238 – Engineer the Design: Mortise & Tenon Sizing

Video - January 22, 2015

Designing furniture can be quite tricky for new and experienced woodworkers alike. Many of us are more than capable of building just about anything, but when posed with the challenge of designing something from scratch we start shaking in our shop aprons. I say “we” because I consider myself a wanna-be designer with minimal skill, but I do my best and I have fun while I’m at it! So as always when I discuss design, take my advice as the sharing of personal experience and not a how-to from an absolute authority.

tww_4_stepsYou might recall a discussion we had a while back where I outlined the four phases in the project design process: The Process is the Project. What I’m going to do in this video is expand a bit on Phase 2: Engineer the Design. Once you have a good-looking form for your project, you have to decide what joints to use and where to put them. This is something that comes a little more naturally to me and it’s something I actually enjoy. Perhaps it’s all those years of putting together LEGO kits! For me, the process occurs in three steps:

Design for Quality

I like to start by designing for the best case scenario. This usually gives me not only the type of joinery I want to use but also the dimensions of that joinery. Bear in mind there usually isn’t one right answer but several. The “best” answer typically comes down to personal opinion and taste. Ultimately, your goal is to have joinery that suits the needs of the piece in the best way possible.

Adjust for Restrictions

Now that we have the ideal situation, we need to think more globally. Does the joint interfere with other joints or project parts? Does the joinery make an adjoining part inherently weak? If so, adjust the dimensions as needed. While this adjustment process takes us away from our ideal situation, it usually doesn’t render the joints ineffective. It’s all about compromise.

Simplify Where Sensible

Since most furniture requires lots of joints, it’s always nice if they can be batched out. And batching out becomes a lot easier when your joints are all the same size. So if it makes sense for the project and doesn’t take away too much from quality, I try to make my joints of consistent dimension.

So the next time you’re designing furniture or even looking at a set of plans wondering why the designer made the choices they did, think about this part of the furniture-building process and the three steps mentioned above. It might help clarify the situation and get you through a tough design road block.

And if you’re interested in the project used for this demonstration, you can purchase access here.


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