Monday, 15 June 2015

Vacuum forming machine

Between other jobs, over the last few weeks, I have been putting together a vacuum forming machine.

When looking at 3D printers I noticed that they cannot do proper transparent areas because they extrude in layers. The vacuum forming machine is to create windows.

I used one at college over 30 years ago, that one was made from a timber frame, some board and an industrial vacuum cleaner. I wanted something smaller so I knew it was fairly easy to make one from bits in my shed and the Internet confirmed that a normal home vacuum cleaner had enough power. All I needed was a box with holes in, some frames to hold the plastic and a heat source.

The design and photos show it all.  Instead of glue I used silicone sealant and screws to hold the joints of the box together. The better the seal the more the suction works where you want it.

By luck I had a 32mm cutter which is the exact size of the vacuum hose end.

In practice the vacuum pulls the hose end in to the hole to make a better seal so I did not need any gasket or other cover for the hose hole. There was plenty of suck to pull down the plastic. The grid of holes in the top of the box are all 4mm diameter in rows and columns 10mm apart and staggered.

I tried to use an old sandwich maker as the heat source but that didn't get hot enough so I resorted to the kitchen oven which I had already identified as suitable.  It was but I had to pay attention. Once the grill was hot it only took a minute for the plastic to droop and a few more seconds for it to run all over the oven shelf! I'll use a lower setting next time.

The grill in our oven only works when the door is closed so I had to remove the handles I had added to the frames to get the frame to fit. I had a very simple bent wire support from a disposable BBQ that was the ideal height to raise the frames, holding the plastic sheet, above the oven shelf.

By experimentation I established that the optimum time to take the plastic out of the oven was as the droop was about half an inch down. I must get round to cleaning the glass on the oven door to make it easier to see that stage.

My first experiments confirmed that the machine worked however my choice of mold was too ambitious. I could not get rid of the webbing on the tall section and the plastic, pulled in to the lowest thin slots, was too thin. That was disappointing but it confirmed in my mind that simpler, lower shapes would work.

Having the vacuum already on before putting the plastic on the mold worked best for me.

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