Fine Dust, Cyclones, and Filter Clogging

The right combination of cyclones and filters, good airflow, and diligent cleaning are part of keeping the dust collection system free from clogging. June 15, 2014

Question (WOODWEB Member) :
I am a one man cabinet shop with a 2hp cyclone. I have had good luck with cyclone until purchasing a 24" double drum sander. The fine particles produced with the sander seems to have clogged the filter media and now cyclone CFM are down, even after changing. I am told by my supplier that new filters are about $300 but I am concerned that even a new filter it will soon clog with the drum sander. My thoughts are to replace the filter with a large bag (similar to what is on Delta's cyclone), and resort to shaking bag once loaded to restore performance. I want 1micron for my basement workshop. My cyclone is a Grizzly 2hp.

Forum Responses
(Dust Collection and Safety Equipment Forum)
From contributor F:
I think your cyclone is not working as it should. The purpose of the cyclone is to remove most of the dust - even the fine dust before it hits the filters. Start by checking your system out and make sure there are no leaks. I don't know what the quality of the Grizzly cyclones is, but most of that dust would be separated in a good cyclone.

As far as filters go more area is always good. When I had new bags made for my cyclone the company figured 2-30" x 8' bags would do the trick so I ordered 3. I have never had a problem with losing suction even running the widebelt for hours. It's even more important to add filter area if you’re going to go to a finer filtration which will reduce airflow. If everything works correctly you will very rarely have to empty anything out of the filter bags.

From the original questioner:
The cyclone worked excellent for several years without losing suction, until I got the drum sander. That said, after some research I learned that the cyclone only separates fines properly if it has proper airflow. I have 6" lines which reduce to 4" at sander (sander has 2x4" ports). I had been running the sander with all other gates closed and probably should have left at least one 6" gate open to keep up airflow. As a result I believe the cyclone wasn't able to remove particles (low velocity in cyclone) and ruined pleated filter media.

What are your thoughts are with regards to having custom fabric bags made vs replacing $400 pleated filter? The bag on bottom of filter is now rock hard when collector is running, and if I take it off and run without exhaust restriction the dust collector performance is restored. Also, can I clean this filter or are only bags cleanable? I have not had it off and have only brushed it off from the inside and blown off from the outside. I don't really want to waste another pleated filter when a custom washable bag may be similar price and long term solution.

From contributor F:

I'm a bit skeptical that you could achieve enough CFM's with a 2hp import collector to efficiently extract from 2-4" and a 6" port all open at the same time. You could try it, but it seems like a lot to ask of that collector? I like the bags as they are easy to clean when necessary. Pleated filters are supposed to provide significantly more filter area though. My experience with them is limited. I only have one that's on a separate 2 hp collector that just runs my RAS. It seems to get clogged too easily, but that's a single stage collector so not a good comparison. With the bag(s) you can have them made to just about any size you want, so if you go that route get as big as you can fit. And you can be creative with shapes also if you’re dealing with low ceilings and such. Regardless of what filters you end up with you'll need to resolve the cyclones performance first. If it keeps blowing the fines into your filters it won't matter what type they are they're going to keep clogging up.

From Contributor H:
I just posted a question about a long standing dust collector run for just the problem you are having. I have a 5hp Oneida system and the fine powder like dust from the sanders goes through and clogs the filter. Even the Oneida tech told me up front that the finest dust would not be spun out by the cyclone action, even with max air flow created by leaving a gate open. As such I ended up taking our widebelt sander off the Oneida system and now want to do the same with our edge sander. You might consider getting an inexpensive dedicated collector for the sander like we did here.

From the original questioner:
To follow up, this morning I did a thorough inspection and cleaning of the cyclone's filter. I guess I have never really cleaned it very well in the past, only relied on an internal brush. I ended up shining a flashlight inside and turned off the shop lights and was able to see how badly it was clogged - many of the pleats were clogged completely. After a couple hours of tapping sides and blowing off 90% of the pleats they are clear - light shines through. I didn't realize how well compressed air works to clean them off. I could never tell without light illuminating the filter from inside. You can literally watch the dust fall off as you clean. The cyclone now works fairly well (I have moved my shop so can't compare to the original performance). I am now thinking of staying with pleated filters and just being more diligent cleaning them. After reading some discussions online I do also have concerns with how well a 12oz felt bag would clean air compared to a quality pleated filter.

From contributor F:
Now that you mention it I found the same thing when I moved my RAS from one side of the shop to the other. The paddles that are used to clean the filter only seem to clean the area they hit, which also drops the dust down and packs it into the bottom of the pleats. Some of the high end machines use compressed air to clean the filters. I don't see why it wouldn't work on these as well. I'd be careful about how much air pressure you use though. Not sure, but too much pressure might damage the filter.

From the original questioner:
Contributor F - what do you have for a RAS? I've picked up a 14" delta (3hp) a couple years ago for about $800. I had to replace the carriage bearings but it works very well and has stayed fairly accurate, even after several moves. Also, do you pick up dust from the blade guard or just have it plugged off? I use mine for sizing rails and styles, as well as the occasional fridge/pantry gable (love the 28-30" crosscut capabilities).

From contributor F:
I had a 14" DeWalt at my last shop but it was in need of work and I wasn't up to the task at the time. I ended up downsizing to a light weight Craftsman out of space requirements. Funny thing is I have about 12 plus years on it and it's doing fine. I have it mounted to the side of the lumber rack and it's mostly used to rough cut stock to length before milling, never really trusted them for accuracy. For accurate cuts I use either an Omga chopsaw, or the slider on my table saw.

For dust collection I have a 2 hp import collector that's been used for various tasks over the years. When I installed my cyclone I got rid of all my smaller collectors except this one, and it's only for the RAS now. I run a 6" duct from the collector to the back of the RAS (about 5' total length) where it's mounted to a rectangular box. I made an angled back on the box to deflect the dust into the duct. It works really well as there's so much air movement dedicated to it. I didn't even have to block the guard port as it's simply overpowered. The only downside is that when I moved my RAS to its current location, it left me short a dust collector for the chopsaws. One of these days I'll get another small unit for them. Just doesn't make sense to use the big collector for them.

From contributor J:
My impression is that pleated cartridge type filters are not well suited to fine sanding dust because of packing in the pleat corners. Needled felt bags or tubes are good at filtering fine dust and can be knocked clean when the fine powder cake builds up inside. A common formula is one square foot of filter media for each ten cfm of system capacity for general woodworking, and a higher ratio for fine sanding dust. A lower ratio results in higher velocity through the filters, and more blow-through of fines.

Cyclones are best at removing larger, heavier particles like planer shavings and sawdust to reduce the volume getting to the filters. One micron filtering is about as good as you will get without going to HEPA filters, but you have to have enough surface area to keep the velocity through the filters down in order to get to that level of filtration. As Contributor F said, overzealous cleaning with compressed air can break down the filter fabric, so keep the pressure low. In terms of system airflow, if you have two 4" ports on your sander, that is the equivalent of one 6" port. That's probably about all your 2hp blower is capable of anyway, so don't bother opening any more gates when the sander is running.