4 September 2020 at 3:47 am #676701Steve SheenParticipant
A friend of mine has asked me to make a set of corner selves for him that sort of zig-zag up the wall (the attached sketch probably gives a better idea). I haven’t made anything like this before and initially planned to join the horizontal quarter-circle shelf pieces to the the vertical pieces with dovetails. I thought of having the tails on the vertical pieces and pins on the shelves.
Then I realised that the pins on one of the two straight edges of the quarter-circle shelves would be along the direction of the grain instead of across and a recent video of Mr Sellers’, where he demonstrated the weakness of dovetails along the grain came to mind.
So my question is, if I re-orientate the quarter-circle shelf pieces by 15 degrees, so that both straight edges run at an angle across the grain, would that increase the strength of the joint (compared to along the grain) or now compromise both sets of dovetails?
I can’t think of any other way to do the joinery other than screw all the pieces together. Since I only agreed to make it so as to practice my skills, screwing it all together would rather defeat the purpose.
The boards that I’ll be using are 3/4″ pine, 11″ wide.4 September 2020 at 8:08 am #676718Colin ScowenParticipant
Joinery notwithstanding, are you sure that the two walls that make up that corner are square and plumb? The design you show in the picture will clearly show gaps if they are not.
What is the plan for attaching them to the wall? I assume screws through a couple of the square parts on one side, in an area where they are not too visible? Or is the plan to mount to both walls?
Once this is on the wall, only you and your friend will know that you dovetailed these pieces together. All anyone else will see is thick finger joints. (Not saying don’t do it, only that it won’t be visible.)
The boards are 11″ wide. Do you have a rough idea what sort of load they will see? Is it for a kitchen where they will be used for pots and pans, or for displaying something lighter?
In terms of the joinery, why not use this as a chance to also practice stopped housings on the long grain to long grain? Similar to the joint used on the desk top organiser.
I would strongly suggest to build a screwed together prototype at nice easy 90 degree corners using cheap material and then test the fit before cutting the board up. Also, making a few of the shelves from the same cheap material will allow you to put one on top of the other, and then check the corner and mark the two as a sort of rotating story stick. Second picture here shows the view from the top.
Colin, Czech Rep.4 September 2020 at 9:01 pm #676801deanbeckerParticipant
You can also adjust the angleS of the housing as you go up if you have access to the corner so they will fit square on the wall.5 September 2020 at 2:59 am #676840Steve SheenParticipant
Thanks for your advice Colin.
I have checked the walls. Actually I’m supposed to be making two of these for opposite corners of the same wall. One of the corners is 90 degrees while the other is a bit bigger. I’ll start with the 90 degree one. The shelves are more decorative than practical and will be fairly lightly loaded. I was thinking to screw them into both walls, either as you say in a couple of unobtrusive places or alternatively plugging the screw holes. I suppose 3/4″ stock would be thick enough for that. If I drilled to a depth of 1/4″ there would still be 1/2″ of would to grip against the wall.
I hadn’t thought of the stopped housing joint as an option. Any housing joints I have done before have been across the grain. In this case it would be long grain to end grain. The quarter-circle shelf piece would be long grain and the square side piece would be end grain. If I used a combination of stopped housing and dovetail joints as in your diagram, but re-orientated by 180 degrees, so the loaded shelf would be sitting on top of the side piece rather than working to pull the housing joint open and the dovetails, would that be stronger? Or does it not really make a difference if the joint is well-fitted and glued up properly? Would stopped housing joints on both pieces be just as effective?
(This kind of relates to something that confused me about the wall-mounted bathroom cabinet project. If I recall correctly this also used the stopped housing joint to join the two sides to the bottom (housing grooves cut into the bottom piece). From a mechanical perspective, the housing joint has one weak direction. Any sideways forces will not open the joint. An upwards for will not open the joint. But a downwards force (in the case of the bottom of the bathroom cabinet) would act to open up the joint. So the strength of the joint depends on the glue. Whereas if the housing grooves were in the side pieces and the bottom fitted into the sides, there would be extra mechanical strength in the direction of loading. I suppose in the case the bathroom cabinet was not going to be under heavy load so the design becomes a pay-off between strength and aesthetics. The cabinet certainly looks better the way Paul designed it and is strong enough for the purpose. I find this element of designing projects almost as interesting as the making!)
Thanks a lot for your time and suggestions. It has been a big help.
Steve5 September 2020 at 8:06 am #676855Colin ScowenParticipant
If they are only lightly loaded, then you will probably be fine. When you cut the rabbet on the bottom of the side piece, remember that you have the side walls, which would be long grain (similar to a stopped lap joint, just long and thin, or a shallow but very long mortise.)
Well fitted, glued up, lightly loaded, it won’t make that much of a difference. And yes, they probably would be as effective.
Colin, Czech Rep.
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