Floating tenon question

[Christian Hawkshaw]

A slightly different view
In my work, joinery should be a tight, well fitted union of the wood components.
In most cases, adhesive is there as a type insurance, only to keep the joint from coming loose. If the glue fails the joint should still hold for a time, no catastrophic failure should occur.

Whether using loose or integral tenon joinery, there should be no need for "gap filling", which is just a euphemism for poorly fitted joinery. If you want "slop" for aligning parts, that's up to you, but you may end up with a weaker joint in the end.

There are countless ways to cut a M&T joint, do what works for you.

JMHO

For mortise and tenon joints, the joints I make usually require light tapping with a rubber mallet. I use PVA glue, and slightly chamfer the corners as well to avoid vacuum lock. How tight do you make mortise and tenon joints? Tight is somewhat relative, so I am just curious. I would assume what I do is slightly tight. Generally, the pieces do not come apart with out lightly tapping as well.

[Edward Weber]

That sounds exactly how I make mine. Good and snug, which usually requires a mallet for final seating.
I like to treat all joints pretty much the same, seen or unseen.

You don't see people leaving gaps in their box-joints or dovetails, M&T joints are no different. A good mechanical fit requires less input from the glue for a solid joint.
JMHO

[chuck van dyck]

Since you are okay with the oversized mortise sounds like it must be blind. If you question it, just plug it and recut it. I use a domino when precision isn’t necessary and there are plenty of other junctions providing security against failure, like a cabinet. If precision matters, nothing beats cutting a line with a sharp chisel or float.
Sometimes its worthwhile to glue the tenons into the aprons prior to final assembly. You can use that basis to fine tune everything.

[Will Blick]

Some great input here...
A few key issues I learned through the years...
snug fit is key, the pieces should hold together without glue, but without weight on the pieces.
too tight, not enough glue on the surface to surface areas.
too loose, u have to use gap filling glue vs. PVA.

I agree with a previous poster, the dominos grooves are a perfect solution for snug, but room for glue in the thickness orientation. And the one tight, two loose premise usually suffices... YMMV based on the stress points of the joint.
Using pencil lines with domino, makes shooting for all tight tenons too difficult.

when I want all of them tight, I use dowels, as a good dowel jigs allows all tennons to be tight. I use grooved dowels to assure room for glue, incredible strength. Not as fast as the domino, but gosh if done right, rock solid.

I think the Rockler BeadLock system is an incredible low cost method of excellent loose tennon for both strength and snugness with very minimal effort, surprised its not more popular. rremendous glue surface area as well. Of course I own one, but never used it yet, as I have too many options, and seem to be a creature of habit...

does anyone use the BeadLock system regularly? curious how it works in real world usage.

[Greg Quenneville]

I have a Domino XL and never use the loose setting and get tight accurate joints. I could see using the loose setting on some mortises if using it like a biscuit joiner for gluing up wide boards but not for joints.

[John TenEyck]

Epoxy does not like a tight fit. I typically make the tenons about 0.005" undersize. 1/64" is pretty sloppy, however, but would be OK if you use filler with the epoxy.

Folks who want to use glue as insurance with a precisely fit joint - that's fine. But modern glues are amazing materials. The shear strength of a glued joint eliminates the need for precisely fit tenons which allows for fore/aft alignment of the joints. I've been using loose tenons for 40 years and I always make the tenon a little narrower than the mortise, and that includes chair joints which get tremendous abuse. I cannot remember one joint ever failing. Will they last for several hundred years? None of us will ever know.

John

[Edwin Santos]

Epoxy does not like a tight fit. I typically make the tenons about 0.005" undersize. 1/64" is pretty sloppy, however, but would be OK if you use filler with the epoxy.

Folks who want to use glue as insurance with a precisely fit joint - that's fine. But modern glues are amazing materials. The shear strength of a glued joint eliminates the need for precisely fit tenons which allows for fore/aft alignment of the joints. I've been using loose tenons for 40 years and I always make the tenon a little narrower than the mortise, and that includes chair joints which get tremendous abuse. I cannot remember one joint ever failing. Will they last for several hundred years? None of us will ever know.

John

I do pretty much as you're describing John.
I've heard it said that if a joint is too tight, there is no room for the glue. We're talking .0002-.0003 between surfaces when I talk about room for glue which if memory serves, is what Titebond recommends.

The rule I've always used is the joint should hold together if you dry fit it and hold it up so the tenon is facing up opposing gravity. If it falls out, it's too loose, if it is snug enough to resist falling out, then you're fine. For me it's too tight if a dry fit requires pounding together with a mallet, unless we're talking about glueless woodworking, which is it's own thing. The other thing is the nature of wood will involve some swelling when water based glue hits it so I have found a snug fit becomes super snug during glue up due to that bit of expansion.

Either way, I think there has been a bit of confusion in this thread. I personally do not believe the OP was talking about being undersized in terms of tenon thickness. I think he was talking about the other dimension i.e. top to bottom. If a tenon is snug in it's thickness but has 1/64" at the top or bottom, I just can't see a cause for concern. Maybe the words "loose" or "slop" just convey the worst possible image.

[George Yetka]

With the Domino I use directional "Slop" as long as it is snug in the direction I want the other direction allows me to slide. Good for panels. For most anything else I like snug.

[Edward Weber]

I do pretty much as you're describing John.
I've heard it said that if a joint is too tight, there is no room for the glue. We're talking .0002-.0003 between surfaces when I talk about room for glue which if memory serves, is what Titebond recommends.

The rule I've always used is the joint should hold together if you dry fit it and hold it up so the tenon is facing up opposing gravity. If it falls out, it's too loose, if it is snug enough to resist falling out, then you're fine. For me it's too tight if a dry fit requires pounding together with a mallet, unless we're talking about glueless woodworking, which is it's own thing. The other thing is the nature of wood will involve some swelling when water based glue hits it so I have found a snug fit becomes super snug during glue up due to that bit of expansion.

Either way, I think there has been a bit of confusion in this thread. I personally do not believe the OP was talking about being undersized in terms of tenon thickness. I think he was talking about the other dimension i.e. top to bottom. If a tenon is snug in it's thickness but has 1/64" at the top or bottom, I just can't see a cause for concern. Maybe the words "loose" or "slop" just convey the worst possible image.

In a "typical" stretcher to leg situation:
The majority of the force is applied to the edge cheeks in the way of "racking". Leaving that direction loose (slop) puts more strain on the glue applied to the cheeks than on the mechanical properties of the joints interlocking design.
If a tenon is too snug on the face cheek, the swelling from water-based adhesives can lead to cracking issues.
In this situation, you'd be better off making the edges tight and the cheeks looser.

Every situation is different.
A M&T joint has too many uses and orientations to mention. You need to know how and in which direction the force will be applied to the joint to build and install it properly. Relying on adhesives alone for the majority of the joints strength can lead to failure in some cases.

[James Jayko]

Either way, I think there has been a bit of confusion in this thread. I personally do not believe the OP was talking about being undersized in terms of tenon thickness. I think he was talking about the other dimension i.e. top to bottom. If a tenon is snug in it's thickness but has 1/64" at the top or bottom, I just can't see a cause for concern. Maybe the words "loose" or "slop" just convey the worst possible image.

Edwin, you're correct. The thickness of the tenon is spot on, but I was working to lines with the router to hit the ends of the mortise. So 1/64" may be more than it actually is, but imagine if you just took the line on one piece and just left the line on the other piece. My question should have been something like "if the mortise is 3" x 1/2", should I cut the tenon 3" x 3/8" to make alignment easier?" or something like that.

Yes, to many posters, I know that a perfect fit would be better!

[John TenEyck]

Edwin, you're correct. The thickness of the tenon is spot on, but I was working to lines with the router to hit the ends of the mortise. So 1/64" may be more than it actually is, but imagine if you just took the line on one piece and just left the line on the other piece. My question should have been something like "if the mortise is 3" x 1/2", should I cut the tenon 3" x 3/8" to make alignment easier?" or something like that.

Yes, to many posters, I know that a perfect fit would be better!

IMO, a 1/64" increase in mortise width over the width of your tenon is nothing; I'm not sure I can even measure that accurately. I typically make mine 1/16" wider, on purpose. As I said before, I can't remember ever having one fail.

Most people chopping mortises by hand would be more than happy to get within 1/64".

John