Leaning Bookcase

[jackellis]

I need bookcases for my office and I'm interested in something a bit different. This design is attractive, not terribly difficult to build and unlike any other I've seen. It helps that LOML likes the design, which I would probably do in walnut for the verticals and braces, and either ash or chestnut for the shelves (I have lots of all 3 searching for a suitable project).

The plans call for a 7 degree angle between the vertical support and the wall, but I can change the plans to use any angle I want (finally a use for high school trig). I've seen other designs with 8 and 10 degree angles.

The question is, could I get away with a 6 degree angle instead? I'm a little concerned about stability at that point, though the bottom of the upright still will be around 12 inches from the wall. Does anyone have practical experience building leaning bookcases like this one?

[radhak]

I am guessing that shelf's stability comes as much from the 7° angle on the base as the base being 12" from the wall. As it is, it seems stable enough not to need any anchoring to the wall.

Still, I'd be wary changing the angle, particularly reducing it. As Shwartz says in that article :

After numerous experiments and revisions, I discovered that these shelves actually are more of an engineering equation than a woodworking project. The leaning angle and the height of the units work together to determine the depth of the shelves. Getting these factors to work together to produce sensible shelving is trickier than it first appears. So take care if you want to modify this design — small alterations make big differences.

I am guessing changing the angle will need you to re-jig the depth of the shelves too.

But I am curious : why do you like 6° more than 7°? What does that get you?

[Pappy]

I am normally a fan of designing my own or 'personalizing' plans but, in this case, I would stick to the plans. The only exception I wold consider would be the height of the desk/work shelf. If I decided to raise or lower it then the width would change slightly (narrower if raised or wider if lowered) to maintain the balance.

[LCHIEN]

After numerous experiments and revisions, I discovered that these shelves actually are more of an engineering equation than a woodworking project. The leaning angle and the height of the units work together to determine the depth of the shelves.

changing the angle will have two important effects to my observation:

1. assuming the same height. shelf spacing etc. the top will be a little wider and the shelves will be increasingly wider from the bottom to the top (~17% wider or about an inch for a 6.5" shelf at the top). Keeping the same base width means the top shelves will be wider and the author's careful use of one sheet of plywood will go out the door.

2. The center of gravity will move slightly closer to the front. I'm guessing about an inch wider at the top shelf. Overall this will move the center of gravity forward about half an inch (since the center of gravity at the bottom is not changed). THis assumes equal loads etc on the shelves which is unlikely, usually you'll have the heavy loads on the wall-side shelves to the bottom, this is probably not a serious thing, I think. But it will in theory make it slightly more easy to tip.

P.S. two more thoughts on the way to work,
there will be a noticeable reduction of the rake which might affect the aesthetics, and
as Cabinetman suggests in the next post following, you might put a screw into the wall on one or more of the verticals. This is probably a good safety thing overall regardless of the 6 or 7 degree thing, due to the height vs. depth, anyway. With the shallow depth of the vertical at the top, you could drill a hole from the front to the back and countersink it for a 3-1/2" screw. Doesn't have to be real strong screw because the initial force to keep from tipping will be quite small.

[chopnhack]

I'm just impressed because I don't think I have ever seen Chris use plywood or pocket screws before! I didn't think he could even bring himself to use them in the same sentence :P

[cabinetman]

Here's my take:

It seems that the dimensions are to maximize a single sheet of plywood. Changes to those might require a different materials list. The overall design is representative of a gusset, and its balance is triangulated. Shear weight (including the unit itself) would have to overcome the point of balance that the furthermost support on the floor will afford.

As a demo, make a sample right triangle (like from posterboard) with a short adjacent side to the hypotenuse and stand it up against the wall. That will represent the points of a triangulated unit. Envision a shorter adjacent side, and how much further the load would have to be to overcome the stability of the angle.

Changing the angle IMO, would affect the centerline of balance if the weight moved appreciably forward of the forward point on the floor. The sheer weight plants the stability downward. The further the weight is moved forward, the more chance the unit could get tipsy. I think one degree might not account for that.

If at all possible, use a single mounting fastener on the three sections (it can be done without being noticeable). Fastening at the desk unit, and then the wing units being attached to the desk might be sufficient. That would eliminate doubt. As it stands from the plans, and not fastened to the wall, it could be pulled forward, like kids visiting, or someone in a drunken rage.

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[jackellis]

A lot of good suggestions. Thanks for taking the time to offer them.

I'm going to use solid wood because I have more than enough of it so Chris's single sheet of plywood constraint...isn't.

I'll also probably make a quick prototype out of construction lumber (a fir 2x4 is already leaning against a wall so I can verify my calculations if I change the angles) and I'm making a floor-to-ceiling (8') unit whereas the plans are for a 7' tall unit. If anyone is interested, I can send you a quick-and-dirty Excel spreadsheet I built to calculate shelf depths.

I hadn't thought about anchoring to the wall but we do get earthquakes up here.

I don't think the 3x31 pieces that support the shelves need to be screwed to the shelves but unless they sit in dadoes, they do need to be screwed to the uprights. Dadoes are a possibility, even if no one does look at the back.

I need to post the couple of projects I've built over the last year. Nothing special...at least not yet.