The vacuum forming process for this former was done over the space of two days.
The vacuum bag was laid out on a clean floor, with a piece of chip board on top to rest between the former and the bag. A small hole was cut in the corner of the bag, about 10cm from the edge, with a piece of wadding leading from the hole (where the vacuum pump enters the bag) to the former, which will bring the vacuum to the former.
The bag was taped up on three sides with gaffer tape and then sealed again with the sealant tubes. The three layers of flexi-ply that was previously cut to size, will be applied in two applications. Two layers of the flexi-ply are laminated together in a sandwich and are taped along the edges with gaffer tape to reduce any movement that might occur within the vacuum process. Once the three sides had been sealed, secured and checked – the sandwiched layers of flexi-ply was slid in on top of the former and lined up along its edge.
The final side of the bag is then sealed and the vacuum turned on. The wood was pushed into the former in attempt to aid the vacuum in its forming process, while the bag began to suck the air from its contents. This part of the process is absolutely crucial to get right, the bag must be constantly checked, to make sure that there are no gaps in it’s seal, and to make sure that the bag doesn’t get sucked between the layers of flexi-ply, and between the flei-ply and the former, as this may cause the back to break. The vacuum takes quite a long time to take effect, and then the affects are almost instantaneous, the flexi-ply no longer needs to be held in place as the vacuum is pulling it in to the former. The vacuum was left on or approx another 5-6 hours, and then turned off. The bag was removed overnight to check how successful the forming process was, but the ply form was left on the former and pulled in on the edges with gaffer tape, as a precaution in case of any warping overnight.
The same process was repeated with the last layer of flexi ply, which was also coated in super strong glue before it was placed on top of the other two layers – which had minimal movement within the process, and had smoothed over and curved around where i had predicted it to. This layer is held, forced into the form already there, until the last side of the bag is sealed and the vacuum takes effect. The third, and final, layer is used to add great strength to the previous layers, and make the structure much more solid in nature, which will reduce any warping.
The vacuum was again left on for approx 4-5 hours, and checked constantly to ensure the process was going smoothly. However, with this application of the sheer force created by the vacuum, the former gave way. The face rib of the former was pushed in so much by the vacuum bag that the support spacers from behind the 16 mm hardwood ply was forced through the ply board, splintering, and was pushing vigorously against the taught vacuum bag. Before it could push through completely, and break the back, i broke the seal on the vacuum and turned off the pump, removing the bag from the top of the former.
Thankfully the bag and vacuum had already been on for over two hours – which is the minimum time necessary for the glue to set – therefore the form had already been sucked into shape. The form was already much more stable, and its rigidity had increased greatly with the addition of another layer. In preventative measures, i screwed into the layers of ply to the former – in case of any movement or spring back overnight – these screws would hold the ply layers together, so they could definitely set, and gaffer tape was used to pull in the sides, which hadn’t pulled completely flush with the form due to the undercut nature of the jig, and the form was left on the former overnight. Despite the early removal from the bag, the third layer had gone on with minimal movement for a former of such a large scale.