Truck Arch Bar Supports

Nelson Riedel,
11/04/2012, last updated 11/10/2012


Cast Arch Bar Supports:

The arch bar supports are the posts on each side of the spring planks as shown in the photos above.   Ken McCauleys castings have a brake hanger mounting on the inside  near the bottom that I cut off.   Because of the hanger mounting there are two castings, a left and a right.      


The details of one of the castings is shown in the drawing above.  As noted, the brake hanger mounting was cut off.   The first step in machining the castings was to mill the 1/2" wide slot  in the bottom to a depth such that the bottom of the slot is even with the bottom of the tabs on each side.   The next step was to machine the slot in the top to a depth so to the distance between the bottom of the upper and lower slot is 2 1/8".   The hole for the 6-32 rod was drilled next.  It is difficult to drill a straight hole that deep.  I chose to drill a 1/8" hole half way from each end.   There is usually an offset where the two holes meet.  I then run the 0.14" drill through from one end -- that smoothes most the offset.   The last step is to drill 1/8" holes in the tabs for the screws that attach the supports to the lower spring plank.   There are dimples in the castings at the approximate location on the drawing.

New Arch Bar Support  Casting:   After several trucks were fabricated using castings some though was given to adding brakes.   One of the biggest challenges with brakes is to provide a place to secure the brake hanger.  Ken made some new castings shown on the right with a tab near the top.  The tab can be drilled and tapped 6-32  for a screw to attach to the brake hanger.    I haven't used these new  castings on a truck yet but the plan is to use them on all future trucks.



 Fabricated Arch Bar Supports:

The first arch bar supports fabricated were merely 1/4" X 1/2" bars with 1/4'' X 1/8" half round slots.   The half round slots were made by gripping two 1/4" X 1/2" bars in the lathe 4 jaw chuck and drilling a 1/4" hole end to end.  The bars were then attached to the lower spring plank with a FH screw and tack welded along the inner side.   The supports are held in position by 1/4"  round bars with a 6-32 clearance hole drilled lengthwise.     Three pair of trucks were made with these supports and they worked quite well.        If I was to fabricate additional supports I'd use the design below.

The arch bar support in drawing above is similar to the arch bar supports on the disconnected log trucks.  The bar is made up of the 4 steel pieces:  a 2 1/8" length of 1/4" X 1/2" steel bar, a 2 1/8" length of 3/8" diameter steel bar, a 3/4" length  of 1/4" diameter steel rod and a 1 9/16" length of 3/32" X 3/8" bar stock. 

The first step in the machining is to mount a pair of the 1/4"X 1/2" bars in the lathe 4 jaw chuck or 1/2" square collet.    A 3/8" hole is then drilled lengthwise through the pair of bars.   Next, a 0.14" hole is drilled lengthwise trhough the 3/8" diameter rod and the rod is then silver soldered in the slot in one of the bars.    A 3/8" wide X 3/32" deep slot is milled in the lower part of the bar for the tab bar.   The tab bar is secured to the slot with a 4-40 FH screw.     The 1/4" rod is drilled and threaded 6-32.    A flat bottom 1/4" hole  is drilled in the side of the rod-bar combination at the location for the 1/4" rod.  A ~1/8" deep hole is then drilled and threaded 6-32 in the center of the flat bottom hole.   A ~ 3/8" 6-32 stud is threaded into that hole.   The 1/4" rod is threaded onto the end of the stud.  The whole assembly is heated again and silver solder added to secure the tab bar and 1/4" rod.   



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