What bit do you recommend for drilling put a blind 100mm deep 1 1/2" (38mm) wide 125mm long mortise in green oak? Long forstner bit, auger?
I’ve made some deep mortises the other day. I drilled holes in the corners with a long 6mm. Went outside of the lines, no need for cleanup of the corners I used a router to cut the sides perfectly sqare then a forstner to remove what was left. The router bit coud not reach the bottom of the mortise, but the square sidewalls made it easy to parr with a chisel. If you can’t use a router then go with a forstner and remove what’s left with smaller bits before final cleanup with a chisel.