Originally Posted by
Kevin Cackler
I knew that 4" stuff sounded off. The Airhand.com guide says that if your machine has a 4" port, then the manufacturer has determined that a 4" branch will support the machine.
What it really means is that the machinery manufacturer has just done what they've done "forever" despite more attention to what's required to fully evacuate dust and chips from machines in recent years. The tools have 4" ports because they have always had 4" ports, in other words. It sounds like Air Handling's guide hasn't changed at all, either. Note, I'm not saying that a 4" port isn't appropriate for a specific machine; I'm only saying that it's not universal as it might appear to be since so many machines just happen to have 4" ports "just because". Consider that many folks have "kicked things up a notch" on table saws by up-sizing the port, having a hood around the blade and simultaneously support over-arm dust collection from that same larger hookup. The results are usually compelling.
I agree with Chris that feeding multiple machines at the same time requires you to insure that the drop supporting multiple machines is adequately sized to handle the air flow required for the number of open ports at one time. So if you have two 4" ports that share a drop, the drop, itself, must be sized to adequately support the air flow that will allow the presumable 400-500 CFM max that can flow through a 4" port times the number of ports. And, of course, the blower on the collector needs to be adequate for the task, too. A 6" drop servicing two 4" ports "likely" will work ok (without doing the math). Designing duct for a shop that has multiple simultaneous machines/workers is a lot more complicated than designing a duct work system for a one-person operation!
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The most expensive tool is the one you buy "cheaply" and often...