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Thread: Floating tenon question

  1. #1
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    Floating tenon question

    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?

  2. #2
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    As a general rule of thumb "slop" and "Joinery" shouldn't be used in the same sentence.

    Quote Originally Posted by James Jayko View Post
    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?

  3. #3
    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.

  4. #4
    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.

  5. #5
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    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.

  6. #6
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    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.

    tenon.jpg

  7. #7
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    Quote Originally Posted by Edwin Santos View Post
    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.

  8. #8
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    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.

  9. #9
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    Quote Originally Posted by Mark Hennebury View Post
    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...

  10. #10
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    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.

  11. #11
    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.
    Last edited by Kevin Jenness; 06-01-2023 at 10:05 PM.

  12. #12
    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

  13. #13
    Quote Originally Posted by Michael Burnside View Post
    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?
    Last edited by Edwin Santos; 06-02-2023 at 11:13 AM.

  14. #14
    Quote Originally Posted by Edwin Santos View Post
    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.

  15. #15
    Quote Originally Posted by Edwin Santos View Post
    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.

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