When you are threading a hole, it's very important to keep the tap aligned with the hole. This is especially critical for the first couple turns of the tap. A drill press can help keep the tap aligned much more accurately than you can do freehand.
There are two functions that the drill press can serve to help you tap a hole. The first thing is to keep the tap aligned with the hole that you're tapping. The other function is to keep light pressure on the tap so that it will cut cleanly as soon as you start turning it into the hole.
Caution: Just to be clear, you should not use the drill press to turn the tap. That type of automation requires special equipment (e.g. a Tapmatic).
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Step 1: What You Will Need:
- Drill Press
- Drill Press Clamp
- Tapping Handle
- Oil (or other tapping fluid)
- Centering Point
- Heavy Weight
Step 2: Setting Up the Drill Press
- Install the centering point in the chuck
- Adjust the table height so that the centering point is just even with the table top when the quill is completely extended
- Tie the twine to one of the feed levers and make a couple turns counter-clockwise around the hub.
- Hang enough weight onto the twine so that it will just start to lower the quill as if falls.
My drill press requires about 20 pounds on the end of the twine to just start pulling the quill down. You will need to play around with the length of the twine so that the weight has enough room to fall freely.
Step 3: Aligning Your Work
- Place your work piece on the table
- Lower the centering point into the hole that you wish to tap
- Clamp your work to the table
Step 4: Tapping the Hole
- Apply a couple of drops of oil or cutting fluid to the hole
- Locate the end of the tap in the hole
- Locate the centering point in the indentation at the back of the tapping handle
- Gently turn the tap into the hole until you meet a little resistance. This resistance is caused by a buildup of chips in front of the cutting teeth
- Back the tap up about 1/2 turn to break the chips
- Continue turning the tap in about one full turn at a time and then backing it out 1/2 turn
- If the hole goes all the way through your work then continue advancing the tap until it spins freely in the hole
- If you're tapping a blind hole you will need to know when the end of the tap reaches the bottom of the hole. You may be able to do this by feel but there is a risk of breaking the tap off if you get this wrong. Another way is to mark the hole depth on the tap with a piece of tape.
- When you're done threading the hole, back the tap out. Be careful not to let it tip to the side as it comes out of the hole. This will prevent any damage to you're beautiful new threads.