Butt-Joint Glue UpSuggestions

[Don_M]

Need some advice/thoughts/suggestions on how best to butt-joint 12” wide x 6’ long plywood sections together.


The plywood (it is actually “wiggle” wood) is 3/8” thick with a Makoree veneer. I am using it as a skirt board for a circular staircase. I need to make the skirt board one continuous section along the entire circumference of the circular stair case (about 18 total feet – so ultimately I will need to glue up three sections)


I guess the traditional method would be some type of finger joint – but my initial thought is a half-lap joint (probably about 1-1/2 or 2 inches of overlap).


Any other thoughts?

[Ohio Mike]

Can you make a butt joint and glue a scrap piece of wiggle wood on the back side of the joint then cut relief into the structure to accept it?


Mike

[mbholden]

I have built iceboats using just WEST system epoxy and butt and lap joints. Some early design flaws led to busting fuselages in half, but they broke in the wood, not the joints. Just ahead of the mast step.
So, I would expect that a good epoxy joint would work well for you.

[Don_M]

Good idea - I could make this work by removing the drywall behind the reinforced joint. It would be hidden by the skirt board - so no issue there. Probably stronger than a lap joint (I could also reinforce with screws if need be). Thanks

[Steve N]

but my initial thought is a half-lap joint (probably about 1-1/2 or 2 inches of overlap).


Any other thoughts?

End grain is such a snot to glue, a lap, or something that would allow face grain to face would get my vote. Sounds like your situation is fairly static though, Franklin's Titebond No drip is made for end grain applications under no stress, so if it was a wall covering it isn't bearing weight, or being pried on, might work. If you did glue a butt joint in that situation, I would glue size the end grain so it didn't act like a sponge.

[Don_M]

Thanks


The only issue there is that once I force the skirt board into a curve to fit around the stair case -I think there will be some stress (tension) on the end joint.


I suppose a scarf joint is probably the classic solution – but I think the backer scrap (with perhaps a lap) will be a good way to go for me.

[dg152]

Don, I'd be interested to see how you end up doing this little project. My knee jerk reaction was to do a finger joint, but the suggestion to do a half lap with a backer strip to reinforce sounds even better. It sounds like once you get the boards glued up, they are going to be bent around in a circular fashion. Will you be making any relief cuts in the back of the skirt to allow it to bend more easily? I'm not sure what kind of radius you can bend 3/8 plywood without relief cuts.

Anyway, it sounds like you've got a good handle on the process. It would be interesting to see how you do it.

[Bill Holt]

I think you might need some relief cuts in the backer board or the bend will likely have a slight hump because of the "stiffer" section even with the drywall removed in that area.

[Don_M]

The radius of the curved staircase (the outer radius) is about 6 feet. I am using flexible plywood (some call it wiggle or wacky wood).

http://packardforestproducts.com/product...g-plywood/

It is plywood where the grain of all the lamination's are oriented in the same direction. It is very flexible. A 4x8 sheet can almost turn back on itself. The veneer I added stiffened it a bit – but it should easily be able to bend to the 6 foot radius w/o kerf cuts. I will keep you posted after I install. Thanks

[Alan S]

A scarf joint will allow a smooth bend.  It is used with plywood that is bent into a gentle curve by those who make stitch and glue kayaks and canoes.  Here is a link to a description: http://www.oneoceankayaks.com/stitchglue...rfjig2.htm