>>>> That's because people who build the stairs works with that order
>>>> of tolerance (mm).
>>>
>>> So... what the hell do you do if you build some stairs, and the sement 
>>> sinks by 0.4 mm while drying? (A perfectly likely outcome.) Then each 
>>> step might be 0.4 mm out...! No noes! o_O
>>
>> Who secures stairs in place by resting them on unset concrete? :-S
>
> I was thinking more that the *stairs* are made of concrete...

Oh you mean like one big pre-fab set of stairs?  If they all shrunk 0.4mm 
after they were taken out of the mold then the usual idea is to make the 
mold 0.4mm bigger than needed...

Anyway, who's going to notice if the last step is 0.4mm less that the 
others?

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scott wrote:

> Anyway, who's going to notice if the last step is 0.4mm less that the 
> others?

...which was why I was amused at the stairs having dimensions to the 
nearest mm. ;-)

Seriously, if I take a tape measure to the finished building, do you 
really think all the measurements will be exactly whole numbers of 
millimeters? I somewhat doubt it. ;-)

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"Orchid XP v7" <voi### [at] devnull> wrote in message

> ...which was why I was amused at the stairs having dimensions to the
> nearest mm. ;-)
>
> Seriously, if I take a tape measure to the finished building, do you
> really think all the measurements will be exactly whole numbers of
> millimeters? I somewhat doubt it. ;-)

If you give builders plans to the nearest meters, you can none of the
dimensions will be accurate to the nearest meter either. Does it all make
sense now?

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>> Anyway, who's going to notice if the last step is 0.4mm less that the 
>> others?
>
> ...which was why I was amused at the stairs having dimensions to the 
> nearest mm. ;-)
>
> Seriously, if I take a tape measure to the finished building, do you 
> really think all the measurements will be exactly whole numbers of 
> millimeters? I somewhat doubt it. ;-)

No, but it's a typical value with some tolerance.  On our drawings we always 
have stuff that is labelled like 16.68 +/- 0.20 mm, if they made all the 
parts with an average of 16.66 mm then some of them wouldn't fit together 
properly.

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scott wrote:
>>> Anyway, who's going to notice if the last step is 0.4mm less that the 
>>> others?
>>
>> ...which was why I was amused at the stairs having dimensions to the 
>> nearest mm. ;-)
>>
>> Seriously, if I take a tape measure to the finished building, do you 
>> really think all the measurements will be exactly whole numbers of 
>> millimeters? I somewhat doubt it. ;-)
> 
> No, but it's a typical value with some tolerance.  On our drawings we 
> always have stuff that is labelled like 16.68 +/- 0.20 mm, if they made 
> all the parts with an average of 16.66 mm then some of them wouldn't fit 
> together properly.

As I understand it, the stuff you make is somewhat smaller than a 
building. ;-)

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>> No, but it's a typical value with some tolerance.  On our drawings we 
>> always have stuff that is labelled like 16.68 +/- 0.20 mm, if they made 
>> all the parts with an average of 16.66 mm then some of them wouldn't fit 
>> together properly.
>
> As I understand it, the stuff you make is somewhat smaller than a 
> building. ;-)

Exactly the same principles though.

Imagine you have a rise of 3050mm that you want to meet with 10 steps, and 
you can make each step with a tolerance of +/- 50 mm.

You might specify each step as 305 +/ 50 mm, which will give you a total 
height of 3050 +/- 50 mm.  Using your argument though, you would say the 305 
is pointless and you may as well just say 300.  That would make every 
staircase 5cm out on average!

In buildings I would imagine that lots of distances add up, and if you don't 
at least aim to make each one correct, then at some point something is not 
going to fit.

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> scott wrote:
>>>> That's because people who build the stairs works with that order
>>>> of tolerance (mm).
>>>
>>> So... what the hell do you do if you build some stairs, and the 
>>> sement sinks by 0.4 mm while drying? (A perfectly likely outcome.) 
>>> Then each step might be 0.4 mm out...! No noes! o_O
>>
>> Who secures stairs in place by resting them on unset concrete? :-S
> 
> I was thinking more that the *stairs* are made of concrete...

Concrete stairs are usually build in a workshop, poured into
a plywood form, upside-down (so the walking surface is at
the bottom of the form, giving a mostly perfect look and
dimensioning to the visible parts).

Fabien.

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Fa3ien wrote:

>> I was thinking more that the *stairs* are made of concrete...
> 
> Concrete stairs are usually build in a workshop, poured into
> a plywood form, upside-down (so the walking surface is at
> the bottom of the form, giving a mostly perfect look and
> dimensioning to the visible parts).

Really? I assumed they made them on-site. (And that that was the 
principle advantage of making stairs out of such an otherwise 
unattractive material when numerious better alternatives exist.)

Oh well, you learn something every day. ;-)

(Did you know, Boron is what makes silly putty so weird?)

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scott wrote:
> You might specify each step as 305 +/ 50 mm, which will give you a total 
> height of 3050 +/- 50 mm. 

Did you mean 305 +/- 5mm?

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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>> You might specify each step as 305 +/ 50 mm, which will give you a total 
>> height of 3050 +/- 50 mm.
>
> Did you mean 305 +/- 5mm?

Oops yes, actually no, thinking a little more about it the correct one would 
be 305 +/- 15.8.  (tolerances like this are normal distributions, not 
uniform...)

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