joint of the month 2

[engineerone]

after thinking about paul chapman's comments about the m/t's on the top of my coffee table, (see projects) i felt it would be a good idea to discuss and revisit m/t's

this table was my first recent attempt at hand made m/t's

the mortices in the legs were hand cut using a chisel, and occassionally a mallet to massage the chisel.
i was actually quite surprised how easy it was to cut the oak, with obviously therefore quite sharp chisels however, i did not cut them in the approved manner, in that i did not stand at the end of the mortices and cut them that way, so they were not as straight as i would have liked, still .

i cut the tenons on the table saw, using the norm method, and no tenoning jig (sorry scrit) after advice from scrit i also cut the tenons on the leg, to allow for a resting and wide enough land at the top of the legs. these are now 20x20mm.

since i measured and did not use a rod, i was pleasantly surprised at the ease with which i was able to get the joints sorted. since they were my first joints, i did not do haunches
but will try that next time

so the reason for this thread is to discuss the idea that putting through mortice and tenon joints in the top of a nearly 900 long by 500 wide top might cause later problems due to expansion and contraction of the top.

the mortices are collared by walnut strips, and the tenons have wedges but will that cause me problems or not.

only time will tell, but what do the other experts think?

paul

[paulchapman]

Paul,

As I raised the problem I will give you my reasoning. The top of your table is a sizeable piece of solid oak. If it does expand and contract (and all wood does to some extent, the amount depending on the conditions in which it is kept), it does so across its width. Any movement along it's length is so slight it can be ignored.

The way you have fitted the top to the legs of your table means that the fitting will try to resist any movement in the top and something may give. What is likely to happen is that the top will develop some cracks as it tries to move.

What you could have done to guard against this is to have fitted rails to the top of the legs at the ends and then fitted the top to those rails with buttons or stretcher plates. This would have secured the top while allowing it to move as it expanded and contracted.

If it does crack, that might not matter. Oak is an open grained wood and the odd small crack here and there can look OK. However, if you find that you get any significant problems, the design of your table is such that the top could be removed and rails added, so all would not be lost.

Having said all that, you might not get any problems - in which case, please disregard all this ;D

Cheers

Paul

[mrgrimsdale]

Looks nice with the fancy mortices.
Usually a table top is fixed loosely with buttons etc to allow for differential movement. If your top moved at all all the stress is transferred to the structure below and so might open joints. It'll be ok as long as you don't move it about too much between environments with very different temperatures/humidity.
Differential movement is allowed for in all sorts of crafty ways, but not always obvious. Through-morticed table legs is a sort of windsor chair construction where either the legs are not framed up with rails etc so diff movement not a prob, or if framed, the whole structure is a bit bendy - not too rigid. With a rigid undercarriage you then need a looser fit of the top.

cheers
Jacob

[engineerone]

paul, i kind of thought that was what you meant, but i did look at other things too.

1/ i am a tighfisted old sod, so it will never live too near a radiator, and thus should not move too much in the room heat ;D

2/ i have seen old items made in a similar way and they have survived. in particular some old serving tables

3/ if it last 10 years then i will say what the hell, and be happy,
if not you are right, i could adapt it again and add some rails,
so really a win win situation.

4/ seems to me that if you want to show off, you need to be a little extreme, and then really smug when you have done it ;D

thanks again for your continued interest


paul

so what would others have done?