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Joinery Problem Solving

5 comments
12 years ago
Joinery

Woodworking QuestionsI think the problem solving aspect of woodworking is one of my favorite elements. You take all of your knowledge of wood movement, joint strength, and technique and bring them to bear on a single issue to devise a solution. Then you get to figure out a way to execute that solution. Usually that method is best done as a repeatable process since often multiple parts are needed over the course of you project. The great part is that once you figure out the steps, the solution, no matter how complex seems like a piece of cake.

Recently I backed myself into a corner by losing track of grain direction in a SketchUp model. My joinery solution looked perfect for strength and execution wasn’t a problem. Then I got to real wood and suddenly realized my joinery would be very weak and I would violate all the space/time laws of wood movement causing uncontrollable tachyon bursts that completely disrupt all sub-space traffic. Funny how the problem and the solution is always those pesky tachyons…

sorry, I turned off the Start Trek episode playing in the background…

So I sat back and began to problem solve. The bottom of the tool box I’m building needs to resist pulling out of the bottom of the carcass as the weight of a drawer will rest on it. But I cannot use dovetails as this would put them cross grain to my sides which are also dovetailed with the grain running parallel to the bottom. A through sliding dovetail would potentially weaken the sides since it would have to be position right by the edge of the board. A simple groove would work fine just like a drawer bottom but without something resisting the outward pull, the bottom panel would be relying entirely on glue strength. A big problem because gluing the entire tongue and groove would then violate wood movement rules bringing back those tachyons again. So why not compromise?

Hybrid sliding dovetail jointMy end solution is a hybrid between a sliding dovetail and a tongue and groove and now the bottom panel is 3 pieces instead of 1. The 3 pieces are dry fit with tongue and groove joinery and the outer parts are glued in to the case with sliding dovetails. Did I mention the whole case is canted in at a compound angle? So all my joinery surfaces need to be at a 10 degree bias.

Remember what I said about solutions seeming complex?

Enter the process. With detailed layout and thinking about the finished joint, I can visualize what parts need to come away and the best order to do that. How I remove the wood plays a big part in this too. With angles everywhere in this joint most of my planes are useless so it comes down to saw and chisel. In the end 6 saw cuts and 2 chisel passes shaped my joint.

Your Turn

Can you figure out where these cuts happened and in what order? How would you create this joint?
Please leave your thoughts in the comments below.

The Hand Tool School**Problem solving like this happens every day in The Hand Tool School. This project is one of 4 covered in Semester alone and it presents many interesting problems to solve. Join today, all the cool kids are already there! 🙂

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Russ Whitney

I’ll give this a try. First I would make the dove tail cut for the full width of the board with two passes of the router. Next I would trim the dove tail off for the tongue and groove area. I can’t tell how wide the board is but if it’s not too wide I would put it on edge and do it on my table saw. Otherwise I would trim it with my bandsaw. Next, the angle of the dove tail needs to be trimmed off the tongue and groove area. That may be easiest to do with a chisel since the router can’t get very close to the tail of the dove tail.

    Shannon

    Excellent someone with a method that would be totally different than mine! I was sincerely hoping for this. Technically the angle of dovetail splay is symmetrical but remember that the end of the tail board has a 10 degree splay and therefore the tail profile is a bit distorted. You will need to adjust your router fence on each side of the tail. Also the base line at the bottom of the tail/tongue isn’t even but canted at 10 degrees too so the dovetail bit in the router cannot have a 90 degree bottom to it. The rest should work though you need to be careful of the angles. The face of the board would be your reference surface so you will need to adjust blade or table angles depending on the tool used.

mitchwilson

Shannon, your neutrinos are drifting…..(Don’t you just wish that Ashley Judd was looking over your shoulder as you worked on this project?)

Jason Young

let’s see, two saw cuts for the shoulders of your tenon/dovetail. Two sawcuts to shape the edges of the dovetail, one to establish the length of the dovetail and the other to reduce the length of the tenon. Then pare away the material to establish the thickness of your tenon. The work seems straight foward enough, but planning and laying out would be key. is this the Roy Underhill tool tote you’re working on? I’d love to try that out. Do all four side of the tool tray splay out? Or just the two ends?

    Shannon

    After cutting 5 of these joints I have quickly discovered that doing it in a certain order to shorten the saw cuts makes for more accuracy. The layout wasn’t too bad but making sure you can get it right multiple times required setting several gauges. I’m glad I have 4 marking gauges! This is for a toolbox I’m building for The Hand Tool School. It is my own design heavily inspired by Tom Fidgen and Roy Underhill. I made the Underhill tote a few months ago and there was nothing more fancy than compound but joints and rabbets in that. The tote does splay in all 4 directions, though Roy mentions making the side towards your leg vertical so it rides better against you when carrying it. I don’t have as long a walk through the forest, across city streets, and over streams like Roy however so I made all 4 sides to splay out.