Using air to Demould, and Hard Points

So, I think my tub is going to be an interesting thing to demould – basically more than 4m2 of cloth and it’s nearly all sloped edges. I’ve heard of people using air to demould and I have an air wedge, but that only gets in from the top. I’ve even optimistically bought a couple. The other way to do this is to build a function into the mould or part to inject air.

So, the way is to somehow get a thread into the part for an air-line connector to make a seal good enough to take some pressure. One needs something that gets through to the mould/part interface, without anything so ungainly as drilling and tapping a thread for said airline connector.

Ideally, one builds it in to the part.

The technique is to stick the face of a nut to the mould, and then build the layers of cloth around it. In order to stop the resin infiltrating the nut, one should take a bolt, coat the threads in wax and put that in the nut. If you just put the bolt in, there’s a strong chance infusion resin will get down the threadsl. Then, when you demould, you turn the bolt, crack the thread and you have a way to get the air in.

In order to get the air in, you need to take something that matches the thread, drill it out and then weld it to a air-line fitting. So, you can connect it to your airline and force air in. The other thing you can do, rather than do this, is just turn a bolt in to apply physical force to push the part off the mould.

OR, you can make one feature do two parts.

So, my plan is to weld the nut to a plate, cross drill the plate with a bunch of holes, and embedd the plate in the stack – like a hard-point. I will replace the core with the actual plate, so I am putting in a 5mm thick plate (ouch for weight).

I will then use this as a harness anchor point. So, rather than adding a couple or air-release points that are convenient for the mould, I’ll be adding four either side. Two below for the crotch straps, and one either side of the thighs for the leg straps. needless to say I need to be quite accurate for my positioning, and I’ll probably have to use 7/16 UNF rather than M10 to stay with the standard larger size anchor points (rather than have to do lots of explaining to scrutinisers that may not understand what I’ve done). The other smart bit of advice Vic gave me was to double up the cloth over the anchor point, which makes a lot of sense.

Conclusion: reuse is best. Anchor points can become release points. Viva El Presedente.


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