On 26/05/2017 14:04, Bill Wright wrote:
On 26/05/2017 09:02, John Rumm wrote:

Is the gate question a trick? H has the brace the wrong way round.

Bill
tesnd to work either way.

No the force has to be compression on the brace.

It does not *have* to be.

No it's fine to do it the other way if you don't mind the gate pulling
apart when a child swings on it.

It won't necessarily anyway. You also seem to be ignoring the point that
when done the "proper" way it still places the top horizontal member in
tension - pulling on its M&T joint at either end. That will also fail if
over stressed and the joint is not either pined / draw bored or wedged /
foxed.




Granted that is the traditional way,

Because it works much better. There's a reason for most traditions.

but it
will also work in tension if its well fixed.

How would you do that? Very difficult to get the same strength as doing
it the correct way would.

Again it depends on the construction. If the diagonal brace is in the
same plane as the existing timbers[1], then its easier to get good
strength in compression. If however its planted on the face of the gate
(as was shown in the picture), then the performance is the same in
either orientation, however you can use a smaller timber if in tension
rather than compression (you don't need the timber to resist buckling),
so you could argue from an engineering PoV that is actually a more
efficient solution.

[1] e.g. like this one I made earlier:

http://wiki.diyfaq.org.uk/index.php/...and_brace_door


What is required to prevent
racking of the gate is a triangulated cross member. Having it in
compression works well since it can be notched into the other timbers
and will hence work and stay put even without much in the way of
fixings. In tension it relies more heavily on the fixings, but will
still work.

If it relies more heavily on the fixings it's not as good a design. If
extra stress can be avoided it should be.

As has been said though, in the context of the question, where all the
other alternatives simply had variations on right angle joints and no
brace, its the only clear correct answer.

It's the correct answer but it shows that the author has no idea about
basic joinery techniques.

Its a mechanics test, not carpentry ;-)




--
Cheers,

John.

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