Sunday, August 13, 2023

Why We Machine

 I was attempting to get the license plate installed, and realized that the paint shop didn't get the bumper cover in the right place.  There was a full 5/8" between the cover and the brace that the plates attach to, and I honestly think the paint shop lost a part that was there to make up the difference.  Alas, it didn't matter, and I could not find official parts that would fit.

While the average mechanic would slap a bunch of washers in there (a farm boy would grab the duct tape and bailing wire), I didn't want things to come loose and fall off if the plates were ever changed.  Plus, the holes for bracket were at the wrong places, so, it was time to make a bracket.

I grabbed some 3/8" aluminum bar stock, and some 1/8" think bar stock.  On one side, I measured 0.680" (less, of course, the thickness of the bumper cover, bringing that one down to 0.610"), and the other side was 0.645, bringing that measurement down to 0.575"), so with the 1/2" of bar stock (and mill scale), I had to make up the difference in shim stock because I didn't want to break out the mill.

With the 3/8" bar stock, I drilled a 1/4" hole to match the thread, and then needed a 1/4"-20 transfer screw for the other side - which I didn't have [sigh].  But, I did have a 1/4"-20 threaded rod.  I chucked it up in a collet, put a 120 degree chamfer on one end and parted it off, and used an angle grinder (precision!) to put a gap on each side.  This gave me a makeshift transfer screw that only needed to be used once.

I threaded it in with my long, narrow needle-nosed pliers, threaded the other end of the block, and gave it a whack.  Then I could drill out to cover that bolt.  That longer, 3/8" bar stock could then get installed temporarily while figuring out the license plate position, and marking those holes.

Once those were laid out, I used two pieces of the 1/8" bar stock and marked through holes and put in #6-32 holes to lock those pieces together, and then simply made brass shims to make up the difference in depth (0.070" on one end, and 0.110" on the other), and then locked the shims, 3/8" bar stock, and 1/8" bar stock into one longer piece.  The machinist in me cried that I didn't break out my mill to get a good finish and get the whole thing within +/-0.002", while the mechanic in me kept complaining that shooting for +/- 0.010" was too much accuracy.  Turns out, I hit -0.003" and that was satisfactory, even if the finish wasn't satisfactory.

A quick install, and the plate is ready, save the bottom bracket (still waiting on real, reproduction parts).

Viola!  I had the plate installed, for the first time in 18 years!  And all because I had the tools to make tools to make a brace that I could not find!  I am wondering if I need to go with brass socket head screws and a brass frame to bring out that gold metallic paint.