Drill guide question

I'm installing a new lockset on the main entry door of the house. I need to drill 2 new through holes, one for a mounting screw and one for the interior turnpiece. I'm changing out an old Baldwin piece for a new one.

Question is how to ensure I drill the hole square/perpedicular to the door. I prefer to drill the hole with the door on its hinges, because the beast is solid mahogany and it ain't light.

Am I making much ado about nothing? On one hand I want the holes to be perfectly square to the door surface. On the other hand, no one will see the holes, and if I mess up a little bit, I can make them a tad bigger and it really won't matter as far as I can see.

Another question on which drill bit to use. One hole is 5/16" and the other is 5/8". Which bit is best for this - forstner, spade or regular twist drill? Thanks.

A forstner bit is nice, but overkill. On mahogany, I wouldn't use a spade bit. A spur point bit or a twist drill (if sharp) would work. If you clamp a piece of plywood over where you want to drill, you should minimize chips. A forstner bit is nice, but you can burn one up if you aren't keeping it even and loading up one point. It would be a waste to ruin one. Drill a pilot hole through using a smaller bit,and use the bigger one from both sides to prevent chips.

A small square held up near the bit helps you keep things level and square. It helps to have a a second person to judge the other orientations.

You can rent a clamp on drill guide for a hand drill that will set the angle perfectly. There are also a million door lockset jigs out there. I gotta believe you can find one at some rental center.

Well I got the job done. I used the drill guide for two of the three holes. It worked pretty good, but in retrospect I probably could have done without it.

I used a brad point drill, and a forstner bit to drill the holes. Both worked great.

Here's a couple pics of the setup. I used 2 bar clamps to clamp the guide to the door.