Nuts and Bolts.
Post date: 26-May-2016 02:09:35
What you always wanted to know about Nuts and Bolts
By Bob Wallis (non-engineer)
June 2016
NUTS & BOLTS
Once upon a time I was fascinated with the history of how nuts and bolts evolved along with threads, yes, Joseph Whitworth sorted the threads out, but the profile of the bolt heads got me.
I believed the square nuts were replaced by the hexagonal about 1900 – Wrong!
The hex head was developed as far back as the very early 1830’s (James Nasmith) , and the square continued mainly in the production of agricultural implements. In Australia the implement manufacturers bought square mild steel bars and made their own, say into the 30’s (Depression). 1/4" Gutter bolts with square nuts are still available.
The common rule was that Square was used where the fastening was not required near the vertical member, or with tension, and then hexagonal were used so as to get closer to the vertical member. If you needed to get even closer, then an Octagonal nut was used – however I have not seen an octagonal but I’m assured that some of the early steam engines used octagonal nuts, again in the early 1800’s.
Today we often see a variety of nut heads used mainly as ‘security’ to ensure you ‘keep out’! – but now you can buy the kits to remove them. During 1974 Rolls Royce had square nuts right down to small. 3BA that held the pipe clips were also square. Also some railways still use square nuts in fixing rails to sleepers etc.
Joseph Whitworth (1803 -1887) During 1841 devised the ‘British Standard Whitworth’ system of standard threads and more so the pitch (55 O) to ensure the greatest strength in the nut and bolt. Before this revolution each manufacturer made his own proprietary thread which in turn meant only he could replace them!On my “ARAB” platen printing press, patented 1872, (and sold in pack form) it has mostly numbered Whitworth nuts and bolts after 1841, but one set of four bolts is definitely proprietary thread. On restoration of the platen one bolt was missing and it had to be remade.
James Hall Nasmith (1808-1890) patented a machine for milling hexagon by 1829. It was tooled to mill the six sides of a hex nut that was mounted in a six-way indexing machine. Nasmith did not suggest that hexagons were anything new, and he refers to the tediousness of the filing process in making them.
Back a little further, innovator and inventor, Henry Maudslay [1771-1831] Nasmith worked in his early years for his partner after Maudslay died, as a Draughtsman, in the Illustrated Table Engine of 1807, hexagon nuts were found to be used. (Again, proprietary) and as used by Maudslay.
In conclusion, on the shape of the nuts we find that two of the differing heads, hexagon and octagon were both developed during the early 1800’s, or even before, and the square head would perhaps be some 100’s of years before, at the time foundries commenced and threading devised. Some consider that the screw thread was invented in 400 BC by Archytas of Tarentum (428 BC – 350 BC) one of the first screws principle to be used was in a press to extract oils from olives and juices from grapes. Archimedes (287 BC-212 BC) developed the screw principle and used it to construct devises to raise water.
LOCK-NUTS
The original concept was that the thinner nut went on the bottom, and the thicker went on top. Then two 3/4 nuts were introduced. This was widely believed as far back as 1893. Then the world went upside down and said the thick went on the bottom and the thin on top, for convenience, then science .
It is now proven that the thick nut goes on the bottom, and the thin locking nut on top. The argument is that when the load nut (thick) is tightened, it butts on the threads and sends the strain down the bolt and actually thins the bolt by that pressure by use of the wedge of the thread. The locking nut only does that, it locks the pressure being applied down the bolt. However, the strain can only be applied to the tensile strength of the bolt. (Below is a diagram showing the forces of the tension)
It is said that in backlash even a precision class 4 bolt, (lower the number the smaller the tolerance) with selected nut, will have some, whilst a class 1 course tolerance bolt it could be as much as ten thou.
For example a class 3 bolt with a quality fit – lying in the middle of the tolerance range, the clearance will be about 3 thou. If the bolt were 4” long in mild steel a stress of no less than 22,500 p.s.i. to take up the clearance, and then a bit more to get the locking action. Remember that by tensioning the bolt it stretches and the nut compresses, the effect here is that the pitch of the thread changes.
On applying the locking nut it now compresses the expanded load nut. If the small nut was on the bottom then the pressure applied to the thinner nut is greater than a thicker nut. The manufacturers of engineering nuts and bolt advise the maximum tension that should apply. If exceeded the bolt will either stretch or break – there is more science applied to the tension under more stressful situations, but for normal use the manufacturer’s details will suffice. (Source 1)
ROLLED THREAD
Up to about 1941 the Aero Engine Industry thought rolled threads were cheap and nasty and they only tried them as a war-time experiment. Now they are accepted as being much superior to threads formed in any other way. (Source 2)
Conclusion: Today, we find that many of the old threads are gone including BSW and most now used are either Metric, or Unified (USA), however there are still many applications where BSW and BSF are still used. The shape of the nut-head now has many profiles, and differing uses.
References:
Source 1. “Model Engineer” November 1974 – Article by Tubal Cain page 1069 - 1073
Source 2. “Model Engineer” December 1974 – Article by R.G. Markham page 1239
Bolt Science. info@boltscience.com
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