Tenons need to be tight on all four sides?

[dlminehart]

I watched Norm build a door from mahogany using loose tenons. He used his mortiser to drill the mortises in both rails and stiles, and then used a planer on a long board to get the loose tenon material to the proper thickness. A router was used to round over the edges of the properly thickened board. The loose tenons were then cut to proper length from this board.

Let's give the tenon's 3 dimensional terms: depth refers to how far the tenon goes into the mortise, thickness refers to the narrowest dimension of the tenon, and width refers to the last tenon dimension, the wider of the two dimensions visible looking at the end of the tenon.

I noted that he specifically said not to worry about the width of the loose tenons, as leaving them a bit loose here would allow some adjustment during the door glue-up. The depth of the tenons was also seemingly not critical, so long as they didn't protrude so far as to prevent a tight joint. The critical dimension was the thickness, which should be a snug fit in the mortise, and the place where the gluing would provide the strength.

Do you agree? Or should the tenon fit snugly in a mortise on all four sides? Is an entry door, with its multiple rails and stiles, an exception?

[Jeffrey Schronce]

I don't think he used the mortising machine, rather I think he routed those mortises. That is why he rounded over the tenons (even though that didn't make a lot of sense since he left so much room in the mortise on each side a square tenon would have been fine).

I only use traditional M&T, not loose M&T. I have always desired to have the shoulders fit just as snugly as the face of the tenon. It could be possible that the way loose M&T is done it could require the space. I know the highly anticipated Festool Domino is basically a loose tenon system and it leaves spaces for adjustment on the sides of the domino tenons.

[Tom Miller]

For a situation like a door, in particular, I guess I would tend to agree. The important factor, as I see it, is that there's no real load bearing going on, which would present a shearing force on the glued interface.

Minor point on tenon length: they should be even shorter than a dry fit would dictate, so that there's room for glue to accumulate at the bottom of the tenon, without building up undue hydraulic pressure.

Regards,
Tom

[dlminehart]

You're right, Jeffrey, he did use the router, now that I recall.

Actually, that was another of his shows that irked me, with his showing how easy it is to mortise out a lock and door hinges if you just have these expensive and specialized gizmos that few amateurs could consider.

If he has to resort to those kinds of tools, why not devote programs to showing how to construct home-made substitutes? One sometimes gets the sense that he's aiming toward a show in which he deposits some wood in a million-dollar machine and out pops a completed project.

[JimD]

The width of the tenon would typically be long grain to long grain glueing which is the strongest joint. The narrow side of the tenon would typically contact end grain in the mortise and form a weaker joint even when it fits well. An advantage of a traditional square mortise and tenon is more long grain to long grain surface. I like it all to fit pretty well, however. I even like the bottom to fit reasonably well and that definitely involves end grain on the tenon. Sometimes I even get glue coming out the side of the mortise (in red oak which is porus). Why make a sloppy joint?

Jim

[Kristofor]

It seems correct that a tight tennon "width" wouldn't add much to the glue strength of the joint, but it seems like it would have a significant impact on the mechanical strenght.

Strictly perpendicular loads (not a real common real world condition) at the joint wouldn't even need glue to hold together if the tennon was well fit on 4 sides.

With a loose fitting tennon the glue would be the only thing holding it in place. If a few square inches are enough to carry the load then I guess it wouldn't matter.

Kristofor.