Through mortise and tenon layout Q

[Randall J Cox]

I'm building a simple stepstool with the tall raised handle. Its an old design, shaker maybe, for reaching top shelves. I'm going to attach the step part to the tall back with through tenons. All my woodworking books show chopping out the mortises down to the center (midway) and flipping the piece over and finishing from other side. As the mortises have to be nice and square, the front is easy with layout lines on front. But, how do you match layout lines on back so the mortises are exactly square all the way through and meet? Randy PS I have never done this joint before, thought its time I learned. Tx. Randy

[Scott Clausen]

You need to get some good marking gauges and pay close attention to which faces you are referencing off of. A good combination square will allow you to transfer knife marks around the piece. A mortice gauge will allow you to mark the mortise side walls even. I saw a unique video from the English woodworker this morning where he uses a router plane, if you have one, to get the side walls dead even. Paul Sellers is a great resource for getting things lined up with hand tools too.

[Kevin Jenness]

You can extend the layout lines for the mortise ends from the face to and around the edge to the back, and define the mortise cheeks using a combination square or marking gauge. The edge must be square or the mortise will be skewed. For precision, a knife is better than a pencil. To avoid scarring the wood, you can lay down masking tape and score it lightly with the knife.

[Randall J Cox]

Unfortunately I have already sculpted the outside of the tall board so it is no longer square. My ignorance of doing this of kind of joint course. I have a Jet bench top mortiser, but can't get the board in far enough to do all the mortises as it about 14" wide and 40" long. I can do some of them close to the edge though. Maybe two on each side with the machine and do the center one wider and in the middle by hand and go all the way down with a backer board to hopefully limit blowout. and I start the last center on from the back so any blowout would be covered by the seat up against it.... This really is a learning project. ha ha

[Kevin Jenness]

Without a square edge you will have to simulate one. You can use a straight stick indexed to your workpiece, perhaps temporarily bonded with spacers and hot melt glue. Set it up parallel to your mortises and use a square and gauge blocks for transferring your layout to the back face.

All projects are learning projects. Some involve more learning than others.

[Randall J Cox]

Thanks. Something about an old dog and new tricks..... I've already learned one lesson the hard way and haven't even done the layout yet.

[Jim Koepke]

If you can layout the mortise on one side, a way of transferring it to the other side is to use a drill press to bore a very small hole through the work in each corner. From this the second side can be drawn.

jtk

[Scott Winners]

Welcome to the rabbit hole. I prefer to lay out my through mortises one both sides of the board and have them meet in the middle, rather than layout on one side and then hope for the best. Really I want at least a knife line and am more comfortable coming down at least a quarter inch or so. When I just chop down all the way through, I get a fair bit of chip out on the back side where the mortise comes out.

So yup, square on all four sides, but I get best results when I
1. Arrange the pieces how I want the grain to look on the finished piece.
2. Mark all my reference edges from a place they can all be seen at once on the finished project. Make the reference edges flat and square, relabel, then work around all four sides of each component.
3. layout the joinery
4 cut the joinery.

You probably could start with choosing reference faces instead of reference edges. I haven't tried that , but it should work. I recently built a dovetailed case where my sidewalls were reference edge up and my end walls ended up reference edge down. Oopsie. I was able to save it, but every little error in squareness gets magnified down the the length and width and thickness of the piece.

It sounds to me like you are building essentially a small scale model of a ladder back chair. Yes? Seat at foot stool height and crest rail at handgrip height? If I am right, imagine the chair is backed against a wall so someone could sit down on it. I would put my reference edges on the visible 'front' of the item in that position so any errors in layout and execution will be on the wall side.

[Kevin Jenness]

If the mortise is large enough, you can mortise out most of the depth, drill through in the center and chase it out from the back side with a flush trim bit in a router.

[Randall J Cox]

Lots of good suggestions. I'm pretty slow at it but its fun. Thanks. Randy

[Luke Dupont]

I'm building a simple stepstool with the tall raised handle. Its an old design, shaker maybe, for reaching top shelves. I'm going to attach the step part to the tall back with through tenons. All my woodworking books show chopping out the mortises down to the center (midway) and flipping the piece over and finishing from other side. As the mortises have to be nice and square, the front is easy with layout lines on front. But, how do you match layout lines on back so the mortises are exactly square all the way through and meet? Randy PS I have never done this joint before, thought its time I learned. Tx. Randy

I think you should learn the basics of marking and layout before you go any further.
A square, a knife, and a marking gauge (and/or mortise gauge) are what you need, and need to learn to use.
Parallel lines can be transfered with the marking / mortise gauges, and crossgrain lines can be carried over with the try square and knife. This should be do-able even if the surface isn't flat, provided you're careful. Depending how shaped the surface is, you may need to make a marking gauge with a larger fence for registration, and for the square, you may need to angle it so that it registers off of the flat face lower down. This is assuming you have 3 flats and one shaped / curved face.