humm, i think i get it: Mark, you bolted the stringer together in order to drill the mortises? I plan to drill one corner or each mortise to get a router started and router out the housings and mortises then use a corner chisel to square out the corners. I'm doing the tenons and wedge kerfs in the treads all on a table saw. I'll use a generous diameter stop drill at the end of each kerf to avoid splitting as it will be hidden in the housing anyway. I think I will also glue all the joints to avoid a creeky stairway.
And then hope for the best.....