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Removing a stud that has sheared off flush

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What is the issue?
Bolts and screws like most every fastening, have a tendency to seize up on boats due to the challenging seagoing environment. Then when it comes to releasing them it is ever so easy to overdo it. We all know that horrible feeling of the tension suddenly becoming soft or rubbery, when you know you have either stripping the threads or broken the bolt. Worse still, when a bolt sheers off it tends to do so close to or just beneath the surface of what it is fastened into so that there is nothing left to get hold of.

Why address this?
A completely seized screw, bolt or nut can bring a project to an incomplete and frustrating halt.

How to address this?
First off, help the situation as best you can by, soaking the threads and applying heat as set out in releasing seized nuts and bolts. This should always be the first step as it also applies a natural break to proceedings. Ploughing on into the next steps whilst carrying the frustration of shearing off the bolt can lead to bad outcomes. The primary options for removing the sheared off bolt in progressing order of difficulty.

Drifting a sheared off bolt out with a screwdriver
Photo: Cruzdelasadas technical

Drift it out: If the bolt is not entirely seized you may be able to drift it out. If there is a burr where it broke off you may be able to get a screwdriver or small chisel behind it and tap it out with a light hammer. Failing that use a centre punch by tapping a hole near the edge and then using it to turn the shaft. You need to be very careful with this approach as, if it does not come out with the first few tries, you are more likely to damage the threads and or widen the head serving to further tighten it.

Left handed drill bits
Photo: Courtesy of SNAP ON

Drill into the head with a left-hand drill bit: Drills normally turn in a clockwise direction but if you apply this to the sheared off bolt it naturally turns it in tighter. If however, you use a left handed drill bit and select reverse on the drill, it cuts the opposite way applying a force that naturally turns the stud out. During the process of drilling with the left-hand bit, aided by the applied pressure and the friction heat, there is every chance that the bit will bite into the bolt and turn it out for you.

Welding a nut or bolt to the sheared off fastening is a highly reliable approach
Photo: notmuchwear

Releasing a sheared off bolt by welding: One of the most reliable approaches to removing a stuck bolt is to get a nut of the same size and welding it over the sheered head. This approach assumes you know how to weld or can get someone to do this for you. A MIG welder is preferred for this task as an arc welder creates a lot of slag which gets included in the weld. The heating and cooling action fractionally expands the metals at different rates helping to break the metals apart. Once it is cool place a breaker bar on the newly welded nut and wiggle it loose.

Bolt Extractor Set
Photo: Courtesy of SNAP ON

Releasing with a bolt extractor: Another option is to use a bolt extractor tool that is to release the sheared off bolt with a bolt extractor. These are small hardened bits with tapered left-hand threads. Because the bits are tapered a single bit may be hammered and screwed tightly into a range of holes. With threads like a drill bit running in the reverse direction, the screw extractor grabs a broken bolt and twists it out of its attachment point.

Screw extractors are not without their own problems. The worst of these being that they can break off inside the screw that is being removed. Since the extractor is an extremely hard material you will not be able to drill into it so a larger element of difficulty is added to the original screw extraction project.

Metric Taps And Dies
Photo: Courtesy of Tekton

Drill it out and retap: If none of these work you are down to drilling out the bolt or screw and re-tapping a new set of treads. This is the last resort and labour intensive. However, if all else has failed and the fastening must be secured, it is the only remaining approach to addressing the problem.

Taps and dies are the tools used to create screw threads. The tap is used to form a thread on the inside surface of a hole that the is the female portion of the mating pair (e.g., nut). A die is used to cut or form the male portion of the mating pair on a cylindrical material, such as a rod, (e.g., a bolt). The process of cutting or forming threads using a tap is called tapping, whereas the process using a die is called threading.

First, the bolt and all its threads must be drilled out. Then the set of the new thread must be taped into the enlarged hole to accommodating a new larger bolt.

If a bigger bolt cannot be used for any reason you can use a reducer or a Helicoil kit (a ready-made threaded adapter) to replace the original treads. The Helicoil approach is the same as above, in that you tap a new thread into the enlarger hole, but the Helicoil is wound in instead of inserting a new bolt or screw. This, in turn, becomes the new mating thread for an original sized bolt or screw. Helicoils are typically harder than the metals you can drill and tap so it is highly unlikely that the thread will strip out again. The key with Helicoils is to match the correct drill bit with the correct Helicoil.

With thanks to:
Michael Harpur, Yacht Obsession.

Remove a broken bolt using a left handed drill bit

Removing a broken bolt or stud with a TIG welder

Removing Broken Fasteners

Seven ways to remove a broken screw

HELICOIL® Screwlock – thread insert

Heli Coil Installation

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