With a Thien separator in front of a HF Dust Collector do I need a full height bag?

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Forum topic by JesseTutt posted 03-08-2013 10:08 PM 3244 views 2 times favorited 11 replies Add to Favorites Watch
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854 posts in 2288 days

03-08-2013 10:08 PM

Topic tags/keywords: dust collection harbor freight thien plastic bag

As time permits I am designing changes to my Harbor Freight (HF) Dust Collector (DC). As I search for information and ideas I have come across several posts that indicate that almost all of the chips and dust is collected in the thien separator and does not make it into the plastic bag.

So in my redesign, would there be any reason I could not reduce the height of the plastic bag to about 12” tall?

What about replacing the bag with a 12” tall solid container (bucket)? I absolute hate trying to get the plastic bag and steel band back on.

-- Jesse, Saint Louis, Missouri

11 replies so far

View DIYaholic's profile


19670 posts in 2853 days

#1 posted 03-08-2013 10:24 PM

Short answer, YES!

There are several posts here on LJs, that show shorter bags. However, I don’t know how short is “too short”.

I will be redoing the bag arrangement, during my Thien Top Hat installation I’m almost done with the Thien build, then it’s onto dissassembling my HF 2HP DC, reposition motor/impellor & hang the filter from the ceiling. I kinda like the idea of a solid container. I may just steal that idea!!!

-- Randy-- I may not be good...but I am slow! If good things come to those who wait.... Why is procrastination a bad thing?

View BTimmons's profile


2303 posts in 2663 days

#2 posted 03-08-2013 10:30 PM

I’ve been doing lots of reading about the HF DC mods, in hopes that I’ll be able to afford setting up a system for myself soon.

It seems like everyone who replaces the bag ends up using a drum of some sort, and those who’ve used anything 30 gallons or smaller always says they wish they’d opted for a 55 gallon drum instead.

So yeah, a 12” tall solid container would have to be emptied very frequently, I bet. Putting the separator in front of the DC doesn’t mean that your bag never fills up. It just means that the dust that does make it past the separator is moving slow enough not to get sucked up into the filter and form clogs up there.

-- Brian Timmons -

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3183 posts in 3409 days

#3 posted 03-08-2013 10:36 PM

Jesse I am experimenting with a 42 gallon contractor trash bag in place of the clear bag that came with the HF dust collector. It is the brand sold at Lowe’s – 3 mil.

I have a plastic drum upstream of the blower but I haven’t finished the Thien style chip separator. I am getting carry over so for now, it will be easy to simply replace the bag when it gets about half full. Looks like the drum will be about the same, so I’ll empty both at the same time.

My hopes are that once I complete the chip separator, I won’t have to deal with the plastic bag very often. For now the clear bag is folded up and stored just in case an emer-gencee arrises! :-)

-- Handcrafted by Mike Henderson - Channelview, Texas

View JesseTutt's profile


854 posts in 2288 days

#4 posted 03-08-2013 10:46 PM

Brian: I think we may be talking of two different things. I am talking of converting my single stage HF DC into a two stage by adding a thien separator on top of a steel container. Previous posts indicate that this separator gets close to 100% of the chips before they pass they pass through the impeller, metal ring and into either the plastic bag or the Wynn filter. If this is correct then I would expect very little if any ending up in the 12” high bag and I would not have to empty it very often.

-- Jesse, Saint Louis, Missouri

View b2rtch's profile


4863 posts in 3226 days

#5 posted 03-08-2013 10:51 PM

I believe that the shorter the bag the more the dust will want to get in the filter ( if you have a filter)

I had a “cyclone inducer” lid, a Thien separator in the trash can and a wok under the filter.
After these modifications I had every little dust in the bag. After one year I had may be 2 to 3 ” of very fine dust in the bag,
I sold this DC about two weeks ago.
It was working very well.

-- Bert

View JesseTutt's profile


854 posts in 2288 days

#6 posted 03-08-2013 10:54 PM

In my work shop floor space is at a premium. Most modifications use a side-by-side arrangement. Thien on the left, metal ring + bag + wynn filter on the right. Hose in the middle.

I am thinking of stacking everything on top of each other. I would envision the following (from bottom to top):
1. moveable base
2. metal trash can with thien separator
3. short 3 – 6” hose
4. impellor with motor
5. hose leaving impellor going upwards
6. shelf
7. short plastic bag that will collect the 1-2% dust that makes it through the thien
8. metal ring with hose connected to it (from 5)
9. wynn filter
10. crank on top of filter with flippers inside (correct name?) to loosen any dust build up.

Is there a problem with stacking the parts this way?

-- Jesse, Saint Louis, Missouri

View DIYaholic's profile


19670 posts in 2853 days

#7 posted 03-08-2013 11:14 PM

As long as you have the height, it will work.

What will connect from the impellor to the HF seperator ring, that has the bag & filter??? Flex hose will reduce air flow. 2-45 degree with a short straight section between the fittings are less restrictive that a 90 fitting.

There are two downsides to your arragement:
1) Any additional/extra length of ducting reduces air flow. Though being a short run, it shouldn’t effect it too much.

2) Any change in direction, (45 or 90 fittings) reduces air flow.

That is why people do a side by side with a “direct” connection. There is less ducting & no change in direction. Hence, an improvement in air flow, over the OEM arragement.

-- Randy-- I may not be good...but I am slow! If good things come to those who wait.... Why is procrastination a bad thing?

View Shawn Masterson's profile

Shawn Masterson

1325 posts in 2126 days

#8 posted 03-09-2013 01:45 AM

when it comes to a small bag just remember if the separator fills it will blow into the bag and up into the filter. this is a mess to clean out a filter. I have a cyclone I am reconfiguring when I first used it I was planning an never paid attention to how fast it filled and I pumped my filters full of planer shavings. it took an hour to get it clean and reassembled. I never hurts to have a safety factor.

View HorizontalMike's profile


7770 posts in 3092 days

#9 posted 03-09-2013 03:47 AM

Even with the Thien separator (mine looks like Bert’s), that clear plastic bag works, on a large part, because of the “large” capacity that is has. That capacity allows the circulating dust to drop out before ending up in the filter. Reducing the ‘bag’ size will reduce the cyclonic efficiency of that last step and, as others have inferred, cause the finest dust to collect more rapidly in the filter.

-- HorizontalMike -- "Woodpeckers understand..."

View mbs's profile


1657 posts in 3118 days

#10 posted 03-09-2013 04:42 AM

I shortened the bag but I put a thein baffel in the spin chamber so once the small dust went into the bag it would stay there. I probably lost some efficiency. It appears to work well but without measuring the air it is difficult to know. Here is the thread.

-- Sorry the reply is so long. I didn't have time to write a short reply.

View Bieser's profile


176 posts in 2212 days

#11 posted 03-09-2013 04:46 AM

I used mine and placed it on top of a cyclone with a 30 some gallon trash can under it with a cabinet built out of MDF. I have not hooked it up to a central system as its going outside the shop in a shed but had it hooked up to one machine and it worked really slick.

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