Meccano Expanding Ball
by Neil Carey  

For more images of the expanding ball see the 2003 Hawera Exhibition.  This model was the winner of the Webmaster's prize & 2nd place in the 15" cube competition  . - Webmaster

I constructed the expanding ball for the 2003 Hawera Convention. At the beginning of the New Year while sitting in the lounge pondering on what sort of Meccano model I could put together in time for the Easter Convention in Hawera, I glanced over to the grand kids toy box and spotted this plastic expanding ball, the type of thing found in the $2 shop. After examining the ball for a while I decided to give it a go at reproducing the ball in Meccano.

I thought if I first construct a 90 degree section of the ball and fine tune it to get any gremlins out of the expanding concertina linkages , then it would be just a matter of repeating the same construction to complete the ball. This I did, but must admit the repetitive construction got a bit tedious towards completion especially the lock-nutting.

My only disappointment with the model was that it didn't expand to the extent that the plastic toy does and I haven't had the time to suss out why.

On completion of the model I put the measuring tape across the ball in its condensed state and found it measured just under the 15" so decided to enter the model in the 15" cube competition with surprisingly some success.

Referring to the concertina circle segment diagram, four of these sections are bolted together to form a concertina circle, two of these circles are bolted vertically at right angles to intersect each other, the third circle is bolted horizontally to intersect the two vertical circles at their mid section.

Referring to the "tripod" leg diagram, three of these sections are attached to Angle Brackets bolted to P/N 77 Triangular Plates to form a "tripod". Eight of these tripods are constructed and positioned in the triangular spaces formed by the three intersecting concertina circles. The legs of the "tripods" are attached to the vacant Angle Brackets that are attached to the 1" square of Fishplates on the concertina circles  

For the record the model contains 192 Angle Brackets, 144 Fishplates and 384 lock-nutted Bolts.

Ed. - We have noted that in addition you will need the following parts:

Anyone with 12 No 10 Sets will have no bother, otherwise please check your stock of the above  parts before embarking on theis fascinating model.  

Why the ball will not fully expand.
by John Ince

The picture on the right is my assembly of one quarter of the expanding ball, built to help understand the intricacies of the mechanism. The completed ball will not fully expand because of dimensional problems caused by the limitations of the Meccano 1/2" hole spacing. The quarter segment will expand but in doing so the two axis do not maintain the 90º relationship with each other.

The easiest way to visualise the problem is to take one quarter circle section and lay it flat. Referring to the diagram on page 3, the horizontal concertina circle and the vertical concertina circle must intersect at right angles. That condition must be maintained in both the fully closed and the fully open state for the ball to function correctly. If you want to solve the problem you will probably need to get to work and drill extra holes in some of your Meccano Strips!

Photograph by Bruce Neilson; diagrams by Neil Carey with text added by John Ince

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