Scarfing alternative?

[jstemwedel]

Long planks are exorbitant, but I have little confidence in my ability to make a decent scarf joint with the necessary 8 to 1 minimum ratio. I am wondering if the following "enhanced" lap joint would work. Every part of the joint would be epoxied, inside and out. Basically, a thin sheet of plywood would be recessed into the plank face, set in epoxy and secured with short screws.




Thin plywood is recessed into plank face, set in epoxy and secured with short screws.

Epoxy in joint

[Brian Palmer]

Scarfing really isn't that hard to get a strong joint, especially with modern epoxy and a sharp plane. You can build a simple jig with side-rails for the plane to run down at an 8-1 angle to give very consistent scarf joints.

Lap joints of any sort will not give you a fair joint if the plank has much curve to it. Otherwise, a butt joint with a block to back it up is the usual way to go in traditional plank on frame construction.

What is the type of boat and construction method? How thick is the planking and is it plywood or solid planking?

--Brian

[nedL]

Either learn to make a proper scarf (not difficult - practice with some cheap pine or something), or learn about butt blocks (perfectly acceptable). In other words - ditto to what Brian said.

[Ian McColgin]

I'll support that you need to learn to scarf. It's incredibly easy.

For scarfing planks you'll want:

A decent low angle plane - easier to work across the grain;

A good combi square for marking;

A fairly wide chisel;

A comfortable mallet for the chisel;

A Japanese pull saw or a decent rip saw.

Mark the wood with the bevel drawn on the two edges and a nice line across the plank to mark the inner end of the bevel.

Use the pull saw to make kerfs in the plank end beveled to just a bit less depth than the final bevel.

Knock off wood between kerfs with the chisel to get rid of a lot of wood quickly.

Finish with the plane, checking frequently with the straight edge that you're keeping it flat. I like working partly across the grain with a slewing, slicing motion. I never had much luck with jigs here, just plane to my marks.

It's very nice if once you have two mating planks beveled to feather edges to get rid of the feathers. I do it by working my plane gently across each face keeping the plane down slope an even bit to make just a little step before the slope starts. This slope happens to be normal to the bevel slope, not the plank face. No problem, once that's made, the two planks can be test fitted together and the feather edges easily planed back to match where they land and, working from one to the other with frequent checks, it will match perfectly in a minute or two. The feather edge is fine but leaves a long epoxy line than, harder than the wood, can leave a hard to fair bump. The little nibble off the feather and the little step down gives a localiced very thin glue line for easier fairing.

G'luck

[drift montana]

Don't fear the scarf! I was paranoid about scarfing planks. After I did it, I realized my fears were false. With a good plane, or even a belt sander, you can knock out a scarf in a few minutes. Make a clamping jig to keep it all straight when gluing and you are set. I like to do my scarfs with a full width board, prior to resizing it to final dimensions. This way I may get several planks, gunwales, or strips out of a single scarfing exercise. Planing and ripping also do a great job of cleaning up the joints.

-Tony

[JimConlin]

Scarphing is not to be feared. If I have several joints to do, i find it best to stack all the parts up, staggering them by the length of the joint, and plane all the bevels at once.

If you're still plane-o-phobic, Dynamite Payson(I think) had a technique where the ends of the pieces to be joined were butted square, thinned slightly on both sides with a belt sander, and joined with fiberglass cloth patches across the joint on both sides. To me, this seemed like more work for a poorer joint than a proper scarph.

[Tar Devil]

Just looking at your pic, seems harder to do than a scarf.

[David G]

I have to echo what the others have said. As a professional woodworker for over 30 years, I might be a little cavalier about the ease of scarfing planks, but I don't think so. When I look at your diagram, I say if you feel comfortable machining that joint, you should have no difficulty with a scarf.

There are a variety of perfectly reasonable ways to do scarf joints. Read Mr. McColgin's instructions, or Google "scarf joint", or look in the archives here, or...

Butt blocks are a perfectly good alternative if the bend won't be severe. There's also something called a "Payson Butt" which I've used successfully a couple of times (involves a butt joint with one or both faces hollowed out & backfilled with fiberglass cloth & epoxy. This will bend almost as fair a curve as a traditional scarf joint.

"Character is forged in the smallest of struggles. Then, when the big challenges come, we are ready"

[BETTY-B]

What kind of boat? Do you think it will hold up in that harsh Arctic environment?

DAN

[merlinron]

another thing to learn along with the scarf is how to keep your block plane absolutely sharp at all times. very important to getting a decent scarf, especially if the ply is thin. it might be another one of those intimidating hurdles, but not beyond the average woodworker. a really sharp blockplane and scarfs go hand in hand. there's plenty of info and help on both here

[jstemwedel]

Once again this forum has steered me away from doing something rash.... After reading the excellent advice in the posted replies I will definitely give conventional scarfing a try. My fears were evidently unfounded.

My original thought with the alternative method was that most of the work could be done on a table saw, thus avoiding planing or belt sanding which I feared would be inconsistant.

[Ian McColgin]

The description I gave is for conventional planking maybe more than 3/4" thick.

If you're using plywood for planking, let us know as the way to plane it down is a little different.

If your planks are really thin the mechanics may different.

However you're building, it sometimes makes sense to glue the planks together not on a straight line to save wood..

Let us know more.

[dmede]

As already stated in abundance, scarphing is easy. And I'll add not as fussy with regard to exactness as you might assume. While you want as clean a lap face and join as possible, you can get away with a small amount of slop, epoxy being fairly forgiving of rough surfaces etc.

And you will most certainly get better as you go. In fact the more you do it the more you will realize the real reason to avoid scarphs is not the skill needed but the endless hand planing or sanding it takes to get the angled face ;)

[chuckm]

I had the same fears and threads of doing a proper scarph. Its no big deal. Even a poor job can be made perfect with extra epoxy goop. Make a jig similiar to the ones seen in all the boatbuilding books and sharpen you Jack. I too at first could'nt even sharpen my Bailey -Jack and did not know how to use it. It will come to you easily. Trust the boatbuilding gods.

[RonW]

Well I will be the oddball and add another point of view and way to scarf. The scarf everyone above is describing is a standard angle scarf that usually ends up around 8 or 10 to 1 ratio.The longer the scarf ratio the stronger the joint as well as being able to bend with out showing a hard spot.Of course the thinner the plywood is, the more you have very fine feathery edges being glued together.

The joint you showed above, a single stepped lapped joint, is a better joint then a angle joint and won't have the feathery edges, and also can obtain a much longer scarf ratio, which also contributes to more glue area contact, which is a stronger joint.

A couple years back I built one of glen-l's 18 ft. river dories (for fishing in the river), and since they are no frames in this type of boat. I decided to make the sides and bottom in one piece. That meant scarfing together 3 sheets of 3/8 ply for the side. I used the heavier ply instead of 1/4.
I used a double stepped lap with each lap being 4inches, for a total scarf area of 8 inches in a 3/8 piece of plywood.
It works beautifully and the joint bent in a constant curve with no hard spots, and you really can't find the joint with out a lot of very close scrutiny. That gave me a scarf ratio of 21 to 1, a lot stronger and smoother joint.

These same stepped scarfs are being used in some of the precut plywood boat kits being sold. Of course they are probably using a cnc machine to make them, but all you need is a slightly modified router.
I took the bottom ring off the router and replaced it with a piece of 3/4 ply that sticks out 3 inches on each side and back, to support the router so you don't have dips in the cut. Use a 2x4 as a straight edge to run the router plate against and a caliper to adjust depth.
I glued the joint together with epoxy, on the floor over 2x10's supporting the joint, then I used copper tacks to nail the joint together, nailing right into the support boards below, holding the joint tight till the next day. Then I rolled over the 23 ft. piece of plywood and simply clinched the copper tacks, setting them in the ply with a nail set. When cutting I ignored the tacks and slowly cut right through the ones that where in the way, leaving the rest permanently for additional strength.
The joint works great is easy and relatively fast, besides being a longer and stronger joint that shows no hard spots. Of course you have to work carefully as with anything.

[Paul Fitzgerald]

Using a West Scarffer and a thin kerf tungsten blade, even I can make good scarfs in no time at all.

http://www.duckworksmagazine.com/05/reviews/scarffer/index.cfm

Leave it set up on an old 71/4 inch saw.

[Steve Lansdowne]

I was also quite apprehensive about my first scarf, but scarfing plywood was much easier than I'd imagined. I found that stacking the lumber in a staggered fashion, waxing the bottom of the plane, and following the lines between the plies made things go fairly well. Just remember that an 8:1 scarf on 1/4" plywood effectively removes 2" from the length of the completed boards once they're glued up.

http://farm2.static.flickr.com/1313/1410242076_b0ff465371.jpg?v=0