Draw bore technique is really quite straight forward when you think about it. The purpose of offsetting the peg hole in the tenon is to force the tenon deeper into the mortise when you drive the peg. So much for the theory. Now the practice. The assumption is that both pieces of wood are accessible and the tenon can be set in the mortise, marked, removed, drilled, back into the mortise, pegged. Obvious is easiest on the ground. Now improve the details.
(for this illustration the tenon is entering the mortise from right to left so the purpose is to draw the tenon even tighter from right to left when pegged.)
1. insert the tenon tightly in the mortise (on some larger sticks a come along is frequently used).
2. Insert the drill bit (without the drill) into then previously drilled peg holes on the side of the mortise. Tap it gently to mark the center of the mortise peg hole on the face of the tenon. remove the bit.
2. disassemmble the joint placing the tenon bearing stick in a position to drill.
3. Find the mark you just made, For ease in visualization draw a circle around the mark about the same diameter as the bit. remount the bit in your drill. set the tip, by about it's own diameter (will vary with wood species and wetness, and how much you want to draw the tenon into the mortise by lateral peg pressure. yes you can split the tenon by drawing too much)in the direction (3 o'clock on imaginary clock face) away from the end of the tenon. Drill your hole carefully. don't blow out the other side.
remove your drill and bit.This places the center of the now drilled tenon peg hole slightly away from the end of the tenon compared to the center mark you made with the bit in the previous step. When you peg it the draw of the bore tightens the fit of the tenon into the mortise.
4. reassemble the joinery and peg em up.
(you may have done multiple marks and drillings depending on the complexity of the partially disassembled frame)
5. like in measuring before cutting read these instructions more than once.
work safe, have fun.
deralte