Rounding Over Tenons for Slot Routed Mortises

[algale]

Looking for tips/techniques for rounding over the ends of tenons to fit in mortises cut with a router bit (or really drilled with a forstner bit)? These aren't through mortises but they are structural and will take substantial weight. The mortises/tenons will be 3/8ths wide if that makes any difference. My current thought is just to go at it with a file.

Thanks in advance.

[rpd]

Disk sander or belt sander.

[mbcabinetmaker]

Sharp chisel.

[algale]

Sharp chisel.

Knock of corners first and then just keep cutting facets until it is more or less round?

[edflorence]

Knock a thin slice, like maybe a splinter about 1/8 inch thick, off all 4 corners with a chisel, then finish rounding with a hand-held rasp. The work goes really quickly. I have done lots this way and as long as the cheeks fit snugly it doesn't seem to make much difference whether the convex curve you rasp on the tenon is a perfect fit with the concave ends of the mortise. Having said that, though, it is pretty easy to match the curves pretty well.

[BuckeyeDennis]

Here's an idea that I've been wanting to try, but haven't gotten to yet. See what you guys think.

The basic idea is to use dowels as the rounded edges of the tenon. Before cutting the tenon, bore two holes at the full tenon width, with the hole diameter equal to the tenon thickness. The hole centerlines would be spaced exactly the same distance apart as the outer bores of the mortise. I would drill them an inch or two deeper than the length of the tenon. Then cut the tenon to width, removing all material outboard of the hole centerline. Then cut the tenon faces.

Now glue a dowel into each hole, extending to the end of the tenon. This gives a built-up tenon with perfectly rounded edges. The resulting joint is sort of a semi-loose tenon, where only the dowels are loose. Alternatively, you could look it as a souped-up dowel joint. For want of a better name, maybe a "dowel-tenon joint".

Are there any "gotchas" that I'm missing? Like maybe the glue would make it a PITA to fine-tune the tenon?

[forrestb]

Buckeyedennis: sounds like a worthwhile - but busy - approach. If you do, I suggest that you make the dowels out of the same wood as the project.

Personally, I prefer to use slip tenons but I always use the same wood, usually from the same piece as the 'tenon' end. I cut mine a wee bit short of the full length, round them over on the router if several are needed (if only 1 or 2, just a sharp chisel ala mbcabinetmaker). The 'short' length gives me a bit of wiggle room at assembly to align things.

Forrest

[BuckeyeDennis]

Buckeyedennis: sounds like a worthwhile - but busy - approach. If you do, I suggest that you make the dowels out of the same wood as the project.

Personally, I prefer to use slip tenons but I always use the same wood, usually from the same piece as the 'tenon' end. I cut mine a wee bit short of the full length, round them over on the router if several are needed (if only 1 or 2, just a sharp chisel ala mbcabinetmaker). The 'short' length gives me a bit of wiggle room at assembly to align things.

Forrest

Why the same wood, Forrest? I was figuring on using store-bought hardwood dowels. (Not from the box store, though. ) Otherwise, I'd have to agree that making the joint that way becomes fussier than a loose tenon, instead of easier.

[rjent]

Buckeyedennis: sounds like a worthwhile - but busy - approach. If you do, I suggest that you make the dowels out of the same wood as the project.

Personally, I prefer to use slip tenons but I always use the same wood, usually from the same piece as the 'tenon' end. I cut mine a wee bit short of the full length, round them over on the router if several are needed (if only 1 or 2, just a sharp chisel ala mbcabinetmaker). The 'short' length gives me a bit of wiggle room at assembly to align things.

Forrest

Different expansion/contraction rates?

Dick

[JPG]

Short to provide 'wiggle room' and to make sure the shoulders seat.