Domino technique for angled joinery in thin bent laminations

[tmbridge]

Hi all,

New domino owner here.  I'm working on a chair with some bent lam horizontal back slats that will mate with the back stiles (see photo for example)

I'm looking to replace the m&t joinery with dominos.

As a new user, it seems I have 2 options: an offset 4x20 or an angled 5x30.

The 4x20 seems like it would be easier (this may be my naivete showing) but would result in a tenon that doesn't get more then about 6mm into the slat due to risking blowing out the front of the slat (see photo) or risk of it loosening/leveraging out eventually.. 

The 5x30 gets deeper into the slat but it will need angled mortises. (See photo)

The slats are 2-3/4" (narrow ones) and 3-1/4" wide (wide ones) so I'll likely be doing double tenons for both.

Curious to hear all your opinions on which method is better and, if the 5x30 is recommended, any tips or tutorials on making these complementary angled cuts?  Perhaps a video that can guide me?

Thanks in advance!

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[ChuckM]

This useful info is missing: the thickness of the slats, and whether the curvature is the same for all the slats.

Assuming the curvature is the same, and the slats have already been cut to their curve shape:

a) 6mm depth of tenon (4mm) into the slat sounds a bit too little for my taste even though double tenons will be used
b) So I'd use the 5mm tenons (assuming the 6mm ones are too big) -- but what is the depth of cut into the slats?
c) See image (not to scale) for the curved/angled shim approach that I'd consider if I were building the chair. There're other factors to consider such as clamping requirements, registration surface, etc.

If everything including the slat blanks is still true and rectangular, it is a different story, and the approach would be different!

Based on my understanding of the chair (which can be wrong), the DF500 is the right tool to do the loose tenon joinery.

 

[tmbridge]

This useful info is missing: the thickness of the slats, and whether the curvature is the same for all the slats.

Assuming the curvature is the same, and the slats have already been cut to their curve shape:

a) 6mm depth of tenon (4mm) into the slat sounds a bit too little for my taste even though double tenons will be used
b) So I'd use the 5mm tenons (assuming the 6mm ones are too big) -- but what is the depth of cut into the slats?
c) See image (not to scale) for the angled shim approach that I'd consider if I were building the chair. There're other factors to consider such as clamping requirements, registration surface, etc.

If everything including the slat blanks is still true and rectangular, it is a different story, and the approach would be different!

Based on my understanding of the chair (which can be wrong), the DF500 is the right tool to do the loose tenon joinery.

Thanks for the comprehensive response, Chuck.

Sorry I left the thickness out, not sure how that happened.  They are all 1/2" thick and all sorts will have the same curvature.

Nothing has been cut yet, in fact, I have yet to even mill the lumber for the slats, the rest of the chair is built.

That said, since I plan to be resawing thin slices for the bent lamination that will make these slats, I'm not sure having them square and flat still help much with cutting the joinery before the bending (since they'll be thin slices and, if I cut the tenons _before_ resawing, the shoulder of the tenons would "move" into a kind of staircase as the slices are bent).

Thanks for the shim idea, I'll do some testing to ight with this idea.

Thank you for the

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[ChuckM]

Tmbridge,

You're welcome. I enjoy all kinds of Domino challenges (pun not intended).

I'd cut the mortises while the blanks are still true and square (first method)!

That's, if possible, cut the mortises on the chair stiles/posts (verticals) and rails/slats (horizontals) when they're still in the rectangular form, then shape/bend them to the desired curves.

It'll be much easier that way from the mortising perspective, and the shim approach (second method) would be the last resort.

Of course, you'd have to allow for spring back and extra lengths for the curvature if the first method is used. There're pros and cons...initially I thought you'd be shaping solid wood rather than bending.

 

[Crazyraceguy]

I think I would do it in the way of the pic/drawing where you have the 5 x 30 in place with it.
Following parallel to the surface, rather than perpendicular to the face of the joint.
Just be aware that you will have to cut a bit deeper (at least on one side) because the long point will hold the machine away from the true face.
The tricky part is getting the angle into the vertical member correct. I find that sticking a wedge-shaped spacer to the Domino's fence with some double-sided tape. This may take some experimenting and testing, but it works.

 

[tmbridge]

I think I would to it in the way of the pic/drawing where you have the 5 x 30 in place with it.
Following parallel to the surface, rather than perpendicular to the face of the joint.
Just be aware that you will have to cut a bit deeper (at least on one side) because the long point will hold the machine away from the true face.
The tricky part is getting the angle into the vertical member correct. I find that sticking a wedge-shaped spacer to the Domino's fence with some double-sided tape. This may take some experimenting and testing, but it works.

Thanks, this was Chuck's recommendation as well. Sounds like the way to go!

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