What is the issue?Bolts and nuts, like almost every fastening, have a tendency to seize up on boats due to the challenging seagoing environment. Apply just a touch too much pressure and the heads can sheer off leaving a seized and often inaccessible bolt shaft.
Why address this?A sheered off bolt can halt a project, cause frustration and cost money.
How to address this?When a bolt has sheared off, and left nothing protruding for a stud extractor to grip upon, one approach is a screw or bolt extractor often also known as 'easy outs'. Success with these can vary but they are not an expensive tool and anything that avoids drilling out the broken off bolt and retapping is well worth trying.
Bolt extractors are small hardened bits with tapered left-hand threads. The tops of each bit have a square head to support turning with a flat or adjustable wrench. 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.
First off and for clarity, there are two kinds of extractors:
- 1. Self-drilling broken screw extractors that you simply use on the screw in a reverse direction and it will drill + extract. These are mostly used for screws that have had their heads stripped
- 2. Where you drill a hole normally, and then extract with the screw extractor in a reverse direction so that it pulls the screw out.
Photo: Courtesy of DORSETA
We are focusing on the latter extractor tool here, as pictured above. As always before any work is attempted on a seized screw or bolt use penetrating oil and heat if possible. The process of removing a sheared off bolt with a stub-remover is as follows:
- 1/ File or grind the remaining head of the bolt until it is flat.
- 2/ Locate and mark the bolt's centre with a centre-punch and tap it.
- 3/ Create a starter-hole with a small drill bit
- 4/ Follow this by drilling in the hole for the stub remover. This should be a size or two smaller than the diameter of the bolt shaft.
- 5/ Hammer the appropriate sized stub remover into the hole until it is securely wedged.
- 6/ Turn anti-clockwise with an adjustable wrench. The stub remover should dig in tight and un-turn the bolt.
Screw extractors are not without their own problems. A drawback to tapered screw extractors is that their wedge action tends to expand the drilled, and thus weakened, screw. This wedging action can lock the screw even more tightly in place, making it difficult or impossible to extract. Even worse being made of hard, brittle steel, they can break off inside the screw that is being removed if too much torque is applied. 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. One way to avoid the risk of this added difficulty is to drill a hole completely through the seized screw. Thus, if the fastener breaks, a punch can be used to drive out the bolt extractor out from the screw, via the back, or end, of the fastener.
With thanks to:Michael Harpur, Yacht Obsession.
Screw extractor | easyout | broken bolt removal process
Self-drilling broken screw extractors
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