angled mortice and tenon joint

[mickthetree]

Morning all!!

My misses has asked me to make a Tripp Trapp style high chair. Her brother has one for their little girl so I have seen one up close. Also got some of the measurements of their website.

It is not going to be a direct copy but use most of the principles of it.

So I took some wood from an old door I got out of a neighbours skip. 100 year old pitch pine. Removed all of the old paint in seconds with an old bosch electric planer.

Planed up on my latest aquisition (axminster ct150) and thicknessed. I now have the four main pieces for the two sides.

My initial idea was to make a lapped joint at the foot and maybe strenthen with some pegs, however whilst lying in bed this morning after the little bundle of joy woke us up, I got to thinking about using a mortice and tenon instead.

I have had much success doing mortices by hand but have not attempted an angles one before. I also have a router which I'll be using on this project. But I cant think how to make a jig to cut an angled mortice safely.

Any ideas?

This image should hopefully show what I intend to do.

Do you think there is enough meat left on the bottom of the angled upright?

 

[Paul Chapman]

The simplest way to do that joint would be to cut a mortice in both pieces with your router and make a loose tenon. That would also leave a bit more material at the base of the upright piece because the mortice would be at an angle.

Hope this helps.

Cheers :wink:

Paul

 

[joiner_sim]

If you continue to go on the traditional m&t route, I think it will be okay. As long as you use a good wood glue like cascamite. A rule I've kind of always stuck to.... not sure if it is a known one or one I've just picked up myself tho.... One shouldered tennon.... the shoulder should be 1/3 of the overall timber. Two shouldered tennon.... the shoulders should be 1/4 each of the overall timber.

 

[9fingers]

Not sure if it is the correct method, but in my recent chair making effort, I have gone for perpendicular mortices cut with a HCM first and angled tenons cut on the table saw/bandsaw to fit.

Compound angled joints were the worst and took a few attempts to get right. I've gone right off chairs and curved work for a while as a result!!

good luck

Bob

 

[mickthetree]

Hi Paul

Ah ha! I see what you mean. I've not done a loose tenon before.
I guess you mean something like this?

I did particularly like the idea of keeping as much strength in the joint as possible as it will be holding the precious little fella. Do you think a loose tenon would do the business here?

A linkyto images of a Tripp Trapp chair incase anyone hasnt seen one before.

I've read a thread on here about someone making one before, but he used all plywood construction.

I guess I could also use a couple of bolts (or threaded rod) and some barrel bolts, like this:

And cheers for the notes on shoulders Simon.

 

[Paul Chapman]

Ah ha! I see what you mean. I've not done a loose tenon before.
I guess you mean something like this?

I did particularly like the idea of keeping as much strength in the joint as possible as it will be holding the precious little fella. Do you think a loose tenon would do the business here?

Yes, that's the idea. I find loose tenons just as strong as conventional M&T joints and they are often easier to do where the pieces to be joined are angled. I've found the best way is to cut the mortice with the router then round over the edges of the loose tenon to match. Just ensure that you make a couple of saw cuts along the length of the loose tenon to enable excess glue to escape when you cramp it together. If you are at all worried about strength, you could always peg them with dowels.

If you decide to use plywood rather than solid wood, I'd consider using knock-down fittings. The ones I favour use threaded cross dowels together with threaded rod and a neat brass head which you tighten with an allen key like these http://www.woodfit.com/product_info.php ... +30mm+long
I find it best to use a dowelling jig to ensure that all the holes line up.

Cheers :wink:

Paul

 

[dickm]

In terms of glueing area, I wonder if the original idea of a halving joint isn't the best? Any form of mortice will probably give a smaller glueing area and leave very short grain at the bottom of the leg, which might not be strong enough. In the circs, and thinking safety, I would be tempted to stick with halving plus short brass screws.

 

[markturner]

You could just make the tenon as normal but overlong and then cut the shoulders at an angle to suit the join?

Cheers, mark

 

[mickthetree]

Hey all

I have made both legs now. I opted to drill out the waste and clean up with a chisel. Very pleased with the result.

I messed up the haunch a bit, but got the next one correct (but no photos)

The joints came together very nicely.

I'm now revisiting the idea of a curved back. I just setup my bandsaw, planned a face of a board and cut a really nice thin slice. Now, one side of that slice is planed flat and the other is rough from the bandsaw. Will they glue together ok? or will I need to somehow sand the rough face? I could rig something up with my belt sander I guess.

I dont think these slices will be able to handle the sharp bend required so I'm thinking of doing just one curve, then finding another way to attach it to the frame.

 

[Tusses]

a bit late maybe, but I'd have put the tenon on an angle on the upright, and a standard mortise on the bottom piece.

 

[mickthetree]

Hi Tusses

Still worth considering as I have a few friends waiting to see how this turns out.

Cheers
Paul

 

[Tusses]

I reckon it would be stronger too, if it mattered. more meat left around the mortise that way.