How to Remove a Broken-Off Tap
Hopefully this never happens to you, but if it does here's a clever solution
I didn't invent this trick (nor did I take the pics) but it's worth adding to my site.
The primary cause of the problem here was not using some sort of oil or cutting fluid or WD-40 to lubricate the tap as it went in, which led to friction, which in turn required more effort, and then suddenly SNAP!
Always use a lubricant. For each full turn of the tap, stop and reverse it half a turn, then procede for another full turn. It helps flush the shaving out of the threads and into the recesses. If it feels like it's getting stuck, back completely out, add a little more lubricant and then try again.
Patience is the key.
As you can see, there's no lubricant. Making it worse is the thick layer of rust.
The tap broke off flush with the top of the hole, which meant there wasn't anything sticking out that could be gripped with a pair of pliers.
For a broken bolt you can use an EZ-Out, which requires drilling a hole in the center of the bolt to insert an extractor, which then allows you to back the bolt out. Unfortunately, a tap is made from hardened steet which is tough to drill into, so the EX-Out won't work here.
You'll need a couple of large cotter pins like this.
The cotter pin needs to be just small enough to fit in the gap between the body of the tap and the inside of the hole. If you don't have cotter pins the right size, you might be able to use nails with the heads cut off.
Put a piece of cotter pin (or nail) into each recess, as shown
Here's the clever part: slide the remaining piece of the tap between the cotter pins.
Use a small hose clamp to tightly hold the pins in place around the tap, then slowly, carefully, cautiously start backing the broken tap out.
This time, use some lubricant. You might need to wiggle the tap back and forth to get it started.
Remember the part about patience.
With a little luck the broken tap will come out just like this.
Here's the reward.
When you go to the hardware store to buy a replacement tap, buy a little bottle of cutting fluid. It makes drilling holes and cutting threads much easier. A couple of bucks can help you avoid having to use this clever trick.