Construction of a first lead screw?
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    Default Construction of a first lead screw?

    I thought I heard that the first lead screw, or a lead screw, could be constructed by making a device and running a screw making process a successive number of times. (I'm missing something here). Can a lead screw be constructed from "nothing" in the same way that surface plates can be made from "nothing" (i.e., starting out with no precision equipment?

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    If you imagine moving the tool (or a lapping disk) along a straight bedway by means of a precision wedge, like a taper attachment but run at a steep angle (the thread helix angle), you could generate a precision helix, because the precision depends on the straightness of the wedge, and that can be checked and improved by hand if necessary. I won't say it would be easy to build this rig, but not impossible.

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    My memory of my first visit to the Science Museum in London in 1978 is that they had a couple of early Maudslay screw-cutting lathes with some description of how they worked. I think they said the first step in making a master lead screw was to build a device that used a variable angle knife blade to generate a shallow sharp V-groove spiraling along the OD of a copper tube. If the knife was set to the exact angle required, it would generate the correct pitch. The knife adjustment could be by trial and error, but you had to have an accurate means of checking the pitch once the tube was cut. The tube would then be used to drive a cutter to cut a true screw thread in a steel bar, making a leadscrew.

    Larry

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    It's a pretty cool process. Make a screw, map the error, use a cam follower on the lead nut to correct error.

    Repeat until desired accuracy achieved.

    Sent via CNC 88HS

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    Quote Originally Posted by Euclidean View Post
    I thought I heard that the first lead screw, or a lead screw, could be constructed by making a device and running a screw making process a successive number of times. (I'm missing something here). Can a lead screw be constructed from "nothing" in the same way that surface plates can be made from "nothing" (i.e., starting out with no precision equipment?
    Yes, there are purely mechanical processes that allow one to iterate, making better and better screws, starting from two rocks and a stick. There is a large literature on this.

    One method is to use a greased wooden nut that is very long (tens of diameters), with a turned metal leadscrew running in the nut, controlling the thread on the work piece, this being a leadscrew as well. The short-length errors in the metal leadscrew are averaged out by the soft wood nut. This will yield very steady motion while cutting the new leadscrew.

    But what isn't fixed by averaging is overall errors of pitch. For this, people added a long cam that served to advance or retard the location of the cutter head to yield a more accurate pitch period than the original leadscrew.

    One measures the pitch period using Johansson Gauge Blocks, using this information to make the cam. And so on.


    Now days, the cutter motion is controlled using a laser Interferometer that counts fringes (wavelengths of light).
    Last edited by Joe Gwinn; 08-04-2021 at 09:07 AM. Reason: typo

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    I thought this was really cool back when it was posted. See image in post #3.
    Maudslay's Tool for originating screw threads

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    Thank you! Is this a project a beginner could tackle?

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    Buy a copy of the Moore Tools book Foundations of Mechanical Accuracy. Then go through there details and trials at making "perfect" feed screws. If you attempt this you won't be a beginner for long. I'm just not sure what you'd learn though. How we got from no accuracy to where we are now is fairly well documented with some gaps if you do enough research.

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    Wrap a triangle of paper around a cylinder and mark the edge. That is the screw thread location. Chisel it out in wood and then use that screw to make a simple lathe and another and so on until it is accurate enough to make a screw press for grapes and olives... That is how it was done 3000 years ago.
    Bill D.

    Threads in antiquity 2 - olive oil and wine press - Threading tools guide | GSR Blog

    Pliny’s Presses: the True Story of the First Century Wine Press

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    yup the first lathe made the 2nd one or part of it

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    Quote Originally Posted by neanderthal mach View Post
    Buy a copy of the Moore Tools book Foundations of Mechanical Accuracy
    This book is fascinating, highly recommend it! I got it out of the library many years ago, it's disappeared since then. Hope the guy who stole it has a twisted lead screw and elliptical half nuts (from the Mikado...)

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    Quote Originally Posted by richard newman View Post
    This book is fascinating, highly recommend it! I got it out of the library many years ago, it's disappeared since then. Hope the guy who stole it has a twisted lead screw and elliptical half nuts (from the Mikado...)
    This thread pushed me over the edge. I went to Amazon, but they wanted $1,150 for a copy. Luckily Moore only wanted $175.

    Unfortunately, Holes and Contours is no longer available directly from them.

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    On my Hendey Tool and Gaugemaker's lathe
    I can cut threads with the feed rod, driving
    the carriage through the rack and pinion.
    It cuts threads just fine, just reverse the
    spindle to back up and don't open the clutch.
    There is some math involved, I forget the difference
    between the leadscrew and feedrod ratio, but not
    impossible to do. So yes, you can cut a thread
    without a leadscrew, just use the feed rack and pinion.

    --Doozer

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    Quote Originally Posted by Euclidean View Post
    Thank you! Is this a project a beginner could tackle?
    Yes - the original inventors were by definition beginners.

    But it'll be a whole lot of work.

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    In the Birmingham science museum is a leadscrew about 2” diameter x 5 ft long, this was cut by hand using a hammer and chisel. It shows that those old boys were pretty skilled and would tackle anything.

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    Quote Originally Posted by Peter Colman View Post
    In the Birmingham science museum is a leadscrew about 2” diameter x 5 ft long, this was cut by hand using a hammer and chisel. It shows that those old boys were pretty skilled and would tackle anything.
    I would love to learn how to do that.

    I still don't quite understand how an iterative process allows you to take a lead screw that's out by such and such tolerance and continue running it through a process until it reaches some arbitrary degree of accuracy, but that says more about me and my research skills than anything else.

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    Quote Originally Posted by richard newman View Post
    This book is fascinating, highly recommend it! I got it out of the library many years ago, it's disappeared since then. Hope the guy who stole it has a twisted lead screw and elliptical half nuts (from the Mikado...)
    I was able to find it online for free!

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    If you find a book online that you can read, but not download, see if it's Hathitrust like here- Holes, contours and surfaces : located, machined, ground, ... - Full View | HathiTrust Digital Library

    Often scanned by Google. If you have a library that's a member, especially a local college library, they can often get you the pdf file for the asking.

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    I am surprised no one commented on my post.
    What I was trying to get across, is you do not
    need a screw to make a screw. A lathe carriage
    can be driven by a rack and pinion, even a
    chain and sprockets. Heck, I have seen some
    very old lathes that had their carriage driven
    by what looked like ship anchor chain. LOL
    Even rope on a spool could serve to drive a
    carriage if the rope were strong enough
    and the cut was light enough.
    You guys just seem to be fixated on the notion
    that you need a screw to make a screw.
    I have an example of that not being true
    right here in my shop with my Hendey lathe.
    So don't believe everything you know.

    ---Doozer



    Quote Originally Posted by Doozer View Post
    On my Hendey Tool and Gaugemaker's lathe
    I can cut threads with the feed rod, driving
    the carriage through the rack and pinion.
    It cuts threads just fine, just reverse the
    spindle to back up and don't open the clutch.
    There is some math involved, I forget the difference
    between the leadscrew and feedrod ratio, but not
    impossible to do. So yes, you can cut a thread
    without a leadscrew, just use the feed rack and pinion.

    --Doozer

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