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Pray at the cross...

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  • Pray at the cross...

    Hey all

    I was wondering if anyone of you knew how to calculate the angle of a cross brace...

    Say you have a 2x4 and you want to put is at an angle between 2 joits that are at x" ... u'd have to calculate the angle.

    I am sure in the old days the carpenters must have had a tool to do so... or a formula.

    I made myself a jig that I use to trace the angle but cannot figure out how to calculate it!

    thanks in advance!

    Richard

  • #2
    Re: Pray at the cross...

    ?? X 1.414=

    we use this in plumbing.

    Vince

    Comment


    • #3
      Re: Pray at the cross...

      Originally posted by Vince the Plumber View Post
      ?? X 1.414=

      we use this in plumbing.

      Vince
      That is from the angle formula for a 45. Square root of 2.

      I'm not sure but it sounds like he wants a more generic formula that would work with different angles. I don't think you'll have one formula that will do the job, but if you know some trig or geometry you can figure it yourself. Of course, in that case he probably wouldn't be asking us

      Comment


      • #4
        Re: Pray at the cross...

        unfortunately, a square + b square = c square is NOT it!

        imagine 2 joist. draw a line from the top of one joist to the bottom of the other joist. the formula above ir right... but this is for a LINE!

        not take your 2x4 and try to fit it inside the joists... your formula is no longer valid.

        what i am trying to do refers to euclidian geometry.

        your 2x4 is actually 3.5 inches high and this does not jive between the joist using pythagore's formula.

        look at the picture i've attached...

        the angle of the line "A" is about 32.5 degrees. The angle of drawing #B is about 28 degrees.... even if the distance between the 2 joists are identical.

        anybody has an idea about how to calculate this?
        Attached Files

        Comment


        • #5
          Re: Pray at the cross...

          just measure it.

          Vince

          Comment


          • #6
            Re: Pray at the cross...

            [quote=stokefire7;224419]
            Originally posted by HornyPotter View Post
            unfortunately, a square + b square = c square is NOT it!

            cause your'e doin it wrong

            well then do it... calculate it! 2 joists 24" apart... try and fit INSIDE a 2x3 or a 2x4 or a 1x1 from the top of one to the bottom of the other using pythagore's theorem. good luck! you'll never make it.

            Comment


            • #7
              Re: Pray at the cross...

              Originally posted by Vince the Plumber View Post
              just measure it.

              Vince
              and you call yourself an expert woodworker?

              Comment


              • #8
                Re: Pray at the cross...

                his name is "vince the plumber"

                I missed "expert" and "woodworker".

                BTW.......the formula is still valid. You just have to account for the thickness of the wood and not just base it on a line of zero thickness. The angles are the same. It will just require a slightly shorter piece. How much shorter depends on the angle you are working with. Using your geometry skills a second time could yield the second dimension.

                Based on the angle you determined and the thickness of the wood you could easily come up with how much shorter the piece will have to be than a line of a certain length but no thickness.

                Comment


                • #9
                  Re: Pray at the cross...

                  Is this something you need to do a few times or a process you need to be able to repeat over and over?

                  I think what you need to do is a combination of calculation and trial and error.

                  Comment


                  • #10
                    Re: Pray at the cross...

                    Carpenters use a framing square. Assuming your joist is 9& 1/4 inches high and14& 1/2 inches between joist (16" on center) lay the square on the 2"x 4' and hold the square at 9 1/4 and 14 1/2 and mark on the 9 1/4 mark (or side) Works whatever dimensions you have.

                    Comment


                    • #11
                      Re: Pray at the cross...

                      on A Good framing square there are rafter tables, which would work in your instance, and there is also a brace table on the better ones, that will tell you the length of knee type braces,

                      on figuring a rafter on can just use the square and stair step it to lay it out or do the math off the chart and calculate the length, and then one uses the rise by 12" of run to get the angles,

                      check out the pages beyond the URL there is a few pages on rafters and then one on the brace scale and some others that you may find useful,
                      http://www.tpub.com/content/construc...s/14044_56.htm
                      this s another on rafters
                      http://zo-d.com/stuff/how-do-i/using...ng-square.html
                      there is some links at the bottom of the second URL that you may find of some help as well,
                      Last edited by BHD; 04-18-2009, 05:19 PM.
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                      Comment


                      • #12
                        Re: Pray at the cross...

                        Originally posted by rofl View Post
                        his name is "vince the plumber"

                        I missed "expert" and "woodworker".

                        BTW.......the formula is still valid. You just have to account for the thickness of the wood and not just base it on a line of zero thickness. The angles are the same. It will just require a slightly shorter piece. How much shorter depends on the angle you are working with. Using your geometry skills a second time could yield the second dimension.

                        Based on the angle you determined and the thickness of the wood you could easily come up with how much shorter the piece will have to be than a line of a certain length but no thickness.


                        wrong! look at the drawing i've enclosed in a prebious post... the angles are different!

                        Comment


                        • #13
                          Re: Pray at the cross...

                          Originally posted by BHD View Post
                          on A Good framing square there are rafter tables, which would work in your instance, and there is also a brace table on the better ones, that will tell you the length of knee type braces,

                          on figuring a rafter on can just use the square and stair step it to lay it out or do the math off the chart and calculate the length, and then one uses the rise by 12" of run to get the angles,

                          check out the pages beyond the URL there is a few pages on rafters and then one on the brace scale and some others that you may find useful,
                          http://www.tpub.com/content/construc...s/14044_56.htm
                          this s another on rafters
                          http://zo-d.com/stuff/how-do-i/using...ng-square.html
                          there is some links at the bottom of the second URL that you may find of some help as well,



                          hey! i'll look at these links! it looks promissing!

                          many thanks! i'll get back to you after analyzing them!

                          cheers!

                          Comment

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