Clean bench help.
 

Laminar flow clean bench.

I'm planning to build something like this. I've got some HEPA filters and aluminium tubing and plastic plug in corners for the frame.
I just have to settle on the size and whether to use plastic or glass for the sides. (solid rear rather than glass)
I was thinking of using a small toilet or bathroom extraction fan to drive the air through the filters and enclosure. (with a variable speed controller)
Mine will also have sealed fold up doors on the front to keep it clean between uses.

I would appreciate any incite on thing to consider or include.

Should I push the filtered air down from the top or from the rear? What's better?

I'm hoping the nuke guys will chime in. ;)

Also... Is it worth getting a small air speed meter for testing??? ($20 on EvilBay)

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Off the top of my head, I don't think a bathroom fan will push very much air through HEPA filters. Any specs of the filters themselves? Most use a manometer to measure pressure drop to indicate when it is time to change the filter media. How "clean" do you want? What are you putting together, a Rolex watch or a carburator?

how important is laminar flow & how laminar?

what speeds? what is your background in this stuff?

What in the world are you working on there? Hard drive repair at home?

I need a paint booth like that!

A clean bench is a sign of a sick mind. Oh wait, what?

HEPA's require decent fans with higher static pressure than what a bathroom fan will probably provide. Depending on how "clean" you want, you may need to perforate the bench deck for adequate flow-thru to avoid particle collection in the stagnation areas near the rear of the bench. I would look for some fan-filter units (FFU's) that integrate a fan and HEPA together in a common case, and then hang a couple on a frame above your workbench. Vertical down-draft hoods generally keeps things cleaner.

Easier to use large particle filters and vent to the outside.