Thread: Newbie - Still very confused regarding dust extraction

For my shed, I have a 2 HP Carbatec FM-300 dust extractor, but it is always located outside the shed, never inside. It is connected to my custom made a Thien style cyclone, and that is very effective when running the table saw and the jointer. Not much, if any, dust goes through the DC impeller. Have recently bought a 5 micron bag for this DC, but am yet to fit it.

For the SCMS, I use a small Triton dust bucket connected to a small 2nd hand back mounted office cleaning style vacuum cleaner. It is quite portable, the bucket and the vacuum cleaner strapped together. When using a hand router, that setup is connected to a dust port on the router - works well too, albeit a bit noisy with the two very loud machines running. I usually like to take it outside the shed.

An SCMS always generates a lot of dust, and there is no really efficient way of capturing it all. The Festool KAPEX 120 probably comes ahead of the field with this, but the adjoining bench and work surfaces are still covered in dust

Nevertheless, I still wear a dust mast , no matter what machine I am running - $3 from Super Cheap autos - the mask with the flap valve in front - it is quite noticeable if I don't wear a mast, as my throat becomes sore and dry, and my nose too.

I don't seem to have any problem with layers of dust in the shed, because it is such a mess. If I had a nice gleaming clean surface, then that might tell a different story

I think that your proposed use of the shed for storing gleaming cars and activities making saw dust are not in the least complementary, and I don't know how you will get around it, other than to dedicate the shed to one or the other

Good luck!

Jill,

I certainly appreciatte your response. I also think you are spot on with your observation that my garage/workshop requirements are strongly at odds with eachother. However, without explaining in an equally long winded fashion as was my original post, its a comprimise I need to live with, and therefore mitigate as much as possible.

I think I can learn a little from what you have said (in particular I never actually knew what SCMS meant.. I have always disregarded the term when I have read it, as I thought I'll only need to know what it is when I have one, and if I had one I'd know what it was.. LOL... I finally looked it up and I now realise it is basically a compound saw )

Im still a little vague though, are you essentially confirmning that the carbatec is used only for "large port" tools... or are any of the tools listed of the small port type? and do you run the extractor in conjunction with your vacuum for any ambient dust extraction duties?

Im guessing though, that all the times I have read people state they have little or no dust in thier workshops from there extraction systems, there may be a little excageration, as essentially you have a set up not too different to that I proposed. And it sounds like I could not expect a great deal more with my tools from a different vacuum, or dedicated extractor.

( In terms of the intermediary collectors, Im of the understanding that these merely assist with the effeciency of collection itself, rather than make any difference to what is 'sucked up')

Actually, working outside of the garage (as opposed to outside the house) is a plan I have tried and tried to work out, but there are several invonveniences. Not least, once the cars are in, the tools and benches will be trapped at the rear of the garage (there is an access door to the side, but I could not fit my bench through, and the area outside the access door is not really usable anyway - slope, moisture retention in the ground, vegitation etc.) . Even out the front (If I moved a car each time, and put wheels on a workbench) I still have no shelter, which obviously limits my safe working window here in Cairns.

Oh well. I will keep thinking. Thanks again for your response.

Originally Posted by CairnsFella

However. Dust Extractors / Collectors. hmmm

I agree that this area is very confusing. It is not helped by manufacturers and sales people making claims without adequate explanations and well beyond their expertise about the ability of small DC and vacuum cleaners to ww minimise dust. One reason they do this is that it is not easy to counteract claims

My reading generally points me toward a dedicated dust extractor, and from what I read, as powerful as possible (so for me, likely a 2HP unit is my maximum I could afford).

There is little chance that a 2HP DC can do much in a shed of your size when it fills with fine dust which it will invariable every time you make some dust. For all practical purposes a standard 2HP DC can only pull about 400 cfm through a 4" diam pipe. A 6 x 8 x 4 m shed is about 5500 - cuft. This means it in theory, provided no other dust is made, a 2HP DC should take ~13 minutes to clear the shed but because of mixing effects it will only reduce the dust level by 50% in the 13 minutes, by 75% in 26 minutes, and by 88% in 39 minutes and by 94% in 52 minutes. This removal rate is too slow and it will basically reach and stay at saturation. This time can be improved somewhat using cross ventilation if available.

Doubling the flow rate by using 2 x 4" pipes will clear the shed a bit faster, 50% in 6.5 minutes, 75% in 13 minutes, 88% in 20 minutes and 94% in 27 minutes. What is needed is a DC that generates a halving time of < 3 minutes - this means 5500 cuft in under 3 minutes or a DC that when it fully loaded up can pull ~1880 cfm. IN practice this is a minimum of a 3.5 -4 HP and 6" ducting. This is consistent with what Bill Pentze recommends for that shed size.

Since no practical DC system can capture all the dust produced by standard ww machines there is absolutely no way around this problem.

However, mostly I read that these extractors are of little use for tools with smaller dust ports (essentially all of my tools) because of air volume versus air speed.

Correct - these should probably not be called dust ports but chip ports.

. . . but I still don’t really understand how a large pipe with low speed high volume is not translated into high speed air when 'choked' via an adaptor.

The lower the air speed the less the sides of the container impacts on the air flow, or putting it another way, the greater the air speed the more frictional effect the sides have on the flow rate. If the increased frictional effect cannot be overcome by the pressure generated by the DC then the flow rate does not increase proportionately. Reducing the size of the pipe is the same as increasing the flow rate and increasing the frictional effect.

A smooth walled 4" pipe can carry a max of 400 cfm under a nominal pressure of 8" static pressure (sp) which translates to an air speed of 4580 fpm.
For the same DC to drive a 400 cfm thru a 2" pipe requires an air speed of 18000 fpm - that is just too high an air speed for such a small pipe and 8" of pressure will not be sufficient to overcome the fictional effects, so the flow rate will drop dramatically to 60 cfm ie hopeless. Under these conditions this low flow rate will just not capture most of the fine dust as it permeates like fart gas all around the shed.

My confusion is furthered when I notice that the likes of carbatec sell accessories that allow - for example - a vacuum attachment with a conventional sized nozzle.

Yeah this is crap and while it works better on some tools than others, none really deal with the finest dust.

. . . BUT the shavings and dust that are not captured is still plenty enough to cause the problems that I am trying to avoid. Specifically I am still getting some piles (dependant on tool) in the local vicinity, and fine dust over most items in the shed (I should note that I haven’t yet moved the cars into the shed until I get this problem resolved.)

Even if all the chips were collected this is still no guarantee about the collection of fine dust. The fine dust can be as little as <0.1% of a WW operation but it is that which we cannot see that needs our attention and what will mess your cars up.

- and lets stick with the compound saw as an example - I could fabricate some intake ports other than those built-in to catch the machines waste. In fact, given that these extractors (or at least the 2hp ones) have two intakes, I could also make some form of hood to pick up some of the ambient dust too.

Hoods are about the best you can do with a SCMS - the rest has to be collected by running a DC with a < 3 minute "halving time", for some time - ie 10-15 minutes after the last use.

With such a large shed your biggest problem will be the need for lots of DC HP. Have you thought about reducing the volume of your shed by using for example a curtain to divide the shed into smaller volumes. This could also be arranged to protect your cars.

I use the Carbatec 2hp DC with large port ( 4 inch) machines, as you say, and the vacuum cleaner and Triton Dust Bucket with the router which has a dust hose attachment I purchased and fitted. With other smaller machines eg, power saw and jig saw, well, that is done outside the shed and the sawdust is swept up when I get around to it. I acknowledge that is not an option in Cairns, with the heavy rainfall - I saw you got 150mm ( 6 inches) one day this week.

The fact that my nose and throat get irritated even when using these machines with dust collectors attached indicates that there is dust in the shed when they are in action, hence the facemask. I really cannot see any way you are going to achieve a HEPA rated air quality in your workshop without huge expenditure

BobL,

Good points well put.

I think it most appropriatte (given that the rest of your post is not really open for debate, but is cold hard fact) is to respond to your last point about redcing workshop volume. And the answer is yes, I have considered this, but have tried to avoid it... however I know think I may have to bring it back into consideration..

As I noted in my first post I will be creating a sort of mezzanine storage level. Essentially this was due to be just to one side (one half of the fill length). I have considered a variation to this wherby I extend the mezzanine to be an L shape covering one car space and the workshop at the rear. The section at the workshop end would be a little higher (leaving just a metre / metre and a half storage above, but could then form the roof of the workshop section. Similarly I could 'curtain off' this section using the edge of the new 'false roof' over the workshop area. I would calculate this area to then be around 6m x 3m x 2.5m

I had another lok at Bill Pentz's site (previously I had only glanced, as I considered the intermediary collectors such as cyclonic collectors as an 'add on') Still for the life of me I couldnt see where/how one calculates the CFM required. My revised workspace would give I beleive around 1600 cu ft. plugging the new figures into your calcs suggest I would be close with a 400cfm extractor (but is close good enough???? I suppose I could offset the physical items in the workshop to pose an argument that it would be even closer... but then I guess the original calcs do not really assume an empty space)

That said, you refer to using 2 x 4" pipes which may then be adequate for the revised space. But, whilst these machines can be ducted through 2 pipes, does this really give me double the CFM of the same fan sucking through one pipe?...

Anyway, sounds as if there is hope. I will spend a little more time on Bill Pentz site to see if I can make mor sense of it.

Thanks you again.

Originally Posted by JillB

I really cannot see any way you are going to achieve a HEPA rated air quality in your workshop without huge expenditure

Jill,

I guess your correct here, though whilst my preference would be total dust elimination, ultimately, I still need to minimise dust as much as I can.

Originally Posted by CairnsFella

BobL,

Good points well put.

I think it most appropriatte (given that the rest of your post is not really open for debate, but is cold hard fact)

I think there is some debate - I have them with myself some times

I had another lok at Bill Pentz's site (previously I had only glanced, as I considered the intermediary collectors such as cyclonic collectors as an 'add on') Still for the life of me I couldnt see where/how one calculates the CFM required.

There's no calc - It's just approximate.
See this page about half way down there is a table showing garage/HP/pressure and approx room size size
Bill's Cyclone Dust Collection Research - Measurement
I took your setup as a large 3 car garage size on the RHS side of the table. Look for the green squares - to pull 10" sp you'd need about 4HP and big impeller (quite a bit bigger than what is found on most basic DCs)

My revised workspace would give I beleive around 1600 cu ft. plugging the new figures into your calcs suggest I would be close with a 400cfm extractor (but is close good enough???? I suppose I could offset the physical items in the workshop to pose an argument that it would be even closer... but then I guess the original calcs do not really assume an empty space)

Offsetting the space occupied by stuff in the room makes the calcs look a bit better but doesn't help in practice because they take up space and slow down air movement - it's best to just ignore them unless they are cupboards that take up large sections of wall.

That said, you refer to using 2 x 4" pipes which may then be adequate for the revised space. But, whilst these machines can be ducted through 2 pipes, does this really give me double the CFM of the same fan sucking through one pipe?...

I agree it wont quite be double but it will be close maybe 300 cfm?
A 2HP DC without any ducting will nominally generate 8" sp which pulls 1200 cfm. 4" ducting at 8"sp will only allow 400 cfm to flow thru the DC. Adding another 4" will pull close to another 400 cf, while adding a third will give a bit more again.

Just 1 x 6" duct can draw 1250 cfm at 8" on its own (but you'll need more than 2HP to pull 1250 cfm).

The inches of static pressure is the most variable factor because that depends on the state of the fliters the numbers and size of leaks, numbers and tightness of junctions etc.

What about increasing the cross flow ventilation with fans, (large flow low pressure) mounted in one side of the garage wall/roof that moves air from outside to inside then on the opposite side of garage moves air from inside to outside, this one might even be larger,also, ideally reversable so as to take advantage of any prevailing breeze direction, this helps with clearance of the floating fine dust that settles on everything, might be a thought??

Pete

Thanks again,

Bobl... found the table. Whilst I still need to read and digest more, its looking like the 2HP in the partitioned section of the garage is likely to be the go. Im sure there will still be dust seepage, but I think its going to be the best option for me.

Pete,

Hadnt thought of your suggestion and I can see how this could help. Dont know about specific figures though? For example, I guess even with the fans a 2HP dusty would still be considered inadequate.

I will see if I can find further info on cross ventilation fans, but its looking like I'll be downsizing my workshop space.

Thanks again all.

PS.. sorry about the newbie error, I didnt realise that there was specifically a "Dust Extraction" section.. sorry.

I'm another Cairns Fella. Your welcome to call in to check out my dust extraction system. PM message sent. Cheers from Bentley Park Cairns

Don't try to absorb all of BP's site in one go, all you will get out of that is a headache. To cut it down to essentially what Bill reckons will do the job is 6" ducting and a motor/fan combination to drive that ducting, Bob has already given performance figures above. This is unlikely to be found in a generic bag type dust collector that we mostly see sold in the stores. In the end it comes down to how much you value your health, as TL has posted above using the smaller dust extractors has not alleviated her fine dust problem and she has to wear supplementary breathing protection. I think TL has in fact pointed out that what you plan is very like what she has done and that is not working well. For fine dust control you have to move a lot of air fairly fast and your plans will not do that. In the end health costs money either before or after the event and before is less painful, ask those who have given away this hobby due to dust issues.