A small detail that can be added to the M4 suspension bogies are the open bolt holes on the front of the bogie bracket. For maximum effect, the hole pattern should be a perfect rectangle and consistent from one bogie to the next. The easiest way to do this is with a simple jig. I fabricated my jig from .010” brass. Cut a strip of brass that is at least as wide as the front face of the bracket and long enough to extend over the face and top after it is bent, Fig. 1. The location of the bend is determined by the vertical dimension of the bracket face, Fig. 2. You do not want this side of the jig to be so long that it blocks the view of the centerline on the bracket.
Transfer this dimension to the brass, Fig. 3. Carefully bend the brass at the location of your mark, Fig. 4. I used a vise and a small steel bar to make this bend.
I don’t have access to an actual bogie so I laid out a pattern of the holes that looked about right, Fig. 5. This first dimension that needs to be transferred to the jig is the distance from the top of the bracket to the first row of holes, Fig. 6.
This dimension needs to be transferred to the front surface of the jig. This means that you need to add the thickness of the jig material (in this case .010”) to the dimension from the previous step. I held the jig against a flat surface and marked the dimension using calipers, Fig. 7. This method is more accurate because the calipers can be held parallel to the surface. Transfer the dimension for the bottom row of holes the same way. Next establish a centerline by measuring from each side of the jig, Fig. 8.
I suggest marking this centerline using a square against the top surface so that you minimize any error that might have been built in with a less-than square bend, Fig 9. Measure out an equal distance from the centerline and mark with a square as in the previous step to establish the center of the holes.
The drawing gives the layout of the jig that I created. Measurements are in decimal inches.
Finally, drill the holes in the jig. I used a #76 (.020) drill. While I laid out the general arrangement as indicated above, I admit that I used my miniature mill/drill press to do the final spacing and drilling of the holes, Fig. 10. When using the jig, line up the centerline of the jig with the centerline of the bogie bracket, Fig. 11.
