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Old 07-18-2021, 09:56 AM
ojh ojh is offline
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Default Problem with paper patterns

How do you make a paper pattern for compound curves? Suppose I'm doing a fender, I lay my paper out and the part I need to pattern is 24" left to right and it has a 1" low crown. I lay my paper directly on it and copy the information then lay the pattern on a flat sheet and it is 25" left to right because of the crown and all my information is wrong.
How do you predict where the information should be?
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Old 07-18-2021, 11:34 AM
blue62 blue62 is offline
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The information on the paper pattern is correct.
If you were to take the panel you describe and flatten it out it would be 25" across just like the paper pattern. it is 24" shaped because of the 1" crown.


The paper pattern gives you the correct size blank (flat sheet) before shaping. They also show you where to stretch and where to shrink along with much other information. Like where the beginning, middle, and end of a radius is. where blend areas are. where returns are. where body lines are. Where profile gauges go. And more.
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Last edited by blue62; 07-18-2021 at 11:39 AM.
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Old 07-18-2021, 12:19 PM
ojh ojh is offline
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For conversation sake, lets say you use the 25" pattern to cut the blank out and then stretched the blank to create the crown and then made a pattern from it - wouldn't it be 26"?
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Old 07-18-2021, 12:51 PM
blue62 blue62 is offline
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Quote:
Originally Posted by ojh View Post
For conversation sake, lets say you use the 25" pattern to cut the blank out and then stretched the blank to create the crown and then made a pattern from it - wouldn't it be 26"?

If you shape the part correctly to fit your profiles and meet your reference marks both patterns would be identical.



Take a flat sheet of paper (pattern) 12" x12" lay it flat on a table it will cover an area 12"x12." Fold it in half then fold in half again. Now it covers an area 4"x4" but the sheet of paper (pattern) is still 12"x12".

Wad it up in a ball now it is a different shape and covers a still different area.
The sheet of paper (pattern) layed out flat is still 12"x12".
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Old 07-18-2021, 04:31 PM
Jaroslav Jaroslav is offline
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Make the same shape from a piece of paper. I use paper tape and wrapping paper. You place the paper imprint of the shape on the table and adjust it so that it is straight. Perimeter = sheet metal neckline. In places where there are gaps in the paper, you have to shorten the fibers. In places where the fibers overlap, you have to extend them. Paper is the law. It will show everything.

There are some examples in this thread, but I also show it in my other threads.



https://www.allmetalshaping.com/showthread.php?t=19171
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