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Thread: A fast example of How to set up a sine bar

  1. #1
    Supporting Member shopandmath's Avatar
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    A fast example of How to set up a sine bar

    A fast example of
    How to set up a sine bar

    This is a video I made for my new students
    hopefully this will save some time and prevent mistakes in the shop
    Video URL

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    mklotz
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    Explanations of this technique of selecting blocks always seem to gloss over the fact that, even with the 81 block set, there are stack heights that cannot be constructed...

    As an example, consider 5 * sin (1.25) = 0.10907 ~= 0.1091

    0.1091 - 0.1001 = 0.009 and there is no block of this size.

    This persists until the second digit to the right reaches 5, e.g....

    0.1501 - 0.1001 = 0.050 and there is a 0.05 block.

    but

    0.15x1 where x is non-zero...

    0.15x1 - 0.1001 - 0.05 = 0.00x and we're in trouble again.
    Last edited by mklotz; 09-13-2019 at 11:15 AM.
    ---
    Regards, Marv


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    I see where you are coming from with this but if we add the 0.009 and drop the 0.0001
    The Hight or angle difference is less than what we can machine
    If its for inspection we can add a 0.100 block to the other side to compensate for the difference
    I hope this makes sense
    Ray

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    mklotz
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    Quote Originally Posted by shopandmath View Post
    I see where you are coming from with this but if we add the 0.009 and drop the 0.0001
    The Hight or angle difference is less than what we can machine
    If its for inspection we can add a 0.100 block to the other side to compensate for the difference
    I hope this makes sense
    Ray
    Well, if you can throw tenths away whenever they are inconvenient, why are you bothering with them in the first place?

    The reality is that the average machinist will probably never need to machine an angle so accurately that he needs to consider the tenths. He really doesn't need gauge blocks except for the convenience when setting sinebars. Just calculate the stack height and machine a block to that dimension.

    I discussed stack height errors at length in this post...

    Sine bar errors

    where I showed that the error equation is...

    dA = (1/cos(A)) * dS/L

    and provided a table of angle errors corresponding to a 0.001 stack height error...


    The error depends on the angle for which the sinebar is set. For:

    L = 5 in
    dS = 0.001 in

    it looks like this:

    5 0.0115029
    10 0.0116359
    15 0.0118634
    20 0.0121946
    25 0.0126438
    30 0.0132319
    35 0.013989
    40 0.0149589
    45 0.0162057
    50 0.0178273
    55 0.0199784
    60 0.0229183
    65 0.0271147
    70 0.0335043
    75 0.0442748
    80 0.0659906
    85 0.131479

    where the first column is the angle, A, in degrees and the second column is
    the error in A, dA, in degrees.

    Since a sinebar is seldom used for angles greater than 40 degrees, we can
    count on an angle error of less than 0.015 deg (0.25 mrad) if we can machine
    the stack block to an accuracy of one thou. Unless you're making highly
    critical components, don't be afraid to machine your own blocks for setting
    the sine bar.
    ---
    Regards, Marv


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    DIYSwede (09-14-2019), shopandmath (09-13-2019)

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    That is deep
    I could not even start to explain this to my students
    Thank you for the reply and the explanation
    Ray

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    Thank you for the link
    I do agree with you that gauge blocks are not always necessary
    In some cases it is just as easy to use an adjustable parallel and might be faster
    Ray

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    All the info given here has my brain locked up. Very good discussion from all. That's why I like this site.

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    Hi Guys
    This video is made for my students that range from this is my first time in a shop to year 3 apprentices
    Check out my other videos and give me your feed back
    https://www.youtube.com/channel/UC0a...hdlJy1OIlo1Qmw

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    You show care when wringing the blocks together, but then set a stack of them with a critical surface down on top of another gauge block's non-precision end in the box.
    Not good practice!

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    mklotz
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    In addition to using an adjustable parallel for the stack, there's another trick if you use a few angles frequently in your work.

    Machine a rectangular block of steel such that each of its dimensions corresponds to the stack height needed for the three angles you set most frequently. Store it with the sinebar.
    ---
    Regards, Marv


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