History of wedges as fasteners

[Tim Wescott]

My understanding is that back in the Before Times, quite a while after it became unnecessary to do animal sacrifices to insure the fertility of your fields, but before you could order 3D printed parts over the Internet, machines were fastened together by tapping wedges into slots, rather than with screws.

Does anyone know of a history of machine building that really gets into this? When did it start? When did it end, and over how long a period? Are there any currently-produced machines that still use this? (Corollary -- don't single-tool tool posts use this?) The obvious advantage/disadvantage is you can make a nice wedge in a blacksmith's forge, but the amount of room it takes up for the fastening is huge compared to a tapped hole and a screw, or a screw and nut. Are there others?

Example use in an 1832 steam engine here:

 

[goldstar31]

I'm sorry as I am not much help as my knowledge/research goes to things like fishbones to hold rafters in position and using wooden wedges and soaking them to split rock in stone quarries.

And then the classic 9 working tools used for building a cathedral.

Regards

Norman

 

[Tim Wescott]

It does seem to be the thing to consider if you're looking at a two-year engine building project and thinking "dangit, I wish this was going to take me a few more years".

 

[Charles Lamont]

Bicycle cranks? 'Antiluce' clips on truck/trailer tailgates and dropsides. The last widespread engineering use that I can think of is in steam locos. Piston rod to crosshead joint is usually a taper held in with a cotter. Takes a sledgehammer to get the cotter out, then you have to part the taper. Con-rod big-ends in inside cylindered steam locos also generally had a gib & cotter. The best machine tools have tapered gibs for adjusting the slides, rather than flat strips and setscrews.

 

[Steamchick]

If you look on the end of the shaft of your hammer, where the head fits, you should see how the wedge fits to expand the tapered shaft so you get a double taper to hold the head securely. It is getting difficult to buy the wedges, I think I have one left in a little draw somewhere, also difficult to buy hammer shafts. I have one new one from 1980... when I bought a few to last me a lifetime!
Wedges go back to the stone age, when wooden structure were held together the same as the wedge holds the hammer head on the shaft. Maybe strange to think the we still use such ancient technology?
Sledge hammers, pick-axes, etc all use this technology. Hard to better it!
K2

 

[Tony Bird]

Hi Tim,

Very old clocks and watches used wedges to hold them together, the attached photographs of the Salisbury 14th century striking clock shows them very well.

T

These wedges developed into being tapper pins which were used along with very a few screws in timekeepers until it became possible to mass produce small screws.

Take care.

Tony.

 

[Steamchick]

The bar tables in my local Cricket club have tapered wedges, just like I remember on my Grandparents large dining table! - You can see them in 1000 year old cathedrals as well. Ironbidge - the first cast iron bridge - is held together that way, as they only had wood-working and stone mason techniques. The "Modern" metal assembly techniques had not been invented!
K2

 

[goldstar31]

I still have my little 'Boy Scout' axe with an axe blade and a hammer at t'ther.
Dad made it for me on the anvil and it was used to dig out unexploded German incendiary bombs from about 1940. The wedge was forged from a bit of mild steel and went onto the hickory sahaft.

Long time since i saw it but it has my name burnt on the haft( I think badly!) but it along side my father in law's Auxiliary Fire Service 'tin hat' and his Service respirator and my late wife's Mickey Mouse' one.

She was 8 years my junior

It was all in the days of men who were "shifters' on the Rolley Way- drawn by horses/ponies.

 

[BWMSBLDR1]

Having seen the Salsbury Cathedral Clock years ago I was glad to see it again in your nice photographs. But for a "more Modern" example of cottered construction try to find a copy or a reprint of the Weed and Parcell book on building a gas engine circa 1903. It offers assembly via threading or for those lacking thread cutting tackle via wedged cotters. Bill in Boulder CO USA

 

[Jamie Barton]

The old steam boiler where I work used wedges to secure the front and rear covers. It was decommissioned last year & made in the late 90s. I kept the wedges & they have since come in very handy for hammering into snapped off threaded pipes stuck in sockets as a means remove them, think hammer-in EZ outs.

 

[Tim Wescott]

Made in the late 1990's, or 1890's? (I mean -- I think I know what you meant!)

 

[Jamie Barton]

Made in the late 1990's, or 1890's? (I mean -- I think I know what you meant!)

90s. I'll see if I have any photos at some point, I'm not sure where the boiler ended up. I've heard rumours it was donated to a training facility.

 

[Jamie Barton]

Made in the late 1990's, or 1890's? (I mean -- I think I know what you meant!)

1990's apologies - answering again with '90s' didn't clear much up.

 

[Peter Twissell]

The principal of the wedge, that is using friction by arranging the parts to contact at opposing angles, is everywhere in machinery today.
The Morse taper is a wedge.
A screw is a wedge, wrapped around into a helix.
Industrial pulleys are often secured to shafts using taper inserts.
I could go on (and often do).
Pete

 

[Tim Wescott]

Hey Pete:

Understood -- and I should have pointed out the various Morse (and other round) tapers in my original post, as well as the fact that in a lot of ways a tight screw and a tight wedge are doing pretty much the same thing at their mating surfaces.

I'm really specifically referring to the practice of sticking a triangular prism (in the geometric sense, not the light-bending sense) into a slot and percussively setting it into place*, for the purposes of holding metallic machinery together, and to the exclusion of screws. At one point, that was just the Way it is Done -- now, that task is almost universally done with screws.

I've already gained some insight, in the fact that's been pointed out that it's an old woodworking practice that was carried over.

* For that matter, I'm just assuming that you tap such wedges into place -- I can't imagine there's a wrench or other lever for that.

 

[tornitore45]

I seem to remember seeing in a museum setting a large gear or pulley cast as 2 halves and assembled with what I can describe with loose dovetails, so loose that the part could be mated frontally rather than sliding. Then a tapered wedge shaped like a jib was pounded in.

 

[Peter Twissell]

The stream museum where I volunteer has numerous examples of wedge fittings. We have a large triple expansion engine whose flywheel is cast in two parts, held together with steel "stitches", each of which is wedged into place.

 

[MRA]

Likewise - except our Crossley OE128 runs on (these days) diesel Flywheel is 13t, in two halves held together with massive tapered oblong wedges which pull into slots cut into a deep mortice-and-tenon arrangement. There are bolts at the hub to keep it together too. Interestingly (to me) the flywheel was cast and perhaps machined in one piece, with two 'tear-along-the-thin-bit' (rather than 'dotted line!) reductions in the rim thickness at 180deg to each other. It was then broken in two, the resulting fractures ensuring that the thing goes back in the right place. Here's a recent video of us putting the crank back in, where you can see what I'm talking about.



I'm the fool in the dirty hi-viz (should that be lo-viz?).

 

[Steamchick]

Fractured joints are not new then... I think they are used by BMW and others to make perfect fitting joints for big-ends of con-rods.... ?
Ken

 

[awake]

Oh, I've made many fractured joints ... but there was nothing perfect fitting about any of them. Maybe it has to be an intentionally fractured joint for that!