Here is the final step in my new method for drilling out legs for stretchers. It's pretty simple. I have always used V blocks held in my vise to hold the leg parallel to the surface of my workbench, then, with a bevel square set to the correct angle (4 legs, 4 angles!) I look in a mirror, hold the drill parallel to the bevel square and drill. Now I do things a bit different.
I start by placing the leg in the V blocks with the mark to be drill pointing straight up. Instead of holding the leg parallel to the top surface of the bench, I raise one of the V blocks until the line marked on the tape becomes parallel to the top of the angle block set on its side. I can easily see this in the mirror.
Here is a shot of Stacy getting used to seeing the drill bit in the mirror. It's important that the drill bit and the measuring block have a small gap between them as they appear in the mirror. It's easier to judge their parallelism with a small gap. It is also important that the mirror is placed on the benchtop parallel to the leg itself and not the edge of the benchtop. You'll notice that because the leg is generally held by two different spots that have different diameters, that it isn't parallel to the edge of the bench, (if you wondered where I got the idea for my caliper, there it is).
Here's Stacy drilling out here mortise. You can see that the measuring block is now standing on its angle cut and she is holding the bit parallel to the side of it.
Now that I've covered the particulars, this process can be reduced to three simple steps. Mark the leg with the angle block, parallel the mark to the table top with the angle block, and drill with the angle block.
A couple of peculiarities may come to any who try this method. One is that it will require that the tops of the legs face different directions while drilling. It does ask for a bit of ambidextrousness but is hardly a deal killer. Also, when working with the complex shape of baluster legs, it may be best to turn the seat upside down to allow easier marking on the taper at the bottom of the leg.
To drill out box style stretchers (where each stretcher spans from one leg to an adjacent one, I found it best to drill and assemble the front two legs and the back two legs. Then after dry fitting them in the seat, I used the string to locate the centers for the side stretchers. By carefully placing this center mark straight up in the V blocks, I avoided any other measuring. It worked nicely on all nine of the chairs that my students made at Peter's Valley.
I haven't used the method for drilling into the side stretchers for an H style stretcher, but it is possible. For now, I am happy to have simplified my life just a bit more. I'd welcome any feedback from anyone that give this method a try. Good luck!