Replies

1. 
   Hudson Valley Carpenter | Mar 22, 2007 05:31am | #1

   I visited my favorite scarf joint this afternoon, just after the lunch crowd left. 

   OK, you're lookin' at it but your description doesn't convey what you see very well, so how about a photo or a drawing?  Even then I'm not sure I'll be the one with the answer but I'll bet someone will come up with a good one.

2. 
   DanH | Mar 22, 2007 06:02am | #2

   Is this what you're talking about:

   View Image

   The two pieces fit together (more tightly than shown) and the two keys hold them together. The keys are just inserted into slots -- no glue or fasteners.

   So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
1. 
   GaryW | Mar 22, 2007 06:15am | #3

   Boatbuilders call this in your sketch a "hooked and locked scarph." The ratio should be at least 6-to-1:  that is the length of the scarf should be at least 6 times the width of the piece the joint is made in. In other words, a 4-in-wide piece would have a 24-in-long scarph. And you're correct:  without glue, and even without its locking keys, I've picked up the long, joined pieces without them falling apart. Locking keys are usually a single pair of married wedges who's force is longitudinal to force the ends of the scarphed pieces tighter into their hooked ends.Gary W

   gwwoodworking.com

2. 
   DanH | Mar 22, 2007 02:27pm | #5

   PS: I think my diagram isn't quite correct -- the keys should be done slightly differently, but it's hard to explain, and I don't have time now to redraw.
   So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin

3. 
   vaughan | Mar 23, 2007 05:04am | #7

   thanks for the drawing  jv

1. 
   DanH | Mar 23, 2007 05:48am | #9

   I remembered how I've seen the key done before. Not exactly like Notchman's, but like this:Cut the pieces about like my diagram. Then, with the pieces together, make a rectangular hole between them, more or less in the middle -- ie, a right triagle is cut out of each piece. (I suspect you could use two or more similar holes, distributed evenly along the long joint faces, but we'll keep it simple.)The exact shape and orientation of the hole/notches is hard to describe, but -- The right triangle notch cut out of each piece has a long edge and a short edge. The long edge is maybe 3-4 times longer than the short edge. The short edge is towards the pointed end of the board, and the long edge is towards the body of the board.A piece of wood cut to roughly fit this rectangle and tapered in the wide dimension to make a wedge is inserted into the rectangle. The working faces of this wedge (the narrow edges) will then tend to push the two halves of the joint closer together.Of course, this is just one that I've seen somewhere, and from memory. I'm sure there are many ways to do it and many refinements.
   So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin

3. 
   Notchman | Mar 22, 2007 07:38am | #4

   The scarf you describe is called a "double-bladed scarf with opposing wedges".

   Most of my beams are Port-Orford Cedar or "Douglas Fir, but I usually use Oak or Pacific Yew for the wedges. (Mostly because I've got a bit of it around). 

   The wedges should be a harder wood than the beam because they'll be in compression tangent to the grain while being forced against the end grain of the beams.  I usually make the slots 2"wide by 1" deep on each blade with the wedges sized and tapered accordingly so that when driven tight, they stand a little proud, because over time, as the beams dry, they may require being tightened a bit.

   On an 8"X8" beam, I would make the scarf 30 to 32 inches long.

   It's best if you make a set of templates to lay it out (doorskin or some kind of thin plywood or hardboard works fine) because your beams may not always be perfectly square and you want the scarf to be a nice snug fit all along its face with the beams staying perfectly aligned.

   Try to locate your scarf joint over a knee brace if possible.  It seems counter-intuitive, but the Timber frame construction tables I've used always show the moment as being more favorable there than over a post.

   ---

   Edited 3/22/2007 12:42 am by Notchman

   
   

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   Edited 3/22/2007 1:07 am by Notchman

4. 
   Notchman | Mar 22, 2007 06:14pm | #6

   The first TF building I ever built was my shop.  I went out last night and took a handful of pics just for your edification, including a double bladed scarf with wedges in a 6X6 Doug Fir timber which is shorter than I suggested in my previous post (about 16").

   I've done an occasional TF project out here in the PNW, although the call for it is less popular than in the NE.

   When I do a TF project, I do most of my joinery by hand and, other than an electric handplane, a skill saw and a Pozzi beam cutter, prefer the use of a slick, an assortment of good framing chisels and a boring machine for cutting the joinery. I love doing it, and the quiet development of heavy joinery is very therapeutic.

   BTW, all the timbers in my shop, I cut on my own mill.....I had a Woodmizer for a number of years but the timbers in the attached pics I cut with an old circular saw mill driven by a big Chrysler V-8 that was dangerous as hell and nearly killed me once.

   All the joints are mortised or let in.  The purlins in the roof structure are all dovetailed but will never be seen unless someone tears the building down piece by piece.

   All the timber is off my own property.

1. 
   vaughan | Mar 23, 2007 05:12am | #8

   Thanks for your insight,I think you have given me the inspiration to go ahead with the task at hand.Hopefully I can locate some nice timbers to make the work all the more satisfying.   jv

2. 
   dovetail97128 | Mar 23, 2007 07:37am | #10

   Beautiful Work!
   Thanks for posting.