As you build more, you will gain a sense of 1) Where dimensions and squareness matter and 2) How larger pieces are made of subassemblies. As you come to understand these things, you will be able to look at a project and think through an order of operations to build the subassemblies and to assemble the subassemblies into the larger pieces.
With regard to squareness and dimensions, let’s use Paul’s box with hinged lid as an example. The box has four sides dovetailed together, a base, and a lid. The lengths of the pairs of sides is critical to having the box assemble cleanly. I would probably choose the inside faces and the top edge as my reference faces and reference edges. They must be flat and square for me to lay out my dovetails and fit them well. The way I do dovetails, squareness of the ends doesn’t matter. The exterior faces also don’t matter much. Thinking in these terms, I know I’m going to prepare the sides of the box in pairs, mark lengths in pairs (transferring, not measuring), and I’m going to build the box sides as a subassembly. The lid and the bottom are separate “assemblies,” even if trivial ones. The inside faces must be flat to meet the box cleanly. The outside surface don’t matter and “looks good is good.” I know I will glue up the box sides, then plane the top and bottom flat (to match the top and bottom of the box) and will plane the ends of the dovetails and exterior surfaces to look good. How’d I know all this? I’ve built a box and learned to think about reference face, reference edge, layout, etc.
Let’s think about a chair like Paul’s dining chair. This chair has two major sub assemblies. The two back posts assemble with the various rails to give the rear frame. The front legs assemble with the various rails to give the front frame. Those are built independently. I know all the rails will be the same length in the back frame and will lay them out together, transferring dimensions all at once (not measuring). Ditto for the front frame, separately. I’ll connect these to assemblies via the front to back seat rails and stretchers. At that point, you have a chair. The ply seat and foam is really a 3rd assembly.
So, you’ll start to see things are assemblies and you’ll collect experience in layout and joinery that will help you think about what has to be built before other things so that you can transfer dimensions. That’s why we build a cabinet first and then fit the doors to the openings. In any given subassembly, it’s not uncommon to build one part first and transfer dimensions to another part. For example, if you make a small wall cupboard with a shelf that fits into housings, I would make the exterior frame first, cut the housings, dry fit the pieces together, and transfer the distance between the bottoms of the housings onto the shelf material to get the length of the shelf. Nothing is more accurate than transferring a dimension with a knife nick.
The book than Sven-Olof suggested is good because it helps you to see how things are built up. Add in Paul’s videos and other “here’s how to build this” sources, and you’ll start to see how to identify the sub assemblies, and start to get a feeling for what dimensions matter. If you were working with machines, you’d probably work by cutting things precisely from drawings. If you are workign by hand, that is a waste of time. You go faster by knowing how things go together and working to the dimensions you have / produce, if that makes any sense. With experience, you’ll start to see that this means that it often doesn’t matter what thickness material you have on hand. You learn to build to it.
So, go build some stuff. If it seems like too much and is too complicated, either do something simpler, or find a video like one of Paul’s that will walk you through it. If you do the latter, always be watching in the video for _why_ he is doing things in the order he is doing them. There’s usually a reason and it usually relates to the things I’ve just described.
- This reply was modified 2 years ago by Ed.