Accucraft Truck Ball Bearing Upgrade

[Jim Kottkamp]

The least expensive way to have ball bearings on your Accucraft 1:20.3 trucks is to install them yourself (this will work on most trucks, the dimensions will just differ).  DO NOT BOTHER to install ball bearings in Accucraft Trucks until after you have first added internal braces to keep the truck side frames perpendicular to the truck bolster (see my blog on "Improving the Rolling Capabilities of Older Accucraft Trucks").  With no side internal braces, the truck side frames will pinch the bearings and reduce their efficiency.

The most difficult part is making a jig to evenly support the truck frame during milling.  If the truck frame is not properly supported the frame will break or shatter during milling.  My support frame is 3 pieces of 1/8th inch thick brass(first photo); the base is 1 X 5 inches, and the two upright supports are 3/8ths X 2 ¾  inches long.  The 2 uprights are silver soldered onto the base 9/16th inch distance between center surfaces.  The centers of the 2 uprights will have 1/16th inch milled away for a length of ¾ inch on the inside surfaces.  This will allow the top and bottom of the truck bolster to drop down inside the center of the supports.  I also had to remove 1/64th inch of material for a length of 7/16ths inch at the ends of the uprights to accommodate the journal ends.  The objective is to get the truck to fit snugly in place with the entire tuck frame resting evenly on top of the upright supports (second photo).

Once the jig is completed, the rest is really pretty simple (these instructions are for 3mm Flange-less ball bearings from "Great Big Trains" in Aurora, CO ).  Locate the center of the bronze bearing by inserting a 5/32 in drill bit (upside down) in the chuck of your drill press, or milling machine.  With the drill bit in the bearing hole clamp the jig and the truck down as shown in the third photo.  I used a ¼ inch; 4 flute, end mill to drill out the excess bearing to a depth of .090 inches (3/32 inch).  Mill slowly and use a cutting oil to keep the bronze bearing from breaking loose from the casting and spinning.  A drill bit will not work...it will over-torque the bearing and cause it to spin inside the casting.  The ¾ inch mill is a little bit bigger than the size of the bearing, but this "slop" allows the bearing to stay aligned when the axles move up and down on uneven track (third photo).

If you mill too deeply, you can insert a 5/32 inch plastic washer between the outside wheel and the truck side frame.  Just be sure if you need one washer, you install it on the same side on both axles to keep the truck from going out of alignment (it needs to be perpendicular to straight rail).  Some bronze bearings will spin in the casting.  I use a center punch to put one, or two small dimples in the inner wall of the bearing to keep it from spinning.

Re-assemble your trucks and you will have a car that moves effortlessly!