Replies

1. 
   SgianDubh | Dec 12, 2008 03:36am | #1

   "Hickory has high bending and crushing strengths, high stiffness and very high shock resistance."

   The terms refer to mechanical properties of the wood.

   For example, high bending strength means that a stick of wood at a specific MC percentage subjected to a specific transverse load, eg, Newtons per square millimetre, will only deflect by a specific amount. This is useful to know for things like ladder rungs where a high or very high bending strength is required. English oak for instance has high bending strength making it suitable for this purpose whereas most willows have low bending strength number making them unsuitable.

   Stiffness brings into play things like modulus of elasticity, ie, the wood's ability to recover from a load applied perpendicularly to the grain, which is again useful for determining the usefulness of a wood where such stress might be applied as in the case of ladder rungs. English oak is high on this score too, so making it doubly suitable for this purpose. 

   Resistance to crushing refers to loads applied to the end grain of the wood, eg, columns, posts, pit props, etc. It is an indication of a wood species' stiffness or ability to resist a load applied vertically.

    Specific values for these properties attached to a wood species is not necessarily an indication of how well that species bends as in steam bending or laminate bending. Going back to the earlier examples of English oak and most willows, the former  has good bending characteristics whereas most willows have relatively poor ones. 

   For these characteristics one test uses wood at 12%MC that is 1" thick steamed for a mininum of 45 minutes. It gives the tightest radius achievable under these conditions that a wood species will bend to with less than a 5% failure rate. So a wood species cut to this thickness at 12% MC, then steamed that will consistently bend to a radius of 150 mm (6") or less with very few failures is classified as 'very good'; English oak falls into this category. Another species, eg, the willows cited earlier, if treated the same way, will only bend to a radius of 510- 750 mm (21"- 30") successfully, ie, with less than a 5% failure rate and its steam bending characteristics are therefore 'poor'. However, one caveat to all of this is that most people attempting steam bending prefer to use wood that is wetter than 12% MC because wetter wood is more supple and bends easier. The most favoured compromise MC for most steam bending jobs is about 20- 23%.

   It is a subject that does take a bit to get your head around, but I hope I have managed to make some of the rudimentary points clearer in this very short post. I suspect you do not want to read everything I have on this subject, ha, ha--- ha, ha, ha. Slainte.

   Richard Jones Furniture

   
   

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   Edited 12/11/2008 7:42 pm by SgianDubh

1. 
   WillGeorge | Dec 12, 2008 04:01am | #2

   This is useful to know for things like ladder rungs where a high or very high bending strength is required.

   As in SPLIT?  NOT a Table sawn 'stick" ! I understand that!

   I once made a Cross Bow out of Willow. Illegal as I recall here in my home town. I have several!.. I WILL not SHOOT AT anything alive...

1. 
   SgianDubh | Dec 12, 2008 11:29am | #4

   "As in SPLIT?  NOT a Table sawn 'stick""

   As in give way or break when you put your foot on the rung. The word split perhaps better indicates longitudinal separation of the fibres rather than a cross grain break. Slainte.Richard Jones Furniture

2. 
   WillGeorge | Dec 12, 2008 04:06am | #3

   rudimentary points clearer .. YES.. And then some..I suspect you do not want to read everything I have on this subject, ha, ha--- ha, ha, ha. Slainte.

   I can read but not sure what I am reading!

   I suspect you do not want to read everything I have on this subject.

   i do...

    

   Edited 12/11/2008 8:21 pm by WillGeorge

1. 
   SgianDubh | Dec 12, 2008 11:33am | #5

   "i do..."

   You'll have to wait a bit then: I'm still working on the book, but when it is out, published and all that, assuming it ever makes it to that stage, I'll be the first to let you know. Then you'll be able to nod off to sleep to order as you skip lightly through the entertaining prose, ha, ha--- ha, ha, ha. Slainte.Richard Jones Furniture

2. 
   roc | Dec 12, 2008 11:58am | #6

   >Bending strength

   I believe another term for this is ' degree of resistance to elastic deformation '. There. But more people will understand the previous term so that is more common out side the halls of higher education. Which I am proud to say I have walked along the side walk near them walls many a time !

   Of course this is not to be confused with the degree of plastic deformation which is going to cost you for another book and classes to learn something about that and you don't get no degree without takin' that class; we will see to that we will. harumph Harumph !

   Another example is on bicycles they have a term they use "bottom bracket" well that is nothing more than the crank bearing but do you think they could just say crank bearing? No that is too clear. My favorite is the European term "central movement". I like that one.

   Headset ? What is a "headset" them's the steering bearings. Never could get those I worked with to write that or say that to the customers.

   roc

   
   

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   Edited 12/12/2008 4:00 am by roc