## Re: [MedievalSawdust] Wood load strength

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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
Message 1 of 9 , Mar 1, 2009
"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 '

• 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 2 of 9 , Mar 1, 2009
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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• 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 3 of 9 , Mar 1, 2009

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 '

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

• 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 5 of 9 , Mar 2, 2009
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