I have always been vexed by having to tap threads in a hole so that the threads are square to the top of the material I was tapping. I found a nice solution using a block with a groove in the side.
Step 1: Insert Tap Into Hole
Start by putting the tap in the hole. Notice the tap I am using has a somewhat flat profile on it’s side.
Step 2: Place Block So Tap Sits in Groove
Next, place the “jig” in place to align the tap. This jig is an old hydraulic valve with the right sized groove in the side of it. Start tapping the hole, while keeping the tap pressed against the inside edge of the groove.
Step 3: Remove Block to Finish the Threads
After you have the threads established, you can slide the jig out the side to run the tap down further.