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Cantilevered Shelf
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03-03-2016, 08:52 AM
JKimel said: Leverage will kill this idea. With it only being held from the end, It is doomed to fail. IMO
Woodwork... It's what I do for a living.
(well, such as it may be, It's my job) ((cept my boss is a @#!*&)) I think I'm gonna fire myself for that
03-03-2016, 09:09 AM
With a cantilever beam the applied load will be reacted out at the side of the frame in a bending moment. This is a bad design, but if you are going to do it this way, then screws must be positioned as close to the upper edge of the shelf as is practical to reduce the tension load in the screws, and of course, the more the better. the lower edge will react out the compression load into the frame so no fasteners needed there.
I think a sliding dovetail would fail the frame, even if it were glued, but it would be a good experiment to see if it failed.
Cellulose runs through my veins!
03-03-2016, 09:34 AM
DonJuvet said: Leverage will kill this idea. With it only being held from the end, It is doomed to fail. IMO [/blockquote] My take exactly. When I was a picture framer I used black nylon coated stainless steel fishing line for the hanging wires. It was very thin and used small black brass collars that got swedged on like electrical connectors. From a distance of a foot or two it will visually disappear. I would suggest that the outboard end of the shelves be supported by this very thin (and very strong) black wire. http://www.cabelas.com/product/AFW-Surfl...3765&rid=20 Here are the pliers: http://www.harborfreight.com/9-1-2-half-...36411.html http://www.wire-cablespecialties.com/pro...b-1000.htm It does not make sense for him to spend all that money on sleeves when he only needs four of them or so. So if the OP will write to me and send me a sample of the wire he gets I will mail him a few of the appropriate sized sleeves.
No animals were injured or killed in the production of this post.
03-03-2016, 09:38 AM
SteveS said: If the verticals were thicker I would be inclined to use drill rod for the "dowels" and drill right though the side. If the rod was ground and polished smooth it would be a decorative element. But with just a 3/4" thick vertical I don't think the wood will take the stress. The other end has to be supported either with a narrow strip of wood, a steel rod (painted matte black) or a wire.
No animals were injured or killed in the production of this post.
03-03-2016, 10:41 AM
I humbly disagree. He is only supporting a few lbs. These shelves are the same concept.
 They are supported with just biscuits and pocket screws from above. Or how about these:  These are just glued and screwed to that narrow vertical piece. They are now at least 4 years old and haven't sagged or broken. If you are only supporting a few pounds and the cantilever is not to large, it doesn't take a whole lot of support. Glue has amazing strength. I'm very sure the OP can support a few lbs. on that shelf with nothing more than glued tenons. John
03-03-2016, 10:51 AM
jteneyck said: But here you are gluing face grain to face grain. And the OP will be gluing end grain to face grain. Not nearly as strong. I built a wine rack similar to your lower photo. I used a couple of screws and glue and I glued a piece of 1/4 round under each shelf. But he has a very long lever arm and a narrow glue up area. So I am suspect. I suggest that the OP make a mock up and allow the glue to dry and then start loading weight on it to see at what point it will fail. It will at the very least give him some loading parameters.
No animals were injured or killed in the production of this post.
03-03-2016, 11:03 AM
His shelf is only 11" long. The tenon in the shelf is long grain to long grain so there's no issue there. In the side the grain will be primarily long to end grain but there are easy ways to enhance that. A simple way would be to drill a few angled holes up into the sides inside the shelf mortise and use epoxy to glue the shelf to the side. That would create little mechanical reinforcements. Or he could use a foxed tenon which would provide a mechanical wedge at both sides of the tenon. Using two glued foxed tenons would be incredibly strong.
John
03-03-2016, 11:30 AM
Multiple tenons like those made in the middle of this video would probably be plenty strong.
These would be essentially box joints, except not cut at the ends of both boards. The link shows these used for supporting shelves designed to hold significant weight. Of course, you don't need his machine to cut them. 
03-03-2016, 12:54 PM
Well, posting this is like opening Pandora's Box, I am now rethinking different design concepts.
I don't think I trust this shelf without additional support at the cantilevered end. It's a TV/ electronics cabinet. The cabinet will likely be moved and bumped at some point if not from moving then from just daily activity around it. I like the m&t ideas but I don't have the experience and limited hand-tools to create these to the quality that will give it the strength. Fishing line wire might work, I like this too, thanks for offer. I might abandon the cantilever design, and use two 1/2" x 1/2" square "legs" at "free end" inset about 1/2" from the corners. I'll post pics if I can ever figure this out. Thanks all.
03-03-2016, 01:07 PM
It certainly is true that it would be much easier to make a strong shelf if it were not cantilevered. If it will have electronics on it, and you are not experienced at mortise and tenon joinery, another support (in back, below, or from above) would be strongly recommended.
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