On the say 6' diameter, might be 1/2" or more. THese are not made to 
aircraft engine tolerances, more like a structural steel fabricating 
shop, and that screw is somewhat difficult to shape and weld together 
with any real precision. Usually there is no machining of the screw O.D.

On 7/22/2010 3:16 AM, Moreira, Luis A wrote:
> Hi,
> I always wandered about clearances, how close coupled do you guys think
> is the screw to the wall of the tube?
> As anyone found any design notes on designing and building one/
> Best Regards
>               Luis
>
> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of alan.b.pearce@stfc.ac.uk
> Sent: 08 July 2010 12:24
> To: piclist@mit.edu
> Subject: RE: [TECH]:: Archimedes Screw - wide range of modern uses
>
>    
>> Found this page while looking for something quite different (as often
>> happens)
>> Liable to be of at least passing interest to many.
>> Possibly even of unexpected practical use to some.
>>
>>
>> http://www.cs.drexel.edu/~crorres/Archimedes/Screw/Applications.html
>>      
> They are being used for power generation in the UK, a reverse use to
> what they are normally put to.
>
> e.g. http://www.westernrenew.co.uk/Archimedes%20screw%20turbines.html
> http://news.bbc.co.uk/1/hi/england/cornwall/7586285.stm
>
> Also referenced here under 'turbine types' ...
> http://en.wikipedia.org/wiki/Micro_hydro
>
>    
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