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Go by full scale drawings off of the plans or, go by the measurements??

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  • Go by full scale drawings off of the plans or, go by the measurements??

    OK, It may seem minor but here's my question..... Go by full scale drawings off of the plans or, go by the measurements?? I'm making templates for my wing spar plates. While doing so, I've noticed that the "full size drawings are about 1/16 " off of what the measurements call for on the plans. I assume that the difference is caused by the copy machine for the plans and I have adjusted my templates to match the measurements by measuring from the center line of each piece. Am I doing this correctly?

    Cameron

  • #2
    Sounds like a good solution. Just make sure you do all the parts the same way. And also cut your adjusted drawings to the center of the line, if that’s how you measured them, so the finished parts are the correct dimension.
    Christopher Owens
    Bearhawk 4-Place Scratch Built, Plans 991
    Bearhawk Patrol Scratch Built, Plans P313
    Germantown, Wisconsin, USA

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    • #3
      Bear in mind that paper grows and shrinks dramatically based on humidity. That is the reason wing templates are on Mylar. Best to scale as you have outlined.

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      • #4
        I didn’t think about the paper growing and shrinking. It has been humid the last week or so. Thank y’all for your replies. This Bearhawk Forum is Great!

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        • #5
          measure 3 times then cut or drill, make sure, it can cost you in time and Money. most of all make sure to enjoy the journey!

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          • #6
            I took the time to make electronic drawings from many of Bob's drawings. I use AutoCad and SolidWorks. I did this to better understand what I was building and if I wanted a particular measurement, I could get that measurement to 3 decimal accuracy. It was especially useful for the spars. Also there are many parts that can be produced on numerical controlled machines and those parts need to be drawn in something that can be translated into machine languages.

            The other advantage of doing electronic drawings is that for things like brackets I can print the part on paper and then glue it to the metal as a cutting template. 3M makes a great spray adhesive for this purpose.

            I feel that the time spend making electronic drawings was more saved in building time and reducing wasted material.

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            • #7
              The autocad sounds awesome but I have zero experience in that sort of thing. I better stick to a ruler and a pencil.

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              • #8
                Always keep in mind production tolerance and the intent of the part being fabricated. Reality is for hand layout/fabrication you likely will be able to hold +/- 1/16" of an inch.

                For example, the spar plates in discussion really should be a snug fit between the upper/lower spar cap strips. If you placed the spar cap strip spacing distance at the outer edge of the tolerance and built the spar splice plate to the low end of the tolerance you could have 1/8" gap which would be undesirable.

                So quite often you will be building parts to "fit", accommodating the tolerance buildup from earlier fabrication/assembly.

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                • #9
                  Originally posted by Cameron Ramsey View Post
                  The autocad sounds awesome but I have zero experience in that sort of thing. I better stick to a ruler and a pencil.
                  SolidWorks has a free program called DraftSight. The program is a free down load and is very much like Auto Cad. There is a very good tutorial program for DraftSight. The program is 2D but will function with AutoCad commands. And you can move drawings between both programs.

                  As a EAA member you can get an educational version of SolidWorks. Depending on the task, I will strat drawing a project with either AutoCad or Solid works depending on what the project involves.

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                  • #10
                    BTAZ has a good point. Having CAD drawings that can give you dimensions to 3 decimal places doesn't help unless you have some sort of CNC cutter in your garage! Also, you need to make allowance for deburring etc after cutting.

                    Having previously built a "flat-pack" RV10, I didn't have to worry too much about this sort of thing but there were still certain brackets and stuff that were cut from angle where things could go wrong if you were too aggressive about getting rid of cut marks with the file and Scotchbrite wheel.

                    I think you can do better than +/-16th and (with care) get to within +/- 32nd. That still only gives you 1/16" as the closest fit you can practically achieve. I'm sure Bob took this into account in his stress calculations!

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                    • Chewie
                      Chewie commented
                      Editing a comment
                      Part of the reason I think Bob overdesigned many of the structural aspects is because he knew people like me would be building it.
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