ALMIRA OBSERVATORY
 

     A suburban observatory in Worcestershire, UK based on a metal garden shed

           
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  Construction 3 - Building the Pier

 

  The pier is made of a 1.5 metre (5 foot) length of 250mm (10 inch) diameter polythene pipe embedded in, and filled with, reinforced concrete.  The wedge for the LX200 telescope is mounted on two adaptor plates which are secured to the pier with four lengths of M12 stainless steel stud embedded in the top of the pier
  It took two hours of hard work to dig the 700mm x 700mm square by 800mm deep hole for the pier. That's over ½ tonne of soil.  The next day my whole body ached!  At 47 years old I'm just not used to this kind of hard physical work anymore.  Below are before and after pictures of the hole (riveting eh!)

 

 

 

My wife and I mixed about ¾ tonne of concrete (with a cement mixer).  Measurements carried out at the start of the build (see 'Starting Work') showed that the pier needed to protrude 1406mm above the ground.

     
  First to go in was a frame of six lengths of rebar held in  place by a lump of concrete. The rebar was placed in a bucket full on concrete and allowed to set for a couple of days. This was taken out of the bucket than dropped in the bottom of the hole.

 

The pipe had already been mounted on a temporary wooden frame and this was then carefully lowered over the rebar and levelled.
 

After bracing the pipe, the concrete was poured.  Reinforcing  bar (rebar) was pushed into the concrete between pours to strengthen the structure even more (probably a bit of overkill).  The bracing was held in place    by screwing it into the plastic pipe. The base was then finished off.  I left the concrete to go off for a few hours before finishing off filling the pier, so that the concrete didn't drain out of the bottom of the pier!

 

 

     

The pier adaptor plate is made from two 19mm thick aluminium plates bolted together. The lower plate was attached to the pier via four stainless steel M12 studs embedding it in the cement in the pier.  After bending the ends of the studs to prevent rotation, the studs (attached to the lower adaptor plate) were pushed into wet cement at the top of the pier and levelled and aligned north.  The plate had to be wedged up a little to prevent it sinking completely into the wet concrete of the pier.  These wedges were removed once the concrete had set.  The operation of the adaptor plates is described  later.

 

 

     
 

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Last updated -  27th April 2013

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