Question on "Structural Miter" Joints

[rudy de haas]

We have a piece of furniture we call "pretty desk" - Danish teak from the 1940s or early 50s. The front legs on it are angled and the drawers "float" 3 inches or so below the bottom of the desk surface. The maker finessed the issue you face by moving the back legs to a more vertical position (so not like your design that way) and by extending the side of the drawer box up and back a little bit relative to your design. If you did that, the side of the box would transmit force downward to the lower two thirds of the leg while preventing sideways movement from stressing the joint. You do not say in your original post what wood you're using, but if this is a reasonable hardwood like Santos Mahogany that should let someone sit on the front of the desk without damaging it.

Further (and please forgive me if you think I'm over-stepping here) that desk design looks like it fits an older PC style computer user. My son's new imac has one small cable, for power: networking, the keyboard, and the mouse are all wireless. Speakers are built in, but wireless speakers are now pretty much standard for external use too. Since Macs are now just PCs with more expensive logos running BSD, I assume you can get comparable wintel world products - and planning for fewer cables and no keyboard tray should let you simplify that design a bit.

[Kesh Ikuma]

@Wayne - Thanks for the info. I'll see if I can source somebody with sandblaster (that's the equipment right?) locally.

On the mending plate, now, I think about it, yeah. I can route the mortise flat bottom, variable depth. Fit an aluminum bar thick enough for the deepest parts (ends), and pattern route the aluminum to match the wood. I did a quick check and using 4"-long Al stock yields 3/16" depth difference between the middle and ends. So, 3/8"-thick bar stock should suffice.

This being said, it's tough to justify the mending plate route (at least to myself). The process is much more involved, but it offers neither aesthetics advantage (can't see'em unless you crawl under it) nor structural benefit over metal dowels + splines. Here is why I think it doesn't offer additional structural strength. These joints in everyday use are subject to shear stress (sliding) and cleavage stress (pivoting about the bottom edge) and a very little of tensile stress (pulling apart). To my eyes and intuition, the structural advantage of mending plates over dowels is against the tensile stress, which we don't really need to worry about (unless I bolt down the legs to the floor and try to lift up the desk )

Yes, I'm over-thinking this...

[Kesh Ikuma]

@Mark - Good call. That article probably was the reason I could accept Pat's idea without any knee-jerk reaction. However, the response I got was "Meh" when showed her the article this morning. lol

[mark mcfarlane]

@Mark - Good call. That article probably was the reason I could accept Pat's idea without any knee-jerk reaction. However, the response I got was "Meh" when showed her the article this morning. lol

It's hard to argue against a 'Meh'.

[Kesh Ikuma]

@Rudy - I did consider various leg placements when I was designing the overall look. The vertical rear legs, without any doubt, would have made things a lot simpler, but also takes away the iconic look of Wish Desk.

> Drawer placement

Hmmm, I cannot quite visualize what you mean by your description. Mine is also about 3 inches or so below the desktop.

> iMac

She's a MBA user for some time (it's her 2nd MBA; I've been trying to bring her back from the dark side but has been unsuccessful so far lol) but prefers to use separate monitor, keyboard, mouse, and speakers. (She only uses it as laptop when she goes off to conferences.) The idea is for the MBA to sit on top of the drawers, and all the cables are to be neatly tucked away under the desk (power, video, audio, & USB). The desktop "cable access panel" is to give her an easy access to the power strip if she needs to use a wall-powered device at her desk. I'm not 100% sold on the current implementation though; so, it'll most likely change by the time I actually get to it.

BTW, my other hobby is building PCs (and future planned hobby of building speakers); so, I won't let her drift off to those all-in-one's too easily

> Keyboard tray

This actually is a requirement. She has been using a keyboard tray/drawer all her life and does not like to type at the normal desktop height. Since this will be her desk for all purposes, lowering desktop was not an option. I already had to talk her into a single-rail tray instead of a keyboard drawer. I wouldn't like at all the look of a keyboard drawer with this style desk.

[rudy de haas]

[QUOTE=Kesh Ikuma;2598141]
> Drawer placement

Hmmm, I cannot quite visualize what you mean by your description. Mine is also about 3 inches or so below the desktop.

Assuming the photo attachment worked.. you can see that the designer used the full sidewall as a design element. Your design is, I think, much nicer than this, but the point is that most of the sidewall on pretty desk is decorative rather than functional. Looking at your diagram I'd say you could use just enough of a sidewall to extend part of the drawer cabinet side up and back to connect the drawer, the top., and the joint where the legs meet together. That would detract a bit, but not much, from the floating drawer look while adding considerable strength.

[Kesh Ikuma]

@rudy - I see what you mean now. Since your photo (thanks for posting BTW) is only from the side, I'm guessing that it has a "floating" look in frontal view because the top drawer is located where the front edge of the sidewall is perpendicular.

I'm reluctant to make the side to go all the way up to the desktop, purely for the aesthetics reason (I like the open look of the current take). Also, I suspect it won't be as effective dispersing the weight as much as in your desk because the sidewall would be only attached to the front leg (the front and back legs are offset).

[Wayne Lomman]

Kesh, the joint will have tensile stress on the outside. It's the whole problem to be resolved with this design. As you would know, timber is not great in tension and the plate underneath does nothing to resist that tension. So I agree with you that it is hard to justify doing it. It's why I wanted a flat plate on the inside but it will be seen so pins are probably tour best bet. Go half inch at least. Cheers

[Kesh Ikuma]

@Wayne - Ah, sorry I misunderstood you. So, you are suggesting using a metal floating tenon instead of a metal dowel. I was so entrenched in figuring out the underneath mending plate, I misinterpreted your comment.

BTW, a mending plate does offer tensile stress relief. Not the plate itself but the screws/bolts.

Anyway, I think I'm pretty set to go with these joints:

LauraDesk Front Leg Joinery v2.pngLauraDesk Rear Leg Joinery v2.jpg

If I see a thick aluminum bar/plate stock at local borg, I'll consider your suggestion. (Otherwise, I have a leftover 3/8" Al rod that I can use.)

Also, just if anyone's curious, here is the current state of the leg pieces (and their templates)
2016-08-28 16.17.31.jpg

And the bottom side of the desktop
2016-08-28 16.11.24.jpg2016-08-28 16.12.06.jpg