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Thread: geometric solution for circular bolt hole

  1. #1

    Default geometric solution for circular bolt hole

    I just came across this geometric solution to laying out bolt hole patterns on a circle. For any diameter circle AD divide the diameter into as many equal part as bolt holes needed. Then draw an arc intersection that has a radius of the diameter of the circle from A and D and labial this E. A,D,E form an equal lateral triangle with A,D as diameter of circle. Now draw a line from E throw the second equal point from A on the diameter to intersect with the far side of arc of the circle and labial this F. Now take dividers and set to length A,F. Use this length to work around circle to divide the circle evenly.

  2. #2
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    Before looking for a mathmatical proof of this, I tried a few examples with my CAD program. It works for 3, 4, and 6 divisions but not for 5, or 12. It appears to be an approximation that is limited to some low count divisions.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  3. #3
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    Why not just use TRIG, it's spot on for any number of holes, or refer to Machinery's Handbook.

  4. #4
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    Yep, Machinery handbook, Everede bolt circle slide rule or DRO. Works perfect everytime.

    BUT, if you have to lay out the bolt circle by hand, then using cordinates don't work. I use the guess work method and keep trying untill all the holes fit evenly on the circumference.
    It's only ink and paper

  5. #5
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    Marvin Klotz posted a program to do this in dos,

    I posted one that does polar holes locations in visual basic.. runs in windows.. It is archived on the www.metalillness.com site in documents section.
    Excuse me, I farted.

  6. #6

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    Paul
    It does work for 5 divisions. I jest ran it on my CAD program. It is not approximate I expect you set your cad program to round to only 3 digits set to 6 or more it is dead nut on.
    Luthor
    Can you measure 100 thousands I cant you can use jest parallels and scribe and careful layout to do it.
    Carld, David
    Yes DRO and dividing head will do it. I have seen posts of Newbes asking how to make dividing plates this will work with jest careful layout.

  7. #7
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    [QUOTE=New chips]Paul
    Luthor
    Can you measure 100 thousands I cant you can use jest parallels and scribe and careful layout to do it.

    Huh????????

  8. #8
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    I've done it with graph paper, caliper and a punch too.

    You can lay it out on cad, print it 1:1 and punch right through the paper.. I used to do printed circuits like this too.. drill right through the paper.

    Stubborn as heck.. You have to be when you are poor.
    Excuse me, I farted.

  9. #9
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    Unhappy

    buy youself a chord rule and a dividers, it works, flanges that fit arent that difficult with a little practice and a lot of faith

  10. #10
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    Quote Originally Posted by New chips
    Paul
    It does work for 5 divisions. I jest ran it on my CAD program. It is not approximate I expect you set your cad program to round to only 3 digits set to 6 or more it is dead nut on.
    Luthor
    Can you measure 100 thousands I cant you can use jest parallels and scribe and careful layout to do it.
    Carld, David
    Yes DRO and dividing head will do it. I have seen posts of Newbes asking how to make dividing plates this will work with jest careful layout.
    My CAD is "set" to more than 6 digits. Five inch circle divided into five and it was off by about 0.002" per hole: total error at the end was about 0.010". Eight inch circle divided into eight and each hole is off by 0.013": total error about 0.104". Six inch circle divided into 12 and each hole was off by almost 0.025": total error about 0.300". I don't know.

    Have you seen any proper mathematical proof of this method? Are you sure you did it properly in the CAD program? There are so many other ways that I wouldn't risk using this.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

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