Tapping a hole
From TheBestCaseScenario
What is tapping? Tapping is adding thread to a hole on your piece so the hole becomes like a nut and can accept a screw.
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[edit] Getting Started
First off you'll need to know what size you need. You're probably better off buying your screws first and then working from there. Once you know what size your screws are you'll need to know what size hole you need to drill. You will be drilling a hole that is the same size as the inner diameter of the thread and the thread will then be cut into the wall of that hole.
[edit] Buying Taps
When buying taps you will more than likely be confronted with several very similiar ones for each size. Namely taper, 2nd and plug taps (not sure if you have different names in the states). A taper tap will suit most needs and the other two only come into play when tapping a blind hole.
[edit] Tap Drill Bit Size Table
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[edit] Drilling The Hole
As with drilling any holes in metal you will want to accurately mark the hole and then centre punch it. Keeping the drill square is more important in this than it is in anything else. Because if the hole is not square the head of the screw will not sit flat potentially ruining the look and strength of a piece. So for this reason use a drill press if at all possible.
[edit] Tapping the hole
- Preferably you will want to hold the piece level in a vice.
- Now take your tap wrench and insert appropriate tap.
- Let the tap sit into the hole but don't force it in (this is where the taper on the tap comes into play).
- Start to turn the tap while applying a small amount of straight downward preassure.
- After the thread has started (about 3 full rotations) you will need to turn the tap a half turn backwards to break off the swarf.
- Now that the thread has started you will feel it pulling the tap in and you won't need to push it down anymore.
- Continue the pattern stared above going clockwise for 2 turns and back half a turn to break off the swarf until you feel that the tap isn't cutting anymore.
- Dont try and go the whole way through a thick piece without breaking off the swarf. The tap WILL snap and believe me, they are not easy to get out!
- Now just screw the tap out and that's you finished!
- You may just want to use a small, round file to tidy-up the edges of the holes.
Now that was easy wasn't it?