My project is the Essential Workbench from FWW. I have cut the mortises as described in the plans and article. I first tried cutting them purely by hand and using the guide jig described in the article. I found this took way too much time so I switched to a router. Since the mortises were 3″ deep I routed from both sides. It seemed to work pretty well but of course there was not perfect allignment so I hand chiseled the sides flat.
Just how smooth do the sides need to be for a good glue joint ?
The plans call for these joints to be double wedged. Do the sides of the mortise need to be flared to allow the tenon to spread a bit to provide a locking effect ? The plans and article do not call for this but I have seen this described in “The Mighty Wedge” article of FWW.
Replies
Hi Mike,
I remember when I was first starting out woodworking. I worked for Harvey, a cement contractor, who also made some furniture and he always wanted "tooth" on his glue surfaces. So he used a rough blade on his table saw to give him plenty of roughness.
Harvey, it turns out, was better at concrete than at furniture making. The misconception comes I think from the variety of glues available. Epoxies likes some roughness, aliphatic resins or yellow glues like smoothness.
Mortise walls need to be smooth but I wouldn't go crazy and try to sand them. More important I think is that the walls remain parallel throughout the length of the mortise. That way your tenon will fill the mortise completely and not have large gaps that a yellow glue won't fill well or with any strength. Your chisel cut will be just fine.
As for opening up mortises for wedges, I'm of the opinion that it's time wasted. If you cut open a wedged mortise mostly you see a lot of compression on the tenon walls as they're being pushed into the mortise ends. So there's plenty of force there.
If you made wedged tenons, be sure to drill a relief hole at the bottom of the wedge slot to prevent any splitting at the bottom of the tenon. Flaring the mortise will only exacerbate this tendency for splitting. The only time I can see it working is when the wedge slots are very close to the ends of the tenon. This way they will flex more easily. But cut that relief hole. For a normal slot, a 3/16" hole works fine.
Good luck. Gary
This forum post is now archived. Commenting has been disabled