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Thread: How to turn ogives

  1. #1
    Supporting Member mklotz's Avatar
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    How to turn ogives

    An ogive is the shape formed by the pointed Gothic style arches. It is formed by the intersection of two circular arcs such that a sharp point is formed at the point of intersection. Of more application to metalworkers, 'ogive' is also used to describe the three dimensional shape typical of a rocket nose cone. Its cross-section has the same mathematical description as the Gothic arch.

    Ogives can be turned incrementally on a lathe by first developing a table of (x,y) values that define the shape, then making a series of plunge cuts based on those values. A final finish is then done with a file and emery paper.

    The attached diagram shows the math to develop the (x,y) value pairs as a function of the parameters of the desired ogive. Tedious work at best; that's why I wrote a program (OGIVE.C) to do this. An input data file is used to specify the ogive parameters and the details of the 'x' step size and tool width then, when the program runs it produces a cutting schedule that can be carried to the lathe to guide the turning.

    How to turn ogives-ogive.jpg

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  2. The Following 4 Users Say Thank You to mklotz For This Useful Post:

    Bony (Apr 20, 2021), NailByte (Apr 21, 2021), NortonDommi (Apr 12, 2021), Toolmaker51 (Apr 13, 2021)

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    Thanks mklotz! We've added your Ogive Turning Calculator to our Machining category,
    as well as to your builder page: mklotz's Homemade Tools. Your receipt:




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    Supporting Member rgsparber's Avatar
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    Quote Originally Posted by mklotz View Post
    An ogive is the shape formed by the pointed Gothic style arches. It is formed by the intersection of two circular arcs such that a sharp point is formed at the point of intersection. Of more application to metalworkers, 'ogive' is also used to describe the three dimensional shape typical of a rocket nose cone. Its cross-section has the same mathematical description as the Gothic arch.

    Ogives can be turned incrementally on a lathe by first developing a table of (x,y) values that define the shape, then making a series of plunge cuts based on those values. A final finish is then done with a file and emery paper.

    The attached diagram shows the math to develop the (x,y) value pairs as a function of the parameters of the desired ogive. Tedious work at best; that's why I wrote a program (OGIVE.C) to do this. An input data file is used to specify the ogive parameters and the details of the 'x' step size and tool width then, when the program runs it produces a cutting schedule that can be carried to the lathe to guide the turning.

    Click image for larger version. 

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    Ah yes, Manual Numeric Control. As I understand it, the technique was first used to make helicopter blades near the end of WWII. Guy Lautard's Bedside Reader has a great article on this. I translated his approach into a pocket calculator but, for the general case, I think a spreadsheet works better.

    Rick
    Rick

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    Supporting Member mklotz's Avatar
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    Quote Originally Posted by rgsparber View Post
    Ah yes, Manual Numeric Control. As I understand it, the technique was first used to make helicopter blades near the end of WWII. Guy Lautard's Bedside Reader has a great article on this. I translated his approach into a pocket calculator but, for the general case, I think a spreadsheet works better.

    Rick
    I prefer to call it HAM - Human Assisted Machining - the flip side of CAM.
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    Supporting Member rgsparber's Avatar
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    Quote Originally Posted by mklotz View Post
    I prefer to call it HAM - Human Assisted Machining - the flip side of CAM.
    Doesn't sound too Kosher to me ;-)

    Rick
    Rick

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    Extracted salient point of Marv's present(tation).
    attached diagram shows the math to develop the (x,y) value pairs as a function of the parameters of the desired ogive. Tedious work at best; that's why I wrote a program (OGIVE.C) to do this.
    So, for the rest of us, adversity factor is...?

    Far as acronyms go, Manual Numerical Control is good, Human Assisted Machining is too; how about MCC?
    Manual Coordinate Control?
    Last edited by Toolmaker51; Apr 13, 2021 at 06:48 PM.
    Sincerely,
    Toolmaker51
    ...we'll learn more by wandering than searching...

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    Does anyone know if the ogive cross section shape has any special characteristics, like a shape for minimal drag.
    I'm helping a mate build an aircraft (full size Mk 1 Spitfire) and it would be useful to know for machining things like pitot tube fairings etc.

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    Somewhere in the depths one of the books I have on fluid dynamics has 1/2 a chapter on the Ogive shape as it pertains to airships,(blimps with engines). From memory much depends on speed and within certain boundaries the shape has minimal drag. Been a good 10 years since I saw it though otherwise I'd copy the relevant pages for you.
    I am sure someone with more in depth knowledge will have the answer.

  10. #9
    Supporting Member mklotz's Avatar
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    Quote Originally Posted by Bony View Post
    Does anyone know if the ogive cross section shape has any special characteristics, like a shape for minimal drag.
    I'm helping a mate build an aircraft (full size Mk 1 Spitfire) and it would be useful to know for machining things like pitot tube fairings etc.
    There's an excellent Wikipedia article which discusses the various shapes and their drag characteristics in different speed domains...

    https://en.wikipedia.org/wiki/Nose_c...haracteristics



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