Thread: How far to span a slab?

Originally Posted by elanjacobs

Yes.

I think you're going waaaaay too far in on this one. Being from the States, you might not be familiar with Jarrah, but, aside from furniture and domestic joinery, it's used to build wharfs and bridges.

A slab of that section could comfortably handle several people jumping up and down on it. Heck, I wouldn't be surprised to see a car parked on top of it without it breaking.

It's going to be a f-in' bar, the biggest load it might see is a few people sitting on it. The cut doesn't matter, the grain doesn't matter; unless there's a giant hole or crack right across the slab, it makes literally ZERO difference for the intended purpose.

amen.

Out of respect for Spelux (it's their post thread after all)... I won't post again on this thread after these 3 query, unless Spelux asks a direct question of me, since it would appear my viewpoints comes from a much different professional perspective than many here...

I would respectfully ask of Ian, Fumbler, elanjacobs, homey, and Wongo these few questions of clarity from your perspectives, since I seem to have failed miserably at conveying my point of concerns or the negative results I have experienced over the decades with students that only consider "strength" when assessing a piece of wood...

1. It is acceptable practice to give emphatic advise of use application for a piece of wood in a furniture project without seeing that piece of wood first?

2. Strength alone is the only concern for the design and building of a project irregardless to other factors since the consensus is that "...cut doesn't matter, the grain doesn't matter..." at all only strength and the rest is pointless to discuss.....

3. A "Sagulator tool" is all that is really needed to understand a piece of woods use criteria within a project?

my perspective ...
in Australia timber bridges are decked using 50 mm hardwood, usually using an unspecified species.
so a 55 mm thick "slab" is over kill for a bar top which at worst will be loaded to some small fraction of the weight of a truck axle.

Spelux asked how far his 2900 mm long slab would span.
Sagulator is an appropriate tool -- applying uniform loading demonstrates that for any reasonable loading a Jarrah slab will not exhibit appreciable sag (60 kg per foot is way above a loading which might be considered reasonable for a bar.)

a bar top is not a structural element as might be found in a piece of furniture or a timber frame building so cut and grain direction are inconsequential.
the consequences of failure of a bar top are trivial if not less than trivial.
It would be different if the slab were proposed for a structural purpose.


the real risk with a bar top -- which has only been briefly touched upon up-thread -- is the strength of the legs and quality of the connection between the legs and the slab.
and this risk is independent of the span adopted for the slab.

The most likely failure mode for a bar is the failure of the legs -- either because they are too lightly constructed, or are insufficiently robust to withstand a knock, or the legs are not properly attached to the slab.
BUT that is a separate discussion to the distance between the legs -- which was Spelux's question

Originally Posted by White Cloud

I would respectfully ask of Ian, Fumbler, elanjacobs, homey, and Wongo these few questions of clarity from your perspectives

The answer to all 3 of your questions is "It depends".

If you're building something where the safety of others relies on you getting it right, go all out with stress grading, cut, grain direction, etc.
If you're building something that is, essentially, a functional piece of art, you don't need to be wasting time on details that don't matter.

I'd also like to note that "...cut doesn't matter, the grain doesn't matter..." was followed with for the intended purpose. If the intended purpose was to use the slab for something structural like a lintel or stair stringer, then I would certainly be in favour of making sure the piece in question was suitable.

I and in at the tail end of thread and it was getting to the point of over constructing a bar top. It's 50mm thick Jarrah, that in itself can withstand quite a lot of pressure and weight and Ian is right, it will be the leg structure that will fail with size thickness of timber.

i think the thread was hijacked by over engineering. I had a similar problem a few years ago where by I needed and engineering certificate to put up a caravan annex. The slab channel I can understand needing to be 400 x 400 as it was extending an existing barely 75mm thick slab and the 2 weren't able to be connected, however the engineer wanted me to secure 2mm thick x 50mm wide aluminium panel channel down with M10 x 120mm bolts, slight over kill, when the aluminium panels themselves for cyclone rating (if there is such a think for Ali lined polystyrene was being secured to the Chanel with 6mm Tech screws.

again I'm getting off track, it's 50mm Jarrah and aesthetics aside the only danger is it tipping over sideways.

i shall head back to the box making where dimensions really do make a difference.

Cheers guys.... I have been following the thread, but dont feel qualified to comment, definately reading and learning though! I ordered the steel the other day, should arrive today... will post some build pics....

We are glad that you have learnt something.

Originally Posted by Spelunx

Cheers guys.... I have been following the thread, but dont feel qualified to comment, definately reading and learning though! I ordered the steel the other day, should arrive today... will post some build pics....

Hi Spelunx,

It's your thread...feeling of qualification is moot, as you can ask or present anything you are thinking about or have question about...Feel free and feel encouraged to do so!!!

As to the viewpoints shared thus far, I will have to agree to disagree on some key points about what is critical in assessing wood for projects...

It matters little if it is a timber frames or furniture which I do both professionally and teach as well...I would also add (for additional validation) that my perspectives shared thus far about..."wood assessment"...are a given standard shared by countless professionals in art, craft and working industry of wood (of whom a few names I have already shared)...

So in closing, please do ask any question you think of, and do enjoy the process of building your bar...I'm sure it will be awesome...!!!

Regards,

j

Originally Posted by Spelunx

Cheers guys.... I have been following the thread, but dont feel qualified to comment, definately reading and learning though! I ordered the steel the other day, should arrive today... will post some build pics....

Of course you would be following, it's your thread, and 1 answer would have solved your problem weeks ago, so much so that if you hadn't waited til all the mechanical engineers had had their say, you'd probably have had a hundred beers on your new bar (hahahaha). That's why I love this forum, loads of input.

Good luck and can't wait to see the pics. I'm tipping your going to need a hand lifting that slab onto the frame. That's one big piece of timber.