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  1. #1
    Senior Member Cruiser51's Avatar
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    Panel Size calculator

    This may be a really simple question and there is a nice, neat answer ... but I am going to ask it anyway.

    Often while sewing you need to make up a panel, rectangle, triangle etc. .... when you try and get a finished panel, it can be a chore to figure out the starting size of fabric required.

    Is there a calculator you can just plug in the hem you are using, finished size and shape you want and it will calculate the starting size?




    Brian

  2. #2
    Senior Member P-Dub's Avatar
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    I don't know of any, but it's really simple -- determine your finished size, decide on your hem width, and add the hem width to the finished size of each edge. (that is, if you're doing a rectangle with 1/2" hems, you need an extra 1" width and 1" length of fabric.)

    I'm not sure if there is something else you are asking....???

  3. #3
    Senior Member Cruiser51's Avatar
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    Quote Originally Posted by P-Dub View Post
    I don't know of any, but it's really simple -- determine your finished size, decide on your hem width, and add the hem width to the finished size of each edge. (that is, if you're doing a rectangle with 1/2" hems, you need an extra 1" width and 1" length of fabric.)

    I'm not sure if there is something else you are asking....???

    It seems simple enough ... but try and apply that sequence to a triangle. It falls apart pretty quickly, when you hem one side it affects the dimensions of all three sides, so as you continue to hem around the triangle it gets a little tricky to calculate. The rectangle I get ... it is straight forward as the hem only impacts only one dimension and that is a direct linear impact, along one vector, with the triangles ... it is not direct and all sides are impacted when you make a hem.




    Brian

  4. #4
    Senior Member jcksparow's Avatar
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    Quote Originally Posted by Cruiser51 View Post
    It seems simple enough ... but try and apply that sequence to a triangle. It falls apart pretty quickly, when you hem one side it affects the dimensions of all three sides, so as you continue to hem around the triangle it gets a little tricky to calculate. The rectangle I get ... it is straight forward as the hem only impacts only one dimension and that is a direct linear impact, along one vector, with the triangles ... it is not direct and all sides are impacted when you make a hem.

    I'm not sure I understand your question. Is it possible to see an example of what you mean?

    If the panel is something you only need to do once or twice, just outline the shape you need on the fabric and mark a 1" border around it to get your cut dimensions. If every line is hemmed in the same amount, the original shape should be preserved. If you're doing a triangle, you'll end up snipping some excess material at the corners created by the hems, but this won't affect the dimensions of the finished shape.
    "Now and then we had a hope that if we lived and were good, God would permit us to be pirates." -Mark Twain

  5. #5
    Senior Member P-Dub's Avatar
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    Quote Originally Posted by jcksparow View Post
    I'm not sure I understand your question. Is it possible to see an example of what you mean?

    If the panel is something you only need to do once or twice, just outline the shape you need on the fabric and mark a 1" border around it to get your cut dimensions. If every line is hemmed in the same amount, the original shape should be preserved. If you're doing a triangle, you'll end up snipping some excess material at the corners created by the hems, but this won't affect the dimensions of the finished shape.
    Yes.

  6. #6
    Senior Member Cruiser51's Avatar
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    Quote Originally Posted by jcksparow View Post
    I'm not sure I understand your question. Is it possible to see an example of what you mean?

    If the panel is something you only need to do once or twice, just outline the shape you need on the fabric and mark a 1" border around it to get your cut dimensions. If every line is hemmed in the same amount, the original shape should be preserved. If you're doing a triangle, you'll end up snipping some excess material at the corners created by the hems, but this won't affect the dimensions of the finished shape.

    I will try and explain it better. Here is a pic of the triangular panel I made



    If I do as suggested and just allow a 1" sewing allowance around the perimeter, initial logic says that will give me the panel I want ... however, lets follow the sequence of what will really happen

    Lets assume we fold the upper left side in a 1/2" double hem, the hem is 1", but doing that fold has reduced the vertical height and also the left width of the bottom and not by 1" ....

    Fold the right top and again, a 1" hem occurs, but the vertical height is again reduced, as well as the bottom right width

    and finally when you fold up the bottom hem, the vertical is reduced by the 1", BUT the bottom width is also impacted on both sides.

    The end result is that with each fold there are multiple reductions in the panels size and a 1" sewing margin doesn't work. The panel I was making is 9" vertical and 36" across the base ... make a paper template and try to apply the 1" sewing margin ... I did, it didn't work for me.


    I was trying to avoid all the math (trig shudder) but after several hours I finally made a workable panel calculator that would reliably give me the initial panel size to yield the final sized panel I required.

    If I overlooked or made this more complicated, please post it and let me know so i can figure where or if I over thought this whole idea.


    Brian

  7. #7
    Senior Member P-Dub's Avatar
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    Yes, the size will decrease as you describe, but since you are cutting your panel larger to allow for the hems, you should end up right where you want to be!

    As jcksprw suggested, draw the final shape you want on the fabric, cut larger to allow for hem allowance, fold edges down to stitch the hem, and end up at the final line that you initially drew.

    I think maybe you are overthinking it?? Or is there still something I'm not following?

  8. #8
    Senior Member Cruiser51's Avatar
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    Quote Originally Posted by P-Dub View Post
    Yes, the size will decrease as you describe, but since you are cutting your panel larger to allow for the hems, you should end up right where you want to be!

    As jcksprw suggested, draw the final shape you want on the fabric, cut larger to allow for hem allowance, fold edges down to stitch the hem, and end up at the final line that you initially drew.

    I think maybe you are overthinking it?? Or is there still something I'm not following?

    Using the example I gave and what JCKSparow suggested, to make it simpler, consider the impact on just the vertical value

    - draw in a 1" hem allowance around the desired shape, this results in a vertical size of the desired 9" +1" at the bottom and ~1.12" at the top (folding on a side is the hypotenuse) for a vertical value of 11.12"
    - make the right side hem and the vertical is reduced by 1.12" ... leaving a vertical of 10"
    - make the left side hem and the vertical is reduced by 1.12" .... leaving a vertical of 8.88"
    - make the bottom hem and the vertical is reduced by 1" .... leaving a vertical of 7.88"
    - we were aiming for 9" and the 1" allowance comes out short, by a lot

    The exact same issue occurs for the width of the bottom (only much more so) ... so the simple seam allowance just doesn't work. You can simply guess and make it much larger and trim up the bottom after the sides are done, but this wasn't about just getting the job done, it was trying to understand how to size these panels properly in the first place.



    Brian
    Last edited by Cruiser51; 08-03-2021 at 23:34.

  9. #9
    Senior Member Cruiser51's Avatar
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    Squares, rectangles and circular panels will all follow the regular sewing allowance process, but triangles are special I guess.

    I would venture that is because hemming on square or rectangular panels only affect 1 dimension at a time, whereas any hem on a triangle will impact two dimensions (vertical and horizontal). The impact is also not a one to one relationship in that the reduction components are usually the hypotenuse of the triangle formed by the hem at each end of the hem.

    In the example above, to achieve a final triangular panel with a 9" vertical and a 36" base, you need to start with a fabric piece of 12.24" vertical and a base of 44.27 .... the actual allowance dimensions are specific to the panel vertical and base being used.

    The whole exercise was to be able to produce bugnet panels for 2 more versions of the comfort bridge I posted ... trial and error or guessing can be a frustrating process, being able to just calculate the specific panel size should make it easier and faster.


    Brian

  10. #10
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    Quote Originally Posted by Cruiser51 View Post
    Using the example I gave and what JCKSparow suggested, to make it simpler, consider the impact on just the vertical value

    - draw in a 1" hem allowance around the desired shape, this results in a vertical size of the desired 9" +1" at the bottom and ~1.12" at the top (folding on a side is the hypotenuse) for a vertical value of 11.12"
    - make the right side hem and the vertical is reduced by 1.12" ... leaving a vertical of 10"
    - make the left side hem and the vertical is reduced by 1.12" .... leaving a vertical of 8.88"
    - make the bottom hem and the vertical is reduced by 1" .... leaving a vertical of 7.88"
    - we were aiming for 9" and the 1" allowance comes out short, by a lot

    The exact same issue occurs for the width of the bottom (only much more so) ... so the simple seam allowance just doesn't work. You can simply guess and make it much larger and trim up the bottom after the sides are done, but this wasn't about just getting the job done, it was trying to understand how to size these panels properly in the first place.



    Brian
    This doesn't make sense! Your second hem along the left side leaves the height the same, or should if you are doing the hem properly. There's some overlap at the corners that makes things a little awkward.

    Try taking out the peaks that form this overlap to form little triangles at each vertex. Hard to describe but you are taking a diamond shape out from each corner so that the desired apexes are exposed. Doing this will mean that each hem is basically a single edge so you aren't "reducing" the opposite dimension.
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