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Thread: Methods for laying out compound angle tenons?

  1. #1

    Methods for laying out compound angle tenons?

    I'm thinking about building a table with legs that are angled outward along two axes. I've been trying to figure out how to accurately lay out and cut compound-angled tenons with hand tools, but I haven't been able to find much information out there.

    Any advice on how to do it?

  2. #2
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    Paul Sellers does an excellent job laying out such joints in his dining room chair video. His basic technique is to draw the joints to scale on some plywood and lay out the lines from those drawings. It's quite ingenious, really.

    If you join his woodworking masterclasses ($15 a month) you can quit any time, so it might be worthwhile of you to join for a single month and download the chair project.

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    Quote Originally Posted by Winston Chang View Post
    I'm thinking about building a table with legs that are angled outward along two axes. I've been trying to figure out how to accurately lay out and cut compound-angled tenons with hand tools, but I haven't been able to find much information out there.

    Any advice on how to do it?
    A little too intricate to explain in a forum post, but no need because here's the gold standard:

    https://www.finewoodworking.com/2000...-angle-joinery

    Membership is required, but if you're starting to build chairs this one article is well worth the price of membership.

    This technique will get you there every time, without head scratching, and without fail. Once you've done a few chairs, whose various angles differ by only a few degrees, you will have done all the drafting and template making you'll need for an entire career's worth of building chairs that require this kind of geometry.
    Last edited by Charles Guest; 07-12-2019 at 6:00 PM.

  4. #4
    Hand tool woodworkers usually do this kind of work differently than machine guys. The machine guys make angled tenons while we make straight tenons and angle the mortise if needed. I remember Phil Lowe making a chair at Williamsburg. He had angled tenons on the stretchers, but when asked point blank, he admitted that the original 18th century chair had straight tenons. Straight tenons are easier to make because you can lay them out with a mortise gauge working from the side of the stock. They are also a bit stronger, being straight grain.

    It is usually difficult to undercut at the end of a mortise with a mortise chisel. So when we do a mortise where the tenon comes in at an angle we slope one end of the mortise with the chisel but the other end we just cut straight in and then make a slight slope on the tenon to acommodate.
    .

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    Quote Originally Posted by Warren Mickley View Post
    Hand tool woodworkers usually do this kind of work differently than machine guys. The machine guys make angled tenons while we make straight tenons and angle the mortise if needed. I remember Phil Lowe making a chair at Williamsburg. He had angled tenons on the stretchers, but when asked point blank, he admitted that the original 18th century chair had straight tenons. Straight tenons are easier to make because you can lay them out with a mortise gauge working from the side of the stock. They are also a bit stronger, being straight grain.

    It is usually difficult to undercut at the end of a mortise with a mortise chisel. So when we do a mortise where the tenon comes in at an angle we slope one end of the mortise with the chisel but the other end we just cut straight in and then make a slight slope on the tenon to acommodate.
    .
    Straight tenons and angled mortises unavoidably cause you to have to shorten the back rail's tenons. Straight tenons are a dodge for those challenged by the relatively simple geometry and layout, and this is their only advantage. As long as you don't select rail stock with wild grain, and this would be a mistake regardless of which joinery option you choose, angled tenons and straight mortises are better in every way that matters except for a slight conceptual challenge on the front-end.

  6. #6
    Charles , I'm sad to hear that some 18th century fine chairs are headed for failure because some chose an inferior
    method.

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    Quote Originally Posted by Winston Chang View Post
    I'm thinking about building a table with legs that are angled outward along two axes. I've been trying to figure out how to accurately lay out and cut compound-angled tenons with hand tools, but I haven't been able to find much information out there.

    Any advice on how to do it?
    Winston, if I understand you, what you want is an angled and splayed leg. If so, this is how to do it ...

    First mortice the legs (and turn them, as in my case) ..



    Calculate the angle and splay you want. I first do this with a practical model, then transfer it to the parts, when these angles can be recorded with a sliding mitre gauge.





    Saw the tenons with the shoulders at the angle you determined ...



    When you glue them together, you will end up with angled, splayed legs ...



    Regards from Perth

    Derek
    Last edited by Derek Cohen; 07-12-2019 at 8:58 PM.

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    Quote Originally Posted by Mel Fulks View Post
    Charles , I'm sad to hear that some 18th century fine chairs are headed for failure because some chose an inferior
    method.
    Given that a tiny fraction of those made survived you should be. Chairs in use fail at these joints inevitably. You need as much wood in the joint as you can get consistent with an aesthetic, and happily cutting clocked tenons allows you to do so without altering the exterior appearance and lines of the chair at all. They were routinely cut this way in Britain and elsewhere during the same time period. It's not new.
    Last edited by Charles Guest; 07-13-2019 at 7:23 AM.

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    Quote Originally Posted by Charles Guest View Post
    Straight tenons and angled mortises unavoidably cause you to have to shorten the back rail's tenons. Straight tenons are a dodge for those challenged by the relatively simple geometry and layout, and this is their only advantage. As long as you don't select rail stock with wild grain, and this would be a mistake regardless of which joinery option you choose, angled tenons and straight mortises are better in every way that matters except for a slight conceptual challenge on the front-end.
    Not at all, straight tenons are required for strength. Angled tenons are all short grain. Barring something unusual angled mortises have no ill effect.

    The difficultly is a wash, they’re equally simple or difficult. Mitigating difficulty is always in the accuracy of your layout, the more accurate the layout the easier the cutout.
    Bumbling forward into the unknown.

  10. #10
    I'd be happy to have angled mortises instead of angled tenons, but then the challenge shifts to the mortise.

    I have done straight tenons with single (non-compound) angled mortises before. I did it by first cutting the tenon, and then I used the tenon as a template and knifed the outline of the mortise. Then I used cut the mortise, and used an angled guide block to make sure the angled sides of the mortise was at the correct angle. I suppose that with a compound-angled mortise, I would use a guide block for all four sides of the mortise.

    How would you recommend making angled mortises?

  11. #11
    As far as I know one just angles the chisel. Therein is the appeal of handtools, especially for the home woodworker.

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    Quote Originally Posted by Brian Holcombe View Post
    Not at all, straight tenons are required for strength. Angled tenons are all short grain. Barring something unusual angled mortises have no ill effect.

    The difficultly is a wash, they’re equally simple or difficult. Mitigating difficulty is always in the accuracy of your layout, the more accurate the layout the easier the cutout.
    Angled tenons aren't all short grain, and again, chopping an angled mortise makes you shorten the back rail tenons, and this is why it's an inferior construction. The layout doesn't have to be drafted, you can wing it until it's pretty close then trim to fit. Once fit is achieved, templates can be made for all future chairs, and the tenons marked off of these. You have templates for everything else on the chair, ones for the angled tenons aren't much extra work. One presumes that it's not only one chair being made but potentially dozens and dozens over time.

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    Very carefully or you'll get a chair that sits wonky and it's not always easy to see how to trim the inside of the mortise to make the angles exactly the same (though mirror images) between the left and right legs. And they have to be dead nuts equal or the chair won't look right, and if the chair has arms they could (will) end up all screwed up, stretchers will be a bigger headache than they already are. You'll be playing catch-up the rest of the way.

    Your angled tenon layouts, as long as they are mirror images of each other (and they will be because they're going to be drafted or marked off templates from a chair that "worked"), are easy to nail to half the width of an incised/scratched line if you already have experience successfully sawing tenons. You simply can't chop a mortise to that degree of accuracy. Chairs with through tenons that were made with angled mortises are often wedged and stuffed, or the tenons tapered and forced through to look good on the outside, all of this because of the trimming inside the mortise that had to happen to get the angles the same on both legs. Not every chair, there were good shops building this way relatively successfully but remember they still had to shorten the back rail tenons, and even if the joints were a good fit this isn't good.

    It's hard enough to chop a mortise at a perfect 90*, try chopping one sighting off of a bevel gauge and see how close you get to that angle without needing to trim the interior of the mortise. You can end up way off, and way off doesn't require it to be that many degrees off. If you are off, you might be lucky enough to be off by the same amount on both legs. It may be that this method clicks for you, rather than clocking the tenons, that's fine but again those back rail tenons have to be shortened if you angle the mortises.

    It's important to understand you may only draft a few versions, or maybe just one. If your chair designs all have the same back leg cant and seat trapezoid angles you'll only draft it once in an entire career. If you want to vary these a little, you might draft and make a couple more sets of templates. If you drafted this more than three or four times for the rest of your life, I'd be shocked. You'd only do this if you become very prolific making chairs with varying back leg cant angles -- many styles have none at all. There is a fairly narrow range, IMO, of back leg cant angles that look good before they become cartoonishly angled or conversely have so little angle it could have been dispensed with.
    Last edited by Charles Guest; 07-20-2019 at 9:43 PM.

  14. #14
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    Quote Originally Posted by Charles Guest View Post
    Very carefully or you'll get a chair that sits wonky and it's not always easy to see how to trim the inside of the mortise to make the angles exactly the same (though mirror images) between the left and right legs. And they have to be dead nuts equal or the chair won't look right, and if the chair has arms they could (will) end up all screwed up, stretchers will be a bigger headache than they already are. You'll be playing catch-up the rest of the way.

    Your angled tenon layouts, as long as they are mirror images of each other (and they will be because they're going to be drafted or marked off templates from a chair that "worked"), are easy to nail to half the width of an incised/scratched line if you already have experience successfully sawing tenons. You simply can't chop a mortise to that degree of accuracy. Chairs with through tenons that were made with angled mortises are often wedged and stuffed, or the tenons tapered and forced through to look good on the outside, all of this because of the trimming inside the mortise that had to happen to get the angles the same on both legs. Not every chair, there were good shops building this way relatively successfully but remember they still had to shorten the back rail tenons, and even if the joints were a good fit this isn't good.

    It's hard enough to chop a mortise at a perfect 90*, try chopping one sighting off of a bevel gauge and see how close you get to that angle without needing to trim the interior of the mortise. You can end up way off, and way off doesn't require it to be that many degrees off. If you are off, you might be lucky enough to be off by the same amount on both legs. It may be that this method clicks for you, rather than clocking the tenons, that's fine but again those back rail tenons have to be shortened if you angle the mortises.

    It's important to understand you may only draft a few versions, or maybe just one. If your chair designs all have the same back leg cant and seat trapezoid angles you'll only draft it once in an entire career. If you want to vary these a little, you might draft and make a couple more sets of templates. If you drafted this more than three or four times for the rest of your life, I'd be shocked. You'd only do this if you become very prolific making chairs with varying back leg cant angles -- many styles have none at all. There is a fairly narrow range, IMO, of back leg cant angles that look good before they become cartoonishly angled or conversely have so little angle it could have been dispensed with.
    Lots of good info here! Thanks

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