Dust Collection Systems

[Greg Needel]

Originally Posted by Don Rotolo

Greg, can you elaborate on this a little bit more? At home, I use my shop vac as a dust collector for my band saw and belt sander, moving the hose from tool to tool. I have found that some particles remain in the band saw housing, and the suction at the belt sander is so high that I have lost workpieces into the vacuum box. It's nothing like my Dad's shop, where he has a decent 'particle collector' (with filter bags in the several dozen micron range) but it's in a different section of the shop so we're not breathing it. That system (hard-plumbed, with automatic-switching blast gates) works pretty nicely.

Sure. From a systems standpoint the main difference is that in a dust collector all the particles go through the impeller while in a shop vac the motor/blower is separated by the filter from the debris tank. There are a few reasons these systems are designed differently and it significantly impacts the way the tool should be used.

CFM and in of water - You can easily compare them to speed and torque. CFM is the velocity of the air, and just like in a robotic system the higher the speed the less torque. For dust collection because all of the particles are small with essentially 0 mass they get caught in the airflow and sucked into a dust collector. The smallest Dust collectors are ~ 600CFM while the best industrial "shop vac" I have ever tested was 180CFM (it cost ~$3000). Inches of water is the vacuum pressure or the torque of the system, it does the heavy lifting. Most shop vacs are designed for general cleanup where they will be picking up piles of dust, wood chips, water, etc so the airflow does not need to be high. The highest static pressure I ever tested on a industrial vac was ~90inches of water which was really incredible for a portable unit. Dust collectors are in the 2-3 inches of water. The reason this is important has to do with the tasking of the different machines. If you are focused on sawdust specifically a shop vac will do a good job of picking up the piles after you are done working, but while the machine is generating dust it just does not have the airflow required to redirect the particles into the vac.

The other major difference between the two is safety. The main reason to have a dust collector (beyond keeping a clean shop) is keeping those tiny particles of wood (10microns or less)out of your lungs to avoid things like obstructive pulmonary disease (COPD) and increased risk of cancer. For this dust collectors are WAY better regardless of if you have a HEPA or other really good filter on your shop vac, as it all comes down to filter placement. Since the filter is after the impeller on dust collectors every particle which is in the air caught by the collector hits the filter. The same can be said for the particles in a shop vac in the stream, but unfortunately the motors in shop vacs are also cooled by air, which is sucked in from the side of the unit and expelled again without passing through a filter. This can basically hyper accelerate the sawdust into the air making it a bad situation not just around the machine but anywhere else with open airflow to your workshop.

Additionally it is important to note that the amount of filter material in the system impacts performance over time because people forget to change/clean their filters. I am guessing but I would say that the average shop vac filter has 20times less the filter capacity than a dust collector which means longer running in between filter blinding. While you can get good filters for shop vacs the average one will be much lower in quality and rating (allows larger particles through) than a dust collector filter bag.

Like I said in my earlier post I could go on talking about this topic for quite a while but those are the major differences. As always your mileage may vary based on each situation you are in, but I hope this helps. I am an advocate of using the correct tool for the job and while you can get a 4"inch adapter to connect your table saw to a shop vac you will probably be better with no dust collection and picking up the piles later.


Greg