Just to make sure:
By "octagon" I assume you mean a tapered cylinder, initially 
consisting of 8 wedge-shaped slices
(i.e. the outer surface is round, not with 8-sided flats) Correct?

Maybe spending time on some kind of jig might help.

For an "external" jig a "tapered trough" into which the leg-wedges 
could lie during glue-up
would be ideal --but a huge amount of work to get it right.  So maybe 
a number of rings
(say an inch tall) to place along the length of the leg might work better.

Or maybe an "internal jig".
  That is, assuming the leg-wedges are "pointy" on the inside (that is,
the inner-most edges are all attempting to come together at a single 
point) perhaps
it might be helpful to shave the "pointy" end off of each wedge, and 
form an interior
octagon  Then there could be octagonal shaped core piece, which could either
serve as removable "jig".  Or the wedges could then be individually 
glued to the
new octagonal center piece and the complete leg built up in this way.

I'm thinking maybe gluing it up in steps might be helpful as well,
That is, hold all 8 pieces together, but initially only glue each pair of
neighboring pieces together forming four pieces.  Then glue each
resulting quarter into halves, and then finally the whole leg.

But in any case I'm betting however you do it, getting it perfect 
"the first time"
is going to be darn near impossible.  So if I were doing it I would count on
there being some final cleanup/trim to bring it all true at the end.

Anyway, just thinking out loud.  And, as others have said, it would
be easier to draw tthis han explain.  In any case, hope there's 
anything useful here.

N



Ed Minch wrote: