Brain cells needed - 1955 test

[NY]

No, all it is saying is that the one with the diagonal bar is much better than any of the other ones in the question, not that it is the *best* solution. Providing the cross-bar is securely fastened (eg screws or bolts) to the vertical and/or horizontal bars, it will resist the tendency for the rectangle to bend out of shape into a parallelogram. But it places a lot more reliance on the fixings that if the cross-bar was in compression rather than tension.

Ideally the question should have shown a couple of rectangular gates, plus one with a compression bar and one with a tension bar. That would have tested people's knowledge even better.

[Nick]

You are preaching to the converted. I loved my Meccano. I would do anything for more, I longed for the motor with gears etc.

I bought my son kits that went unopened. He just wasn't interested.

[Graham Nye]

In school? I learnt this sort of stuff in my own time, playing with Meccano.

[John Rumm]

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.

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:

Its a mechanics test, not carpentry ;-)

[John Rumm]

[spuorgelgoog]

Isn't mechanics just theoretical carpentry though?

With harder sums but less likely to lose a finger.

Owain

[Bill Wright]

But why present an answer that relies on an incorrect depiction when it could be a correct one? The only possible reason is that the author must have no idea about how to make a gate and never bothered to ask a joiner. That's very sloppy.

Since the thing is supposed to be about engineering principles and not the behaviour of wood the correct answer will be the gate that used the brace to form a triangle for strength, and nothing to do with the wood warping. On that basis the gate as shown is just plain wrong.

It doesn't mention that the gate is made of wood, so the 'wood' argument clearly wrong.

Bill

[Bill Wright]

In which the braces are the correct way!

Bill

[Dave Liquorice]

interested.

Yep, Lego NXT here. What could be better these days, building things, with servo motors, sensors, all easyly programable. A few of the things in the book where built but no playing as in "what can I make this stuff do".

Yet the same lad has "built" an 8 bit adder with input/output registers in Minecraft from scratch. Started by looking up circuits for adders and went from there, I think he still works on building a

8 bit microprocessor from time to time. Builds all manner of space ships in Kerbal Space Program, so the imgination and "what if" is there. I guess the reward feedback loop is much shorter, want to change something? click, click, drag, click, test. Rather than 15 minutes or longer deconstructing and reconstructing...

[Bill Wright]

Contradiction is not an argument.

Bill

[Bill Wright]

A properly made gate or door doesn't need to stress the joints (which are much weaker than the timber members) because the brace pushes up against the cross members.

If you rely on pins the first bit of rot and the thing falls apart.

Bill

[Graham.]

I hadn't noticed that. Still, it's a strange implementation of "crossing out"

[The Natural Philosopher]

Nowt wrong in that.

When I were a lad it was meccano and model planes. Then it was soldering transistors together which became my first career. Programming mainframes == too bloody slow

Then micros arrived with screens and keyboards and computing was now minutes, not days.

And computers cost hundreds, not millions

Today you wouldn't make something out of meccano. You would solid model it and get it 3D printed. Or laser cut.

[The Natural Philosopher]

Dont be silly

[The Natural Philosopher]

No structural truss exists without some members being in tension

In the case of 'your' gate design its the top horizontal member.Ergo the joint to the upright at the hinge post will fail instead

[spuorgelgoog]

It was the deconstructing part that put me off meccano.

Owain

[Roger Hayter]

snip

33 He is doing the same amount of work (force X distance moved) wherever on the capstan he pushes. If they meant force they should have said so.

[Roger Hayter]

But too near the end of the strut to last long in tension without splitting the wood. Agree with you re the answer.

[Roger Hayter]

I've made an internal ledged and braced door and then changed my mind about the hinge side at a late stage. It is so over-engineered I am not worried about the danger of it failing, just the embarassment of anyone seeing it and knowing I made it!

[John Rumm]

I made a picket gate once (on saloon hinges, to keep the dog out of the kitchen!) Since the brace was planted onto the face of the pickets rather than built into the plane of the other timbers it made no difference which way it went. I was content to let SWMBO choose after construction and needless to say it ended up in tension.