Many thanks to those kind people who have already taken the time to
reply to my recent enquiry about the rotational speed for centrifugal
type fans.  I would like to explain that as I'm now retired from work
I'll be looking for a cost-effective solution, so the purchase of an
expensive purpose-built unit could be out of my reach.

I'm not sure if the unit that I have will take a speed of 3000 rpm
as it has no identifying marks indicating max rpm or manufacturer.
One suggestion I like is the use of a fan from a hover type electric
lawnmower (Flymow) and -- would you believe it -- I happen to have
one sitting unused and stored under the house.  (The wife prefers her
four-stroke petrol mower, the best present I think I ever bought her;
she won't let me use it!)

I will explore the possibility of making a casing of MCF or chipboard,
as suggested, and run the Flymow fan in that.  When it's built I'll let
you all know how it performs.

Best wishes to all

Michael J Taylor
Australia