Simple wedged scarf by a complete novice

[Andeep]

Hi
I am a novice to this timber frame malarkey but I am a keen woodworker of 57 years, a Brit living in the Normandy countryside of France.
I would like to construct a small arbour/windbreak for the west end of our terrace to give us some protection from the prevailing winds.

Here is the plan, not to scale.




I have made the 8 corner braces


and knocked up a simplified wedged scarf



All of the wedged scarf joints I have seen here and on line are made with sloping faces. Why is this? It is far simpler for me to make with horizontal faces and for a non load bearing beam I think that it would suffice.

I would welcome comments from the experts.

Many thanks

Andy

[LeeB]

Not being a timber framer either, I'll volunteer my take on the angled cuts. Without them the joint would rely solely on friction and any pressure on it would surely invite failure. The angles impart a physical resistance to lock the joint together. Does that make sense anyone else? 

[Don P]

Under squinting is one way to develop more stiffness and bending resistance in the joint. There are many forms of scarf joint. It is one method Hewett used to date buildings and he did an extensive study of them, I've seen that online. This is a paper from testing some forms of scarfing;
https://purehost.bath.ac.uk/ws/files/112264820/WCTE_2008_Hirst_et_al_Traditional_joints.pdf

[Andeep]

I know I must be wrong or more joints would be made this may. The joint as I have made it seems to be locked by the angled cuts from top and bottom. I can't see how cutting the much longer faces at an angle as well would provide a greater locking force . 

[Andeep]

Under squinting is one way to develop more stiffness and bending resistance in the joint. There are many forms of scarf joint. It is one method Hewett used to date buildings and he did an extensive study of them, I've seen that online. This is a paper from testing some forms of scarfing;
https://purehost.bath.ac.uk/ws/files/112264820/WCTE_2008_Hirst_et_al_Traditional_joints.pdf

Don, my lost post crossed with yours. Thank you for that very informative link. I knew I was wrong and know I can see that those tests have proved it, albeit with a slight variation in my joint.
As the scarf joint in my project will not be subject to any load I will stick with it or perhaps make it simpler still and do away with the wedges and go for the under-squinted butt in halved scarf with two pegs as in the study.

[Don P]

Some more reading, this is Hewett's scarf joint chapter;
http://www.woodworkinghistory.com/hewett_scarfs_in_evolutionary_sequence_1969.pdf

Another describing some scarf failures;
http://www.dowsingarchaeology.org.uk/Ironwork/Chapter%202/2.1%20Failures.htm

[Andeep]

Oh Don, you have started something now. Firstly I just might have to find a copy of Alec Hewett's tome. Secondly a visit to Cressing Temple in Essex, is a must. And thirdly I now want to try to replicate those joints just to see if my skills are up to it.

After a visit to to Igtham Mote in Kent many years ago I made, just to see if I could, a scissor scarf (described in your link as a double splayed and halved scarf). It was not that hard to do.


Many thanks

Andy

[Don P]

It is well worth putting on the bookshelf, mine appears to be on someone else's at the moment :D
https://www.amazon.com/English-Historic-Carpentry-Cecil-Hewett/dp/0941936414

This is Jack Sobon's "Historic American Timber Joinery", there is a chapter on scarfs there as well;
https://www.ncptt.nps.gov/wp-content/uploads/2004-08.pdf

[Dana Stanley]

I know I must be wrong or more joints would be made this may. The joint as I have made it seems to be locked by the angled cuts from top and bottom. I can't see how cutting the much longer faces at an angle as well would provide a greater locking force .

I'm no expert but, I can see how a short scarf like you show would be weaker than a long one. If you think of the members as levers, the short scarf will allow a lot more force on the joint than the long one.