Question about wedged through tenons

[Aram]

I want to make some wedged through tenons. They will be 3/8" thick, probably less than 1 1/2" wide, and the board they go through will be less than an inch thick.

I want the tenons to be rounded, instead of squared off (picture a routed mortise, and a tenon to match). My understanding of wedged tenons is that you make a trumpet-shaped flare in the mortise (but not so dramatic, just a few degrees) at the edges, cut slits in the tenon, and drive the wedge home; the top portion bends out at an angle. I have done this once, but that was on a small, hand-crafted piece. To make the flared parts, I routed the mortise, then carefully cut the angled parts with a small gouge. I don't want that hassle for this particular piece -- it's not worth the time. 

What is the easiest process to make wedged tenon + mortise, rounded edges, with power tools, and hopefully not a ton of fixture making? Square-edged flare is easy with a chisel.

Thanks all.

[DaveR1]

I want to make some wedged through tenons. They will be 3/8" thick, probably less than 1 1/2" wide, and the board they go through will be less than an inch thick.

I want the tenons to be rounded, instead of squared off (picture a routed mortise, and a tenon to match). My understanding of wedged tenons is that you make a trumpet-shaped flare in the mortise (but not so dramatic, just a few degrees) at the edges, cut slits in the tenon, and drive the wedge home; the top portion bends out at an angle. I have done this once, but that was on a small, hand-crafted piece. To make the flared parts, I routed the mortise, then carefully cut the angled parts with a small gouge. I don't want that hassle for this particular piece -- it's not worth the time. 

What is the easiest process to make wedged tenon + mortise, rounded edges, with power tools, and hopefully not a ton of fixture making? Square-edged flare is easy with a chisel.

Thanks all.

The first thought would be to get a custom ground router bit with a slight taper however with a moritise that's rounded on the ends that's a problem because the tenon won't expand toward the ends. My inclination you be to not taper the mortises at all and use a thinner wedge or make the slot for the wedge wider.

[Aram]

The first thought would be to get a custom ground router bit with a slight taper however with a moritise that's rounded on the ends that's a problem because the tenon won't expand toward the ends. My inclination you be to not taper the mortises at all and use a thinner wedge or make the slot for the wedge wider.

Thanks. That sounds like a great idea.

[jteneyck]

A tapered mortise with rounded edges would be easy to make with my horizontal router mortiser.  You would start by cutting a typical mortise at 90° to the edge.  




Then you would add a tapered piece of wood between the workpiece and fence for whatever angle you want the taper to be and cut the ends of the mortise, first one side, then flip the tapered piece of wood to the other side and cut the other end.  

You can build my machine for around $100 plus router from free plans available here:  Horizontal Router Mortiser

John

[jteneyck]

Today I went to see if I could cut a rounded edge tapered mortise on my horizontal router table.  I started by cutting a straight sided 3/8" through mortise in some 1" x 1-1/8" stock.  






I made a small 10 deg wedge and used that to angle the workpiece against the fence then cut the tapers on the ends of the mortise. 



Here's the flared side:



The back side:



And looking down into the taper:



The process works well, just as I thought.  However, it's limited to mortises in relatively short and relatively narrow parts.  If the mortise needs to be in the middle of a long part, or the part is very wide, the mortiser won't be able to reach over the back rest far enough to cut the mortise (shallower angles would allow for longer, wider parts).  In order to work with those parts I would have to redesign the machine specifically for that purpose.  

John

[fredhargis]

I'm guessing, but I'll bet that would work better without tapering the ends. By "work better" I mean the wedged tenon would fill the cavity more completely...with the tapered end it looks like the tenon would have to expand cheek to cheek as well as end to end. (If that makes any sense at all).

[jteneyck]

I'm guessing, but I'll bet that would work better without tapering the ends. By "work better" I mean the wedged tenon would fill the cavity more completely...with the tapered end it looks like the tenon would have to expand cheek to cheek as well as end to end. (If that makes any sense at all).

It's that way only because I had to plunge the bit in so far that it started to ride up the shank of the router bit.  Had I used a longer 3/8" bit the mortise would have been a crisp 3/8" from end to end, like it is on the backside.  

The approach works well, it's just limited in angle or where it can be placed by the design of my machine.  Given enough motivation, it wouldn't be hard to design a version to make these mortises anywhere needed along the length of a part in parts as wide as you can purchase a long enough router bit.  

I was thinking of a hybrid approach where you first would drill angled holes on the drill press to define the ends of the mortise, and then route out the center section on my HRM.  No new equipment needed and the mortise could go just about anywhere on parts up to about 8 ft long.  

John