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Where is my dimension ?

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  • Where is my dimension ?

    Hi again yall.....
    Im trying to catch myself in any mistakes before I unknowingly just roll past them and waste effort and materials.
    I just noticed this. I have finished my cutting jig and about 1/2 way through making the form block (nose ribs)
    I just went and looked through the plans---- and I cant find anywhere that there are diameters called out for the rib lightening holes. I hadnt really thought to look---
    Page 4 shows the centers of the holes but nothing else.

    What I did earlier was I had my blueprint shop blow up 3B which shows the holes. 3B says it is a 1/2 scale drawing so I had them blow it up 2X bigger.
    I used the hole diameters from that without thinking. I did discover that the hole center marks on 3B do not match mylar wing form drawing #4. THIS
    makes me think I shouldnt use 3B for any exact measurements..........
    The ONLY dimensions I see, on 3B, are the skin rivet spacing and stiffener widths.

    Am I correct making them match the blown up drawing 3B ?????? Dont see anything in the Bob book or Eric's CD.......
    I am noticing the bend lines for the bevel on the holes will end up just barely fitting between the stiffeners it appears....... (the way I have the holes now.....)

    I dont want to proceed till I think im on the right track........ and not going down a rabbit hole.....

    Tim
    Last edited by fairchild; 12-09-2017, 11:24 PM.

  • #2
    I just went by Bob's instructions, "Scale drawing for dimensions not show"

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    • #3
      One thing I did was to make my own drawings from the originals where I had questions or wanted to be very accurate. I use both SolidWorks and AutoCAD. Because I have done a lot of fabricating from my own drawings, I find that making drawings can be a real time saver. I also planned out how I am going to make the part as I do the drawing.

      Something I did recently was to take an old drawing I had (a master drawing for a race car I built decades ago) and have my local office supply shop scan the drawing to a PDF file. From that I was able to open that drawing in AutoCAD, scale it to actual size and then trace the drawing for details I needed. I did not think to do this earlier in the building process of my Bearhawk.
      Last edited by S Lathrop; 12-10-2017, 10:56 AM.

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      • #4
        The holes are drawn "half size" Set a compass to the OD of the drawn hole and it is now set to the radius of the finished hole.

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        • #5
          BTAZ- thats effectively what I did-- blew the drawing up 2X--- then measured off it. I was just bothered that i dont know if that drawing (and those circles) are
          the correct diameters.

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          • #6
            Both methods work. Either use an engineering scale or double the drawing size. Essentially the same thing. As long as you've got enough space between the holes for the stiffeners. Mine had plenty of space.

            I started getting the ribs ready for the attach angles today. Beginning with the nose ribs, i jigged it up vertically like I learned in EAA SportAir Sheet Metal
            Christopher Owens
            Bearhawk 4-Place Scratch Built, Plans 991
            Bearhawk Patrol Scratch Built, Plans P313
            Germantown, Wisconsin, USA

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            • BTAZ
              BTAZ commented
              Editing a comment
              One thing(that I think I found in Eric's manual) was to bevel the ends of the stiffener angles at about 30 degrees to make sure they aren't in the bucking bar's way when installing the skin. Some of the skin rivets might fall on the stiffener locations and give you a headache.

            • Chris In Milwaukee
              Chris In Milwaukee commented
              Editing a comment
              Good idea. :-)

          • #7
            I sent Maria an e-mail with the question. She confirmed to use the "centers" off the mylar and the diameter off page 3B. She said everything should be to scale unless noted
            otherwise. I pointed out that the centers on 3B wernt in the correct place- that I used centers from mylar. I suggested that they might consider making a notation on the plans
            to clarify. (and save on future e-mails)
            Tim

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