[Griff]

I used an inch and a quarter bit in a hand drill. There are some really cool old-timey mortising rigs you can use but for the house frame I only had a long auger bit on a heavy duty Milwalkee drill. I'm sure there are ratios that could be used, but I don't get too caught up in my lack of knowlege, when in doubt I overbuild. Most of timber framing is received knowledge from failures and successes since forever. These are probably as reliable as strength of materials indexes with the exception being old growth lumber had much tighter growth rings and was (is) stronger than modern trees which grew more quickly in less dense environments.