I've always resisted making sample parts. Most of the time, when I have something in my head, I can successfully turn it into a real thing. I'd like to think it's because I'm skilled. Or maybe I've just been lucky. These days I have a new theory.
I've noticed that I typically don't push myself to make big enough steps from one design to the next. These small iterations can be really useful when you're making refinements to a design that you already like. But sometimes you need to make a bigger leap.
Last night I started work on a desk for our seven year old. As a staked desk, it's a large departure from any form of work that I've built in the past. It's full of joinery that I've never used for a case piece. Tapered mortise and tenon joints, sliding dovetails, curved drawer fronts with dovetailed joinery. It's going to be a challenge. It's going to be fun!
The first parts I tackled were the legs. I've made legs for chairs before, but they were almost exclusively turned on the lathe. And I was working from someone else's (tested and proven) plan. This desk will feature tapered hexagonal legs with tapered round tenons to join them to the top. With such a long leg I want to make the taper as dramatic as possible. my initial plan was to taper the leg first, all the way down to the 5/8" diameter that will be the smaller diameter of the tenon. I was about to start milling up some beautiful straight grain ash when a pile of silver maple off-cuts caught my attention and I had the thought to make a sample leg.
After cutting the entire length of the blank to the shape of the hexagon on the larger end, I found the center at the top and bottom. On the top end I scribed a 5/8" diameter circle and drew a smaller hexagon with faces that were tangent to the circle. One facet at a time, I used a jack plane to create the tapered form.
With that done I planned to use a lathe to turn a tenon with a six degree taper at the top end to match my reamer. Here is where the sample part proved it's worth. It turns out that the overall taper of the leg was less than the six degrees I needed to make my joint. Since I had planed the blank down to a 5/8" hexagon on the thin end, I had already removed too much material. If I had started with a thicker blank, or was making a shorter leg, I think I would have been fine. But if I had gone straight to making a stack of these parts out of the ash, they would have ended up in the bone yard.
It was an easy decision to make another sample leg to test out the revised design. I left a little more stock on the skinny end when I made my taper. I also got a chance to test the setup on the jointer that I planned to use when I tapered the ash stock. I even made a small mistake that caused me to rearrange the order of operations I had planned to use when making the finished parts.
Tonight I'm hoping to move on to the tapered sliding dovetail battens. And you can bet I'll be making a sample of the joint before I commit to cutting it in the finished top.