# History of wedges as fasteners



## Tim Wescott (Apr 7, 2021)

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:


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## goldstar31 (Apr 7, 2021)

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


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## Tim Wescott (Apr 7, 2021)

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".


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## Charles Lamont (Apr 7, 2021)

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.


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## Steamchick (Apr 8, 2021)

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


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## Tony Bird (Apr 8, 2021)

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.


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## Steamchick (Apr 8, 2021)

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


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## goldstar31 (Apr 8, 2021)

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.


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## BWMSBLDR1 (Apr 8, 2021)

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


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## Jamie Barton (Apr 8, 2021)

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.


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## Tim Wescott (Apr 8, 2021)

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


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## Jamie Barton (Apr 9, 2021)

Tim Wescott said:


> 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.


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## Jamie Barton (Apr 9, 2021)

Tim Wescott said:


> 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.


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## Peter Twissell (Apr 9, 2021)

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


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## Tim Wescott (Apr 9, 2021)

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.


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## tornitore45 (Apr 10, 2021)

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.


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## Peter Twissell (Apr 10, 2021)

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.


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## MRA (Apr 11, 2021)

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?).


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## Steamchick (Apr 11, 2021)

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


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## awake (Apr 12, 2021)

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!


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## MRA (Apr 12, 2021)

How they achieved just the right kind of brittle fracture, such that there was no bending and the parts went back together perfectly-aligned - I don't know.  I guess cast iron is a bit like that, though if it went wrong it might shatter.  As each flywheel half is about 6t, that would be a serious bummer - I wonder what the re-work plan B was.


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## awake (Apr 12, 2021)

Employee to boss: "If one fracture is good ... surely that means 157 fractures are even better - right? Right??"


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## ajoeiam (Apr 13, 2021)

awake said:


> 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!



Boy do I resemble that implication  - - - - and I'm almost lmho - - - love that last sentence!!!


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## willray (Apr 13, 2021)

Tim Wescott said:


> ...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 think the difference isn't so much that the fundamental technology used for fastening has changed, but rather that the fundamental technology used for producing fasteners/fastenings has changed.

When all you had was a hammer and anvil, it was easier to beat things generally flat and rectangular, punch rectangular holes, pound out a triangular wedge, and use a through-mortise with a wedged tenon to hold pieces together, than to try to forge cylinders, make round holes and cut or swage threads.

With the advent to spinny things, it became easier to drill/ream tapered holes rather than to punch holes, to turn taper pins rather than hammer out wedges, and to put the wedge (spiral-wise) onto the part itself, rather than punching holes and using a separate wedge.

Fundamentally, the wedged tenon shown by Tony in post #6 is identical to such a joint where the end of the tenon was threaded and a nut applied to secure the joint - the difference is only in that the wedged tenon shown was the easiest way to implement an inclined plane using poundy tools, and the thread/nut would be the easiest way using spinny tools.

One might wonder more, perhaps, about rectangular-wedge-type joinery that is _not_ equivalent to round/spiral wedge-type joinery.   The wedged blind mortise/tenon would not appear to have a direct analog in the round/spinny world.  This may be because, in that joint, the wedge is deforming one of the members, rather than simply applying pressure.


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## maybach_man (Apr 14, 2021)

Slight thread creep..but aircraft propellors on merlin engines are driven on the taper not the splines, apparently...


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## MRA (Apr 14, 2021)

I have a small motorcycle whose clutch sits on a taper with no key.  If you fit it correctly (with heat in the right places) it stays on all by itself, and a well-fitted one is quite hard to get off.  Lots of people (including me, years ago) don't appreciate how to do it, and they can spin and pick up, messing-up male and female parts permanently.  But then, once they are messed up, you can change your main bearings and seals (it is a two stroke) and then weld the clutch on


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## Tim Wescott (Apr 14, 2021)

willray said:


> I think the difference isn't so much that the fundamental technology used for fastening has changed, but rather that the fundamental technology used for producing fasteners/fastenings has changed.



I think you're right -- with some lag for folks to wrap their heads around the new-fangled spinny fastener technology.


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## goldstar31 (Apr 15, 2021)

maybach_man said:


> Slight thread creep..but aircraft propellors on merlin engines are driven on the taper not the splines, apparently...



I seem to recall 'Lots' of Merlin propellors  dating back to BEFORE I had spots and-- I'm now nearly 90.
Now at 19,  I was boss of the Technical Library at RAF  Technical Wing at Hendon- with my RAF 31 Squadron, the Famous 3 Spits and 601 and 604 Squadrons. 
There was- a LOT of Merlin powered  planes and boats powered by Merlins.
Merlins are almost as old as me. The original spec is the same - 1930.
As a snotty nosed urchin, I recall a Hurricane which had been 'winged' and streaming glycol before. ploughing the local potato field- with what was left of its prop.
A Bit of Hyperbole???


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## terryd (Apr 15, 2021)

Steamchick said:


> 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


 Hi 'Steamchick',

Great to speak to you again.  The wedge has been used for all sorts of purposes since time immemorial.  They exert a powerful force which locks into place but easily and quickly released in most circumstances.  I once had a technician who would use wedges to lift heavy machinery high enough to get a set of machine skates underneath so that it could be moved.  Folding wedges (two similar wedges used in opposition) are useful for parallel spacing and can be used by woodworkers for clamping purposes.  Another old trick by woodworkers is to use loose wedges vertically to hold the leg frames in position on their workbenches.  If there is any movement in the leg frames by say, heavy planing of wood, the wedges gradually slip down in their 'pocket' and compensate for any movement of the legs unlike fixed joints which can become loosened eventually .  Very difficult to describe but simple to do so I've included a simple sketch of what I mean.  This obviates the need for angled braces which can get in the way.




Of course large dining tables and benches were once built with wedged stretcher rails so that they could be dismantled and moved out of the way for dancing and entertainment after the banquet.  They were also useful as monarchs used to traverse the country visiting 'lucky' nobles in their castles and the retinue that the monarch headed would carry a number of these dining tables and benches in disimantled form.  An early version of IKEAthinking  perhaps 

It is interesting to note that a screw thread is simply a wedge wrapped around a cylindrical form.  If you could unwrap it you get a wedge.  There are various ways of  demonstrating this, the easiest being a graphical construction which most of us did in tech drawing classes.  So in effect the 'wedge' is _*still *_used in countless numbers to hold things together just not in the original straight form but the technology is the same as it's always been.

Stay safe and healthy,

TerryD


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## terryd (Apr 15, 2021)

willray said:


> I think the difference isn't so much that the fundamental technology used for fastening has changed, but rather that the fundamental technology used for producing fasteners/fastenings has changed.
> 
> When all you had was a hammer and anvil, it was easier to beat things generally flat and rectangular, punch rectangular holes, pound out a triangular wedge, and use a through-mortise with a wedged tenon to hold pieces together, than to try to forge cylinders, make round holes and cut or swage threads.
> 
> ...



Hi Tim,

by definition a 'wedge' is defined as a tapered or triangular form of inclined plane, there is no such thing as a 'rectangular' wedge..  The woodwork joint you are describing is using a mortise, not a wedge into a tenon.  Hence 'mortise and tenon' joint, small wedges are occasionally added into the end of a through mortise to make it less likely to fail, these wedges are often of a contrasting timber used for decorative as well as practical effect,

stay safe and healthy,

TerryD


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## Charles Lamont (Apr 15, 2021)

Terry, the joint in post no 6 has 'keyed' tenons, typically used in joinery for the stretcher rails in things like refectory tables and benches, or for demountable stuctures, in which case it is also a 'loose tenon'. *

A wedge has a rectangular cross-section more often than not.

You have got it cross-threaded, probably a momentary lapse, but the hole or recess is the mortice, and the tongue is the tenon. The mortice and tenon joint you are describing has a 'wedged through tenon'.

* Paraphrasing the bible: Ernest Joyce - The Technique of Furniture Making


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## terryd (Apr 15, 2021)

Charles Lamont said:


> Terry, the joint in post no 6 has 'keyed' tenons, typically used in joinery for the stretcher rails in things like refectory tables and benches, or for demountable stuctures, in which case it is also a 'loose tenon'. *
> 
> A wedge has a rectangular cross-section more often than not.
> 
> ...


Hi,

I think that you misunderstood my post.  see my earlier posting which described the the 'wedged tenon' used in refectory tables and benches etc.  As a woodworker I am very aware of different types of jointing methods used in cabinet making, joinery and carpentry both European and Japanese styles - especially the mortise and tenon, even the blind tenon reinforced with 'foxtail' wedges.

Stay safe and healthy,

TerryD


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## willray (Apr 16, 2021)

terryd said:


> by definition a 'wedge' is defined as a tapered or triangular form of inclined plane, there is no such thing as a 'rectangular' wedge..  The woodwork joint you are describing is using a mortise, not a wedge into a tenon.  Hence 'mortise and tenon' joint, small wedges are occasionally added into the end of a through mortise to make it less likely to fail, these wedges are often of a contrasting timber used for decorative as well as practical effect,



My apologies, please read "rectangular-wedge-type joinery" in what I wrote, as "rectangular joinery retained by wedges"...   The joint I was attempting to describe is the wedged blind tenon, such as the blind fox-wedged tenon.  Unlike many wedged joints, this use of the wedge in joinery does not appear to have an analogous "round" version that evolved from it.


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