My idea is for an alternative type of expanding bolt. It consist of a bolt (whose head protrudes very little past it's edge. onto this bolt is placed conical washers so that the large ends face away from the bolt head. A large diameter washer follows these with a nut securing all of this in place. The end of the bolt it flattened so as to be easily gripped by locking pliers.

To use said bolt one places it in the hole head first and grips the flattened end with a pair of locking pliers. one then uses a wrench to turn the protruding nut. this pulls up on the bolt compressing the stack of conical washers and forcing them to expand and grip the sides of the hole. Alternatively should you want to use said bolt with a power drill or any bitted drill whose bit goes over bolt heads you could hold the nut and have a the protruding bolt tip bitted.
-- RichardT, Jan 06 2010

Dynaset drop in anchors http://www.ramset.c...choring/Dynaset.pdf
Not exactly what is described here - just showing that there are already designs that do this job quite well. [Custardguts, Jan 07 2010]

//compressing the stack of conical washers and forcing them to expand and grip the sides of the hole//

Methinks perhaps you underestimate the forces required to significantly expand a presumably steel washer like that. Something like this could be used for low-clearance holes in a steel structure (although I don't know why this would be more advantageous than other existing fastening methods).
-- Custardguts, Jan 06 2010


hmm [+]
-- FlyingToaster, Jan 06 2010


What [Custard] said. But the conical washers could be designed to be more easily "spreadable".

Presumably you've already encountered other expanding bolts? There are some which have a sleeve which, as the bolt is tightened, is shortened and expanded outwards - sort of similar idea.
-- MaxwellBuchanan, Jan 06 2010


I've used Dyna bolts before and was quite surprised that only the last centimeter of the bolt expands to grip the sides of the hole. Probably because for that section to fail the rest of the hole would have to fail too.

Ever since I always wanted to make an expanding bolt for use as a universal fastener. something that could work on any hole with a few standard sizes. these were the ideas I considered.

The first design I thought might work was a thin metal strip coiled around a tapered threaded bolt. both sides of the sheet would be textured so as to provide more grip for bolt bolt and hole threads. The interior sheet end would be cut at an extreme angle so as to provide a sloped inner hole. As the tapered bolt was screwed in the sleeve would expand and grip the sides of the hole. This design would allow about 1/3 expansion from original diameter as long as length did not become a restriction

My second design called for a metal strip which would be attached to a nut at one end and a non threaded grippable end plate end plate at the other. The metal strip would be wound like those paper towel and toilet paper rolls except the side of the strip would be cut at an angle so that when pushed together they would slide over one another. One inserts a bolt of the correct size into the sleeve and then inserts the bolt and sleeve assembly into the hole with the materials to be fastened in between. one then tightend the bolt while still gripping andpreventing the turning of the end piece. this pulls and twists the nut at the end of the sleeve pulling it towards the end plate. this in turn forces the coiled strip to twist around itself and expand the sleeve. The advantage here is that it could use a standard bolt with an expanding sleeve rather than have an entire specialized bolt assembly.

the design I propose here replaces the coiled strip with conical steel washers.

PS:What is the protocol when you submit an already baked(here on half bakery) idea? Do you add your material to the other page and delete the one you started? What about comments? Is there an accepted protocol?
-- RichardT, Jan 06 2010


//What [Custard] said. But the conical washers could be designed to be more easily "spreadable".//

yeah, just use split washers.

Hey [RichardT] - not sure what country you're from, but here in Australia dyna bolts are sold by Ramset. Ramset issue a specifiers resource book which provides information on the different anchors available including dynabolts - their load capacities in different materials, failure modes etc. You might be surprised when you see the failure mode of a dyna bolt. A whole lot of material needs to come out to pull the bolt. Other companies issue similar for their own brands - it's just the ramset one is really easy to use. They'll usually email you a copy on request.

I do a lot of "field engineering" in my role and often find myself needing to specify odd-job designs to facillitate plant maintenance -like fixing lifting/pulling points to concrete walls in odd places, lifting jigs, etc. I use the specifiers book extensively.

Coming to the point - I think you'll find that there are commercially available designs that do this job already. Dynaset drop in anchors spring to mind.
-- Custardguts, Jan 07 2010



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