I won’t say that this happens regularly, but there are quite a lot of cases of broken studs during repair work in auto mechanics. And for these cases, they have already come up with a special tool called an extractor.
They are usually sold in sets of different diameters, a universal repair kit so to speak.
Each extractor has its own number.
On top of the box or inside, in the instructions, each number has its own applicable range of values. In this case there are three lines. The topmost one is the serial number. Below is the initial and final hole size for which this extractor may be suitable in inches. And the last line is the initial and final thread size.
Working with such tools is straightforward. First, drill a hole in the center of the piece.Next, insert the extractor and use it to turn out the thread fragment.
Removing stud fragments using extractors
Let's move on from theory to practice. I don’t have any specially broken or stuck threads, but I will do a complete simulation to clearly show the whole process. I prepared a thick-walled profile with holes in which threads were cut. I prepared bolts for these holes.
I take these bolts, roughen the threads with a hammer and tighten them with a wrench into the profile. Everything is very tight and you won’t be able to tell me that this doesn’t resemble real conditions one bit.
I use a grinder to cut the heads flush.
The first thing to do is drill a hole exactly in the middle. To do this, take a core and center a point so that the drill does not jump at the beginning of drilling.
Punching point.
Now you need to drill a hole, the diameter of which should be approximately equal to half the thickness of the bolt. In this case, the bolt is M16, its thread diameter is 16 mm. We take a drill half the size and drill a hole with a diameter of approximately 8 mm.
It turned out pretty straight in the center.
We insert the appropriate extractor and begin rotating to the left. To turn the extractor, a wrench is usually used, but if you don’t have one, an adjustable wrench will do just fine.
As soon as the extractor makes a hook, the thread fragment itself will begin to turn out.
I hope it's clear. Now we move on to the larger bolt. Everything is exactly the same: we drill a hole in the center.
Insert the extractor and unscrew it to the left.
To release the tool, we clamp the piece in a vice or hand clamps. And turn the key to the right side relative to the piece of thread. It's pretty easy to unscrew everything.
This is a simple method that has been proven over the years.
I would like to add that you should not drill a hole with a diameter that is too large relative to the thread, since the thin walls in the stud will flare the thread itself, which will negatively affect unscrewing.
Particular care must be taken when handling small-diameter extractors, as they break very often.
If the fragment does not want to give in, heat the assembly and spray it with lubricant.
