2014.11.20 - UPDATE! - !!! WHITE WHEELS & HUBCAPS RETURN...!!!
Took a small break from the rear tubing exercise to take advantage of an offer for some free CNC time from a local friend of mine.
I'd been thinking about the best way to fit an undersized 16.5" wheel center into the 17" hoops that I bought, and decided to just experiment a little bit and see where it took me.
The first order of business was to prep the wheel center. Each of the 4 mounting flanges had 3 through-holes for the factory rivets. I decided to weld those up solid and then redrill them from the rim-side later on. Trying to get a drill on the inside of the finished & assembled wheel would be a nightmare anyway.
Then I decided that instead of trying to hand-fit a thin shim of steel between the centers and the hoop, I'd try building up the flanges with my MIG welder. I only needed about .040" of an inch so it seemed like a simple enough idea......
But it wasn't:
It took FOREVER to get a setting that worked and didn't just pour a bunch of unnecessary heat into the flanges. Obviously, I pulled the trigger about ONE TRILLION TIMES to get all those tack welds on there.
After a couple of hours I had all 4 sides completed.
Last night, I took the parts over to my friends shop and he set up the parts to do a nice match-fitting of the center to the hoop.
I've never spent any time in a machine shop, and it was REALLY cool to see how the CNC was "indexed" to the part to set the "X' and "Y" axis dimensions and just how simple it was to ask it for a circle program to then cut material away. We did a lot of checking and double-checking and took VERY small bites out of the material to confirm everything was working right. As it turned out, the hoops were actually quite good dimensionally right from the vendor, so we only removed a few thousandths from the mounting surface and ended up with a perfect landing spot for the wheel center.
The wheel center ended up being a bit of a disappointment. Although the welding didn't distort the part, the welds themselves were really inconsistent in their depth and spacing... so even after we trimmed it down (to leave a 0.005" interference fit with the hoop) there were still a LOT of craters and voids in the welded areas.
Here's a shot when we were about 1/2 way through the machining process.... the flanges got a lot more uniform later on, but they still had significant "pockmarks" everywhere.
Live and learn!
The good part of the evening was the test fit of the wheel center and outer hoop. We settled on a 0.005" fitment and that ended up being snug enough that the center would start to drop into place, but required some firm tapping with a hammer to set it all the way in. Not too loose, and not too tight either!
The next step will be for me to go back a second time and weld-up low spots in the 4 flanges and remachine it to get a nice, flat surface with 100% surface contact to the hoop. For the remaining 4 wheel centers, I have decided to cut strips of 1/8" steel, bend them to fit to contour of the flanges and then perimeter weld, and plug weld them into place. That will give us a much nicer starting point for the machining, and the end-result will be better quality and less effort.
-G
