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Thread: trying to figure an arc

  1. #1
    Join Date
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    Default trying to figure an arc

    I have some metal peices 1.42" long. One end is .375 wide and the other end is .355 wide. I am trying to draw a file where I can copy this piece 30 times and put them side by side and find out the arc that it creates since one end is larger than the other it would make an arc.
    I really think that this is simple but I cant seem to get a grip on it. Can anyone give me a bit of direction?

  2. #2
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    so do you need to find tangent points? if so, there is a tangent gadget available, which gives you the exterior (perimeter) tangents, and the interior (criss-cross) tangents instantly.
    Last edited by Bob T; 12-19-2015 at 01:31 PM. Reason: more information

  3. #3
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    Being metal you could probe it with a small bit or take a picture of it and trace it. I remember someone said they used a bit instead of the probe to probe a part that they wrapped foil around

  4. #4
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    I ran lines off ext circle tangents to their intersection. radius approx 22.45, height approx .72

  5. #5
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    At this point you have described a mathematically indeterminate problem. You need at least 3 points, or two tangencies to find your arc. You would need the maximum(or minimum) width near the middle to get your solution.

    You can actually use most cad programs, including vcarve/aspire to find this for you. You simply need to draw the three points and use the "draw an arc" command in vcarve/aspire and use the 3 points you have. Something like Draftsight (free 2D CAD software) gives you more options when drawing circles and arcs from limited data. In this case your maxima (or minima) is not dead center, so you would create a line at the dimension and use a tangent to that line.

    Your other option would be to place the item on a flatbed scanner and scan it. Then bring it into your design software and trace the item.

  6. #6
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    If I understand what you were asking. I put it on cad program, the 0.375 end would have a radius of 26.62566 and the 0.355 end would have a radius of 25.20566. This measure is at the sides and not the center line of piece. If this helps good, if not ask for more information.
    TFix
    T Fix
    2000 ShopBot PRT 96 CNC Tool

  7. #7
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    Quote Originally Posted by cwshop View Post
    If I understand what you were asking. I put it on cad program, the 0.375 end would have a radius of 26.62566 and the 0.355 end would have a radius of 25.20566. This measure is at the sides and not the center line of piece. If this helps good, if not ask for more information.
    TFix
    As I said, you will never solve the problem without the dimension in the middle.

    Draw a rectangle that is the same length as your part and the same height as your tallest dimension. Draw circles at the corners to represent your short dimensions (.375 and .355). Us the arc to to draw your arc. (there is an image to illustrate below)
    circle.jpg

  8. #8
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    You can draw a balanced trapezoid with those 3 dimensions, array it your 30 times, and then create the inner and outer arcs
    If your figures on sizes and radii are correct then you can figure the centerpoint and degrees rotation for each part.
    You can even do it manually by copying, pasting new copy with overlapping point at the wide end and rotating the part til it's aligned and then repeat using both, then 4, etc. Won't take long, but it may work better if your radius measurement is off a little.

  9. #9
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    Yes, what I did was draw the balanced trapezoid, then extended the long sides until they intersected. At that point is centered of Arc.
    T Fix
    2000 ShopBot PRT 96 CNC Tool

  10. #10
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    Thanks so much for your help!!!. I can always count on yall for help. Thanks again and merry Christmas!!!!!

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