Linear division in early 20th century

Does anyone know specifically what the preferred method of linear indexing would be in a workshop nearly 100 years ago?

Today things are different but when vertical mills were less common would a rotary dividing head and gear engaging a rack be the preference over a leadscrew with changewheels? The aim being 1 turn per division to make production foolproof.

Some special precision linear dividers were screw based but what would a small production shop use?

Hi there, all,

There's a device called a 'Merton Nut', basically a sleeve of cork or other naturally elastic material, that engages with several threads of the most precise screw you can make. The idea is that it averages out the pitch errors of the screw.

It isn't load-bearing so you can't use it as a leadscrew.

Best regards,

Swarf, Mostly.

I thoughtMaudsley generated his 'master leadscrew' by using an angled blade mounted on a free-moving carrier against a rotating bar of soft metal. This created a groove sufficient to guide a cutter that could replicate the accurately cut spiral to make a proper screw... and some have argued that all modern screws are descended from taht one!

Neil

I think it's some where in vol 1 ME (1898), an artical about cutting threads free hand with chasers.

Ian S C

Sorry Michael but you CAN improve on the internal reference by adding complexity. Maudsley's template corrected leadscrew was one such example as was his method of using an auxillary screw to compensate for errors in the average pitch of a leadscrew.

Billy.

But how did he know he had pitch errors unless he had something accurate as a reference?

Ian

I have a Hauser rotary table here that has a band around the bottom of the table.

This band is scraped to compensate for any errors and these errors are transmitted by a bell crank assembly to the zero mark on the dial.

So in effect it moves the zero to compensate for any errors.

A lot of jig borer's also had this hand scaped linear beam to compensate for pitch errors

John S.

Bazyle,

http://www.practicalmachinist.com/vb/general/expiriments-leadscrew-lapping-218177/

is worth reading ... especially Posts #19 and #20

MichaelG.

Thanks for the responses and some interesting insights. Actually I wasn't so interested in accuracy as 'hackuracy' and whether for a drilling jig a local works machine shop who certainly wouldn't have a jig borer or want to sub out would be more likely to use the rack method or a geared leadscrew.

Ho Neil,

You are quite right. Maudslay built a screw generating machine that held a blade at the required helix angle and cut into a soft metal bar, this was followed by a cutting tool which actally cut the reference thread in the bar. He built a table micrometer known as 'The Lord Chancellor' with a thread around 5 feet long which could measure to within 0.0001 (ten thousandth) of an inch.

James Watt claimed that his later micrometer (shown at the Great Exhibition 1851, could measure to within one millionth of an inch, but this was later disproven by the National Physical Laboratory - it could only manage to within one fortythousandth. So very accurate threads were available from the early 19th century. In fact Jesse Ramsden was making some extremely accurate machinery in the 1770s.

Maudslay's Screw Generating Machine (in the Science Museum):

Best regards

Terry

Edited By Terryd on 02/04/2012 21:22:15

Bazyle,

"hackuracy" is a great term ... it made me smile.

I think your local works would have either relied upon a leadscrew, or spaced it out with dividers.

For the benefit of future readers: It's worth mentioning that a Gaertner-style "effective pitch adjuster" could be used [for example] to convert a 26tpi leadscrew to 1mm pitch [or vice versa] ... very handy for those occasional jobs.

MichaelG.

Terry,

If you can find it ... "The Whitworth Measuring Machine" by Goodeve and Shelley is well worth reading.

Edited By David Clark 1 on 03/04/2012 08:10:43

Thanks Michael,

I found a facsimile reprint sold by Amazon for a good price and have ordered a copy at quite a good price after reading the restricted pages. Looks to be quite a fascinating book.

Best regards

Terry

Michael,

Thank you that was in my mind the most accurate definition.

Bob

Hi Michael W,.

I think that you will find that Maudslays generating machine was very capable of producing long accurate screw threads. His original screw cutting lathe is on display in the Science Museum London and it feels quite strange handling the same handles that Maudslay himself operated. What does interest me is how Jesse Ramsden was able to produce the extremely accurate screws that he used in his dividing engines to generate the very accurate astronomical devices in the early half of the 18thC.

The system for cutting threads in wood using three cutters set in a block at the required helical angle to a bored hole with the intended screw in the form of a wooden blank which was screwed through to generate a thread was in use for many centuries and was certainly used by Gutenberg to produce the hardwood screws for his printing presses. The Greeks at least, used the method to make screws in wood for Olive and Grape presses.

The generated screw was then used to drive a length of wood fitted with a cutting tool to generate a fitted 'nut'.

Best regards

Terry

John,

Probably because it is interesting!

Please feel free to ignore my next post, where I shall reply to Terry regarding Jesse Ramsden [the 18th century Pioneer].

MichaelG

Terry,

The full text of Jesse Ramsden's paper is available here: http:// http://www.fer3.com/arc/imgx/Text.pdf

and an excellent commentary, here: http://www.fer3.com/arc/imgx/Commentary-on-Jesse-Ramsdens.pdf

Both thanks to the expert Mr Morris

http://sextantbook.com/category/chasing-tenths-of-an-arcminute/

MichaelG.

My point was that by the early 20th century these problems must have been substantially solved. Lathes had accurate leadscrews, people were making IC engines, diffraction gratings were being ruled etc. So I wasn't quite sure why the question was asked. The earlier history is interesting though, a project to reproduce as a "model" Maudslay's screw generating machine would be an interesting project to prove that he could have done it. Rather like the Science Museum making Babbage's Analytical Engine to show that it was feasible, or the group recreating Harrison's RAS Regulator, or the re-creation of "Rocket".

John,

Yes, you are right ... the problems were substantially solved.

What is interesting, and a little depressing, is how much of that knowledge has since been forgotten or ignored. That's why, every once in a while, we need to dig through the history.

MichaelG.