A tapping fixture allows more precise cutting of threads with a tap than can be done by hand. I adapted a drill press so the quill can be used as the heart of a tapping fixture. Here is a commercial tapping fixture. The photo shows my tapping fixture ready to use. My attachment handle gives me leverage for turning the quill. The arms on the quill allows me to keep some downward pressure on the quill. This helps the tap bite into the metal when cutting.
- 1 1/2 inch black iron pipe
- 5/16 x 3/4 inch bolt
- 1/2 inch black iron pipe
- Metal cutting bandsaw
- Center punch (spring loaded)
- Drill and bits
- 5/16 x 18 inch thread tap
- Metal lathe
- MIG welder
- Digital caliper
- Spring clamp
Step 1: Size the Tube or Pipe
1 1/2 inch black pipe has an internal diameter very near to the diameter of the lower part of the drill chuck on my drill press.
I cut a piece from the pipe about 3/4 inch wide. See the second photo.
Step 2: Enlarge the Internal Diameter to Fit the Chuck
I am thankful to have an old Atlas metal lathe I could use to enlarge the internal diameter of the pipe until it fit over the lower part of the drill chuck. A digital caliper was very handy for checking progress. I also smoothed the saw cuts with the lathe. The second photo shows the piece of black pipe enlarged enough to slip over the end of the drill chuck.
Without a lathe, it would be possible to use a file or a grinder (with a cylindrical stone) to enlarge the internal diameter, but some patience would be required.
Step 3: Attachment Locking Mechanism
Something needs to lock the pipe collar to the drill chuck and provide leverage for turning the drill press quill when cutting threads. I chose something very simple.
The holes in the chuck for the chuck wrench are 5/16 inch in diameter. I used the end of a drill bit to determine the size. See the first photo.
I used a digital caliper to determine the distance between the bottom of the part of the chuck turned with the chuck wrench and the center of the holes for the chuck wrench. The second photo shows a faint line scratched into the outer surface of the black pipe collar. I used a spring loaded center punch for drilling exactly on that line.
I began with a very small drill bit and worked up to larger bits until I had drilled a hole about right for tapping to make threads for a 5/16 inch bolt. I tapped the threads. See the third photo.
Test the fit with a 5/16 inch bolt. See the fourth photo. The end of the bolt screws into the hole for the chuck wrench.
Step 4: Weld the Bolt Into the Handle
I used a spring clamp to hold the pipe collar to a piece of aluminum angle in a vise. I slipped 1/2 inch black iron pipe over the head of the bolt and tack welded the 1/2 inch pipe to the bolt.
I finished welding the bolt inside the 1/2 inch pipe. See the second photo.
Cut the pipe handle to length. See the third photo.
The fourth photo shows my attachment ready to use.
Step 5: Use
A drill press vise clamped to the drill press table is handy. Add a little downward pressure on the quill arms as if you are drilling a hole. Use the fixture handle to turn the quill and begin cutting threads. Because the chuck has three jaws but the tap is made for a four sided holder, it is difficult to keep the chuck from slipping on the tap. I could carefully grind three flats on the tap, or I could use the tapping fixture to start threads and then finish in a vise.