Filter above separator? (stage 2 above stage 1)

[grant]

I've recently fallen deep down the Thien baffle rabbit hole. I appreciate the contributions many of you have made here, especially those such as retired2 who have experimented with different configurations and provided detailed data. Very valuable and helpful. Oh and Phil too. :) I've spent a lot of time thinking and reading about how to set up dust collection for my garage woodshop. I'm currently just using a 5gal Ridgid shop vac which fills up so fast it's usually clogged. I don't even bother connecting it to my planer. I'm eager to have a more robust solution that I don't have to empty as often. I've got parts on the way (including the Harbor Freight 2HP Dust Collector and some 1/16 polycarbonate for a top hat). Yesterday I got a 55gal drum to collect chips, and I've started on the top hat.

So, getting to my question
In all my research, I haven't seen anyone put a secondary stage of filtration above the first stage as I've sketched below. Normally, what I've labeled part B is next to part A, which roughly doubles the footprint. A stacked configuration could fit in the average garage, because (1) the Thien baffle is so much shorter than a cyclone, and (2) the dust bag/bucket for the secondary stage doesn't need much capacity when it's preceded by the first stage.

Is there some reason this is not a good solution? These are the potential drawbacks I speculate about:

• I imagine there would be some loss in efficiency from having to bend 180 degrees up into the secondary stage, rather than shooting straight into it. In my case, I have a small shop and am planning on just connecting to one tool at a time with that quick change handle from Rockler, without doing any long runs of pipe. So depending on the severity, I may be willing to sacrifice some efficiency for saving floor space.
• The whole assembly could get top-heavy if it's intended to be mobile. And the more you kick out the casters to stabilize, the less you're actually saving floor space. In my case, I'm using a metal 55gal drum which would help keep the center of gravity low. And the components of "part B" are not heavy. Plus I may end up mounting to a wall.
• Maybe I'm wrong and the dust bag/bucket for the secondary stage does need to be tall to minimize scrubbing.

Bonus question: I can't find a 1 micron filter bag right now. I'm looking for something like the Powertec part #70001 (I'd post a link if I could) but I can't find it in stock anywhere. Was the COVID-19 pandemic a bad time to nerd out about micron-level air filtration?  ;) That is, are they normally easier to find? I'm not ready to nearly double the cost of this project by getting a Wynn filter at this time. I'm planning to forego the second stage and duct the output from the first stage outside the garage door, at least as a short term solution. Any input on getting a cheap <=1 micron filter would be most welcome!

Thanks for reading!

[alan m]

that should work. that 180 bend is going to increase resistance  . if you could put it straight into the second part it would work better. I think you will need a center pipe on the second seperater to make it spin properly

[retired2]

I really question the value of a second separator.  I?d argue that the first top hat will separate more than 90% of your waste with a system loss of 35% or more.  Add a second separator and the system loss is likely to be as great or even greater than the first.  And you are adding all that loss to MAYBE capture another 1or 2 % of waste.  Keep in mind the second separator won?t see anything but fines and separators are not very good at separating out fines, so most of it is going to wind up in your filter.

If you think my numbers are a bit extreme, consider this.  I have emptied my waste drum more times than I can count.  The bag under my pleated filter has never been removed and the amount of fines in it would not fill a 1 gallon can.

I think you are going to have a top heavy, unstable dust collection system that is probably going to underwhelm you with its performance.  You?ve already mentioned mounting it on a wall.  If you do that, it will no longer be close to all your tools unless you bring all the tools to the dust collector.  If you add pipe or hose to that design, I fear you may not have enough velocity to keep the waste entrained.

And I bet many people who start out with the intent of moving their dust collector to each tool, soon give up.  Consider the simple task of dressing and sizing a piece of stock.  You will use a thickness planer, a jointer, and a saw, and you will spend far more time moving your dust collector than using those tools.

[alan m]

a lot of dust collectors use a ring between the filter and bag like the op is suggestion. im guessing that a lot of the losses  are cause by  that part . its basically a separator  but without the top and baffle .. the losses are from the change in direction and friction against the sides etc.  has any one ran test on their system to see where the majority of the losses are compared to stages of the build of a separator.

either way I agree with retired 2 that's its probably not worth it but you could always try and see  how it works

[retired2]

My Delta DC is in fact a two stage separator as you describe. Actually it is just one, but my top hat brings the count to two. Unfortunately, the Delta is built in a way that the I cannot remove the second stage without destroying it, or I would.  Over a long period of time the second stage has separated a small amount of fines, but the price is full time system losses. 

[alan m]

you say you have practically no dust in the bag  . do you think you could do away with that bag  and build something else instead..
I wonder could you make a bucket  with a pipe in the centre that passed through . then attach the filter to the top  and the dust collector to the pipe. you would have no changes in direction of the air flow  so it should be better. this contraption would need to be vertical though so the dust would fall into the bucket part  when you clean the filter

[retired2]

I?m not sure I follow you Alan, but here is my DC:

https://www.finewoodworking.com/2006/04/01/50-760-portable-dust-collector-review

There Is nothing that can be done to modify it without destroying it.  I replaced the bag filter with a pleated Wynn filter and just left the plastic bag alone.  I could dramatically shorten the bag, but there is no point in messing with it.

And most importantly, the amount of work I do in my shop no longer justifies any equipment purchases or time spent modifying what I already have in place.  I?m at the time in my life where I am starting to worry about leaving someone with the task of dismantling things and selling it off.  There are drawers and cabinets filled with accessories, and no one but me knows what belongs to which tool.  I suspect an heir will bring in a local auction house and ask them to buy it at a dime on a dollar and remove it!

[alan m]

that's very sad.
ultimately all our collections will go the same way


for some reason I thought you dc  was in 2 parts like the OP is talking about.

[grant]

retired2 has brought us to this fundamental truth which is of course the cornerstone of all dust collection systems:

I hated all my toil in which I toil under the sun, seeing that I must leave it to the man who will come after me, and who knows whether he will be wise or a fool? Yet he will be master of all for which I toiled and used my wisdom under the sun. This also is vanity. So I turned about and gave my heart up to despair over all the toil of my labors under the sun, because sometimes a person who has toiled with wisdom and knowledge and skill must leave everything to be enjoyed by someone who did not toil for it. This also is vanity and a great evil. What has a man from all the toil and striving of heart with which he toils beneath the sun? For all his days are full of sorrow, and his work is a vexation. Even in the night his heart does not rest. This also is vanity.

...

Behold, what I have seen to be good and fitting is to eat and drink and find enjoyment in all the toil with which one toils under the sun the few days of his life that God has given him, for this is his lot.

Ecclesiastes 2:18-21, 5:18

[retired2]

Grant, I?m not sure your scripture would be quite as accurate if I substitute ?play? for ?toil?.  I never thought of any of my time spent in the shop as toil.  And for sure my wife always thought of it as playtime.

[davegraves]

regarding availability of 1 micron filter bags -

I recently found the same issue with bags, none were to be found anywhere.  I also was considering an oversized bag to reduce back pressure from the filter, so I started researching felt material.  I found some material from Duda Energy (dudadiesel.com).  If you have access to a capable thread injector (some lady folk call them sewing machines) it cant be a difficult build.  I just received 5.5 meters of material wide enough for a 20 inch diam bag for the price of one small bag ready-made. And I can make the bag as long as I have room in my shop.

Not saying its the perfect choice, but I'm betting I can get better performance from my oversized bag than if I bought a standard bag - for not much effort.