Cutting Mortises

This morning I cut mortises. I broke my last coping saw blade for wood while cutting dovetails last night, so i shifted over to work on a shelf for my reference books for woodworking — partly so all the books I have (and borrow) stay in one place, and partly so I don’t buy more books than I need (like that will stop me!).

Each shelf will be held in place by a pair of mortise and tenon joints. You can see in this first picture where I’ve drilled out the holes for the mortises. I wound up cutting six mortises today, much more cleanly and square than you see here.

mortise is a hole in a piece of wood, designed to be square (or at least the right shape to accept) to a matched tenon, or integral peg, in another piece of wood.  In furniture making, mortise and tenon joints are usually used in furniture intended to be collapsed for travel; it’s very common in medieval furniture where kings went on progress between manors, for example; and a lot of modern furniture built for the Society of Creative Anachronism (SCA) is similarly mortised and tenoned.  A secondary mortise is usually cut in the tenon, as well, to hold a wedge-shaped peg.  I plan to do that, too.

I had initially planned to cut all six mortises on each shelf upright, and the four on each of the three shelves, by hand.  But one took an hour, and so I drilled the other five out on one shelf with a powered drill press.  I plan to cut the other six mortises with not-just-a-drill-press but also a Forstner bit, to remove more of the waste material much more cleanly and faster.  The shelf panels are 3/4″ wide board which is nominally 1″x10″ (really 3/4″ x 9 1/2″-ish… even the 1/2″ isn’t accurate over the length of the board.)

The design of this bookshelf is pretty easy, really: it is three shelves with tenons— a tall shelf on the bottom for tradesman’s paperbacks and Popular Woodworking hardcovers; the middle shelf serves for hardcovers and trade paperbacks; and an open shelf on top for whatever happens to come my way. The three shelves are each half of a 6′-long board, and the verticals are also each a half of a 6′-long board.  The pegs in the tenons are going to be bits of 1″x 1″ square doweling cut and shaped to fit the holes; I may drill in screws or nails to hold bits of brass chain to hold the pegs, so the pegs don’t get separated from the uprights during transportation.  I plan to cut the tops of the uprights into a gothic arch, and maybe in the long run add some decorative carving — both to improve the look of a simple pine bookcase, and to reduce the overall weight of the parts.

I think my biggest challenge is going to be getting the mortises on the second upright cut so that the shelves lie mostly parallel to the floor and square.  Cutting the mortises in the shelf tenons will be relatively easy — I can drill out the waste and then use a chisel to make them mostly-square; the use of a peg there will help hold the shelf together, but so will the weight of the books on the shelf itself, as will the tension and pressure provided by the pegs.  I may have to add a secondary diagonal brace of some kind, but I have some ideas on how to do that; but most shelf designs like this don’t seem to need them — the three shelves themselves help keep things tight and square.

I did cut one end of one of the shelf boards with the tenons, and managed to fit them into the shelf mortises. They fit, but my tendency, I see, is to cut the mortises too wide and not high/tall enough.  I’ll have to correct this in future iterations.

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  1. Thank you for explaining what a mortise and tenon joint is! I’m a visual and hands on learner, so your pictures helped a lot. I’ve been researching carpentry lately, and the technical terms always throw me off, especially if I can’t SEE what the person is talking about. Hope to see more of your work soon!

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