timber and the crown

[happyhero]

Hi I was watching a program the other day and the guy was putting up a massive fence and he paid more attention to detail than some would. He kept making reference to checking for the crown on the timber so that when he fitted a piece of timber he would fit it a certain way round so that it would struggle to bow ie implying by knowing where the crown is will indicate which way it will bow, if it does.

So can anyone tell me what the crown is and how to recognise it and maybe point me to a link that has pictures please?

Will every piece of timber have a crown?

Not all wood bows so is that perhaps when it has no crown or is it pot luck and it all has a crown?

Any info appreciated.

 

[anobium]

Most lengths of timber are not straight.
Normally when fitting say roof rafters or floor joists the carpenter will check the length and fit the item in question with curve uppermost, on the basis that it will eventually settle straight.
If it was the other way and can you imagine the effect on say your ceiling in your lounge.
I have heard of the phrase bowing, but crown in this contex is a new one to me.

 

[Jaffa72]

The crown refers to the annular rings of the tree.If you look at the end grain of a piece of timber you will see the growth rings,they will look like small semi-circular lines.Now if a piece of timber is going to 'crown' or cup it will do so in the direction of the line across the width of the timber & not the length(bowing).
Its hard to explain without images but basically if you imagine a bow & arrow,then the timber will cup in the direction similar you pulling the string on the bow.........does this make any sense or am i over complicating things?

 

[happyhero]

Most lengths of timber are not straight.
Normally when fitting say roof rafters or floor joists the carpenter will check the length and fit the item in question with curve uppermost, on the basis that it will eventually settle straight.
If it was the other way and can you imagine the effect on say your ceiling in your lounge.
I have heard of the phrase bowing, but crown in this contex is a new one to me.

Hi anobium thanks for your info, if it helps I saw it on a American/Canadian program so its possible we have a different name for it in UK I suppose, but it seemed like a definite thing you could find in the wood, in the grain I suppose.

 

[Jaffa72]

I just found this site,it might help you understand a little clearer http://www.geoffswoodwork.co.uk/timber growth.htm

 

[Jaffa72]

Or try this link,second line down picture on the left.
http://www.romex.co.uk/Products_Defects.htm#

 

[happyhero]

Or try this link,second line down picture on the left.
http://www.romex.co.uk/Products_Defects.htm#[/QUOTE]

Cheers Jaffa72, I think we are getting there, so would you say the 4th picture shows it best?

It shows on its edge, little rings that look like humps. So would the top be the crown then?

 

[Jaffa72]

Yes,the 4th pic is crowning,the other pics illustrate other defects found in timber.
I dont think that the 'crowning' bit is refering to the top of the board but is merely a term used for this defect.Im sure you will get other answers on this topic from someone who is more knowledable

 

[ModernMaterials]

Sorry bout this but thats not the right definition of crowning. That picture shows cupping, which is bowing across the grain.

Crowning is bowing ALONG the grain. Framers will normally have one stud 'crown up' and the next 'crown down' along a run so that they don't bend the wall out in one particular direction.

The easiest way to think of a crown is your knee being the crown in the middle of your leg.

Pick one end of a length of timber off the floor and look down its edgesright to the floor on the other end. If it curves out the left, the crown is 'up' on the left.

This is mainly a north american term and i think we would probably just say 'bowing' but because we dont build as much timber framed stuff as them, we dont really have any equivalents for 'crown up' or 'crown down'

I think what jaffa is getting at is an older and less used english meaning of crown which refers to the top part of an arch. So that when you see arch shapes in a length of timber it may be more inclined to 'cup' because of the angle of the growth rings in relation to the cut. I dont think this is what the fencing guy was talking about tho.

 

[ModernMaterials]

An American site with a pic on the right of their definition of 'crowning' :

http://www.bestdecksite.com/introPlanPg1.htm


A glossary of traditional English terms with the crown of an arch illustrated at no.83:

http://doit101.com/boycarpentry/chapter7.html

 

[happyhero]

An American site with a pic on the right of their definition of 'crowning' :

http://www.bestdecksite.com/introPlanPg1.htm


A glossary of traditional English terms with the crown of an arch illustrated at no.83:

http://doit101.com/boycarpentry/chapter7.html[/QUOTE]

Thanks ModernMaterials the first link, you hit it on the nose, that sounds exactly like what the guy was saying on the program, and thanks to you I fully understand it now, cheers mate.