I'd recommend reading Dust Collection Basics (from Woodstock Intl.). They are pretty clear about running bare wire all the way through a pvc system and making sure its grounded at both ends. They mention wrapping the pipe in bare wire as well, as a secondary measure. The book also says that wire reinforced plastic pipe has no grounding effect at all because its insulated by the pipe itself.
Anyway, if your'e planning to machine any plastics, I'd urge you to ground your pipe properly! A long time ago I worked in a place that had a vacuum take-up for polypropylene filiment coming out of an extruder. When there was no humidity in the air, I'd see first hand what happens to an ungrounded pipe. The build up discharged inside the pipe and sounded like a shotgun going off. I could see the arc through the wall of the pipe. The pipe was grounded at each end, but nothing going through it. I'm sure it would have made a difference.
I have also read in at least one woodworking magazine (publication's name escapes me just now) that most wood dust is immune to static build up because of the moisture content. Sounded like a lot of hogwash to me.
Be safe, hth
Doug  |