design / joint question


rookie wrecker working on my second piece. drafting plans for a small writing desk. standard 4 leg, m&t aprons and glued-up top design with the pencil drawer the full height of the apron. the plan is to have two stretches run from the front aprons to the rear for structural support and for the drawer guide. the question is: how best to attach the stretchers? some ideas:
1) sliding dovetails set back an inch or so from the apron edge. is a 7/8th inch apron deep enough for this? 2) through tennon? 3) shallow dado with a block glued and screwed to the inside corners?
or is this not really a structural concern?
thanks for helping me not ruin more wood than necessary.
brian
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Just built a Shaker replica with the same configuration. First, add a third "rail" across the back to the two you're putting along the sides. Now, tongue these three members and groove your apron panels. You may have to fiddle the ends to accommodate the legs, depending on how you place your apron. Then, tenons on the ends of the side pieces go into a groove (easiest) or mortises (classiest) on that back piece. If you're putting in a dust panel, the groove method wins; the tenons on the side pieces just slip into the dust panel groove. The pieces look like they're from a jigsaw puzzle with tongues, grooves, and tenons everywhere.
The sliding dovetails would be cool, but imho wouldn't add much structurally. Go for it, but do add that back piece.
You'll have something going across the front to support it in lieu of an apron. How you attach the side pieces to that is up to you; it depends on the sizes you pick. I just let mine float because that lower crosspiece was too little to put in a mortise.
--
"Keep your ass behind you."

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Australopithecus scobis wrote:

thanks for the input. i'd like to see you piece; is a pic posted somewhere?
if i understand your post correctly i think i did a poor job of describing what i had in my head. i plan on cutting the drawer face from the center of the front apron. so i'll have several inches of front apron to the left and right of the drawer face. the "stretchers" (maybe a wrong term) will be (roughly) the same size and orientation as the side aprons, only set further inside the frame (just on the outside of the drawer).
ascii art top view. it's the stretchers made from ! marks that i'm thinking of.
back []-------------------[] | ! ! | | ! drawer ! | | ! area ! | []---a b----[]
front
since the drawer face will be the same height as the apron, there will be no support between points a & b. my thinking is that the stretchers along with the top secured to the aprons points a& b will provide the support and stability for the "lose" apron ends.
The question is how best to attach the stretchers at a & b.
brian
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If a & b were were simple right angles, I would go for a half-blind dovetail. It's plenty strong. The blind side is on the front ( it's not an appropriate place to display the joinery) and the strngth of the joint is oriented corectly.
If the stretchers are inset slightly from a & b, I would go for a double or triple blind M&T. Although the SD would work well in the back, I would be concerned that there would not be enough relish in the joint to support it.
Double or triple the M&T because the glue surfaces that count are the top and bottom. Segmenting the tennon maximizes that area. Think of it as a box joint that is not at a corner.
-Steve

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Stephen M wrote:

thanks. i didn't realize that about the m&t glue surfaces. why is that?
i kinda like the half-blind dove tail idea (with double m&t in back). never cut dt's before but maybe now is a good time to learn.
lots to consider between you and swingman.
brian
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Regular wood glue works best, then the grain of the mating surfaces are parallel. It works nearly as well if the grain is oriented at 90 degree (as in a half-lap joint). If one or more of the mating surfaces are end grain, the strength of the joint is much much less.
On a normal tennon, there are 5 contact faces (excluding shoulders). Three of them are edge to end grain. In the case of a simple door frame the biggest faces are cross-grain surfaces. With your case of apron to stretcher, the smallest facets of the tennon are the cross-grain surfaces.... unless you divide the tennon into multiple parts.
Fortunately, a good M&T joint relies more on the structure of the joint than the glue. But, forces in the direction of tennon withdrawal are *only* counteracted by the sheer strength of the glue.
-Steve
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Stephen M wrote:

thanks! that's very informative. i knew that about end-grain gluing but didn't stop to consider the orientation of m&t's on the wood.
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Ah. Yeah, well, that's why I ran the drawer the other way, you see. :)
Those sliding dovetails would be set into the top, and the parts a and b would hang? Until the top expands That way and the supports expand This way... Pocket screws?
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Since you're in the design stage, consider keeping the integrity of the front drawer rail, and thus making the desk stronger, as follows:
http://www.e-woodshop.net/Projects4.htm
Then scroll down to ' A method for matching the grain of an inset drawer front and its apron"
You end up with matching grain, including the drawer front, across the entire front apron and with much more integrity for your writing desk.

It is if you're using wood and not plywood.
In your case, since the drawer does not run the full width of the apron, you will use "dividers" or "runers" between the front and back aprons.
These are generally attached to the front and back apron by notching them and using ledger strips, glued to the front and back apron long grain to long grain, to support the dividers/runners.
For more ideas on how to design/use/make wooden runners and kickers for your situation, go to:
http://www.e-woodshop.net/Projects3.htm
... and scroll down to "Wooden drawer slide details".
The latter should be a good start on design ideas for your drawer detail/method of attachment.
... and while you're there, on Page5 is a writing desk I designed and made for my wife using some of the above methods.
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Last update: 5/6/06
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"Swingman" articulated "dividers" and "runners" wisdom

You should get some kind of award for cramming all that stuff into a small space. And still having an obviously functional shop.
Have you thought about adding on ten feet or so on one side of the shop?
Anyway, good job on the website. It gives lots of ideas to other woodorkers.
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"Lee Michaels" wrote in message

A "reward", not "award" ... I get to make stuff for everybody else while scratching an itch. ;)

Wish I could get away with adding that much. The plan is to eventually demolish the building and re-build, but I have a zoning comission to deal with and will still be limited to max of 24 x 20 instead of 18 x 18.
... that would still be a bit closer to "heaven", though.
I keep threatening to retire to a 1000sf house and 3500sf shop, but the taxing authorities and a kid in college won't let me.
.... one of these days.

Thanks, Lee ... appreciate the kind words.
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Swingman wrote:

thanks for the advice. i've only had a chance to glance at your site but it looks like there's lots of good stuff to be learned from it.
brian
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