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Re: [MedievalSawdust] Wood load strength

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  • Conal O'hAirt Jim Hart
    There is an option that would do two things.... allow you to use thinner stock making it less expensive and smaller pieces for less waste. ( which might allow
    Message 1 of 9 , Mar 1, 2009
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      There is an option that would do two things....

      allow you to use thinner stock making it less expensive
      and smaller pieces for less waste. ( which might allow
      you to use a more expensive and stronger wood.... )

      and

      allowing you to slightly change the orientation of the grain
      making it a little stronger.


      You could glue two pieces of 3/4" thick together to make 1 1/2"
      thickness..... ( might be a little hard to visualize and to explain )

      but you would still have the weak point at the center pivot....hmm....




       
      Baron Conal O'hAirt / Jim Hart

      Aude Aliquid Dignum
      ' Dare Something Worthy '

    • AlbionWood
      Period problems have period solutions! (quoting Duke Cariadoc) Don t futz around with laminating etc., just figure out how the same issue was treated by the
      Message 2 of 9 , Mar 1, 2009
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        "Period problems have period solutions!"  (quoting Duke Cariadoc)

        Don't futz around with laminating etc., just figure out how the same issue was treated by the people who made the chairs 500 years ago... some of which are still around today... guess they managed to solve this question!

        /rant

        Tim


        Conal O'hAirt Jim Hart wrote:
        There is an option that would do two things....

        allow you to use thinner stock making it less expensive
        and smaller pieces for less waste. ( which might allow
        you to use a more expensive and stronger wood.... )

        and

        allowing you to slightly change the orientation of the grain
        making it a little stronger.


        You could glue two pieces of 3/4" thick together to make 1 1/2"
        thickness..... ( might be a little hard to visualize and to explain )

        but you would still have the weak point at the center pivot....hmm....




         
        Baron Conal O'hAirt / Jim Hart

        Aude Aliquid Dignum
        ' Dare Something Worthy '

      • AlbionWood
        USDA publishes a book of engineering data for wood structures. That would be your best bet. It will give you shear strengths and other values for most commonly
        Message 3 of 9 , Mar 1, 2009
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          USDA publishes a book of engineering data for wood structures.  That would be your best bet.  It will give you shear strengths and other values for most commonly used woods.  You'll have to do the engineering calcs yourself - resolving the stress vectors, calculating bending moments, shear stress, etc, before you can use any of the values in the book.  Anyone who struggled through Strength of Materials in college will tell you that's not a trivial exercise!

          But you can't go too far off by using the same wood and the same dimensions as the original chairs.  Dantescas are pretty strong if you cut that crossing-joint carefully and use good wood.  Avoid red oak or other coarse-grained, easily-split wood.  If you're really concerned for strength, find some elm.

          Cheers,
          Tim




          Talmoor wrote:
          Does anyone have a good site or book for figuring the weight load a 
          piece of wood can take? I am making a dantesca chair and wonder how 
          much of a limit it can take and if there is any way to strengthen it.
          
          
          Alasdair
          
          
          
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        • Bill McNutt
          Generally, my response to the observation: Geeze, that looks flimsy has been 1) Use a denser wood. Oak, Hickory, and even walnut hold up better than pine
          Message 4 of 9 , Mar 1, 2009
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            Generally, my response to the observation: “Geeze, that looks flimsy” has been 1) Use a denser wood.  Oak, Hickory, and even walnut hold up better than pine and poplar.  2) Use MORE wood.  2” thick is stronger than 1” thick.  And, finally, 3, re-inenforce it with metal.

             

            All period solutions.  All add more weight.

             

            Will

             

            From: medievalsawdust@yahoogroups.com [mailto:medievalsawdust@yahoogroups.com] On Behalf Of AlbionWood
            Sent: Sunday, March 01, 2009 6:39 PM
            To: medievalsawdust@yahoogroups.com
            Subject: Re: [MedievalSawdust] Wood load strength

             

            "Period problems have period solutions!"  (quoting Duke Cariadoc)

            Don't futz around with laminating etc., just figure out how the same issue was treated by the people who made the chairs 500 years ago... some of which are still around today... guess they managed to solve this question!

            /rant

            Tim


            Conal O'hAirt Jim Hart wrote:

            There is an option that would do two things....

            allow you to use thinner stock making it less expensive
            and smaller pieces for less waste. ( which might allow
            you to use a more expensive and stronger wood.... )

            and

            allowing you to slightly change the orientation of the grain
            making it a little stronger.


            You could glue two pieces of 3/4" thick together to make 1 1/2"
            thickness..... ( might be a little hard to visualize and to explain )

            but you would still have the weak point at the center pivot....hmm....



             

            Baron Conal O'hAirt / Jim Hart

            Aude Aliquid Dignum
            ' Dare Something Worthy '

             

          • Dave Manley
            Here is a link to Chapter 4 - The Mechanical Properties of Wood from the Wood Handbook Posted by the US Forest Service Website.
            Message 5 of 9 , Mar 2, 2009
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              Here is a link to "Chapter 4 - The Mechanical Properties of Wood" from the Wood Handbook Posted by the US Forest Service Website. 


              this gives the Modulus of Elasticity and Rupture plus a work to maximum load ratio of many different types of wood.

              It may be more info than what you are looking for, but interesting reading for engineering types. :-D
               
              Dave Manley
              Et in Arcadia ego


            • Alex Haugland
              With the dantesca chair style, much of the strain on the joint can be alleviated by making sure that the legs make good, solid contact to both sides of the
              Message 6 of 9 , Mar 2, 2009
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                With the dantesca chair style, much of the strain on the joint can be alleviated by making sure that the legs make good, solid contact to both sides of the pivot joint, before the lap joint for the pivot.  That transfers much of the weight and downward force on the chair directly from the arms and seats to the legs without passing it through the pivot joint, which keeps the chair strong.

                --Alysaundre Weldon d'Ath
                Barony of Adiantum, An Tir

                Talmoor wrote:

                Does anyone have a good site or book for figuring the weight load a
                piece of wood can take? I am making a dantesca chair and wonder how
                much of a limit it can take and if there is any way to strengthen it.

                Alasdair


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