Step 1: Drilling
Also, I found I can go to Lowe's or Home Depot and buy ready-made 5/8" x 5/8" square dowels. Using them saves a lot of time over making my own square stock. The drilling jig shown in this Instructable is made to accept 5/8" x 5/8" square dowels. They work very well for making these wooden puzzles.
Step 2: Special Drilling Jig
I decided to make this special drilling jig for use with a handheld electric drill. I began by welding two pieces of steel bar to make a 90 degree corner. I needed a crisp internal corner. Angle iron off of the shelf usually has a rounded internal corner. When I welded these pieces together, the hot welding beads contracted and the corner was suddenly greater than 90 degrees. I used a hammer and a vise to bring the angle of the corner back to 90 degrees.
Step 3: Custom Sleeve
Step 4: Place the Nipple for Welding
See the second illustration for this step. It shows the nipple sleeve in its place with two short pieces of steel rod filling the space between the nipple and the angle. Weld a bead where you see the lime green. This is to be a precision guide, but welding always causes things to move when the weld bead cools. Making these welds first reduces the movement that can take place.
See the third illustration for this step. Make tack welds shown in dark blue to secure the nipple in place. (If the nipple is galvinized, remove the zinc coating before welding.) The rods limit any possible movement on the pipe when the weld beads cool.
Step 5: End Stop
Step 6: To Use
Cut the square stock to length. Insert it in the angle of the jig. Insert the drill bit into the nipple sleeve. Drill to the required depth. Remove the drill. Tap and blow sawdust from the hole.
This little jig makes producing the wooden puzzles much faster. My holes are not perfectly aligned on center, but are close enough that the puzzles work very well. The jig will last long enough to make quite a few of these puzzles.
In the second photo with this step you can see I used an engraver to label the jig so I will always know what it is and why I am saving it.