olden days - hand cut threads ?

[steamingbill]

Hey,

Am currently wondering how Henry Maudsley made his first screw cutting lathe - ie how did people manage to start cutting accurate threads by hand so that Maudsley could use them to make his first screw cutting lathe. This would have been 1790's.

I get the impression from TMBR books (yes managed to buy them reasonable price at last - plough books ebay australia) that people chalked a spiral on a bar and then cut it manually.

Will continue to google.

Was wondering if anybody could recommend some other good books regarding how Maudsley did it with the resources available at the time and how we became progressively more accurate from hand cut threads to machine cut threads.

From what I've read so far we have Maudsleys screw cutting lathes started in late 1790s then we have Whitworth popping up in the mid 1800's with a device that measured lengths with an accuracy of plus/minus a few millionths of an inch - am interested in what happened in between.

So any good books to get me from just before Maudsley to just after Whitworth ?

Have tried Foundations of Mechanical Accuracy and although fascinating it doesnt quite cover what I was looking for.

I found this ............ "Henry Maudslay & the Pioneers of the Machine Age" and theres a copy in Victorian State library if anyone else is interested.

So ....... could anybody recommend any other books or web pages that would cover this period ?


Bill

[anglesmith]

Studies in the History of Machine Tools by Robert s Woodbury is vey good if you can get it at the right price. The cheapest on BookFinder at the moment is $83.00 and the dearest is $285.00 !!??? His books were published separately but it is better value to get all four in one volume.
Graeme

[cba_melbourne]

Hey,

Am currently wondering how Henry Maudsley made his first screw cutting lathe - ie how did people manage to start cutting accurate threads by hand so that Maudsley could use them to make his first screw cutting lathe. This would have been 1790's.

I get the impression from TMBR books (yes managed to buy them reasonable price at last - plough books ebay australia) that people chalked a spiral on a bar and then cut it manually..................
Bill

Bill, screwcutting is MUCH older than 1790. Look here, the third pic from top shown a German clock maker's screwcutting lathe from circa 1480: http://homepages.ihug.com.au/~dispater/turning.htm
Lots of links to ancient lathes on that site too.

Here you find on page 106 titled "SCREW-THREAD CUTTING BY THE MASTER-SCREW METHOD SINCE 1480" a more detailed description of the above lathe and many later models: http://www.gutenberg.org/files/31756...-h/31756-h.htm

Already in 1520 Augustus Kotter of Nuernberg invented spiral rifling for guns. Can't find a pic anymore. This is a later replica of a rifling lathe that would have been used in 1700 (rifling is a form of internal threading):
riflingbench1.jpg

[.RC.]

I thought multiple hand cut screws were used together to drive one carriage and that tended to average out any errors, or some other method to average out errors... A long nut maybe...

[DSEL74]

Prior to screw cutting blacksmiths wrapped a shaft with a small bar to make the thread and brazed it in place. That is how the early vice screws were made anyway.

[steamingbill]

Thanks for all the replies

I didn't realise that thread cutting was so well developed and understood before Maudslay

From the first link in cba's post above

Like Ramsden before him, Maudslay went to infinite pains to obtain accurate threads for leadscrews. He tried all known methods and finally settled on the inclined knife. The knife was mounted on a prismatic guideway on a swivelling toolholder. The oblique incision made by the knife in soft metal or wood carried it along the blank cylinder of the work as it was rotated, and by adjusting the inclination of the tool, a groove of any pitch could be cut. Using this groove as a basis, the thread was then cut by hand.

The gutenberg book is interesting and I'll keep a search open for the other book "studies in the history of machine tools"

Am fascinated by the concept that we started off with very crude hand tools and end up with super accurate modern machine tools - seems to me that at various times along that evolution, people had to do something very slowly and very carefully in order to achieve the next quantum leap in accuracy.

Bill

[bob ward]

I have read, don't have a reference, that in early times a length of thread was spiral wound around the object as a guide, and the thread was chased with hand tools. Which is where the terms thread and threading come from in relation to screw cutting.

[cba_melbourne]

..................

Am fascinated by the concept that we started off with very crude hand tools and end up with super accurate modern machine tools - seems to me that at various times along that evolution, people had to do something very slowly and very carefully in order to achieve the next quantum leap in accuracy..............

Bill

Bill, it is in the nature of machine tools, that they can be used to make parts to a higher precision than they were originally made of.

And it is often said about the lathe, that it is the only machine tool versatile enough to be capable of reproducing itself.

This is a clip about a working model of Leonardo da Vinci's "screw making machine":
http://www.youtube.com/watch?v=dwS4zHa-Eew

[steamingbill]

Bill, it is in the nature of machine tools, that they can be used to make parts to a higher precision than they were originally made of.

cba,

I believe you.

We wouldn't have a lot of modern machinery if this wasn't true.

I just don't understand how something "more precise" can be made by something "less precise" - Brain refuses to believe ........... it seems counter intuitive to me.

But the proof is all around me every day.

I guess I need to learn a bit more.

(sighs theatrically, shakes head and says to self .... "Learning how to use the wood lathe was much easier than this metal lathe caper")

Bill

[Michael G]

I just don't understand how something "more precise" can be made by something "less precise" - Brain refuses to believe ........... it seems counter intuitive to me.

There are a couple of key points that you need to understand to stop your brain protesting.

• There are techniques that 'converge' to more accurate. The classic example is scraping in three surface plates. Once you have that accurate surface then using that as a master to get flat ways is straight forward
• Most importantly the less accurate item does not automatically produce a more accurate item. It does it by combining it with some sort of manipulation that minimises the error. So for example you make a leadscrew, determine the pitch error, compensate using a flat cam and make another. Repeat...
• Measurement is really important. Provided you can measure deviations you should be able to correct them. Modern CNC uses this principle - on top of the line units position is not determined by revolutions of a screw but by direct measurement. In theory the leadscrews used can be pretty average but the measurement feedback negates the effect.

Michael

[jhovel]

.... "Learning how to use the wood lathe was much easier than this metal lathe caper"

Bill, if you were making metal items on the metal lathe to "have pretty shapes", then it's as easy as pie.
If you were to make - say - a wooden clock screwed together with wooden screws and the gears running on wooden spindles in accurately located replaceable bearings/bushes (any material), then you would find the woodlathe quite a difficult machine to use....
I guess in the end it's about precision and repeatability. If something only has to be close to the nearest millimeter or more, that's easy. If it has to be close to the nearest 100th - or it won't fit - then things get a bit more complicated.

[steamingbill]

Bill, if you were making metal items on the metal lathe to "have pretty shapes", then it's as easy as pie.
If you were to make - say - a wooden clock screwed together with wooden screws and the gears running on wooden spindles in accurately located replaceable bearings/bushes (any material), then you would find the woodlathe quite a difficult machine to use....
I guess in the end it's about precision and repeatability. If something only has to be close to the nearest millimeter or more, that's easy. If it has to be close to the nearest 100th - or it won't fit - then things get a bit more complicated.

Thanks Joe,

Never quite looked at it like that - you're right.

My wood lathe activities never needed any accuracy - and really am only a beginner at that too - closest would be an attempt at a chess set and ........ yes ......... am having trouble with consistency ..... on the pawns- I assumed it was simply lack of experience plus a clumsy hand that will get better with time and practice and some measuring and templates are required.. It did seem to me that I was achieving something far more useful on the woodlathe compared to the metal lathe for the same amount of time spent learning.

Will go and do some googling to find accurate (as opposed to pretty) work on woodlathes.

Am laid up with a sprained ankle so lotsa time for reading writing and internetting.


Bill

[cba_melbourne]

........Will go and do some googling to find accurate (as opposed to pretty) work on woodlathes.........

Well said. Because precisely made items do actually not look pretty to our brain. We prefer objects that are well finished but not geometrically perfect. Not only in wood, in metal too. Think of jewellery. A finger ring made by hand is never perfectly regular in shape. Our brain interprets this as the object hawing some charm to it. As opposed to a ring made on machine tools, our brain interprets this as cold and devoid of a soul and rejects it. This is why jewellers have not yet be replaced by CNC machines.