When I first saw M3G's Instructable, How to Drill Straight Holes with a Hand Drill (Using Lego), I was impressed with the simple elegance of such a straightforward idea. It was one of those ideas that you kick yourself for not thinking of it.
I did think there was some room for improvement, so here is my stab at it. I added some tabs on the outer corners to allow a place to hold the guide. Also with the proper placement of different thickness and widths of blocks, it now can guide the drill at four different angles. It is small enough to not need glue to hold it together which allows pieces, damage by use, to be replaced.
Step 1: Acquire the Blocks
You will need:
4 - 2 x 4 bricks
2 - 2 x 3 bricks
2 - 2 x 2 bricks
1 - 1 x 2 bricks
1 - 2 x 2 plate
2 - 1 x 2 plates
I went to raid my Granddaughter's Lego stash but she quickly explained to me that that would not be acceptable. (Her actual words were, "No Papa, mine, go away!" So I bought mine, used, from a local brick seller (Fallout Games Tempe AZ) and paid 8 dollars for enough pieces to make eight of these.
Step 2: First Layer
Lay out a 1 x 2 brick, two 2 x 4 bricks, and a 2 x 3 brick as shown in the photo. You can picture the two arms with the two finger tabs.
Step 3: Add a Second Layer, Then a Third Layer
The second layer consists of a 2x 4 brick and two 2 x 2 bricks placed on top of the first layer as shown in the photo.
The third layer consists of a 2 x 4 brick and a 2 x 3 brick placed on top of the second layer as shown in the photo.
Step 4: Add a 2 X2 Plate to the First Layer
Place the 2 x 2 plate at the open position on the first layer arm as shown in the photo.
Step 5: Add 1 X 2 Plates to the First Layer
Attach the two 1 x 2 plates at the open position on top of the first layer of the other arm, as shown in the photo. The guide is now ready to use.
Step 6: Drilling a Straight Hole
Place the bit in the inside corner, making sure it touches both sides.
Step 7: Drill 45 Degree Holes
The end of one arm has a notch the is 16mm wide and 16mm (9.6 + 9.6 - 3.2) tall. This makes a 45 degree angle when the drill bit touches both corners.
Step 8: Drill 40 Degree Holes
This tab has a notch that is 8mm wide and 9.6mm tall. This makes a 40 degree angle when the drill bit touches both corners.
Step 9: Drill 22-1/2 Degree Holes
This tab has a notch that is 8mm wide and 19.2mm (9.6 + 9.6) tall. This makes a 22-1/2 degree angle when the drill bit touches both corners.
Step 10: Drill 30 Degree Holes
This arm has a notch that is 8mm wide and 12.8mm (9.6 + 9.6 - 3.2 - 3.2) tall. This makes a 32 degree angle when the drill bit touches both corners. But move the bit about a 1/2mm away for the top corner and you now have a 30 degree angle.