practice scarf joint

[Greg]

Here's my first attempt at making a 8 foot timber into a 6 foot timber ;-)

Turned out kinda rough. The piece of timber I was practicing on wasn't the greatest. Especially since there is a large check right through the middle of my wedge/key.

Anyways, got the idea now. Whew, it was alot of work getting it to fit snug!

Sorry the picture quality kinda sucks in order get it to upload here... I'll try to snip a smaller closeup of the joint itself. (Any tips in image quality send me a private message.)

I'll be using a scarf to create the two 16 foot plates for my shed. I'm going to have fun raising the scarfed plate into place. I assume your assemble the scarfed members then raise as one unit.

Hmmm....

Greg

[Greg]

Ok, here's a better closeup shot of my slipshod joinery ;-)

Greg

[Thehardway]

Greg,

Can you show us a picture of your scarf joint disassembled?

[Modat22]

what holds a joint like that together?

[Greg]

Greg,

Can you show us a picture of your scarf joint disassembled?

Sure, will do. Give me a day or two...

Good idea,
Greg

[Greg]

what holds a joint like that together?

The wedges, when driven in, widen and push the two pieces into each other. Usually the scarf is placed over a brace and a post offering support from below. See the pic on this link:

http://www.arlingtontimberframes.com/scarfjoint.htm

Other types of scarf joints use several vertical pegs to limit twisting, though I've seen this diagonal scarf used without pegs.

Greg

[Thehardway]

Greg,

I think what Modat is asking is how does the wedge/key in your scarf hold it together?  That was my first thought and why I asked for additional pictures of the joint disassembled.  It appears from the initial pictures that when the wedge is driven in they would simply separate the joint rather than tighten it as there is no offset in the peices at the wedge location.  Maybe the breakdown pictures will explain?  The type of scarf your picture seems to display would indicate trunnels or pegs from the top down to hold it together rether than a key/wedge arrangement.  The scarf in the link you provide uses a much different topology in which the key/wedge function is apparent.

[Ernie]

Yeah me too, looks like if you hit those wedges, the whole joint would fall apart,   But being old, I'm probably missing something.

[Jim_Rogers]

There are many types of scarf joints.

The one that Greg has tried is called a "stop splayed scarf joint with under squinted butts".

It would work better if it had a larger, what is called a "stop" or "table"  in it:



If you are interested in looking at drawings of scarfs, the guild had a book of "Historic joints" and you can buy it online.

Also, you can download the pdf files for free.

Go to the guild site and look under Publications/joinery/historic from the home page pull down menu.

If you click on section 6 you'll open a pdf file showing these joints. If you click "save as" you can save these to your own computer for future review.

I use my book of these drawings all the time to see joints and how they work.

Hope this helps

Jim Rogers

[Greg]

Greg,

I think what Modat is asking is how does the wedge/key in your scarf hold it together?  That was my first thought and why I asked for additional pictures of the joint disassembled.  It appears from the initial pictures that when the wedge is driven in they would simply separate the joint rather than tighten it as there is no offset in the peices at the wedge location.  Maybe the breakdown pictures will explain?  The type of scarf your picture seems to display would indicate trunnels or pegs from the top down to hold it together rether than a key/wedge arrangement.  The scarf in the link you provide uses a much different topology in which the key/wedge function is apparent.

Hey guys,

No the wedges don't separate it, they tighten it.

The function of the wedge is the same in any scarf joint, it pushes against the wall of the keyhole (sorry if this is wrong term) and forces the opposite (in my case) undersquinted surfaces together. I will try to put some annotations in a future pic of the joint opened up which may help.

Two followup comments,

1) I am not explaining this very well (obviously) and my terminology is probably not the best

2) I am not suggesting my first try is either stronger or better than any other scarf joint. It was simply a first try, before I ruin two 10 foot timbers!

I agree the one pic JimR posted today with the significant stop in the middle would be better. But I can also tell you this would be harder to cut correctly. I am looking for something that is fairly straightforward and simple to cut, but strong enough to keep two plates together.

Believe me there is a definite art to fine tuning one of these things to get all the surfaces to match tightly. The more surfaces you have, the harder it gets.

When I began laying out my practice scarf, I was referring to a brief article on scarfs from issue #37 of Joiners Quarterly, published by Fox Maple school, from Spring of 1999. You can still order PDF copies of back issues for $5 at

http://www.foxmaple.com/back.html

Cheers,
Greg

[Jim_Rogers]

What holds that joint together is that the ends of the two pieces are forced into the "v" in the other piece by the wedges being driven in.
The "v" is where the butts are "under squinted" which holds them in place.
If it is pegged correctly this will hold the two pieces from shifting from the sides.
And often pegs are not all driven in at the same angle, some are angled one way a little and the others are angled the other way or the opposite way so that they won't all be in the same line. These angles are from end to end like this:



Jim Rogers

[RoadKill]

I'm no expert, but it's pretty clear that the joint in the picture is different than the drawing that Jim posted.  The long diagonal cut can't be in one line - it has to be offset.  Pegging the joint in the photo would help hold it together, but not as much as the wedged version.  I had to draw it myself to see the difference.

[Greg]

I'm no expert, but it's pretty clear that the joint in the picture is different than the drawing that Jim posted.  The long diagonal cut can't be in one line - it has to be offset.  Pegging the joint in the photo would help hold it together, but not as much as the wedged version.  I had to draw it myself to see the difference.

100% correct.

The one I cut does not have a "stop" in it. The one in the drawing does. I can clearly see the advantage of the stop, I may very well end up using that scarf in my building. The one I cut, no stop and wedges, I agree is probably not very useful, esp. without pins.

Again I see several aspects to choosing a scarf:

1) how easily can it be cut (correctly), given the experience of the joiner
2) how strong/appropriate is the joinery for that part of the structure
3) how the scarf is assembled and lifed into place in the structure.

#3 is still very much a mystery to me. No discussion of this in any materials I've read. I guess you simply have to experience it...

Some of these scarf variations I think would HAVE TO BE assemblied on the ground, and clamped together in one piece before raising into place. Others, I'd think, could be better candidates to be assembled "in the air".

I'd love to hear anyone's experiences with raising of long plates with scarfs in them.

FWIW, I also remembered, Sobon's red book spends about 3 or 4 pages on various types of scarfs.

Greg

[Thehardway]

Greg,

You are correct that putting the "table" or "stop" in the joint make it more difficult to cut, but without it you have an inferior and structurally unsound joint as the pegs rather than the squinted butts and tables bear the load forces.  The tables in the joint shown by Jim serve three primary purposes, (1) they prevent the joint from separating in the case of lateral force, (2) they prevent the joint from separating under horizontal tension and (3) they provide a bearing surface for the wedge to tighten against. 

I would still like to see a disassembled pic as there are some other aspects of that scarf that I am suspect of.  The wedge/key combination, if not done correctly can allow for structural failure over time as well.  If wedges/keys are not cut so that the compresson forces are distributed evenly over the entire length of the wedges surface, the wood fiber will crush and fail under stress at its tightest point or could work loose. 

What type of "plate" is this going to become?  What are the actual dimesions of the timbers and the LOA of the plate assembly?  These items would dictate assembly practice.

I also noticed the holes and the hewing marks.  I assume these are salvaged timbers?

Have you tried making a template?  Much easier to cut both joints to fit a common template than continuously move and test the fit of the timbers as you work the joint.

Happy chiseling

[Raphael]

Thanks to the flu :-\
I've finally had the chance to edit pictures.
Here is my first scarf joint (this January) of this type.

[Greg]

Very nice work.

How did you make the diagonal cuts?

What is the overall length of the scarf?

Thanks,
Greg

[Raphael]

> Very nice work.

Thanks, actually there is one errant saw kerf that will unfortunately show on the underside >:(
Fortunately it isn't affecting the strength of the joint.

> How did you make the diagonal cuts?

I made the first cut with a large panel size rip saw until the kerf wandered inside on me and I had to shift the scarf.  The second one I ripped with a 300mm Japanese saw which gave me the control to keep the kerf proud in the center.
I only ripped the tables then kerfed across and hogged out the lower slope with a variety of edged weapons; 1.5" chisel, 3.5" slick and bench rabbet plane.



> What is the overall length of the scarf?

It's 27" point to point and the timber is a full 9" deep.

[trigger_andy]

Go to the guild site and look under Publications/joinery/historic from the home page pull down menu.

Sorry to bring up an old thread but where is this guild site?

Cheers,

Andy

[Jim_Rogers]

Go to the guild site and look under Publications/joinery/historic from the home page pull down menu.

Sorry to bring up an old thread but where is this guild site?

Cheers,

Andy

Direct link is here:
https://www.ncptt.nps.gov/wp-content/uploads/2004-08.pdf
Jim Rogers