here is what i do , now im no expert but i find this works really well for me...

i mark out the centerline on the horizontal and drill 2 holes , one at the front one at the back , so that a peice of piano wire is a tight fit , the peice of wire is about an inch long , then i press and ca the wire into the holes on the horiz , mark the posistion on the centerline of the vertical and the right spacing just by laying it flat on one side of the horiz to mark the posistion , then drill holes in there ,,, next , put the epoxy on the horiz along the centerline , then .. put ca on the tips of the two wire peices sticking up. then quickly push the vertical down onto the wire. if you dont do it quick enough the ca sometimes sets before its snug home.. anyway , i find that the ca sets almost instantly and holds it rock solid , then you can just adjust it a bit after checking with a square and it will hold it rigid as anything until the epoxy dries