On 5 Feb, 22:09, Housemartin wrote:
I have to join some extra wide work top at approx 90 deg.

What do you mean by "oak"? If it's real timber, then remember to
allow for expansion & contraction with moisture, which can be sizable
across the grain. It sounds like you're building a cross-grain joint
here, so that's potentially 1/2", maybe even 1" you're looking at.