History of wedges as fasteners

[MRA]

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.

 

[awake]

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

 

[ajoeiam]

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!!!

 

[willray]

...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.

 

[maybach_man]

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

 

[MRA]

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

 

[Tim Wescott]

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.

 

[goldstar31]

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???

 

[terryd]

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

 

[terryd]

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.

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

 

[Charles Lamont]

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

 

[terryd]

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

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

 

[willray]

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.