Help with Mortise and Tenon

[Scott Thornton]

I need a little help with this joinery method. I getting ready to do my first mortise and tenon joint. I have a benchtop mortiser to do the mortises and a Europeon slider that i am going to use to make the tenons.

My questions are:

1. How do you start to lay out the joint?
2. What are the best proportions to use for the tenons and mortises?
3. How deep do you go?
4. Do you make the tenon first, then trace it out on the piece that will have the mortise?

Thanks for your time!

[Jesse Cloud]

Well Scot, here goes my two cents worth.

1. How you lay it out depends on how you plan to cut it. If you are doing many of these, it will be worth the $ to buy a marking guage for m&t. They have a wooden fence that runs along your stock and two 'scratchers' that you set to the width of the tenon or mortise. You only need to mark up a setup piece (or two :rolleyes: ) out of scrap that you have milled to the same size as your real stock. Use the setup block to calibrate your mortiser and once its calibrated, use a stop on the mortiser's fence to consistently place the pieces. Always mark each piece to show which side is the 'reference' side. I mark it with an 'F' for fence.

2& 3 generally, the tenon should be about 1/3 the width of the stock its cut from, though I usually go 3/8 on 3/4 stock. The deeper the tenon the better. The wider the tenon, the better, up to about 4 inches, then you need to worry about wood movement.

4 Since you have no play on your mortiser, I would cut the mortise first, then cut tenons that are a little fat, tuning to a tight fit with a plane, sharp chisel or sandpaper.

There are lots of different ways to do this and most of them produce good results when done carefully. I suspect this will be a long and interesting thread as there are strong feelings on this topic and, as far as I'm concerned, not a single right answer.

Have fun and let us know how it works out!

[Mark Singer]

Jesse,
Perfect...just what I would have said ....

[Mike Cutler]

Rule of thumb. 3-3-5. Not etched in stone.

Tenon is one third(3) the thickness of the tenon stock. I use 3/8" on 4/4 stock. A 1/4" hollow chisel mortiser is kind of fragile. DAMHIKT.

The tenon length is 2/3(3) the width of the mortise stock.Eastern techniques are as Jesse stated, as deep as possible.

The width of the tenon is 5(5) times the thickness of the tenon. Like Jesse said though. If they get to wde they can exert enough torsional, and shrink swell stress on the mortised piece to blow the mortise out. I use 3" if I know it will be divided, 4" like Jesse said if it will stand alone

Tenon are located at least one board thickness of the mortised piece form the end to stop the tenon from being able to blow out the mortise by acting as a lever.

It would also help to know the application for the tenon(s) in question. There are different techniques, and variations of the M&T joint depending on use, and the plane(s) it will be subject to stress in.

90% of the time you are better of cutting the mortise first, and then fitting the tenon. It's a lot easier to tune a tenon, than a mortise. I've been dealing with that 10% though the last week or so.;)

If you are making a lot of repetetive mortises, where the dimensions have to be symetrical. Use stop blocks on your benchtop mortiser to define both ends of the mortise for each piece that needs to be uniform.Then come back and clear out the rest of the mortise. It will take you longer, but your assembly time will go quicker and easier. 32nds count in M&T joints.

[Scott Thornton]

Thanks for the tips.

I am making a coffee table and end table. The tenons will be in the aprons and the mortises in the legs. The legs are around 2 inches thick the aprons are about 13/16.

I was thinking about making the mortises about an inch long, that way they don't run into each other, is that a concern?

Thanks.

[Norman Hitt]

Thanks for the tips.

I am making a coffee table and end table. The tenons will be in the aprons and the mortises in the legs. The legs are around 2 inches thick the aprons are about 13/16.

I was thinking about making the mortises about an inch long, that way they don't run into each other, is that a concern?
Thanks.

It's not a concern, as many, (especially older HANDMADE pieces) have mortices that intersect with each other, you just cut a 45* on the end of each of the tenons so that they mate up inside those mortices.

[Luther Oswalt]

This site can provide some of your answers: http://www.newwoodworker.com/tipsmortenon.html

Leo

[Mike Cutler]

Thanks for the tips.

I am making a coffee table and end table. The tenons will be in the aprons and the mortises in the legs. The legs are around 2 inches thick the aprons are about 13/16.

I was thinking about making the mortises about an inch long, that way they don't run into each other, is that a concern?

Thanks.

Should work out just fine. The 45 degree internal miters suggested are a nice idea. Remeber to leave a little bit of room internally for the glue to squeeze into.

You may even consider pinning the tenons externally. It's a nice aesthetic touch, and gives more long term mechanical reliability to the joint.

[Allen Bookout]

Here is a general purpose chart that I got somewhere that can be helpful.

[Dan Barr]

just wondering if anyboy has ever used the method of finger joints on the tenons on the end of the aprons inside the mortises in the legs.

might be a little too much aye? :D

Dan

[Mike Cutler]

just wondering if anyboy has ever used the method of finger joints on the tenons on the end of the aprons inside the mortises in the legs.

might be a little too much aye? :D

Dan

They're hard to cut. They sound easy, but the tolerances can break ya'. I've only done them once, and if I do them again I am cutting the tenons first. Then I'll mark out the mortises on a test piece until I get them right. Usually I'm an advocate of match the tenon to the mortise, but in this case..... Well, It about drove me nuts matching everything up.

Double tenons can be arranged in rows, side by side, and one on top of the other.

[glenn bradley]

Jesse's got it. Shaving your tenon to fit a known mortise is the easier way to tune the fit.

[Jim Becker]

Jesse's got it. Shaving your tenon to fit a known mortise is the easier way to tune the fit.

Indeed. It's a lot harder to put material back on!

[Pete Bradley]

This isn't too bad, and you've got better machines than many. Neanderthals will rightfully howl in pain, but I treat these as a pure machining problem. I'd use 3/8" tenons with bevels that almost meet in the corners. Some things to think about:

Make a 5th leg so you can try each operation out on it first. Have a test piece of apron also.

For laying out the mortises, figure out how much reveal or setback you want between the legs and the aprons. 1/16-1/8" is typical. You'll also need some shoulder on the outside of the tenon. 1/8" or a little bigger is in the ballpark. You need enough so the side of the leg doesn't blow out, but the more you add, the shorter your tenons will have to be. Add these two distances up to get the distance from the mortiser chisel to the fence.

Draw the top of the leg full size from above and the side, showing the aprons, tenons, and mortises meeting inside the leg. This will help you to visualize and sanity check your design. Remember the length of the tenon to cut is measured from the outside of the tenon. You can just lop off the bevel at the end.

Mark the outside and inside faces of the aprons, the tops and bottoms of the aprons, and the outside and inside faces of the legs. There's noting worse than cutting something backwards.

Make sure the outside faces of the legs are dead square. These are the surfaces that will determine how straight the mortises go in. Do all mortises in one setup, so the distance from the edge is identical.

The thickness of the apron is relatively unimportant because you'll only see one side. However, you really want to register all your cuts against the outside face of the apron. It gets a lot more complicated to maintain tenon thickness if you have to cut from two sides.

Good luck!

Pete

[Richard McComas]

Some good "stuff" to read on mortis and tenon joints.
http://www.google.com/search?hl=en&q=tenon+thickness

[Cliff Rohrabacher]

Ya might want to consider loose tenons. It's easier to plane stock to a very tight tolerance and you can produce a fair bit of them in a hurry.