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Discussion Starter · #1 ·
Excuse the grade school drawing but hopefully will address my point. I’m new to mortise and tenon jointing so I bought the Trend MT JIG and I'm going to attempt to make a stool. This jig apparently has the capability for complex MT jointing but I’m wondering what the “standard “ or maybe correct way to make this MT. These pieces join at a 10 degree slant. Should tenon be parallel to ground or at the same 10 degree slant or does it make a difference.



Thanks
Eric
 

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Problems like this are why we strongly encourage members to fill out their profiles. I don't really know what I should suggest to you because I don't know what you have to work with. I'm not sure how easy it is to match angles on both pieces but the website says you can. The wood above the tenon is fairly short which will make it fragile so I would either make a narrow tenon (up and down) to fit at the bottom of the cross member or just do a saddle type joint joint and maybe pin through the tenon with a few small dowels. Do you plan on doing lots of MT joints? That's an expensive jig.
 

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Hi and welcome. Don't know what tools you have yet, so here goes.

I think it is far easier to cut a mortise at 90 degrees to the surface of the leg. Easier to hog out and shape the recess that way. The tennon, then, has to be cut as shown, at the same angle as the end pieces, but still 90 to the angled end cut.

I would make a pattern out of card stock first, with the angles laid out. Draw the tennon first, then use it to mark the location of the mortise on the leg pattern piece.

The challenge will be cutting the long grain piece to the correct angle. There are several ways to do that, most easily on a band saw, then hand work with a chisel to get it just right. If you don't have a band saw to work with, then I suggest getting a Japanese Dozuki hand saw. It is wicked sharp, but because it cuts on the pull stroke,it is easily controlled and very precise. To increase accuracy, while holding the handle, place your index finger on the side of the blade. It will reduce side movement of the blade--same as controlling a chef's knife.

To remove the shoulders, if you have a table saw, you will have to use your miter gauge and a flat top tooth blade set to a precise height (or a Dado set). The miter gauge will have to be set to the exact angle of the stool's splay. Take multiple passes to shave the tennon to the size you want, but it is almost always a good idea to have the tennon 3/8ths or so to make it easier to drill out the mortise. Leave just a little extra thickness (1/16th or so) so you can use some sandpaper or a chisel or hand plane to fit it to the mortise.

Mark the location of the mortise using the pattern, then carry the mark around to the narrow dimension of the board. Now you can use a drill press if you have one, to hog out the length and width of the mortise. If you don't have a drill press, you might try it with a drill guide of some sort. You could also use a plunge router, by sandwiching the leg in a number of thicknesses of scrap wood, to give you a flat surface for the router to ride on. Drill 3/8ths holes a little deeper than the tennon is long, then use a chisel to carve away until the sides are straight. You chisel must be ultra sharp. If you can't shave hair off your arm easily, it is not sharp enough.

The inside walls of the mortise should be flat and as smooth as possible.

Next, you will shave the sides of the tennon to make a snug fit in the tennon. Once it fits snugly (without forcing it in place), apply glue to both mortise and tennon and press them together. I would do this last, and I'd number both mortise and tennon so during glue up, you don't get confused about what goes where. Remember, each joint is custom fitted.

I am not familiar with the setup you have, but these are some options. If the jig will do any of these tasks, use it. But for me, the basic answer to your question is to allow the tennon to look like the drawing. Easier to cut the tennon angle than the mortise. And all the strength will be from the glue. I'd use some extended open glue. and be careful that the clamps don't throw the stool's structure out of square.

That's my opinion anyhow.
 

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Discussion Starter · #4 ·
Wow Tom,
I can't thank you enough for the detailed answer. Totally understand what you're saying. Much more useful than the canadian shame I received.

Eric
 

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You are likely to get different opinions on which tenon is stronger...inline or angled. One side will opt for the inline tenon as the cut will not cross the grain and the entire tenon will be along the grain lines. The other side will opt for the angled as it will require the angle cut on the shoulder of the tenon versus cutting the mortise at an angle.

On your Trend jig it looks like the angled mortise can be accommodated but you will need to match the angle to the angle of the shoulder on the inline tenon. You will also need to cut the end of the tenon to the same angle to accommodate the angled mortise (at the bottom).

Don't know the Trend jig but you might need to cut the angled mortise in a separate operation than the inline tenon as opposed to the Trend advantage of cutting the mortise and tenon with one setup when the M&T is square.

Good luck...hoping there will be lots of discussion on this as I've grown an interest in the Trend M&T jig versus a dedicated mortising machine.

Good luck...let us know what you decide and what you needed to do to accommodate...
 

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for legs and aprons inline M&T's are stronger...
they more shear and pull out resistant...
the compound angled M&T shown slide apart when the joint is stressed because of the up angle of the tenon...
inline (full horizontal) will loosen but resist sliding apart...
to improve even further, make the tenon a down angle...

for the M&T glue up...
Bob Van **** Shop Tip: Glue Squeeze Out...
and see the PDF...
 

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I wouldn't be too concerned about the strength of the tenon, there is more than enough straight through grain on it, but the reason I suggested to keep it horizontal is what Stick said. Eric what I said wasn't meant to shame you, it was meant to encourage you to fill out your profile so we know what you have to work with. Otherwise it's like being expected to hit a bullseye using a gun with no sights.
 

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I think the glue will prevent the problem Stick suggested, just don't let a gogo dancer work out on top of that stool.
 

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The problem Tom is that it stresses the glue joint more than a horizontal tenon does making it more likely to fail.
 

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Actually, I like Charles' idea of in his first post "just do a saddle type joint". Lots of glue area and the cross member ends will be longer.
 
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Actually, I like Charles' idea of in his first post "just do a saddle type joint". Lots of glue area and the cross member ends will be longer.
This is a stool with four legs, so a saddle joint probably isn't appropriate. This means there will need to be two mortises in each leg. Given that, I'd make the legs nice and thick at the top and move the cross piece (whatever that's called) and move it closer to the edge of the leg. It also suggests making a longer tennon, or even overlapping them, or drilling and placing a couple of dowels through the joint to reinforce it. Hide the dowels on the inside. And really good glue.

If necessary, he could taper the legs to give them a lighter look.
 

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The saddle joint is what was typically used in sash window and door construction. Rather than leave a little bit of short grain wood (as Tage Frid called it in the 1st book he published) which has very little strength, just go ahead and mill the mortise all the way through the end which vastly increases the glue area. This essentially creates a very long groove for a very long and wide mating tongue. Doweling it increases the racking strength. One of the issues here is modern glues. Yellow glues and the Titebond glues (1, 2, and 3) all seem to glue with hard, inflexible glue lines. Traditionally, from what I've read, glues were hide based glues which would stretch before they fractured. Hide glues are water soluble and have very short open times which make them hard to use. Which is why woodworkers have moved away from them. But from my experience with very old furniture they still outperform. Weldbond is one of the only modern glues that still has some stretch to it. It might work with that angled tenon approach but I wouldn't expect one of the other glues to survive that long. They tend to fracture over time as they get brittle. With the horizontal tenon a large portion of the force is straight downward on the wood at the bottom of the mortise. The rest of the force is torque which has to shear the fairly large glue line between the parts. But with the angled tenon there is a component of the force on the joint that is downward not against the wood of the mortise. So now the glue has to hold what the wood is holding in the other scenario.

Some consideration has to be given with what is my most likely method for success with what I have to work with and what my skill set is. Certainly a couple of dowels or so through the mortise and tenon assembly will help with that if you aren't certain that what you've done so far is good enough. There isn't always an absolute answer.
 

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I'm looking at the fact that the legs will be splayed at the 10-degree angle both ways and I would be mitering the legs at the corners so the saddle joint ends would be inside the joint and not show from the outside of the joint. I would also splint the mitered legs to reinforce that joint.
 

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Discussion Starter · #14 ·
Step Stool Plans

Thank you all for your experienced opinions. As I said, I'm new to MT jointing. The explosion view of a folding step stool might give you a better idea of what I'm talking about. This is a fairly old plan that maybe some of you have run across in the past. (it's from a blog called "The sorted details") The plans are just pictures and dimensions. So I was confused on why the side rails attached with 2 mortises. Then I realized something basic that I didn't know about: the floating or loose tenon. However I played with the Trend MT Jig and was able to make pretty good straight aligned tenons for the side rails. The mortises were a different story because the jig did not allow me to tilt 10 degrees on the bottom support rail. So I think I will make these mortises using my drill press that tilts. I'll try to eventually post an end result.

Thanks again all.

Eric
 

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a blind joint would be extremely strong and easy to do..

.
 

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