Choosing a dust collector

      Matching your system to the required CFM. March 16, 2001

In my shop, I will have:
sliding table saw (1100 cfm)
standard table saw
router table
miter saw
sanding station
portable planer

For a while, no more than two of the machines will be in use at once. For dust collection, I think the larger Delta or Jet machine (5hp) will meet my needs. When I outgrow it, it will be easy to sell. But the "professional" machine brands with the same hp are much more expensive. What am I missing?

Forum Responses
Before looking at a dust collector, you must first determine your requirements.

1) The CFM you need the machine to pull, which would be divvied up between the amount of branches you have open at one time.
2) Resistance put on the collector as a result of your pipe runs, etc. Once you know the CFM and resistance, you can purchase the proper collector.

Example: you need 1,335 CFM at 8 resistance (also known as static pressure, measured in inches of water gauge). That means the dust collector would have to deliver 1,335 CFM after it overcomes the resistance level. This example would provide vacuum for 1, 5 dia and 1, 6 dia branch under simultaneous suction.

A guide for CFM is as follows (cfm at a velocity of 4,000 feet per minute):
4 dia = 350 cfm
5 dia = 550 cfm
6 dia = 785 cfm
7 dia = 1,100 cfm

Most dust collection companies will have performance ratings available on their collectors. If they don't have performance ratings, it is a guess as to how much air they will deliver at different levels of resistance. As far as CFM required to evacuate machinery, some manufacturers want a branch velocity higher than 4,000 feet per minute. This means the CFM will be higher. The only way to make air go faster than 4,000 fpm in a pipe is to pull more air, which increases resistance and usually requires more horse power. I have seen these requirements for power fed, high production machinery. The assumption is that they create more waste, much faster. This type of machine will have to be factored into the initial design and will inevitably mean more horsepower.

Pertaining to pricing, it's the old story--you get what you pay for. A two-stage collector is recommended for wood shop dust collection. In the line of two-stage collectors and single-stage collectors, just like automobiles, you have your Geo Metros, Oldsmobiles, and Cadillacs. Quality of construction, performance, engineering, safety, and longevity are criteria for dust collectors as well as other machinery.

Curt Corum, forum technical advisor

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