Dont install the corbies, until 80% of your handle is done with coarse grit
On glue up use a bolt, waxed to secure the scale material. When dry remove the bolt and shape your handle.
When almost done install the corbies, I use maxi cure CA.
Then trim with saw and grind on slow with a coarse grit as close as you dare, then use a higher grit to finish off the corby.