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Thread: Improvised tangent bar

  1. #11
    rossbotics rossbotics's Avatar
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    I agree on the mechanical movement and what you say about a table, I thought maybe you might be up for a challenge like myself, if someone doesn't need that high end precision then this design would work for that, there is another way to elevate the upper bar but you couldn't raise it only about 20° not 44°, this is the only way I see to accomplish such movement (mechanically)

    I'll make a deal with you, I'll give you the measurements of the 3 points of my triangle, you then in return tell me what the T.P.I. are on the screw I'll be making, figure it to where one revolution on the dial would be equal to say .250" - .500" rise on the upper bar ? doesn't matter there to much, just as long as it's nothing oddball, I can change the three measurements on triangle to whatever anytime.

    I think you and I could come up with something that would be satisfactory for your home shop machinist,

    Doug
    Last edited by rossbotics; 06-20-2018 at 02:16 AM.
    Comments are always welcome

    Doug

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  3. #12
    mklotz mklotz's Avatar
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    Well, I worked out the geometrical relationship for what you pictured. In a word, it's not pretty. I knew the relation of angle to screw movement would be nonlinear but it's even worse than I thought.

    The attached diagram shows the relevant equations that relate the angle of the upper plate, 'z', to the location of the pivot on the moving nut, 'x'.

    At the risk of insulting your intelligence, I'll point out that mathematics always works with angles in radian measure, so the pi/2 is the equivalent of 90 degrees.

    Improvised tangent bar-001.jpg
    ---
    Regards, Marv


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  5. #13
    philipUsesWood&Brass's Avatar
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    I know this is a little off tangent (attempt of Pun) but I saw this while shopping for "V" Blocks and Bought one:

    Now, To have energy to SPARE for hobby time!!!!

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    philip The Pacific NorthWET is dry!
    Last edited by philipUsesWood&Brass; 06-20-2018 at 04:18 PM. Reason: spelN Airs

  6. #14
    mklotz mklotz's Avatar
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    Quote Originally Posted by philipUsesWood&Brass View Post
    I know this is a little off tangent (attempt of Pun) but I saw this while shopping for "V" Blocks and Bought one:

    Now, To have energy to SPARE for hobby time!!!!

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    philip The Pacific NorthWET is dry!
    I've got one. Save your money.

    The scale is too tiny to read easily and the vernier is a joke. It works OK as an adjustable holder if you have precision angle blocks or a sine bar with which to set it. (Of course, if you have those you don't need it.) The adjustment locking screw is on the bottom - a master stroke of bad design.

    Too small to serve as a boat anchor, it's only real utility is as a paper weight.
    ---
    Regards, Marv


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  8. #15
    rossbotics rossbotics's Avatar
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    Quote Originally Posted by philipUsesWood&Brass View Post
    I know this is a little off tangent (attempt of Pun) but I saw this while shopping for "V" Blocks and Bought one:

    Now, To have energy to SPARE for hobby time!!!!

    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    philip The Pacific NorthWET is dry!

    Don't waist your money
    Comments are always welcome

    Doug

  9. #16
    rossbotics rossbotics's Avatar
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    The math will never work out just right to use with a calibrated handwheel , got on cad this morning, no way, to many variables, waisted time, oh well Marv we tried, looked good anyway LOL

    Doug
    Last edited by rossbotics; 06-21-2018 at 01:34 AM.
    Comments are always welcome

    Doug

  10. #17
    mklotz mklotz's Avatar
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    Searching "tangent bar" on Google Images led to this device...

    VERTEX Micrometric Tangent Bar & Angle Gauge Block Set - Secure Tooling Sdn Bhd

    which is emphatically NOT a tangent bar. Rather, it's a limited range sine bar with the conventional gauge block stack replaced by a calibrated screw. Now, you can get away with this as long as the angle is very small. When sin(A) is small, it's true that:

    sin(A) ~= A

    (angles expressed in radians). In another thread...

    Getting an angle on angles

    I showed this chart...

    angle = 1 deg: sine = 0.017452, radians = 0.017453, error = 0.005077 %
    angle = 2 deg: sine = 0.034899, radians = 0.034907, error = 0.020311 %
    angle = 3 deg: sine = 0.052336, radians = 0.052360, error = 0.045707 %
    angle = 4 deg: sine = 0.069756, radians = 0.069813, error = 0.081278 %
    angle = 5 deg: sine = 0.087156, radians = 0.087266, error = 0.127037 %
    angle = 6 deg: sine = 0.104528, radians = 0.104720, error = 0.183005 %
    angle = 7 deg: sine = 0.121869, radians = 0.122173, error = 0.249205 %
    angle = 8 deg: sine = 0.139173, radians = 0.139626, error = 0.325666 %
    angle = 9 deg: sine = 0.156434, radians = 0.157080, error = 0.412420 %
    angle = 10 deg: sine = 0.173648, radians = 0.174533, error = 0.509506 %

    Because of the very linear relationship, especially in the range of 0 to 5 degrees, a calibrated screw as pictured in the earlier reference is possible. But it's still a sine bar, not a tangent bar.

    The simplest conception of a tangent bar would look roughly like a sine bar. The gauge block stack would be replaced with a bar of fixed height, "Y". A screw would allow this bar to be slid back and forth beneath the bar holding the work such that the distance of the bar from the pivot, "X", could be adjusted. Then the bar angle could be found from:

    tan(A) = Y / X

    Of course, the dial on the screw could not be easily calibrated because of the very non-linear form of the tangent function. This explains why one never sees commercial versions of such a device.
    ---
    Regards, Marv


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  11. #18
    rossbotics rossbotics's Avatar
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    This is exactly why I said we could not use a graduated dial, oh well off to something beter


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    Comments are always welcome

    Doug

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