Tuesday, September 6, 2011

Lateral profiles of rocker table & Mega Clamp!

I've just uploaded another version of Board-Off that includes a new tab there the lateral profiles of the rocker table are generated. Previously the Rocker Jigs in Board-Off where for a rocker table design where the surface material is bent over a central and 2 side jigs that bend the right rocker and concave into the surface. The lateral jigs would be used perpendicular to these jigs to provide additional support to the surface to eliminate the chance of the surface being distorted.

Rocker Ribs plot

Why is this useful? A few different scenarios: i) You are trying to bend a core material that is stiffer than the surface material e.g a plywood core over a thinner ply surface or plexiglass/ perspex surface with just about anything. ii) If you are applying positive pressure to the surface of the board in addition to or in place of the vacuum. e.g. you a clamping the core onto the rocker table under a sheet of ply wood like when trying to clamp stiff core material or adding additional pressure to the surface to get greater than 1 atmosphere clamping pressure to squeeze out more excess resin; or (iii)Rather than deal wit #%@ing tackytape/table surface issues, you want to place the entire rocker table inside a bag and evacuate it. This would make the vacuum bag reusable and avoid the need to search endlessly for leaks every time you make a board.


Part of the motivation for drawing these up is an idea I have been thinking about for working at greater than 1 atmosphere without having access to a pressure vessel.

The idea is use a deep layer of sand over the top of the vacuum bag set up and then use a layer of thick plywood over the sand that can then be clamped down to achieve much higher pressures. The idea of the sand is to allow the pressure applied by the plywood cover to be distributed evenly over the surface of the board ( and so avoid dry spots).

Practically, the sand could be placed inside a large bag to make handling easier and to prevent sand flowing away (indeed removes the need to have a retaining barrier around the top of the table to keep the sand in.

This idea is a variation on the 'Quickstep' process for creating high performance composites for aerospace industry. Here, they use a plastics 'bladder' over the top of the part and fill it with hot water. This provides both the heat and the pressure they need to do away with the need for an Autoclave.

The questions I haven't yet found answers for is how much pressure will lead to dry spots in the reinforcement and what resin/fibre ratio might be able to be achieved.

.... to be continued.

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