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small or medium size vacformer basic questions

 
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graham_mca



Joined: 11 Dec 2008
Posts: 1
Location: Wisconsin

PostPosted: Fri Dec 12, 2008 4:03 pm    Post subject: small or medium size vacformer basic questions Reply with quote

My first post so I have some basic questions to ask about a vac former I have in mind. My appologies if these topics have been covered but I didn't find all the answers while searching so far.

I want to form a small boat hull. Length will be about 13" with a width of less than 6" and a depth of pull of about 4" maximum. My first question is how much space beyond that shape is required on the plastic frame. In other words what would be the size of openning in the frame and therefore plastic sheet to pull such a shape. Material wise I am thinking of either a thin styrene or possibly one of the clear plastics. I am learning about the various options as quickly as I can.

Making a smooth shape that size would I need to raise the platen to the heat on an over/under style machine do you think. I may consider a sliding heater if I can afford the space. Vacuum will be via a shopvac, single hole platen with no air space below.

Thank you in advance for your comments.
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cod
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Joined: 05 Nov 2006
Posts: 322
Location: San Francisco

PostPosted: Fri Dec 12, 2008 4:27 pm    Post subject: Reply with quote

I think the rule is add as much as your depth, so 17" x 10" seems about right?

this is an odd size for a frame though, so if you are going to do a lot of plastic buying you might consider a size that is divisible by a sheet size that is available to you- i.e. if you can only buy 48x48 sheets you would want to minimize waste and maximize forming area- so your sheet size would be a multiple of 48(something like 12x24) or for even better economics try to fit it into a 12x16 sheet, at an angle. This assumes you are planning on making a bunch of boats, of course. If this is a one shot project and you arent planning on doing other vacuforming then just add about 4" to the size should be adequate


I think building a frame size that is a divisor of 48 is probably a good idea.
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spektr
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Joined: 07 Jan 2008
Posts: 425

PostPosted: Sat Dec 13, 2008 8:40 am    Post subject: Thoughts on sheet size. Reply with quote

The answer to your question has a lot to do with thinning of the part. If you wish to have consistant part thickness, you need more edge margin on the sheet. The way vac works is that you seal the sheet against the edge of the mold base/platen and then stretch the sheet as it sucks down against the tool surface. The part will always be thinner than the starting stock thickness........... If you want to figure thinning, a fast way that is close is to think of the straight line distance from the high spot on the tool to where the plastic seals. Multiply this distance by the material thickness to get an AREA. Then divide this area by the distance along the mold surface in the sucked down position to get the after molding distance. This will give you the approx after mold thickness of the part. This isnt a perfect method because there are non-linear things going on like sheet drag, stiction, sheet cooling and vacuum drop over time, but it gets you thinking....... Oh Yeah, make sure you put a layer of silicone seal on the sheet sealng area and get it smooth before it sets up. This lets it seal without hurting the platen/mold face and allows you to use Black Magic Tire Wet as a mold lube to help limit thinning bu letting the sheet slide well as it is pulled.......... Hope this helps. Scott.
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