Another joint question for the experts

georgeandpat · Post by **georgeandpat** » Wed Jan 17, 2007 3:22 pm

If a butt joint is acceptable on the planking strips, and a 1:7 scarf joint across the "thickness" of the strip is okay, wouldn't any ratio in-between be acceptable as well? The reason I ask is this: If you use the 1:7 scarf joint (the joint that looks like a butt joint from the outside) I'm hearing that the glue tends to be more visible when sanding and planing because of the shallow angle of the scarf. Wouldn't a scarf joint with, say, a 1:4 ratio be less likely to show the glue yet be stronger than a butt joint because of the increased surface area of the mating surfaces? I swear, this is the last question I'll ask about joints.

Thanks, George.

Glen Smith · Post by **Glen Smith** » Wed Jan 17, 2007 3:32 pm

If you mean to do a 1:4 scarf on the hull strips, I think it would be ok. I have tried the 1:7 scarf on hull strips and I didn't like the glue-line that was apparent so I went back to butt joints. I would make the glue joint on the boat and not before hand as I'm not sure the small glue surface would accept much manipulation without breaking.

I say give it a try and let us know the outcome.

georgeandpat · Post by **georgeandpat** » Wed Jan 17, 2007 3:37 pm

Thanks Glen, I think I'm starting to get it. George.

canoeblderinmt · Post by **canoeblderinmt** » Wed Jan 17, 2007 6:01 pm

George,
You are right, any ratio greater than 1:1 will be stronger than a butt joint. I don't know if there is any magic in the 1:7 ratio. I've not seen it referred to anywhere but here.

A quick trip to Pythagorias-Land tells us that for a 1:4 joint on 1/4" stock, your joint length will be 1.030" (1/4" rise and 1" run) while your 1:7 joint length will be 1.767", a difference of .737".

BTW are you guys REALLY doing this on your strips? It seems to me to be pretty fine slices....

Anyway, the strength, as has been stated ad nasuem in other posts, is in the sandwich, not the joint. For sanding purposes, re: glue exposed, you should probably look at something closer to a butt joint, like 22.5 degrees or thereabouts. Just take care if they get a load put on them as you put them on, they probably won't hold very well.

Greg

georgeandpat · Post by **georgeandpat** » Wed Jan 17, 2007 10:42 pm

Thanks Greg, Butt joints will work for me but I read that the first sheer strip should use scarf joints so I wanted that joint to look good. George.

Glen Smith · Post by **Glen Smith** » Wed Jan 17, 2007 10:51 pm

George, the sheer strip is usually covered by the gunwales, at least in the center portion of the boat so you don't have to make the joint look good. I normally joint the sheer strips before installing them on the boat since I want to achieve a nice, fair line with this first strip and this calls for a long scarf joint like 7:1 or 8:1.

Edited:I make this joint along the length of the strip, not the thickness.

Bassbug · Post by **Bassbug** » Thu Jan 18, 2007 11:56 am

BTW are you guys REALLY doing this on your strips? It seems to me to be pretty fine slices....

Are you referring to the 1:7 scarf? If so, YES!. I know Glen favors the butt joint but I really like the scarf. I scarf the planks then glue them (held together with 2" binder clips-an idea taken from some other builder) before installing them. The joint is nearly invisible.

I use a jig (the same one for scarfing the gunwales to cut the scarfs.

georgeandpat · Post by **georgeandpat** » Thu Jan 18, 2007 12:15 pm

Glen, I forgot that the gunwales will cover these shear strip joints. Thanks!
Bassbug- Thanks for the pictues. Those are redwood strips right? Did the redwood darken naturally or when you fiberglassed it? Thanks, George.

Bassbug · Post by **Bassbug** » Thu Jan 18, 2007 12:27 pm

George,

Yes, those are redwood strips and yes they do darken a good deal with epoxy. The strips also seem to darken with time.

Bear_Ludo · Post by **Bear_Ludo** » Thu Jan 18, 2007 12:30 pm

Hello Dale,

I deduct from the pictures that you join the strips before milling them, any particular reasons for doing joints first ??? I am interested ... ;o)

If I remember right, you had lots of pictures of your redbird construction. I don't see them on your web site .... Are they still available somewhere on the Web ??
I admire the way you work wood as Ed (Ealger) and many others on this forum. Thanks to all of you for sharing your pictures and experiences ;o))

Ludovic

canoeblderinmt · Post by **canoeblderinmt** » Thu Jan 18, 2007 12:35 pm

Bassbug,
George's original question, unless I misunderstood it, was regarding scarfing on the 1/4" width, not on the face, like the joints you posted pics of. Nice pics, BTW. That's where I was having trouble with the idea and the execution. A 1:7 scarf would require a VERY shallow 1 3/4" bevel across a 1/4" thickness. I fancy myself a fairly competent woodworker, but I don't know how I would even approach such a cut, much less make it repetitively so that it would mate perfectly for glueing. I make the joints like you showed all the time and know them to be strong and nearly invisible with a little care matching grain and ensuring a good joint. But flip the scarf the other way...

Greg

Bassbug · Post by **Bassbug** » Thu Jan 18, 2007 12:39 pm

My mistake, I misread his question. It would seem that a 45 degree cut across the 1/4" section would not be difficult to do. However, I would just butt joint instead of making that cut (if I wasn't going to scarf lengthwise).

canoeblderinmt · Post by **canoeblderinmt** » Thu Jan 18, 2007 12:48 pm

" I would just butt joint instead of making that cut...:

Me Too!

Greg

Tom in MN · Post by **Tom in MN** » Thu Jan 18, 2007 5:59 pm

bassbug,

Not to get too technical, but for the sake of accuracy you are making a mitre joint in your photographs. A scarf joint is technically a bevel, cut under the face of the board, not across it (which is a mitre). The mitre joint is much easier to make, but it is not as strong a scarf (or bevel). But for the first strip, just to get a fair sheer line, this mitre joint is perfectly fine as it will be sandwiched in the gunnels. Actually the mitre, if it stays together to get the strip on the canoe, works just as well as the fiberglass provides the strenght, not the type of joint used.

There is much debate on this topic. There is no difference in appearance or strength when butting the strips or scarfing the strips on the final canoe. It takes a lot of time to build a canoe, so why add in a bunch of extra time scarfing the joints when butting them on the canoe looks the same when it is all done. In fact, scarf jointed strips can show the seam more than butt jointed strips after you sand, as the glue face shows more in a scarf joint and will appear different than the wood. With a butt joint, the width of the joint stays the same no matter how much you sand.

Use butt joints and save yourself the extra work.

Bassbug · Post by **Bassbug** » Fri Jan 19, 2007 10:30 am

I deduct from the pictures that you join the strips before milling them, any particular reasons for doing joints first ??? I am interested ... ;o)

The joints are made after the strips are cut to thickness but before they the bead and cove are routed. I have made the joints after bead & cove, but it is very difficult to align the strips while glueing.

If I remember right, you had lots of pictures of your redbird construction. I don't see them on your web site .... Are they still available somewhere on the Web ??

I took hundreds of photos of building the redbird, since it was my first boat, but I never did post them on my website. I did a better job with the kayak.