Introduction: Double Mirror Right Angle Drilling Guide
Drilling a straight hole can be difficult because you can only see one side of the bit at a time. Without a lot of practice, many of the holes end up perpendicular in one plane and not so perpendicular in the other. Drilling with a conventional guide (2 blocks at 90°) works in some applications, but when using short bits there's not enough room. This is quick, cheap & easy drilling guide will help you bore accurate holes even with small bits. Using two small mirrors, it works similar to a dressing room mirror to help you view the bit from all angles. When all the bits are parallel, start drilling. It's that easy.
Step 1: What You Need
Basically what you need to make the guide is 2 wood blocks, 2 mirrors and a means of sticking them together. In my case, I used double stick carpet tape. If you don't have 2 small mirrors, you will also need a glass cutting kit & a straight edge.
Step 2: Making the Drill Guide
I happened to have a couple 3/4" thick scraps already glued together from a previous box joint project which was convenient. But starting from scratch, you'll want to cut your pieces 2 1/2" x 4 3/4" and 3 1/4" x 4 3/4" if using 3/4" material. If you have precut mirrors, you'll want to cut your boards to match your mirrors. I like the 3/4" board because it gives the guide a bit more weight and stands nicely. The measurements aren't exact so use the odds & ends you have lying around. Even if you've burned some holes in 'em like I did, they'll still work just fine. Attach the 2 wood pieces together at 90° with glue and a couple screws.
I wasn't able to take pics while cutting the mirrors, but it's very easy on thin glass. Simply dip the cutter wheel in oil and then run it along a straight edge lined up on your mark. If it makes a scratchy "fingers on the chalkboard" sound, you doing great. Light pressure is all it takes to score the mirror which can then be snapped off. When breaking it, I like to support one side of the glass on my workbench top with the scoreline even with the edge of the bench. This makes it easy to break the piece by deflecting the other side downward. It is always a good idea to wear leather gloves & eye protection when cutting glass and mirror. Remember that one mirror needs to be slightly narrower to accommodate the width of the other mirror (i.e. 2 1/2" wide and 2 3/8" wide if using 1/8" mirror).
Once your glue has dried and your mirrors are cut, attach the mirrors using double stick carpet tape or an adhesive.
Step 3: Using the Double Mirror Drill Guide
To use the guide simply place it behind the bit and bring all four bits you see into alignment with each other. In the first picture it is obvious that my bit is not close to 90° in any direction because the bits are not parallel in the mirrors. In the second picture, you can see I am much closer to 90° although still not perfectly aligned. Snapping this picture proved to be a bit "testy" but you get the idea.
The beauty of this simple guide is that you can make adjustments as you drill to keep the bit at 90° to the surface. While not as precise as a drill press, it is quite accurate when drilling pieces too big for the press. The other advantage is that the guide is out of the way of the drill allowing the use of any size bit whether large or small.
I hope this little drill guide will be useful to you. I look forward to your comments & suggestions!