This is becoming rather contentious, but it's not true to say a glued joint will be stronger.
A glued joint *can be* stronger, if the joint is well designed, has very cl ose tolerances, the glue is used exactly as the manufacturer recommends, an d a high clamping force is used. That's pretty much what engineered timber does, but requires carefully controlled conditions to achieve it.
Any significant notch in machine strength graded timber has to be regarded as considerably reducing its strength. The effects of a deep notch aren't v ery predictable.
AS my description may have caused this 'debate' .... here is a sketch of the joint I will use.
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This is a Pergola project ... a number of 100x100 posts fitted to ground brackets, running along top edge of posts on each longitudinal side is a
200x47 beam.
At 90 deg to this beam are the 100x47 'joists' which I intend notching out to the 30mm shown. These will be glue fitted ... probably use Polyurethane, as it's foaming will also seal any gaps form water ingress.
y close tolerances, the glue is used exactly as the manufacturer recommends , and a high clamping force is used. That's pretty much what engineered tim ber does, but requires carefully controlled conditions to achieve it.
ded as considerably reducing its strength. The effects of a deep notch aren 't very predictable.
What span on the 100*47 timbers?
Notching them to a third of their depth will considerably weaken them.
Indeed - joist hangers etc are designed to "de-skill" constructional joinery. They give quick consistent results. Harry highlights some of the advantages - however you also highlight some of the limitations.
They are certainly less suited to older style properties where accommodating building movement was part of the design goal (unlike modern places, where eliminating movement is the aim)
Your typical joist hanger will terminate a trimmer at a joist, and provide slightly more loading capacity in the vertical direction than say a traditional tusked tenon, but at the expense of very little racking or twisting restraint, and no real pull out resistance. Nice for modern floors, but poor for wood framed buildings.
As for furniture, I can't begin to imagine what Harry's idea of a dining suit would look like with half a galvanized scrap yard nailed to every joint!
There are metal jonts for furniture too. Again cheaper and stronger. Unless you have antique furniture you probably have them in the house. You find them in kitchen and bedroom furniture, especially where the main component is particle board. Apart from being pretty, traditional joints have nothing to commend them.
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You can't cut away half or a third of a bit of wood to form a joint and not expect strength to be severely compromised, often at the very point where shear/bending forces are at maximum..
No one uses king/queen post trusses in rood construction now for this very reason.
It all arises from years ago when almost the only wood available was oak in most of the country.
Now you are just being silly. A cam and dowel joint is feeble compared to pretty much any traditional surface to surface corner joint. It does not enhance the glue area at all, and its strength is limited by the pull out resistance of a short section of screw thread. The cam alone removes a section of timber, and then concentrates the forces onto the remaining bits - but without the benefit of glued restraint. Joining chipboard tat together is about all they are good for.
That does not make sense in this circumstance. Sure take a notch out a single joist and you weaken it. However we are not talking about weakening one piece of timber in this case, but looking at ways of corner jointing two separate pieces. What you are proposing is a small step up from a straight butt joint. It will be ok in tension, and poor in bending.
The joints performance would be absolutely trounced by a finger joint, or a dovetail. A mitre lock joint cut with a router will be better. Even a simple glued rabbet joint.
Cam and dowel joints really only have a role in flat particle board furniture. Biscuits and pocket hole screws will work better in solid timber.
You are proposing cam and dowel for roof joinery now, or did you just change topic again?
Roof "joinery" these days is pretty much all prefab trusses held together with nail plates.
You can't realistically extrapolate data from building construction to furniture making, and back again and hope that one size will fit all.
My old copy of Part A (when it still had span tables), sets the limit to 2.02m for a 400mm joist spacing. That's for a building floor of course. So your 2.18m span doesn't sound out of order.
Oak is a timber pretty much unsuited to any purpose. It's only virtues were/are it was available, easy to cut/work when green and fairly rot proof. It looks pretty if cut radially and is quite hard when dry. Oak is a relatively weak and brittle wood. Ergo stuff made out of oak has to be grossly thick.
Having read the previously posted drivel, I can see no-one here knows how to make accurate cuts in timber. This is how Chippendale used to do it. You need a metal ruler, trysquare, sharp knife and a fine tooth saw, mallet, chisels, marking guage and dividers.
Mark your cut(s) using the trysquare with a knife. Total accuracy cn only be assured by using a metal rule and the dividers. The cut needs to be around 1mm deep. For a notch, mark the other side of the cut using the divders and metal rule. On the waste side of the wood cut in a "scarf up to the knife mark using the chisel. You end up with an assymetic V notch in the wood with one leg (the knife cut) at right angles to the face side. The bottom of the notch should be marked with the guage (which cuts into the wood.) The cuts are made with the fine tooth saw. If the grain is wavy, more then two cuts can be made. The saw is forced into the correct position by the cut and scarf. The cut also prevents wood fibres/splinters forming Cutting the wood away with the chisel should be done progressively from both sides leaving a "tump"in the middle which is removed last. Again the guage mark prevents splintering/ensures accuracy.
Using this method, accuracy of around 1/100" can be achieved (supposing your eyesight is good enough)
This is the correct way to make accurate halving joints tenons, bridle joints etc.
How Chippendale did it not "handymen".
It's not possible to make accurate cuts with your average power saw. And nowhere near the accurcacy this method gives with any power tool.
Which is why I'd take 15 mm from each. It would also mean that the smaller timber wouldn't need any additional fixing to stop it sliding sideways along the top of the larger. Niether bit would be able to move relative to the other.
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