I have seen the burr you describe in some cases. I'm curious is your drive a failed drive or a preemptive rebuild?
For purposes of visualizing the shim having an "up" and a "down" side, imagine the FD cover sitting on your bench with the inside of the cover facing up. The shim sits in the recess the is the seat for the crownwheel bearing. When the shim is sitting in this recess the "up" side is the side you are looking at and the "down" side of the shim is facing down against the FD bearing seat.
The shim is loaded when the cover is bolted onto the FD housing. This pressure can cause the outer edge of the shim to be bent up a little inside the cover and the inner edge bent down by the bearing race into the opening of the FD cover. This is what creates the burrs you are describing.
However, I have noticed this mostly on the thinner shims, and on FD where the bearing has failed and the rider continued to ride for a while. This can result in a spun bearing. When the outer race spins in the cover, the shims can become quite distorted.
In the case of the thinnest shim (0.15mm) which is used in combination with other shims to get a 0.05mm thickness, there can be some interesting distortions. Attached it a pic of a 0.15mm shim from a drive in which the outer bearing race spun in its seat. There is an oil channel in the FD cover which "catches" the shim as it is spinning, and crumples the shim as shown here.
Any shim that has had this kind of event may have burrs which, as you have noted interfere with accurate mic'ing of the shim thickness. As far as lying flat in one plane, even new shims don't; this is much more noticable with the thinner shims as they bend very easily, the thicker ones resist bending more. No matter, once the shim is in place and the FD cover it torqued into place, the shim will be flattened out.
I imagine it is a little difficult to measure shim thickness with a dial indicator, a caliper micrometer would be easier. Using a micrometer I have found that shims often vary in thickness at different locations around its circumference; the variation can be as much as 0.03mm.
Originally Posted by sparky_k1200lt
I'm in the middle of rebuilding my FD, and the shim I removed was 0.75 to 0.80 mm, best I can tell (0.033 inch is what I measured, with dial indicator). I am noticing burrs on the shim, possibly from the punch that was used in manufacture. With the shim laying flat on my table, the inner edge has a burr pointing down, and the outer edge has a burr pointing up. Also the outer edge is not flat on the table, whereas the inner edge is. I measured 0.038 inch thickness this way, and 0.042 inch when I flipped it over (that's how I first noticed the lack of planarity. Compensating for the angle, I measured the 0.033 inch minimum thickness. Using a digital caliper, I measured 0.78 mm, but not sure if the burrs are included in that measurement or not. The burr is enough to explain the mysterious cut I found on my fingertip after dismantling the drive.
Since you have a large collection of similar size shims, Curtis, do any of those exhibit a burr, or the non-planarity I'm describing?