Structure, v1

For a first PVC structure test, we stuck to a pretty straightforward rectilinear frame.  Using two sets of box-frame “legs” that extend beyond the table surface vertically, we can support 1 polycarbonate panel (plus two additional ends of panels, on either side).  See below for diagram.

Cutting the PVC to desired lengths is quick and easy, but there is some strength needed to push the joints firmly together.   Though generally stable once erected, its not that easy to set up the structure with only one or two people.  The legs have to be set up at the right distance, and then the table top is lowered onto the frame.  If the distance is right, it works the first time.  If not, you have to do a little bit of nudging on both sides to get the right span.  This could be solved with a pre-measured rope-tool included in the kit, helping you to place where the legs should be.

The great thing about this simple modular structure is that it is endlessly repeatable – the further you want the table to span, the more legs you construct.

preliminary structural test #1

Next, we tried something a bit different – a unified structure that uses triangulation and cross-bracing to make a more stable table.  This actually works really well in terms of lateral stability, and ease of placing the table top.  Also, it is nice to not have verticals that come past the table plane.

On the downside, the structure is lacking in tension strength pulling the end legs in towards the center.  We might need to add some cross-tensioning cables along the bottom.  Also, this type of design is much more complicated to prepare and join the PVC.  It is also not as flexible in terms of table size.

preliminary structural test #2

For the Maker Faire, we constructed a variation on the rectilinear structure.  Adding an additional short cross-piece on all of the lower legs helped to stabilize the table supports.  We also converted the bottom of the legs (where they come to the ground) to elbow joints, rather than pipe ends.

structure diagram for prototype alpha, shown at Maker Faire

As a final note, one thing we learned from erecting the Super Table on a dusty site – PVC joints do not like extraneous material.  It was fairly easy to push joints together in sheltered environments, but once it got dusty, the joints would not come together in the way that we wanted.  This contributed (as well as an uneven ground surface) to a relatively wobbly structure.  We later found sand bags to weight down the legs, which helped quite a bit.  It would be great to improve the structure such that it can adapt to many different kinds of ground surfaces with minimal problems.

 

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