Dovetail orientation

[Alex Yeilding]

It is my understanding that with modern glues, the mechanical advantage of a dovetail joint is pretty irrelevant, and a finger joint is just as good structurally. That said, I like using dovetails, and using them in a way that "makes sense" mechanically--I wouldn't put tails on the front of a drawer and pins on the sides! But I've run up on a situation where it is not so clear:

Designing a wall-mounted tool cabinet, which is an open box, 8" deep, with a plywood back panel in a dado. In this case, I would put tails on the vertical pieces, feeling that the main stresses on the DT joints would come from tools resting on the bottom "shelf", or from the entire weight of the cabinet hanging on the top DT's if the french cleat is attatched to the back panel rather than the uprights.

But the next interation of design complicates the situation. Add a piano hinge to the left front, and attach a second identical box that "clam shells" with the first. On most of the corners, it seems like the same considerations call for tails on the vertical pieces. But the greatest stresses (it seesm to this non-engineer) are from horizontal forces on the joints next to the top of the hinge.

So, I have three options:
1) Tails on the uprights, either because my intuition of the forces at the top corners is wrong, or it is not a major factor.
2) Tails on the horizontals, since the vertical stresses on the other joints are much smaller than the horizontal ones on the joints at the hinge-top corners
3) Mixed--with horizontal tails on the hinge-top corners, and vertical on the rest. This would work assembly-wise as long as it is only one corner of each, but my initial reaction to the assymetry is negative.

Opinions or engineering expertise, please?

[Dave Richards]

I think I would stick to the tails on the verticals both top and bottom. This would provide design consistency and as you allude to, with modern adhesives, the strength of the dovetail is superfluous. Glued box joints would be as strong.

Edited to add: IMO (H or not) I think of dovetails as a joining method that should be done for appearance. With today's adhesives, there's little need to create fiddly joints. Box joints would be an easier machine setup and would save time in construction.

If dovetails are going to be used they should be good looking. Fine pins, tail widths that are proportionate to the piece and nice layouts should rule. I find dovetails cut with carbide router cutters to be fat and graceless. Handcut DTs can be lovely things and the closest I've found to those are made with HSS router cutters which are much more slender than their carbide cutters. I've also see some nice looking large dovetails cut with tablesaw and/or bandsaw.

[Neil Lamens]

Hi Alex:

To answer you question, I'd go tails on the vertical.......BUT!!!....

Are you firm on the design being cabinets face to face attached with piano hinge????

Question: Why not 2 cabinets side by side with individual doors??? Not knowing the full dimensions of stoack and cabinets, intuitively I would sense alot of stress on the piano hinge.

[Alex Yeilding]

If dovetails are going to be used they should be good looking. Fine pins, tail widths that are proportionate to the piece and nice layouts should rule. I find dovetails cut with carbide router cutters to be fat and graceless. Handcut DTs can be lovely things and the closest I've found to those are made with HSS router cutters which are much more slender than their carbide cutters.

I agree, but why settle for "close"?<g> Seriously, I plan to hand-cut the dovetails. Not claiming that they will be "better" than machine-cut, but for me, more satisfaction in the doing and the result. While my plans show evenly spaced DTs (I was just following your SU tutorial!), in practice, I tend to use smaller tails towrd the edges, and larger in the middle.

[Dave Richards]

Oh, Alex, I wasn't suggesting that you use machine cut dovetails, I was just saying that dovetails should be aesthetically pleasing if they are going to be used at all. In my opinion carbide dovetail cutters aren't the way to achieve that.

I like you're idea of varying the width of the tails across the board.

I hope the tutorial was useful.

Cheers.

[Alex Yeilding]

Are you firm on the design being cabinets face to face attached with piano hinge????

Question: Why not 2 cabinets side by side with individual doors??? Not knowing the full dimensions of stoack and cabinets, intuitively I would sense alot of stress on the piano hinge.

No, nothing is firm at this point. Kinda blue-skying ideas. Several iterations have a shallower box as the "door", with lighter weight tools such as rules, squares, calipers, dividers, etc. on the door. But even in that case, the principle of my question remains. If I go with a deep/potentially heavy door, I think I would need some kind of ledge on the wall where it opens to bear some of the weight.

[Alex Yeilding]

I hope the tutorial was useful.

Very much so. I (and probably most people) learn by doing, not by watching and having something explained. Following your tutorial as I did my own dovetails helped some ideas (like mirror image parts) sink in.