Safety warnings, cautions and general questions
The Vacuum coupler system is designed for high volume low pressure usually from a shop vac or household vacuum cleaner system. This allows for loss of vacuum from the fit between work piece and rubber sealing plate and the various seals and fittings. In is actually important for the vacuum cleaner type system to have a by pass flow of air to keep the motor cool.
It is essential to provide an air bleed (a deliberate leak) in this type of system to prolong the life of the vacuum cleaner as the motor relies on the air flow to keep cool. If you have a perfect seal, you will burn the cleaner motor out The vacuum type pump produces a high vacuum, but has low capacity to extract air (so that the pump cant keep ahead of the in flow of air)
It is difficult to maintain a good seal between work piece and vacuum chuck face. The high volume of the vacuum cleaner means that the pressure against the faceplate will be maintained under turning conditions regardless of the movement or flexing of the work piece. With a low volume pump there is a danger of any loss of seal causing the vacuum to de-pressurerise and the work piece coming loose. The margin between successful holding and loss of work piece pressure is very finite. It is not recommended to use a vacuum pump , but if one is used the pump needs to be able to deliver good volume.
In general vacuum chucking needs to be treated with caution and turning should always be done at low speeds , a faceplate and other precautions are required. Only light cutting and sanding finishing should be attempted.
Vacuum chucking works successfully with larger diameter pieces as the diameter reduces the pressure differential holding force reduces , small pieces may not hold successfully.
Avoid too much pressure - higher vacuums can impose high forces and break or distort a work piece , monitor pressure with a gauge and regulate with some by pass.