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I need to create a container which hold ~150 to 500 ml water. My plan is to create something like a inverse cone. I will apply pressure (~20psi) on the top of the cone and I want to create a hole at and only at the tip of the cone.

I plan to make the tip of the cone thinner, so that it will be easier to be break. However, I am new to plastic. Would anyone please give me some suggestion of material that I should use?

Thanks

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Are you actually trying to make something that will break under pressure, or are you just trying to make something that shape and thinking that pressure would be a good method? –  Aesin Dec 20 '12 at 22:02
    
From my experience with plastic (not much but some) it's not good idea to create a hole with applying pressure to it. I think it would be better to heat the tool which you would use or use curving drills such as applied to wood. –  java_xof Dec 25 '12 at 20:59
    
I think he wants to create an automatic drain. Plastics respond to stress concentration- change in direction worse than metals- the point of the cone would most likely to fail. Just the forming of a range of plastics would put a lot of stress on the point. Try high density polyethylene- its really all the design. How is this container going to be supported? –  user2617804 Dec 20 '13 at 15:12
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If you need good control, put a spring-loaded or cantilever-loaded valve at the tip. Rupture diaphragms typically have a needle point at the far end. The bubble deforms with pressure, contacting the point that then ruptures the diaphragm that is under tension. It is much easier to control and reproduce deformation than it is to engineer catastrophic failure at maximum deformation.

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