Joinery

So what makes a stronger joint, starting or lapping


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RE: Joinery

An unstarted joint is still quite weak.

Once you've started though, a scarfed joint is better than a butt block because the base material's stiffness is preserved through the joint (no hard spots), and a scarf is lighter than a butt block, and doesn't impose into the boat's interior.

If you're intimidated by cutting scarfs, practice on some scraps. If it doesn't work out, go for a butt block. It won't ruin your boat.

RE: Joinery

   The computer said "starting". I said scarfing. which is stronger, scarfing or lapping? I've done both. For gunnels I clamp two together side by side. Then I  run them through the band saw on a sliding plate with a fence set at the desired angle.

RE: Joinery

   Lapping is not butting.

RE: Joinery

   A lapped joint, or half-lap, where each piece is haunched or rabbeted to half thickness and joined, is almost exactly half the strength of the parent pieces, and half the strength of a scarf or butt block. That's why I assumed by "lapped" you meant that you would overlap the joint with a butt block. A traditional joinery lap is nearly useless for end-to-end joining.

(Note various lapped joints are used in some parts of larger traditional timber-built boats, but their gunnels and covering boards serve different funtions than the equivalent parts on a lightly constructed ply-epoxy small craft.)

RE: Joinery

   I found this with a quick search.  There is a post down towards the bottom of the page which shows the reason why the scarf is stronger than the lap joint for the application of lengthening panels for our boats.

http://lumberjocks.com/topics/30026

-Matt

 

RE: Joinery

I agree that a dry half-lap joint is half the strength of the parent pieces, but why would a properly epoxy-glued half-lap joint be that weak?

RE: Joinery

No glue- not even epoxy- is very effective at purely end-grain joins.

And, of course, if only half of the joint contains intact fibers, the joint is actually 1/4 strength (in bending), not half.

RE: Joinery

   I think I shall experiment

RE: Joinery

   I think I shall experiment

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