Replies

1. 
   pzgren | Apr 14, 2006 08:56pm | #1

   If you're looking for stability and a rock-solid end result, then you might consider using sliding dovetails on your shelves. Much, much stronger than biscuits and more rack-resistant than dados. Also, sliding DTs give you a mechanical locking joint at both ends of each shelf.... It's a little more work, but the end result is much stronger and more stable.

1. 
   Glaucon | Apr 14, 2006 09:18pm | #2

   Agree 110%.Neither biscuits nor dados provide a srong enough joint to support the weight of books. The tendency of laden shelves to sag and for the case to rack argues for a more robust joint such as sliding DTs.Glaucon

   If you don't think too good, then don't think too much...

1. 
   SgianDubh | Apr 14, 2006 09:49pm | #3

   Presumably both yourself, Glaucon, and pzgren meant tapered sliding dovetails for the usual reasons, even though they are harder to execute than regular sliding dovetails?

   However, having said that, both housings (dado joints) or biscuits can work very well for bookcases. It depends on the span, how thick the shelf is, what material it's made of, or if the shelf has a reinforcing return front or/and back, or has rear support brackets of some sort, the weight of the books the shelves are intended to carry, and so on.

   I use a rough and ready figure of 25 lbs of load per linear foot as a typical requirement. Many a bookcase has adjustable shelves, i.e., not attached solidly to the inner faces of the gable ends spanning 30" or 36" that work successfully.

   I believe it's incorrect to say that the only way to attach shelves to the gable ends of a bookcase is with sliding dovetails, tapered or not. It's my experience that's not the only way to do it to achieve a successful end result. Slainte.

   Richard Jones Furniture

   Edited 4/14/2006 3:06 pm by SgianDubh

1. 
   pzgren | Apr 14, 2006 10:37pm | #5

   Richard,

     Can't/won't speak for Glaucon, but for myself, yes, what I had in mind was tapered sliding DTs; should have been a bit more specific.

     I certainly won't (and did not intend to in my previous post) claim that sliding DTs of whichever flavour are the only way to attach shelves to the sides of a book case; they are merely the most stable method I've found so far.

     I've built about a dozen and a half book cases -- so my statistical sample is pretty small :-) -- the last 4 of which used sliding (tapered) DTs to attach the shelves. The earlier ones were almost all built using dados, some "reinforced" with dowels. My experience with this is that all but the sliding DT versions racked considerably when loaded up with books. (As a side note, only a few of the book cases had/have a full back, and even though the ones that did have a back didn't rack very much, it was still more than I would have liked.)

     At any rate, my intention was not to imply that the only way to attach shelves to the sides of a book case is sliding DTs, but simply to suggest a very strong and stable (if somewhat complicated/difficult) method to do so.

   Tschüß!

   James

    

2. 
   Glaucon | Apr 14, 2006 11:37pm | #6

   I've made a few bookcases, and I agree that there is more than one way to do it. In my mind a sliding DT is the best, but not the only way to join it. I make my bookcases for myself, and they generally hold professional texts and bound journals. The weight is considerable, and probably more than many bookcases intended for more casual use.Just speaking for myself, I favor:1. Hardwood shelves (rather than plywood), final milled thickness 4/4,2. Span of no more than 30" (~75 cm), 3. Not adjustable (most people actually don't change the original spacing)- this makes for a very solid, strong case. Measure the books before you cut, and plan the shelves accordingly.4. Sliding dovetail for joinery. You can make a true tapered sliding DT, or ease the female portion of a standard DT with a router plane. Glue the front inch of the female and the back inch of the male (instead of the whole joint) and it will come together without binding.As I said, this is not the only way to do it, but it will never sag or rack. If I were building for the Library of Congress, this is what I'd build.Just my 2p,Glaucon

   If you don't think too good, then don't think too much...

2. 
   jes | Apr 14, 2006 10:06pm | #4

   I imagine you're probably right. In scouring the net I've found plenty of examples of biscuited shelves, and not much advice against it, but my gut said I should pose the question here. I know there are a lot of fast DIY plans that employ methods that might last a while, but not likely for generations. I like the idea of sliding dovetails, and I hadn't really thought of that yet. I reckon the extra work will probably be worth it in the long run - at the very least, it'll keep me from having anxiety attacks at 3am that a pile of heavy books might suddenly crash down on my niece. However, I do like to keep my mind open to modern effeciencies. I try to balance both sides of the coin - whether it be knee-jerk reactions from traditionalists rejecting newer techniques that might actually work quite well (I don't regard you're response as such, btw!), or the ubiquitous misuse of time saving methods (like biscuits or pocket screws) to cut corners on just about everything.
   That said, do you know of any particularly good resources for guidance on making effective sliding dovetails? I think I have the know-how to make them without detailed instruction, but any specific considerations or tips would be welcome.
   Thanks for your two cents.Jesse DavidEdited 4/14/2006 3:07 pm by jesEdited 4/14/2006 3:08 pm by jes

   Edited 4/14/2006 3:09 pm by jes

1. 
   pzgren | Apr 15, 2006 12:20am | #7

   Jesse,

   <<That said, do you know of any particularly good resources for guidance on making effective sliding dovetails? I think I have the know-how to make them without detailed instruction, but any specific considerations or tips would be welcome.>>

     For doing them with hand tools, try this link: http://www.norsewoodsmith.com/   At the bottom of the page is a link to a photo tutorial on making dados with hand tools. Doing straight sliding dovetails is the same method, except that the walls are cut at the angle to match your male dovetail. For tapered sliding dovetails, the layout is slightly tapered from back to front (assuming that you want to do stopped tapered sliding dovetails) to create a self-tightening joint.

   I remember reading -- quite some time ago -- another site with a method to do them with a router, but can't find it right now; I'll post it, if I do.

   <<I try to balance both sides of the coin - whether it be knee-jerk reactions from traditionalists rejecting newer techniques that might actually work quite well (I don't regard you're response as such, btw!), or the ubiquitous misuse of time saving methods (like biscuits or pocket screws) to cut corners on just about everything.>>

   I do all of my woodworking by hand, so I guess that makes me a bit of a traditionalist. Regardless, while I frequently recommend to people that they at least try a project using only hand tools, it makes absolutely no difference to me either way how someone does their woodworking; that's entirely up to them. My opinion on that is -- if you're a hobbyist woodworker -- you should do your woodworking in the way that brings you the most enjoyment and the best results. (If you're doing woodworking for a living, and/or in a production-line operation, then power tool woodworking is probably the only thing that makes [economical] sense, unless you're one of the very few who have gained a reputation that allows them to do custom hand work for a living....) So....I would be one of the last to denigrate someone for their choice in woodworking methods.

   Anyway, most of the better books on joinery should have a section on sliding dovetails. I'll take a look through my books and post a couple of suggestions later.

   Hope this is of some use to you.

   James

2. 
   Lataxe | Apr 15, 2006 01:22am | #8

   Jes,

   You need to calculate the loads your shelves are going to take.  Short shelves with paperback novels on them will be fine with the flimsiest of joints between shelf and carcase. 4 foot spans with large hardback art books on them weighing many kilos will need shelves that resist the bending forces that will try to pull the shelf-ends away from the sides of the case.

   Since the task of a bookshelf cannot always be predicted, I tend to go for overkill - sliding dovetails.  They look nice too. I am a fan of biscuits but never use them for bookshelves because of the nature of the forces acting on shelves (as opposed to carcase sides, drawer rails, etc.).  Dovetails provide mechanical strength to keep the shelves locked to the carcase sides whereas biscuits and dadoes rely on the glue only. There is a lot less glue with biscuits than with dadoes.

   Funnily enough, if you have a very strong case, loose shelves are the least stressful, even if the books are very heavy and the shelf long.  Assuming the shelf supports themselves are substantial (nice fat,  brass hoops deeply inset in the carcase sides, for instance) all the force of the book-weight simply bends the shelves and stresses the support pins.  The carcase itself has no stress and there is no joint to fail.  The shelves will bow downwards of course and this never looks good, even if it's perfectly safe.

   Personally I like the Taunton series of books on design, as they are straightforward English with excellent illustrations and no woffling.  Try the Construction and the Joinery ones for basic stuff about bookshelf design considerations or options.

   Lataxe

1. 
   user-137699 | Apr 15, 2006 04:53pm | #9

   Hi - as a newbiew to all this - can someone explain what a tapered sliding dovetail is. I think I know what a sliding dovetail is, but I don't quite see what a tapered sliding dovetail is, and why it is so much better.cheers-
   Rob

1. 
   QCInspector | Apr 15, 2006 09:21pm | #11

   First off, welcome to the forum.A tapered sliding dovetail has a slight difference in width over its length of the joint, (like a long wedge). The purpose is to allow the assembly to slide together easily without binding and having the glue set before the boards are in final position. I believe it would have been "invented" / "developed" a long time ago when hide glues were the only viable wood glues. (No proof, only a logical conclusion.) The joint could be put together before the hot hide glue cooled off and set.

1. 
   user-137699 | Apr 18, 2006 11:05pm | #13

   thanks - the forums are great.I guess it should have been obvious what a tapered dovetail is. At first it seemed so imossible to get right (to make right that is). But I suppose its just a fixed angle for the straight edge for the router. Still - it must be tricky to get right!Rob

3. 
   rr_mdi | Apr 15, 2006 08:07pm | #10

   In my home I built a 7'x7' bookshelves and used biscuits. I guess I should note that it is more like a book cabinet. The bottom of the book shelve is resting on a base much like a kitchen cabinet. The unit is fastened to the wall by only 3 screws. Also, instead of long shelve spans I decided to biscuit the verticals 16" apart and adjustable shelves due to the fact that the books are not the same size.
   Visually, the unit looks like a large grid with the shelves at various heights. So, I have a 7'x7' unit fully loaded with books (from large art books to small paperbacks), no saggy shelves, no empty spaces. The biscuits have held up beautifully which is probably due to the base.
   Something to consider if you have the space to do so.

   Richard

4. 
   cicero | Apr 16, 2006 09:05am | #12

   If I were to make with biscuits,I would add a stretcher under each shelf at the back,of say 3"x 3/4" and clash a 1"x 1" piece to the front of each shelf to make it more rigid.

    

   (clash = edgeband.)