Matching tenon shoulders to an arc...

[Dave Norris]

Hi,
I’m pretty much stumped on how to do this…

I want to make an arts and crafts bed. The head and foot boards have rails across their width that have slats going into them. The bottom of the top rail has a gentle arc. The slats are mortise and tenon’d into the rails, meaning the slats have the tenons and the rails have the mortises.

How would I match the shoulders of the tenon to the arc of the rail?

[Chris Padilla]

Make a template of the arc so you can use a router to shape the tenon shoulder. If you could be talked into floating tenons, I think this becomes much easier to cut.

Do you know if the arc is a chord (ie. part of a circle)? If so, you can match it to that. Otherwise, cut the arc in the larger piece and then use it to mark off the slats and to make a template to reference a router against.

[Michael Peet]

I don't know much about woodworking yet, but my bed has a headboard similar to that in your Sketchup file. It uses floating tenons.

[Dave Norris]

So make a large template for the arc, then I could use my handy dandy Whiteside inlay kit to cut the arc in the rail, and then use the same template to make the slats...

and then use the floating tenons...

and would you cut the mortises in the rail and the slats before cutting on the arc?

[Chris Padilla]

Yes, cutting the mortises is usually much easier on squared up stock. Just keep in mind about the depth of the mortise knowing that you'll be removing a certain amount. Even if you need to increase the depth, at least you'll have a guide for making it deeper.

[Dave Norris]

But now that I think about it, it's going to be a pretty small floating tenon. I hadn't gotten to the point of figuring out how thick the slats will be, but probably not much more than half an inch... That'll be a pretty small floating tenon. Go with a 1/4 inch mortise and make 1/4 inch tenons? I guess that would work, but not a lot of room for error...

Not that I need much room... I can pretty much fit an error in anywhere...

[Chris Padilla]

Small slats...small tenons...it should be fine. 1/4" thick floating tenons will work fine with 1/8" shoulder widths. Perhaps a bit small. You could go for 3/16" thick floating tenons if that makes you feel better to get an extra 1/32" on both shoulders. :)

[Jamie Buxton]

Don't make tenons on the upper ends of the slats. Just cut mortises which will accept the full-dimension end of the slats. Use tenons on the bottom end of the slats.