Ok, that was the sort of clarification I required.  Thanks Dave.


David P Harris wrote:

> Yes, but he does this commercially in his Plexiglass shop while forming 
> full thickness plexiglass.  For people like us, much smaller tanks can 
> be used. David
> 
> Shawn Wilton wrote:
> 
>> 8x2.  You mean one of those massive propane tanks people in the 
>> country usually have?
>>
>>
>> David P Harris wrote:
>>
>>> Shawn-
>>> 28 mmHg  with a 8x2'  propane tank --- the initial rush is to make 
>>> sure a good seal happens. He said for smaller parts with polystyrene, 
>>> you can use a old barbeque propane tank with a new valve on it and 
>>> attached to a air compressor.
>>> No pictures, but essentially a flat square board with lots of holes, 
>>> a frame around it, and a chamber below attached to your vacuum.  Set 
>>> the plastic on top and then heat with a heat gun or hair dryer until 
>>> sagging, then let 'er rip.
>>> David
>>>
>>>
>>>
>>> Shawn Wilton wrote:
>>>
>>>> David, can you get some pictures from your buddy, perhaps a few more 
>>>> details.  What sort of vacuum are we looking at?  100's of PSI's, or 
>>>> what?
>>>>
>>>> -Shawn
>>>>
>>>> David P Harris wrote:
>>>>
>>>>> My friend does plexiglass forming.  Wooden frame, kitchen oven 
>>>>> element for heater.  Large air-tanks connected to a pump.  These 
>>>>> are pumped out, then a valve opens and the vacuum forming happens 
>>>>> very quickly. David
>>>>>
>>>>> Roland wrote:
>>>>>
>>>>>>> BTW, the hard parts of vacuum forming seem to be the matter of an 
>>>>>>> oven big
>>>>>>> enough for the work and creating a vacuum source (or is it sink?) 
>>>>>>> with
>>>>>>> enough volume to draw down the material before the material cools 
>>>>>>> out of the
>>>>>>> plastic condition...
>>>>>>>   
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Hi
>>>>>> I've watched vacuum forming done, and it was a very simple set-up. 
>>>>>> They
>>>>>> were forming polystyrene(not foam!)
>>>>>> The positive/pattern was simple wood fabrications, and there was 
>>>>>> no oven,
>>>>>> rather a big element and a few fans blowing the air down. I think the
>>>>>> vacuum part was just an industrial blower, as a sucker.
>>>>>>
>>>>>> The force required will depend on the temperature, depth of draw 
>>>>>> required,
>>>>>> thickness of sheet, resolution of pattern. Although a nice convoluted
>>>>>> surface can be obtained, the edges always pose a problem, same with
>>>>>> fibreglass moulds. Trimming them to an exact size, and polishing 
>>>>>> to hide
>>>>>> the work, is almost impossible.
>>>>>>
>>>>>>
>>>>>>  
>>>>>>
>>>>>>> A home vacuum cleaner arrangement is not really up to the task. 
>>>>>>> Besides, my
>>>>>>> earlier experiments with home vacuums lead me to believe a lot of 
>>>>>>> air FLOW
>>>>>>> is essential to avoid toasting the motors.
>>>>>>>   
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> maybe a powerful blower and a venturi will be better??
>>>>>>
>>>>>> Regards
>>>>>> Roland Jollivet
>>>>>>
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>>>>>>
>>>>>
>>>>>
>>>>>
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