Dust Collector Filter Idea

Filters a filter after all, if you can shoot air through it should work

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With all due respect, I have to disagree.

First, filter efficiency is a measurement of the ability of the filter to trap particles of a given size, and depends on the pore size of the filter. As a rule, higher efficiency filters (able to trap very small particles) cost more than those with low efficiency (that trap large particles only).

The Home Depot filters have an "FPR 4" rating. FPR seems to be an in-house HD "standard" that cannot be compared with accepted ratings, such as MERV. FPR 4 is claimed to be "good", and can filter "large particles like household dust and lint, and dust mites..." The size of a dust mite is about 250 to 300 microns. Given that degree of filtration efficiency, the OP would be better sticking with the bag filter that comes with the HF DC.

Second, you need to consider the amount of filter surface area. The smaller the area, the greater the resistance to air flow out of the DC, and the lower the DC performance. You can probably design a box with 4 HD furnace filters, and not have too much resistance to air flow, but that's only because the pore size is so huge that it doesn't restrict flow to air (or small particles).

A 20"x20"x1" HD filter has about 3.9 square feet of filtration area. The Wynn filter has 274 sq ft of filtration area, so if you can find a furnace filter with the same efficiency as the Wynn, you'll need about 70 furnace filters to allow the same air flow.

The bottom line:
1) There's no easy or cheap home brew way of getting the efficiency- both in particle filtration and air flow- of a cartridge air filter.
2) Cheap ($2.58) HD furnace filters aren't worth anything as far as dust collection is concerned. They probably do more harm than good, since the they'll allow the DC to keep circulating small particles in the shop air.
3) That said, I do think there's a place for a decent furnace filter in the shop: as a pre-filter in an air cleaner to trap larger particles and extend the useful life of a more expensive final filter.

Just my .02

jdonhowe said:

With all due respect, I have to disagree.

First, filter efficiency is a measurement of the ability of the filter to trap particles of a given size, and depends on the pore size of the filter. As a rule, higher efficiency filters (able to trap very small particles) cost more than those with low efficiency (that trap large particles only).

The Home Depot filters have an "FPR 4" rating. FPR seems to be an in-house HD "standard" that cannot be compared with accepted ratings, such as MERV. FPR 4 is claimed to be "good", and can filter "large particles like household dust and lint, and dust mites..." The size of a dust mite is about 250 to 300 microns. Given that degree of filtration efficiency, the OP would be better sticking with the bag filter that comes with the HF DC.

Second, you need to consider the amount of filter surface area. The smaller the area, the greater the resistance to air flow out of the DC, and the lower the DC performance. You can probably design a box with 4 HD furnace filters, and not have too much resistance to air flow, but that's only because the pore size is so huge that it doesn't restrict flow to air (or small particles).

A 20"x20"x1" HD filter has about 3.9 square feet of filtration area. The Wynn filter has 274 sq ft of filtration area, so if you can find a furnace filter with the same efficiency as the Wynn, you'll need about 70 furnace filters to allow the same air flow.

The bottom line:
1) There's no easy or cheap home brew way of getting the efficiency- both in particle filtration and air flow- of a cartridge air filter.
2) Cheap ($2.58) HD furnace filters aren't worth anything as far as dust collection is concerned. They probably do more harm than good, since the they'll allow the DC to keep circulating small particles in the shop air.
3) That said, I do think there's a place for a decent furnace filter in the shop: as a pre-filter in an air cleaner to trap larger particles and extend the useful life of a more expensive final filter.

Just my .02

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No offense taken, and i hope you wont take offense with my disagreeing with your disagreement. I wont deny that a higher filter grade will work better than a low grade one, nor will i deny that a larger filter is a better choice than a smaller one, thats comparing apples to oranges.

Say you have 2 filters, x and y. Filter x is a car air filter lets say, rated to filter particles down to 5 microns. Filter y is also rated to 5 microns, but is meant for a HVAC unit. Both filters are going to filter particles equally well, and given that automotive filters generally have tighter pleats odds are both are nearly the same in filter area, the only difference is the intended application.

Sorry if i seem churlish, i just feel the need to explain my position. Id be willing to wager that if you set up a filter box with a a few good furnace filters (allergen or HEPA rated filters, not those crappy green filament things) and put it head to head with a wynn filter, youd get the same result.

EDIT: Just went and checked wynns site, and it looks like the smaller filters im guessing are meant for your standard, smaller hobbiest grade DC the filter area is rated at 100 square feet. A quick, very inaccurate calculation of a 20x25x4 furnace filter (((20*25*5)/12))*.6[that would be my estimate of how much of the volume of the cube is actual filtering area]), i get a filtering surface area of 100 square feet. Get one of those that are rated for allergen reduction and add a box, and boom, ghetto wynn filter

Sorry if i seem churlish, i just feel the need to explain my position. Id be willing to wager that if you set up a filter box with a a few good furnace filters (allergen or HEPA rated filters, not those crappy green filament things) and put it head to head with a wynn filter, youd get the same result.

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Not churlish at all- I think we're on the same wavelength. The example I used was the cheapo HD filter that another poster mentioned- I didn't intend to pin that on you! I agree completely that with comparable media- a good HEPA or high MERV furnace filter will trap the same particles as a Wynn-type filter.

I am a bit confused about your calculation for furnace filter area, though. I was looking at a picture of a MERV 12 20x25x4" filter (CF200A1016) on the Honeywell site, and count 14 to 15 pleats- they say that filter is actually 4.5 inches deep. Let's say with 15 pleats there are 30 surfaces (one up, one down), each 4.5 inches wide and 25 inches long. So, the total filtering area is 4.5x30x25=3375 sq. inches. 3375 Sq.in x 1 Sq.ft/144 Sq.in = 23.4 Sq.ft per filter, so you still need four filters to get close to 100 Sq.ft., if my math is correct. At $30-$40 each, you're getting into cartridge-type costs, so I'm not sure how much you save, esp. considering the furnace filters have to be replaced periodically. Please don't hesitate to correct me, particularly if my math is wrong.

I didn't know if there was really that much dust being exhausted by the HF DC when using a Thien baffle or Cyclone to warrant a Wynn filter.

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From what I have read, particularly on the Bill Pentz and Phil Thien web sites, neither a Thien separator nor a high powered (3+hp) DC with a Pentz type cyclone will remove all of the really fine particles. The Pentz design can apparently get down to 5 microns, but note that the "Pentz approved" Clearvue does have a final filter.

My take is the advantage of a pre-separator (Thien or cyclone) is that it captures most of the dust before it reaches the filter, so it puts less of a burden for filtering on the filter itself. This means it won't clog or cake as quickly, and it will allow good air flow for a longer time before needing cleaning (or replacement for a disposable filter). A second advantage is that a separator will also trap large debris (wood chunks, screws, etc.) that can get sucked up and possible damage the DC impeller.

For completeness, you could make an SEP system by eliminating the filter and venting directly outside. (Somebody Else's Problem, courtesy Douglas Adams) :shifty:

Just an observation,please correct me if this wrong?

HVAC filters generally aren't 'sposed to be cleaned....vs...spending monies on a Wynn cartridge filter which can be?

Which leads into,how effective and what damage is being done to a pleated filter when cleaning?And is this cleaning specific.....IOW's,if I'm a klutz and shoot 125# of shop air at the filter does that basically destroy it?

For the record all three of our DC's have cartridge filters.It scares me to clean them.....just have to be so careful.Am seriously considering building a baghouse style next,with appropriate "industrial" rated bag material,not the HF stuff.And yes we have a sewing machine capable of sewing leather,so DC bags ain't nuthin.The Singer machine was 75$,got it from the original owner,it's a 1957(too lazy to look at the model #).

Bag shakers,within a baghouse would be easypeasy build,just sayin from a complete laziness standpoint.The bennys are that the baghouse can be shaped/sized to wherever much more efficiently than the usual,round,cartridges.

diver165 said:

And couple that with the Thien or Cyclone mods, I can't see how they would clog up very fast to quite honest.

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You have a very interesting observation. Here is my experience with adding a Thien Top Hat to my DC. I created a Thien Top Hat in the spring of 2014. Here is my thread: http://www.woodworkingtalk.com/f32/pipe-diameter-vs-performance-59625/. (You can read the details, if you have some time. It is pretty long.)

After using the Top Hat for the last year, I have only had to clean my Jet DC-1100 canister twice after creating about 1800 gallons of saw dust (45 gallons per barrel X 40 barrel empties). The saw dust bag plus the amount of saw dust in the canister amounted to less than 2 gallons of saw dust that got past the Top Hat (roughly 0.1 percent of the total saw dust. Your "gallon-age" may vary depending on the dimensions of your Top Hat and the unique specifications of your dust collection hoses, pipes, impeller, motor, etc.)

I work with rough lumber that has to be jointed, planed, resawn and planed again. On those days, I sometimes empty my 45 gallon barrel four (4) times, and fill up three (3) 55 gallon garbage bags.

So, your observation is correct that with the correct pre-separator or cyclone, your dust collector shouldn't be putting many "fines" into your shop air. But there will still be some......

That is why I also have:
1. Dylos DC 1100 (http://www.dylosproducts.com/wocrandshair.html) that monitors the particle count in my shop

2. Two (2) Jet AFS-1000b units that filter out the particles in the shop air

3. And when the Dylos gets too high, I have a 2500 cfm 20" exhaust fan at one end of the shop with a 6' x 8' overhead door at the other end.

diver165 said:

To be honest. LOL I am actually a Respiratory Therapist and just a hobbyist wood worker.

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As a "Respiratory Therapist and just a hobbyist wood worker", you probably council patients on being overly cautious as being the better choice in the long run......

Woodworkers are very creative people. They can find more ways to save a buck than my grandmother, who lived through the Great Depression saving pennies....So, if you can built a cheaper solution that provides the same or better quality, then please do. Just make sure that you tell us about it, so that we can learn and benefit also.

By the way, have you heard the joke about the Respiratory Therapist and the woodworker? (I haven't either, I just thought that you might have one for us.)