Complex angle tenons on chair joinery

[Bob]

I am starting a set of 10 dining chairs and have a few questions/problems regarding complex angles on the tenons.

First a little background: A couple years ago I did a test chair which had a curved back leg which was then rotated outward by about 15 degrees to allow the legs to curve outward when viewed from the front and the side. To get around complex angles on the joinery, I re-cut each face of the leg such that it was at right angles to the cross rails attached to it. For example, the inner face of the leg was cut to be at right angles to the back seat rail and headrail. The back of the leg was square to the inner face. The front face of the leg was angled out by about 6 degrees to be at right angles to the side seat rail. The outer face of the leg was square to the leg front face. This made the mortises and tenons very simple, all square or only simple angles, but as you might guess, shaping the legs was quite difficult and would be a problem in making 10 chairs.

For my 10 chairs I wanted to simplify the legs somewhat by not cutting each face to be perpendicular to the rails. This now makes the mortices and tenons more difficult. My plan was to still make the mortises perpendicular to the face of the legs. However the tenons are then more difficult because the shoulders are not perpendicular to any of the sides of the rails and the cheeks are not in line with the rails in either plane. For example, on the headrail, the tenons should be angled forward by about 15% to account for the rotation of the leg, and downward by a few degrees to account for the outward curve of the upper part of the leg.

Looking at the standard tenon jigs (Delta, etc), there appear to be some limitations. If I tilt the blade by about 15 degrees to account for the rotation of the inner leg face, and lean the rail forward on the face of the fence by a few degrees to account for the outward angle of the leg, it looks like I have to change the height of the blade between the two cheek cuts. In addition, since the jig only allows the work piece to lean away from the blade, I would need to figure out another way to lean it toward the blade for the mirror image cut on the other end of the rail.

To do the tenon I am picturing it seems it would be better if the blade were at 90 degrees and the fence that the rail is clamped to could be tilted away from the blade at the top by the 15 degrees. I would also need to lean the rail both toward and away from the blade to account for the mirror image cut on the opposite end of the headrail. Perhaps wooden wedges at the appropriate angles would help here? Does anyone have any ideas as to how to handle this? How do other people handle this problem? Any suggestions will be appreciated.

I know the above joints are difficult to explain in words. Let me know if i can explain anything more thoroughly. Thanks in advance for your help.

Thanks, Bob Abbott

[Lowell Holmes]

I cut the angled tenons with a back saw after laying them out with a mortise gauge and a bevel square. :-) It's much easier than trying to set up a machine to do it. :-) You may want to view the Frank Klausz video on mortise and tenon joints. He has a very good segment on this issue. He uses wedges and a hollow chisel mortise.

snip

[bridger]

sounds like a router op.

[Robert Galloway]

That would be the approach I would take also. Ten chairs sounds like about the right number to forego the hand approach and do it by machine.

bob g.

[charlie b]

Sounds like loose tenons would be the way to go. With ten chairs the time used to make fixtures to hold the parts for mortising would be worth while.

Though the jig shown at the following url is for a horizontal mortising machine, it may give you some ideas for your jigs.

out the third page to see it set up for a curved chair leg.

charlie b

[Bob]

I'm not clear on how a router can help me here. Do you have any URL's that would give me an idea as to how to make the jigs for the complex angle tenons I need? Bob

[Bob]

Charlie,

This looks like it could have some promise. I had planned on mortises perpendicular to the leg faces, but if I guess I could angle them to make them in line with the rails. Making jigs for mortises in the legs won't be so hard. However since I normally make mortises on my bench drill press, I'm not sure how I can accurately cut the mortises for the loose tenons in the ends of the rails. It looks like they should be cut prior to angling the end face of the rails. So do you have a URL for a jig for accurately drilling mortises in the end of the rails?

Bob

[Mark Wells]

Get "Chairmaking and Design" by Jeff Miller. It's a very well written book. Basically the entire book is the answer to your question.

local library had it, so you might want to check there, also. It is one of the very few books that I read from the library and has very, very seriously considered purchasing.

Mark

perpendicular

[bridger]

[Bob]

Mark,

Actually I have the Miller book and had referenced it a lot while I made my test chair. However since I simplified the M/T on the test chair by angleing the faces of the legs, I didn't have a need for the router jig. I could easily make simple angle tenons with the table saw/dado. I had forgotten about the compound angle discussion in the book and the router jig.

It looks like I now need to decide whether I want to use a router jig for compound angle tenons into perpendicular leg mortises, or loose tenons into mortises angled to be in-line with the rails. Any thoughts on the matter?

Thanks, Bob

[Pat Barber]

I saw the inventor of this build a complete chair at the 2002 IWF....

It works...

man's m&t jig....

Bob wrote:

[charlie b]

Loose tenon would be the way I'd go. Blow a tenon cut and you may have to make another complete part. Blow a loose tenon and you just make another - much lower risk. And you can use some of those hardwood scraps you've been saving Two birds - one stone.

charlie b

[Mark Wells]

Oh, you are mistaking me for someone who has actually built a chair. All I've done is read about it! ;-)

Mark

>

[bridger]

an armchair armchairist?

[Routerman P. Warner]

Jig at the

link will swing through >30 degrees. To get the compound angle will require a wedge but not rocket science to produce. Plans avaiable.

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[Bob]

Looking at the site, since the rabbet bit runs on the sides of the rail, it looks like the size of the tenon is a function of the bearing and the width of the workpiece. This means that the tenon is not necessarily a fixed size (ie 1/2"). Do you then cut the mortise to fit the tenon rather than the other way around? I prefer to fit the tenon to a fixed size mortise.

In addition, if you angle the workpiece in both directions to get a compound angle tenon, it looks like the shoulders would all be different sizes. Have I interpreted this properly? How do you account for this?

Bob

[Routerman P. Warner]

Understanding correct; to rout compound angles requires an edge guide and straight bit to get the shoulder in one plane; sides of tenon can still be cut with rabbet bits, however. The use of an edge guide (for the 4 faces of the tenon) implies continuous adjustability so the tenon can be tuned to mortice width. Using rabbeters will require tuning mortice to tenon width.

****************************************** If rabbet bits