Occasionally, it is necessary to drill a very straight hole through a very thick piece of material. It can be vital to come out on the other side exactly aligned in every way with the entrance hole.

There are lots of devices out there to accomplish this but they all cost money and are of limited use for 99% of the time. What's more, part of the device usually ends up permanently fastened to the drill and getting in the way for all of that 99% of the time.

Here are two other options.

1. The Human Eye

The human eye is astoundingly accurate in detecting angles. Most people can easily see that something is crooked or out of plumb to the level of fractions of a degree. Here's how to use that natural-born facility.

When you need to drill a very straight hole through a thickness of material, place a small mirror next to the drill bit. You will instantly see when the drill is carried off plumb by even the smallest amount. It works for both the lateral and vertical orientations. A reader in Massachusetts has very adroitly recommended a modification to the above. Get a plexliglass or mylar mirror and drill a hole in the middle. That way you can put the drill bit right through the center of the mirror and have a little better field of view. I know I'm going to try it!

2. A Straight Nipple

If by some misfortune you only have one eye (the ability to detect the crookedness of the drill bit is compromised without both eyes) then get a short plumbing nipple just a little larger than the dimension of the drill bit that you are using. Also get a floor flange to fit the nipple. Use a long bit (like an electrician's bit, they come in all sizes). Screw the floor flange to the surface of the material, screw in the plumbing nipple, insert the drill bit and hit the trigger. If you have sized things even remotely correctly you will have a straight hole. Of course, with both of these techniques, the material you are drilling into will need to be flat.