On Wed, 9 Jan 2013 00:09:49 -0500, you wrote:
>Is PVC sheet sold at Lowes, Walmart or similar type of store?
>
I used Vinyl from a craft store (jo-ann fabrics) which has heavier
fabrics for upholstery. Very inexpensive. Similar stores ought to
have it, so yes, Walmart ∗may∗ have it.
Vinyl can be melted and heat sealed with an old soldering iron, you'll
need some practice to do it. However, if you build a vacuum frame
(easy to do with lumber, you only need cross cuts and a drill), you
only need a single layer.
Harvey
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>Jeff
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> _____
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>From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
>On Behalf Of Robin Whittle
>Sent: Tuesday, January 08, 2013 11:48 PM
>To: Homebrew_PCBs@yahoogroups.com
>Cc: Harvey White
>Subject: [Homebrew_PCBs] Vacuum-seal bags, DIY PVC bag vacuum "frames" &
>500W halogen light sources
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>A video http://www.youtube.com/watch?v=8WJn5YFANxU demonstrates exposing
>the Riston-like Puretch negative photoresist film:
>
>http://www.capefearpress.com/puretchpcb.html
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>using a vacuum bag for sealing clothes or food. This has a zip lock and
>a valve for removing the air with a vacuum cleaner and retaining the
>vacuum after the vacuum cleaner hose is removed.
>
>Exposure is via a 500 watt halogen incandescent lamp from a hardware
>store. I use a lamp such as this at a closer distance, with the lamp
>pointing downwards (without its glass cover, to improve airflow cleaning
>of the lamp). I use the glass cover to press the phototool onto the
>PCB, which is supported by foam. However, it would be better to use
>vacuum and a flexible top cover in place of the inflexible glass, since
>the flexible cover and air pressure would press the phototool right up
>to the PCB, even if the PCB was not flat, with less effects due to dust
>between the phototool and the PCB, and with little or no problems due to
>dust between the phototool and the flexible cover.
>
>This vacuum-sealed bag approach looks inexpensive and effective.
>However, I think it is important to blow air on the PCB so it doesn't
>heat up too much. Temperature changes could cause the phototool to
>expand at a different rate to the PCB, leading to loss of resolution.
>
>As Harvey White wrote ("UV nail lamps - . . .":
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>http://tech.groups.yahoo.com/group/Homebrew_PCBs/message/31264
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>it would also be possible to make a custom-size bag using PVC sheet from
>a furniture store. Vacuum could come via a small tube inserted into one
>corner of the bag, with the other end connected to a vacuum cleaner or a
>pump from a desolderer. There's no need for a valve - just run the
>vacuum cleaner while the exposure is taking place.
>
>Since the ~0.5mm PVC is cheap and the bags can be made easily with
>scissors and adhesive tape etc. in sizes which are most suitable for PCB
>work, I think this may be a good alternative to a vacuum frame with a
>flexible top and a solid or foam-and-solid base or to any vacuum frame
>with a rigid (glass or acrylic) top.
>
>The PVC would be less likely to wrinkle or become scratched during use
>than the polyethylene of the vacuum-seal bags. The PVC is so cheap that
>if it does become scratched, then it will be easy and inexpensive to
>make another bag.
>
>I will write to the list when I try this - which could be a few months
>or more.
>
>- Robin http://www.firstpr.com.au/pcb-diy/
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