Floating tenon question

[James Jayko]

Hey all, I just built the “Morley Mortiser” for loose tenon joinery. I’m using it on my first project.

When using this sort of loose tenon joinery, now much slop do you leave in the tenons? I’m going to glue up with epoxy so it should fill any gaps. The alignment is just slightly off in some places (1/64” maybe?)…any rule of thumb here?

[Mark Hennebury]

As a general rule of thumb "slop" and "Joinery" shouldn't be used in the same sentence.


Hey all, I just built the “Morley Mortiser” for loose tenon joinery. I’m using it on my first project.

When using this sort of loose tenon joinery, now much slop do you leave in the tenons? I’m going to glue up with epoxy so it should fill any gaps. The alignment is just slightly off in some places (1/64” maybe?)…any rule of thumb here?

[Bert McMahan]

I don't have an answer for you, just wanted to say thanks for introducing me to the Morley Mortiser. It looks like a fun project.

[Edwin Santos]

If the "slop" you mention is in the top and bottom edges of the tenon (i.e. the rounded ends), it really doesn't matter because the strength is in the tenon cheeks where they glue to the mortise side walls.
In fact, some people like a slight bit of vertical alignment room during glue up. I don't own a Domino, but I believe it has settings to create this very condition at the user's option.

[Richard Coers]

a 1/64 is like a mile in joinery. I fit the tenons so they just barely slide in by hand with glue on them. I don't want to use hammer but I don't want it flopping around hoping for the epoxy to fill up a gap. On the edges, I chamfer the edges but they are snug at a 1/8 flat between the 2 chamfers.

[Mark Hennebury]

There is no need for slop in joinery!

If you learn how to mark out and cut accurately your joinery will fit together precisely where it should.

The chair in the photo is about 25 years old and was a test one for a set of 10.
The joints were tight 25 years ago and are still tight today.

502154

[James Jayko]

If the "slop" you mention is in the top and bottom edges of the tenon (i.e. the rounded ends), it really doesn't matter because the strength is in the tenon cheeks where they glue to the mortise side walls.
In fact, some people like a slight bit of vertical alignment room during glue up. I don't own a Domino, but I believe it has settings to create this very condition at the user's option.

Yes, this is what I mean. I think if your setup is absolutely perfect, it doesn't matter as you could, say, orient both legs in the same direction (eg show face in on one, show face out on the other), and use the stops to get perfectly identical joinery. However, I was off a tiny bit, so the mortises are maybe ~1/64" closer to the show faces (if even that), and I made sure to cut them all with the show faces in. But this meant resetting the stops for each mortise, which introduced a tiny bit of error. So I figure I can just shave ~1/32-1/64" off the narrow ends of the tenon stock to give myself enough wiggle room to keep everything square, with the epoxy filling any small gaps that may arise. The tenons are a snug fit on the important dimension.

I'm sure I'm thinking too hard about this, but it seems reasonable in my mind.

[Joe Calhoon]

Generally, you should be able to close a dry M&T joint with hand pressure. If it’s too sloppy you will know. If it is too tight you will have problems when glue is applied. This is with PVA glue.
Now if using epoxies it might be different. I set up a tenoner in a door shop staffed by former boat builders that were using epoxies for window and door construction. They wanted very loose fits for dowel and tenon construction because of the gap filling of epoxy. Don’t know enough to comment on this.
Agree with mark, don’t make the width sloppy for adjustment. Dial in your joinery.

[James Jayko]

There is no need for slop in joinery!

If you learn how to mark out and cut accurately your joinery will fit together precisely where it should.

I get your point, and I agree 100% if you're cutting a traditional M&T. But I think you might be missing the point of loose tenons...the comment above was spot on, its why the domino has one tight and two looser settings so you can get everything to line up if you miss by a small fraction...

[Michael Burnside]

There are plenty of good reasons to have a mortise that is elongated. I would say the top two are flexibility in alignment of the two pieces coming together, especially when they are not the primary sources of strength, and the type of glue being used for the tenon. I always use loose mortises for outdoor furniture because I prefer to use epoxy rather than TB3 or other type glues.

[Kevin Jenness]

I use the same tolerances for loose tenon joinery with epoxy as for integral tenons with pva glue, shooting for a .002" glueline which can be assembled and disassembled by hand. If your layout and milling are accurate the mortises don't need to be extra wide and an accurate fit gives mechanical strength against the joint moving under load in conjunction with the glue bond. Epoxy will fill gaps but need not be relied on for that, and the pieces will wind up where they need to be without coaxing. Epoxy slides easily and makes for an easily assembled joint without any more than normal clearance. "If you can put the joint together with your hat it's too loose, if you need a hammer it's too tight."

I cut mortises with a Domino 500 and a stationary slot mortiser. The Domino has an accurate center mark, the slot mortiser has an adjustable front fence with a center mark which takes a couple of test fits to get located properly with each setup. On your rig you may want to have a center mark inside the slot of the plate the router rides on and corresponding marks spanning the mortised faces on the workpieces. I find that working with end/edge stops to locate the workpiece is more complicated and no more accurate. Once you have the mortise length accurately centered on the jig center mark and the workpieces registered and clamped to that mark you should get repeatable, precisely placed mortises.

[Edward Weber]

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

[Edwin Santos]

There are plenty of good reasons to have a mortise that is elongated. I would say the top two are flexibility in alignment of the two pieces coming together, especially when they are not the primary sources of strength, and the type of glue being used for the tenon. I always use loose mortises for outdoor furniture because I prefer to use epoxy rather than TB3 or other type glues.

Another reason for a (slightly) elongated mortise is to allow an escape route for air when the joint is coming together.
If a mortise and tenon joint is a conventional blind tenon (not a through tenon), and if it were perfectly fitted like the photo above, once you apply glue to the parts, as you slide them together there can easily be a vacuum lock and a trapped air pocket.

Another way of resolving this problem is cutting a small channel in the tenon with say, a veining tool. This is why dominos have the cross hatch pattern.
Again, the strength in the joint is the tenon cheeks which should be snug.
A minimal amount of vertical adjustability during glue up can be a good thing. What's the saying? Perfection is the enemy of good?

[Edward Weber]

Another reason for a (slightly) elongated mortise is to allow an escape route for air when the joint is coming together.
If a mortise and tenon joint is a conventional blind tenon (not a through tenon), and if it were perfectly fitted like the photo above, once you apply glue to the parts, as you slide them together there can easily be a vacuum lock and a trapped air pocket.

Another way of resolving this problem is cutting a small channel in the tenon with say, a veining tool. This is why dominos have the cross hatch pattern.
Again, the strength in the joint is the tenon cheeks which should be snug.
A minimal amount of vertical adjustability during glue up can be a good thing. What's the saying? Perfection is the enemy of good?

Speaking only for myself,
To avoid what you mention, I chamfer the four corners of the tenon very slightly. This allows for glue and/or air to have an egress when fitting the joints without compromising the fit in either direction.
M&T joints derive their strength from more than the cheeks only, depending on where and how they are used.

[Kevin Jenness]

Another reason for a (slightly) elongated mortise is to allow an escape route for air when the joint is coming together.
If a mortise and tenon joint is a conventional blind tenon (not a through tenon), and if it were perfectly fitted like the photo above, once you apply glue to the parts, as you slide them together there can easily be a vacuum lock and a trapped air pocket.

Another way of resolving this problem is cutting a small channel in the tenon with say, a veining tool. This is why dominos have the cross hatch pattern.
Again, the strength in the joint is the tenon cheeks which should be snug.
A minimal amount of vertical adjustability during glue up can be a good thing. What's the saying? Perfection is the enemy of good?

When making spline tenons I leave a small flat on the rounded edges for glue relief while the tenon fits snugly in the mortises.

[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