Harold,

That sounds like a good test. I'd either need something long enough to
clamp on either side of the test area, or I could turn my vise. I don't
remember whether the bolt slots align with the t-slots near 90 degrees,
but I could put the angle base on it long enough to try it. The vise
would not need to be precision aligned at 90 degrees, right?



Right, unless you intend to do other work on the item in question, mill
edges or other features, drill holes, etc. For surfacing, it clearly
isn't important. I do like to have it close, though, so if more than one
pass is taken there's not a tell tale line that shows the part wasn't
square
with the cut.


That makes it fairly painless to clamp someting for facing with the
saddle. I'll probably try it the next time I have reason to take down
the vise.

I think I was making this a lot harder than necessary. Do you care how
much motion there is in the saddle, or merely that a given strip of
metal "sees the entire flycutter"? Assuming the latter, and needing to
face a small block, I did some roughing with a 3/4 endmill and then ran
the flycutter over it (queue drum roll) using the saddle: I got a cross
hatch pattern

Unless I am missing something, I plan to leisurely buy another pack of
shims, and _not_ bother using them until I see a problem. Do you agree?

Bill