Q. I have read several articles on the pros and cons of using metal instead of PVC piping for dust collection systems. There are also articles stating that grounding and bonding PVC does little good in the effort to prevent static discharge. Can someone put this issue to rest by providing a definitive answer to the metal vs. PVC question? Is PVC piping safe with proper grounding and bonding or should it be avoided altogether?
A. Michael Dresdner: "The woodworking shop is inherently unsafe, but as safety levels go, plastic piping might be the least of your worries. That is not to say that metal is not a better choice - it is. Metal is also a more expensive choice.
"We could get into a long discussion about the relatively low odds of plastic pipe being able to generate a sufficiently strong static discharge to ignite a column of dusty, fast-moving air inside dust collector piping. It would go nowhere, except to prove that scientists, like most of us, fail to agree on much of anything. In short, you will continue to see all sides weigh in.
"You want my opinion? My own shop dust collection system is piped with 4" plastic sewer pipe, which, by the way, is ABS, a plastic both tougher and more flexible than PVC. That's the same plastic used in the old days for telephones, back when Western Electric made them to last fifty years no matter how often they were dropped. Ah, those were the days."
A. Rob Johnstone: "The last time I answered a similar question my tendency to wisecrack got me in a good bit of trouble. So this time around I will play it straight. It is my opinion that the concern over the danger of static electric charges building up in PVC exhaust ducting is significantly overblown. With that as a groundwork, I would never tell a person to go against their concerns • if the possibility of a discharge of electricity causes you to worry, go with metal ductwork."
Q. Table saw dust collection What is the best method of collecting dust from a table saw? I have a Craftsman. I could build a box below or incorporate a port on the blade guard. Which is more effective?
A. Michael Dresdner: "Most of the dust from the table saw goes below the blade, not above it, so a box would be my choice."
A. Ellis Walentine: "Neither is totally effective. Dust coming off the top of the blade can be extremely annoying and is typically finer in size, but by far the greater amount of dust is carried downward by the blade.
"For this reason, I'd build an enclosure with a dust port under the saw chassis first. Remember that if your saw is a contractor's type (with the motor cantilevered out the back), it can be tricky to close off the opening, so your dust collection may be less than wonderful, but it will be better than none at all. You can improve the performance of the dust collection if necessary by providing more CFM (cubic feet per minute) on that branch duct."
Q. I am in the market for a dust collection system. How do I know what is the right size for my needs? Do I try to size it for future growth? At present, I have a small shop with only four tools that need to be connected. I am planning on adding a couple of more. What do I look for ... volume, FMP? Is there some general publication for first timers?
A. Rob Johnstone: Dust collection is important and a bit complicated. The good news is that newer and more efficient dust collection units are coming on the market all the time. But each shop situation is a bit different. Do you want a single mobile unit that you can roll from tool to tool or are you considering a larger centralized unit? How long a run of ducting will you have from the collector to the various tools? The best thing I can do for you is to point you to a great book, "Woodshop Dust Control by Sandor Nagyszalanczy" - from Taunton Press. ISBN-156158-116-X. It is the best and most complete book on the subject that I know of.