Hi,
I watched your video on mortise and tenon on the site, it was very informative, thanks! I need to improve my mortising techniques. My question is about how snug should the tenons be in the mortise slots and can there be any play in the length of the mortise.
My problem is for a bookcase I have been working on. I used a router template to cut the mortises in the ends of the strechers and rails, and on a few of the legs. This design uses floating tenons. Unfortunately I cut a few of the mortises too long (> the 3″ tenon size).
When I put the tenon in the mortise, several have about 1/4″ of longitudinal play (slot turned out to be 3.25″). I think this is too much to expect glue to fill the slot.
I could cut some special tenons which are 3.25″ wide for 1/2 of their length and 3″ for the rest. Or should I try to fill the extra space in the mortise with some wood and glue?
What do you recommend?
thanks very much.
‘mark
Edited 10/8/2007 11:35 pm ET by m_ahlenius
Replies
I know your question isn't for me, but I can't resist. Can't believe you are so worried about the length of a mortise . . . best case: extra room for squeezout; worst case: extra room for sqeezout. why not spend your valuable time with tenon fit and glue application?I'm just saying don't worry . . . about mortise length . . .
Brian,here is the problem. I think perhaps I used confusing or the wrong term. I am referring to the length of the mortise slot (aka the height of a tenon) and am *not* referring to the depth of cut. The length of the mortise in the leg is about 1/4" too long, but its not in the adjoining rail. So there is tons of slop when dry fitting things together.My question is that how tight should these be? This is way too much room for glue run over. The mortise is about 7/8" deep, 1/4" wide and 3" long (but this one in my bookcase leg is unfortunately 3-1/4" long).so that is my question. Should it get filled with extra wood, or should I make a new tenon which is 3-1/4" wide for 1/2 its length and 3" wide for the other part which goes in the rail.'mark
Edited 10/11/2007 10:02 pm ET by m_ahlenius
The strength of a mortise and tenon joint comes from the face-to-face glue joints. Slop at the three "end grain locations"-- the end of the tenon and the two narrow ends of the mortise--is relatively unimportant. If the face-to-face glue joints are poor enough that you have to rely on the ends of the mortise to restrain the tenon and prevent racking, the joint is toast anyway.
-Steve
Hi, I reviewed your question. Your issue is with what I think of as the 'width' (vs. thickness or depth) of a mortise if I understand. Still say it's not much of an issue as far as strength is concerned as long as you're within 1/4 in.; the glue will do it's job even when it doesn't fill those cavities. The thickness of a tenon is usually most critical. The reason why you might want a more accurate width is mostly to key in to exactly the right location, without worry of the two pieces slipping one way or another during glue-up. So, I say, don't sweat the small stuff. How's the piece coming? Brian.
Mark,
My opinion, for what it's worth, is that that extra air inside a tenon does make a difference but way down the road. If the glue is doing its job then any racking issues should be taken up by your tenon shoulders and the shear strength of the glue. But if the glue ever gives up, then all the space inside the joint will allow for more movement even if a joint is pinned. This is why horns were left on the tops of mortised stiles. You'd make a tight fit on your tenon to mortise in all directions and cut off the extra material, the horn, once the joint was fit home and glued.
It's not a huge matter, but I'd probably glue in some scrap to the mortise. Good luck. Gary
This forum post is now archived. Commenting has been disabled