A tapping fixture is one the most useful tools you can have in your shop. Not only will it help you thread holes perfectly perpendicular, it will also reduce the number of taps you accidentally break. They are far superior to a tapping block and once you use one you'll wonder how you ever got along without it.

This is a simple project that can easily be completed in an afternoon and is also fairly inexpensive, the total cost of parts is around $20.00. The basic building material for this is 1/2 inch galvanized pipe and fittings which are readily available at your local hardware store. I used a piece of stainless tube I had in my scrap box for the extension on the tap holder, but I'm sure piece of thick wall conduit or even another piece of pipe would work just as well.

I haven't made a drawing for this since it's built from 1/2 galvanized pipe. The parts list is fairly straightforward and the pictures explain it all. I suggest that you assemble the nipple and elbow in the store and check to make sure they form a perfect right angle, many of the elbows are not tapped perfectly square. That way you can sort through the stock and find the best of the lot. I also checked the floor flange to see if it was relatively perpendicular, this isn't so critical since you face it off, but it's best to start with one that is half way reasonable.

If you click on each picture you'll get a bit more information.

Parts	Tap Handle	Turning the body
Extended handle	Drilling the tee	Countersinking the flange
Facing the flange	Tapping the base	Finished product