Another 4" model (30-gallon can)

[phil (admin)]

Some time ago I purchased one of those little Harbor Freight mini portable dust collectors.  I got a helluva deal on it ($70 after stacking some discounts).  It is this one:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94029

It sat unused for a while because I was pretty happy with my Ridgid vac-based cyclone.

HF claims 914-CFM and 9.4" of SP.  We know that the CFM is nonsense, though.  It has a single 4" inlet.  According to BP a 4" pipe can carry about 400-CFM.  My somewhat scientific testing (using two different anemometers) seems to indicate that this unit pulls about 370-CFM.

This unit is only twenty pounds but achieves some pretty impressive specs by using a universal motor spinning a small airfoil type impeller at 6400-RPM (typical DC's use radial impellers spinning at half that speed).

So I decided I'd build a larger cyclone separator and start using it.  I started w/ a 30-gallon can and an MDF top.  Added 4" fittings and my baffle and did some additional testing.  I was happy to discover that adding the cyclone lid only causes an 18% hit to my CFM.  That is pretty spectacular by cyclone standards.

I also had a chance to try connecting the entire assembly to my router table's downdraft box.  I had to do this with a 2.25" reducer to a 2.25" hose, so NOT optimum.  I was stunned to discover that airflow through the tiny (1.5"?) aperture in my router lift was sucking plenty of air.  I had always imagined that real dust collectors would have difficulty moving air through such small holes, but this clearly isn't so, plenty of SP here.

I did limited testing with actual dust because I only have the stock (30-micron) bag filter for the DC at this time.  It was able to separate 98.7% (by weight) of the dust I fed it (mostly fines from machining MDF and hardboard).  It was perhaps a little better but I did have difficulty gathering all the dust from the garbage can when I was done with the test.

I had previously posted that the DC is noisy.  It still is.  Part of that is the noise form the air movement, but certainly part of it is the universal motor, too.  Still impressed with what a $70 machine can do, though.  While this still doesn't provide the 600-800 CFM that some say is needed for fines collection, it is providing over twice the CFM of my current solution and is still compact enough to use, so it will become my new DC until I can make my giant separator lid with 6" outlet and twin 4" inlets, and run 6" PVC to my tools (yeah, right).

[windmill]

I'm impressed a DC that small actually pulls enough air to work, especially with a trash can separator. I wonder - would it be possible to hook two of them up in parallel? I.e. have two outlets on the trash can? That way, you could run a larger pipe for the intake without losing too much velocity.

It may not be that difficult to change the design. A 6" outlet that splits into two 4" branches ought to do it.

Bas.

[phil (admin)]

I'm impressed a DC that small actually pulls enough air to work, especially with a trash can separator. I wonder - would it be possible to hook two of them up in parallel? I.e. have two outlets on the trash can? That way, you could run a larger pipe for the intake without losing too much velocity.

It may not be that difficult to change the design. A 6" outlet that splits into two 4" branches ought to do it.

Bas.

I guess it is the design of the impeller for one.  It is an airfoil, which is more efficient than a radial vaned impeller.  Also, it is spinning twice as fast.

And I suppose you could run two of them in tandem.  If I did this I'd be inclined to not only increase the outlet size, but add another input, too.  There would be some (minimal) loss from the splits, and it might be kinda loud.

[LittleRob]

I couple questions. I'm new but have looked thru each thread/topic. This forum is great!!!! I was considering that mini DC from HF. Was wondering how it performed by itself, than see you guys spiced it up a bit making it better i'm guessing. Now here is my question before i start building. The 30g can has ridges on it. so does the baffle inside actually seal with the can(with arrow in pic) or does it not matter. Also while its running for example like on pic 3 do you still attach the filter bag on it? And does this setup work better with a shop vac or the mini dc? If the S Vac what size would you recommend?

[phil (admin)]

I couple questions. I'm new but have looked thru each thread/topic. This forum is great!!!! I was considering that mini DC from HF. Was wondering how it performed by itself, than see you guys spiced it up a bit making it better i'm guessing. Now here is my question before i start building. The 30g can has ridges on it. so does the baffle inside actually seal with the can(with arrow in pic) or does it not matter. Also while its running for example like on pic 3 do you still attach the filter bag on it? And does this setup work better with a shop vac or the mini dc? If the S Vac what size would you recommend?

(1) Don't worry about the ridges, they aren't large enough to cause problems.  (2) Some final filter (like a bag) is required, or you need to exhaust outside.  (3) This unit moves a lot of air.  It is a great compromise between a shop vac and a DC.  The caveat is:  It is LOUD.

[LittleRob]

Sweet, ear plugs is a must in a woodshop or garage anyways so loud is okay while the saw or what ever is being used, these dowels in the picture they are about 5inches? and is there a rule of thumb as far as dowel length & the PVC size? If i did use the shop vac i could use it for more stuff thou vs the HF one purpose, what size vac for the 30g can do you recmd to get the most outta both? Thanks for the quik reply by the way :)

[servant74]

http://www.wynnenv.com/cartridge_filters.htm

You might consider these folks filters for fines.  It is the ones
Clear Vue uses (the clear plastic design of Bill Pentz collectors).

[LittleRob]

Actually came across those before i found this forum. Great filters. Pricey but worth it.  The reason i ask which would be more worth it is, i would like a shop vac to be able to vacuum the cars. And with the Mini costing $99, that almost the price of a good vac i would think. Either way im building this lid, just wanna get the most bang for my buck. but if i need a real expensive vac to make this work correctly effeciently i get the hf mini with a coupon or find one used ... :) :)

[TomH in WI]

Hi Phil,
Hate to get sidetracked here, but could you show some pictures of your table saw. I was wondering how you mounted the extension and router onto the BT saw rail.
Thanks,
Tom

[rhossack]

It is a great compromise between a shop vac and a DC.  The caveat is:  It is LOUD.

Phil ... when you say loud like it would wake the neighbors?  My rigid shop vac is pretty loud and I put a muffler on it.

[phil (admin)]

It is a great compromise between a shop vac and a DC.  The caveat is:  It is LOUD.

Phil ... when you say loud like it would wake the neighbors?  My rigid shop vac is pretty loud and I put a muffler on it.

I'd say it is about as loud as the loudest shop vac I've heard.

[Adam]

HF claims 914-CFM and 9.4" of SP.  We know that the CFM is nonsense, though.  It has a single 4" inlet.  According to BP a 4" pipe can carry about 400-CFM.  My somewhat scientific testing (using two different anemometers) seems to indicate that this unit pulls about 370-CFM.

What it's only pulling 370 CFM.  I thought it felt rather weak and was suspect of the 900 number.  So why so you think there is such a large differance.  That not even in the ball park of 900CFM.  Are there any units that actuall pull what they say or are close? 

[phil (admin)]

Are there any units that actuall pull what they say or are close? 

I don't think so.

[dbhost]

HF claims 914-CFM and 9.4" of SP.  We know that the CFM is nonsense, though.  It has a single 4" inlet.  According to BP a 4" pipe can carry about 400-CFM.  My somewhat scientific testing (using two different anemometers) seems to indicate that this unit pulls about 370-CFM.

What it's only pulling 370 CFM.  I thought it felt rather weak and was suspect of the 900 number.  So why so you think there is such a large differance.  That not even in the ball park of 900CFM.  Are there any units that actuall pull what they say or are close? 

The ratings are done, pretty dishonestly, with no hoses, no filter bags, just wide open...

It's sort of like taking a Suburban, yanking the body off of it, and big V-8 out of it, putting a little 2 liter 4 banger and an aluminum / plexiglass bubble in place for a body and getting the EPA estimated MPG for the truck that way...

On average, I believe CFM ratings are easily twice or more what the end user will actually see. And that is not specific to Harbor Freight, it is across the industry.

Wood Magazine did an honest air flow test a couple of years ago, when they did the comparison of lower dollar dust collectors. But they only reviewed the upright two bag type, not the smaller horizontal single bag jobs... The Harbor Freight units, aside from their filtering capacity, compare favorably to the competition...

[bridger]

another down side to cheap, loud universal motors is short life span. factor that in when deciding if it is the right deal for your situation...