Mortise and Tennon - How to ??

[ByronBlack]

Ok

Following on from the previous thread with the excellent photo's from Marc and others. I wanted to ask this:

I'm going to be making a lean-to greenhouse for SWMBO soon, and I need to make a frame in which I'll be adding polycarbonate glazing. I'll be using M&T joinery, but don't know the best way of attaching the various parts.

For example, I have 1 upright, (left hand side of the frame) and attached to the top of this at 90 degrees is the top-bar part of the frame. I then need to have another piece attached at 90 degrees to the back of the upright which extends backwards to provide the depth.. god, does any of that make sense?

Basically, I can't visualise how two tennons fit into mortises at opposing angles on a single upright.

 

[JesseM]

The way I have seen it done (not having done it myself) is to cut the tenons of equal length and at the end of each tenon make a 45 degree angle. The 2 tenons then meet in the middle of the mortise. You can then reinforce it with a dowels probably glues into place. I am guessing you probably wouldn't glue the joint though. I guess another way would be to just stagger the M&T on each side of the post. But I think either way would be a strong joint.

My brother bought a good book on Japanese structural joints. While it doesn't give you directions for cutting the joints it does explain what works where. There are a lot of different joints, most variations on M&T with added complexities.

 

[garywayne]

Byron. Think of it as a giant table leg with the front and side rails coming off of it.

I hope this is of some help.
Good luck.

 

[paulm]

Might be better/easier not to approach it that way and instead make up the side panel as one unit and the roof as a seperate panel (and the front and other side as individual units also), and then you can place the roof panel on top of the sides and front and fasten through.

Don't know if I explained that well, but similar technique to that used when erecting a shed, each component bieng seperate and complete in it's own right and then they are all brought together to make the whole, which avoids complicated joints, unless of course you want complicated joints for the fun of it :shock: :lol:

Hope this makes some sort of sense !

Cheers, Paul.

 

[dedee]

I made mine from 4 separate frames which were then bolted together. Makes for easy transportation too.

Check out the Mini Greenhouse link on my website - below

Andy

edit here's a few more shots from my old site that I forgot to move

http://www.geocities.com/dedeeswoodwork ... ogress.htm

 

[woodbloke]

The 'shed' technique sounds about right to me....make it all in separate bits and bolt, or use SS coach screws (from Screwfix) to put it all together...makes the whole construction much simpler - Rob

 

[ByronBlack]

Guy;s

Thanks for all the suggestions. I think I might go ahead and use the more complicated double-tenon method (now that I can visualise it) for a couple of reasons:

It's important that this looks nice, and by doing it all in seperate frames, i'll end up with thicker parts where they meet, and also I don't like the look of bolts/screws and I would have to hide these with plugs.

The second reason why I think i'll go the joint route is it uses less wood. Which is important as i'll actually be making two of these, as SWMBO wants to use each one for a specific use (and it aids portability).

While i'm on this subject, I have a couple of other small queries:

First off, what sort of dimensions should I use for the frame? (I have some in mind, but want to see what others suggest, to confirm my thoughts). And also, what is a good relatively cheap wood to use?

I notice Dedee, that you used Wester Red Cedar, what is the price/workability on that like?

Can oak or redwood be used and would they be good choices?

All opinions as ever gratefully received.

 

[dedee]

BB,
Cedar is used in the manufacture of the vast majority of commercial wooden greenhouses precisely because it is the best wood for the purpose.

It is however quite soft, one only has to look at it for a dent or ding to appear. Its natural properties mean that it will not require treating with preservative and should last outdoors for years - and it smells gorgeous.

I spent about £150 on 2" and 1" boards from WL Wests. I have a lot of the 1" left so at a guess I used about £100-£120 worth. The shiplap back is also Cedar came from Champions and was £56.89 (found the receipt for that) and I used it all - could really have done with a wee bit more.

Andy[/code]

 

[garywayne]

Byron. This is not advice on what wood to use.

Years ago I assisted in the building of 17 Century timber buildings, (reconstruction. I'm not quite that old). We used green oak. We also had to make the joints using authentic tools. No electricery.