the peg end ever breaks off.

The moving rails model was replaced on 6/5/24 with a newer version that addressed cosmetic flaws of the first version.