Instructables
Picture of Retrofit Mortise and Tenon Joints
I once had a large table that would have been great except for weak joints between the apron and table legs, which made the table wobbly.  I wanted to strengthen the table without modifying it, and decided to see if I could retrofit mortise and tenon joints.

After removing the top, I drew in ¼” x 3” rectangles where I planned to add hardwood splines, at all 4 corners of the table.
 First, I drilled ¼” x 2” deep starter holes at one end of the rectangles. Then I used my router, with a ¼” upcutting bit, to rout in several passes ¼” wide by 2” deep grooves along the length of the rectangles. Next, I glued and tapped in ¼” x 3” long x 2” deep hardwood splines.

The final result was a rock solid table, finally with strong joints.

This sketch shows the concept; looking down at the 2x2 leg and the 1x4 aprons that support the top. In dark is the added spline.
 
Remove these adsRemove these ads by Signing Up

Step 1: Mark out location for reinforcement

Picture of Mark out location for reinforcement
As you see in this photo, I marked with black felt pen where I will cut a groove with the router. The board held with the C clamp serves as a guide for the router. I have a 1/4" straight cut bit in the router.

Step 2: Cut the groove

Picture of Cut the groove
This photo shows the start of the cutting of the groove. You should take several passes with the router, extending the bit about 1/4" deeper each time. You should end up with a groove at least 1 1/2" deep.

Step 3: Groove completed

Picture of Groove completed
This photo shows the completed groove (first if 4!) between the table leg 2x2 and the support apron rail 1x4.

The grooves were about 2" deep.

Step 4: Glue and tap in the spline

Picture of Glue and tap in the spline
Here goes one of the hardwood splines. I'm just reinforcing in the long diminsion.
The grain on the spline should be legthwise, that is, from left to right in the photo.

Step 5: Completed spline

Picture of Completed spline
This photo shows first of four splines.

Looks kinda ugly here, but it is really strong!

Step 6: Finished project

Picture of Finished project
With the table top back on, no wobbles, and it still looks OK.
Balord1 year ago
Bill, attach a small cleat on your guide protruding about 1/2 inch form under the guide, this (in your photo example) would give you a nice level surface for the router. If I ever get the ambition to do so, I have a nice coffee table I built which has a system I would have used on the table you tightened up, I'll take a few pics and send them up....all I need to do is loosen a wing nut and I can take the legs off for compact transport! You can actually buy metal cleats to do it as well but my whole table is a custom one off design completely from my head though the top is only 3/16" oak ply I can jump up and down on it!
Bill WW (author)  Balord1 year ago
Thanks, Balord -
I actually did this project several years ago, might have been one of my first projects with a router. However, in retrospect, I still believe it is a reasonable way to reinforce a rail-to-leg connection.
Would like to see your photos.
Regards,
Bill

Greg11091 year ago
Two words... pocket screws.
Bill WW (author)  Greg11091 year ago
Thanks Greg, you are correct of course. This was the first of this design I had made, and had actually already tried pocket screws which did not work out well. Could have benefitted from a pocket screw jig.
So, went to option #2, which is why I called this "retrofit" mortise and tenon.
Actually did this project about three years ago so by now maybe I could have got it right the first time!

Bill
Even if this could have been done with pocket screws and an expensive jig, this method is tons stronger. It's also a good deal stronger than the work that a power biscuit joiner can do. For this application, I think that this was hands-down the best way you could have done it. Solid work!
trog20001 year ago
Aren't these really biscuit joints? Any nice job and far superior to pocket screws.
Bill WW (author)  trog20001 year ago
I guess they could be considered biscuit joints. My friend has a biscuit joint cutter I once borrowed, the biscuits were quite a bit smaller than the oak splines I used for the table.

The rest of the story - This was a project I did several years ago, and had tried pocket screws. They did not work for me, table was wobbly! So I did this "retrofit" to correct my pocket screw failure. Was really not much harder than the pocket screws, but again, I did not have a nice pocket screw jig, like sold by Kreg.

Thanks for the comment.
Bill
rimar20001 year ago
Thanks for sharing this useful info, Bill.
Bill WW (author)  rimar20001 year ago
Muchas gracias, Osvaldo!

Bill