Broken Seized Studs and Bolts.
How many times have you tried to undo a tight bolt or a stud in a metal block or casting and it has snapped off? You are left with a stud sticking out or a broken bolt in a threaded hole flush with the surface. Although these can be tricky, there are many ways and tools to remove them.
Stud Sticking Out.
If there are any threads left on the stud, you can put on a nut of the same thread. Tighten this down the thread of the stud and then put on another nut. Using two spanners, tighten these nuts against each other, TIGHT! Using your spanner on the inner nut, undo the stud. If the stud is too tight you can put a weld on the nut to the stud. This will lock the nut to the stud and also the heat generated will expand the bolt and help break the seal, stud to metal. Once again use your spanner to undo the stud.
If there are no good threads on the stud you can try using a pair of Mole Grips. Tighten these as tight as you can on the stud. Turn the Mole Grips to undo the stud. If the stud is too tight and the grips turn on the stud, you can buy a Stud Extractor from a good tool supplier. This is a special tool that works with an eccentric knurled disc to grip the stud. It has tremendous turning force and grip, but is a little bulky and so needs room to work in.
Bolt Broken Flush in a Hole
This may look un repairable but once again can be done with some careful work. Using a centre punch and a hammer, carefully make an indent as close to the centre of the broken bolt as you can manage, by eye.
You can purchase a different set of studs removers (Easy Outs). These come in different diameter sizes and have a left handed gripping, gradual thread on them. When they are put in a drilled hole and turned anti clockwise, they will turn until they grip solid. When they have gripped they will start turning the broken bolt undone. When it is out the broken bolt can be gripped in the vice, and the EASY OUT turned clockwise to release it.
Drill a hole smaller than the bolt diameter into your broken bolt/stud, very carefully and accurately. Use one of the Easy Outs that will locate into your drilled hole and turn it anti clockwise with either a spanner or a TapWrench. If the stud comes out, JOB DONE. If it is so tight that the easy out cannot remove it, it will have to be drilled and tapped out to the correct thread size.
Refer to your thread charts in a Engineering Handbook and find the tapping drill size for the thread of the broken bolt.
I:E A metric 8mm diameter bolt (M8) has a tapping drill size of 6.8mm diameter.
Drill down your hole in the centre of your broken bolt to the appropriate depth, using the correct size tapping drill for your stud/bolt. Now use the correct size tap I:E M8 and re-cut a new thread into the hole. The tap will also clear out the debris of the old broken bolt.
Thread Cutting.
Thread cutting taps normally come in sets of 3. A start tap, second tap, and a bottom tap. The start tap has a longer lead in, so it will align itself when it starts to cut in your drilled hole. When tapping (cutting a thread) use a Tap Wrench, to turn the tap, and use a cutting compound to lubricate the tool and keep it sharp. Too much force can break a Tap when cutting so be careful and use a bit of common sense. Normally you would turn your Tap Wrench one complete turn and then half a turn backwards to break off the metal swarf you are cutting. Continue this sequence until you get to depth and you should not break any taps.
If you need a lot of force to turn the tap, then turn it backwards to clear the swarf, but if the tap is continually tight to turn, there is a good chance it is worn and blunt, so replace it with a new one before it breaks in a hole. If a Tap is broken deep in a hole it will have to be removed by professional equipment, called Spark Eroding
If you are Tapping into a blind hole (a hole in a metal block that does not come out the other side) you must tap to depth starting with the lead (1st) Tap, then tap with the 2nd Tap and finally the bottom Tap. The bottom Tap has no lead on it, and so will tap the thread full size to full depth in the hole. If you have a compressor and air line, blow out the freshly tapped hole to clear out any metal swarf inside. Now you can try a new bolt/stud in your tapped hole and make sure it runs down full depth freely (perfect fit). Ideally to stop a seizure happening again, when you finally fit the stud/bolt in the hole, it should be coated with a copper grease.
