Thread: Flow loss using a Dust Deputy

Originally Posted by BobL

I agree with you about the bags etc but hearing and feeling are no substitute for measurement especially where sanding is concerned.
The dust to worry about is so fine you can't see it and even a 1/4 of a thimble full is enough to contaminate a 100 m^2 shed well above OHS levels.

Don't suggested maximum levels quote m^3?

Hi Bob

I am not sure if there are two issues here running along parallel tracks. The one appears to be that the DD (or similar) reduces flow, and that this places the workshop at risk as fine dust is less likely to be collected - I do not see any argument with this. The other is that the DD is not really used primarily to filter dust but rather to separate chips and act as a collector for these. In doing so it can make a VC more efficient - however this is a relative term, since they are not terribly efficient to begin with.

I have a related question, if this is not going off on too much of a tangent ...

My own use of a similar combination (Festool and Dust Commander, or a Fein and DD) is when using a router, or to sweep up the workshop. I do not sand, unless occasionally hand sanding with a hand Mirka and Abranet mesh (As you know I mainly use handtools - incidentally, did you know that Lee Valley once built a VC for a handplane? It was an April Fool joke, but it was for real ).

The question: if there a difference in the dust that comes from the chips off a router or tablesaw vs the dust from a sander? And related to this, is a VC/DD suitable for any of these modes?

Cheers

Derek

Originally Posted by BobL

The dust to worry about is so fine you can't see it and even a 1/4 of a thimble full is enough to contaminate a 100 m^2 shed well above OHS levels.

I don't use a shopvac to clear the shed of fine dust. The shopvac has no chance, not enough volume, not even close....and it seems to make more fine dust than it could collect.

I use a shopvac to remove bigger chunks of dust which act as ball bearings reducing my sanding efficiency and therefore increasing my sanding time. Same thing for routing, I use the shopvac to hopefully suck up the chips so they don't get between the fence and routeredge or bearing guide forcing me to do the same router pass twice. same thing for jigsawing, I use the shopvac to suck up the crap which seems to want to collect infront of my cutting path making it hard to see where I am going.

I have a open 6" port in my main 3hp dust collection system which I have running while sanding/routing/jigsawing. That handles the fine dust well enough

OK I did a VC test.

My test VC is a well used (not by me) 1500 W Ryobi W&D VC with a 30 mm ID x 3m long hose.
I figure this is a good candidate because many DIYers are not likely to have a VC much better than this.

The setup is VC, attached by 30 mm hose to the DD and then the DD is attached by a 2m long 50 mm hose to a 100 mm (negligible resistance) diameter x 600 mm long test duct.
The test duct is necessary to reduce the air speed to within the range my anemometers can measure

To test without the DD I remove it and attach the 30 mm VC hose to the 50 mm hose and 100 mm test pipe.

I emptied the drum and cleaned the filter before the test. The filter wasn't that dirty because I don't use the VC much.

Without the DD the flow was 73.4 CFM and with the DD connected the flow was a clear 69.8 CFM so as I expected there is a small (~5%) loss of flow.
5% is not worth worrying about especially if it keeps the VC filters clean and maintains air flow and in the long run saves on bags et .

I then vacuumed the floor not using DD because I deliberately wanted to clog up the filter.
Our 2 dogs continually track lots of crap into the shed from the sandy lawn and there was a some MDF sawdust on the floor as well because I forgot to turn on the DC when I was bandsawing some pieces of MDF earlier in the week.
When I looked inside the drum it was about 1/3rd full of crap and there was some caking of fine dust on the filter.
FWIW this is not the same as 1/3rd of a drum of fine sanding dust but there was still enough there to make it some sort of test at least enough to see if there would be a significantly reduced flow through the VC.

The air flow of the VC did drop, but only to 72.6 CFM i.e. still better that the VC with DD and clean filters???
I have to admit I am very surprised as I thought the flow would drop to less that that.
I will say straight up this is NOT a definitive test, it is a test of sorts and the whole things needs to be done more rigorously using fine sanding dust.
I don't know when I'll get around to doing because I do my sanding on a 150 x 1m long belt sander and there's no way I'm trying to grab dust off that sucker with a VC.

What I will do is extract a bucket of sawdust out of my DC collector bags - there's lots of MDF dust in there - and then suck that up with the VC, with and without the DD.
That's also when I will check the filtration efficiency.

Now here is something interesting - I get 7% more flow using the DC with the DD connected, than I did with the VC and no DD?
That is almost certainly the limitation imposed by using a 30 mm VC hose as opposed to the 50 mm DC hose.
I will get some more 50 mm hose so I can do the testing using all 50 mm hose.

Originally Posted by Kuffy

I I have a open 6" port in my main 3hp dust collection system which I have running while sanding/routing/jigsawing. That handles the fine dust well enough

If you are running the DC why not also use the DC to extract the dust direct from your sander? That's one less machine making a racket in the shed.
If your sander has a fan in it (they nearly all do) it's the fan in the sander that is the limiting step in extraction and all the DC or VC does is collect what the fan supplies to it.
I don't do this very often but when I do this I use a 50 mm hose from the sander to the DC duct and support the hose from the ceiling using an cocky strap, its at least as effective as a VC and sometimes better.
With a big belt sander I use a 100 mm flexy and this is MUCH better than a VC.

I agree that hand held routers are trickier because you want the hose a light as possible to maintain a good feel for the tool. I nearly always use mine in a table and I now have excellent fine and coarse dust extraction from that.

I have thought about it Bob, but my sander doesnt have an inbuilt fan so I think it wont be very effective. I would also need to add extra 6" piping to reduce the length of 50mm flexi needed. So I havent done it yet given the cost versus unknown sucess.

My routertable is connected to main dc system.

I'm very amazed that your tests didn't report a drastic drop when using the DD.

My setup is a Festool CT33 -- ~1m of 60mm black hose (don't know where it came from) -- DD on a bucket -- 50mm gray hose from CT.

A very basic test, just by putting my hand over the opening, is that the DD dramatically drops the air volume. Just detatching the DD and putting a hand over the black hose is a very powerful suck. Attach the hose and put the hand directly onto the inlet of the DD and it is significantly down.

Certainly not 5%, but more like HALF.

Removing the DD and the Festool positively roars. (IMO the pissy 33mm green Festool hose is hopelessly inadequate as well).

I previously tried doing the suggestion above of using the DC, but the suck was so powerful on the Festool RO150 sander, that it was adhering to the surface!

My only use for the DD is that it irritates me cleaning out the Festool vac. I've the cloth bags and HEPA filters, but it's a disgusting job. The DD saves me the mess

BTW, thanks for the tests BobL.

Given the inadequacy of the DD, perhaps you can suggest a design suitable for a 50mm solution?

Originally Posted by woodPixel

I'm very amazed that your tests didn't report a drastic drop when using the DD.
A very basic test, just by putting my hand over the opening, is that the DD dramatically drops the air volume. Just detatching the DD and putting a hand over the black hose is a very powerful suck. Attach the hose and put the hand directly onto the inlet of the DD and it is significantly down..

Certainly not 5%, but more like HALF.[/QUOTE]
Ah, greater flow to being with using the CT33 and a 50 mm hose so more to lose when using the DD.
I will at least test the 50 mm hose

I previously tried doing the suggestion above of using the DC, but the suck was so powerful on the Festool RO150 sander, that it was adhering to the surface!

Just crack open one of your other ports and you will be OK

My only use for the DD is that it irritates me cleaning out the Festool vac. I've the cloth bags and HEPA filters, but it's a disgusting job. The DD saves me the mess

Yep that alone is a worthy/good use for it.

Originally Posted by woodPixel

BTW, thanks for the tests BobL.

no worries

Given the inadequacy of the DD, perhaps you can suggest a design suitable for a 50mm solution?

I don't think I have done anything definitive yet except clearly demonstrate that the DD should not be used on a DC.

With my Festool CTM 26 AC vac I was using a Cyclone Mini (CV06?, not a DD) and a cloth bag. There was virtually nil in the bag after quite some time (numerous emptied cyclone bins) so I figured I had wasted my dough on the very expensive cloth bag (bought the cyclone after the bag).

I did some rudimentary testing (which Bob may remember - with my womanometer). This testing seemed to indicate what I "felt" I was experiencing, and that was about a 10% loss of airflow. Given that the CTM is a pretty powerful unit I figured that a 10% loss for the associated benefit was all good.

Bear in mind that this was all running through a custom ducted system with a few gates (which also results in perhaps 10-15% loss). The longest run of duct was about 3.5m.

However, in the end I was glad of the cloth bag. My testing had caused the cyclone so suck it guts in without me noticing. That weakened the walls and they stayed that way, which vastly reduced capacity. I did pop them out and braced them with some sticks screwed on to the walls, but things were never the same again. Removing the lid from the misshapen bucket became a hassle, air leaks introduced, and so on.

So the summary is:
the CV06 was an absolute benefit with a small loss of suck. The vac filter stayed pristine almost (but it's an Autoclean filter with a whacker built in)
don't close the end of a tube half filled with water for suction testing, and run the vac for very long

Originally Posted by derekcohen

Hi Bob
I am not sure if there are two issues here running along parallel tracks. The one appears to be that the DD (or similar) reduces flow, and that this places the workshop at risk as fine dust is less likely to be collected - I do not see any argument with this. The other is that the DD is not really used primarily to filter dust but rather to separate chips and act as a collector for these. In doing so it can make a VC more efficient - however this is a relative term, since they are not terribly efficient to begin with.

Correct, chip collectors allow either a DC or VC to collect more chips and are labour saving in that the DC/VC collection don't need to be emptied as often. What I want to know is a) how much flow loss they cause, and b) how well do they really protect the filters. Apart from a bit of hand waving and touchy feely stuff I haven't seen any sort of quantitative testing on these key parameters.

if there a difference in the dust that comes from the chips off a router or tablesaw vs the dust from a sander? And related to this, is a VC/DD suitable for any of these modes?

The dust profile depends on factors like; the dust making action (router/saw/buzzer/sander), sharpness of blades/cutters, operator skill and the timber (size and hardness) being used.
Higher cutter speeds, shallow cutter profile, blunter blades, forcing a machine and harder/dryer wood makes finer and finer dust.

In general terms saws and routers make dust with a higher "chip to fine dust" ratio but they also make a greater volume of total sawdust so they can still make a lot of fine dust.
On a well maintained, correctly used machines like routers and saws the cutting action tends to fling the chips away from the cutting point so they don't grind chips/dust into finer and finer dust as much as sanders, which generally make fine dust to start with and then mince it finer during the sanding action.

Particle size analyses of fine (invisible) dust (<10 microns) for some manual versus machine operations shows the overall profile of the "number of particles versus mass of dust ejected into workshop air" curves, are not that different except for machine sanding/sawing.

The table below shows some data for this. I posted this in 2011? but it has been lost.

What is interesting here is the mass that gets past all the dust collection stages and is collected by a back up filter finer than 0.43 microns by sawing and machine sanding of oak and beech.
OK, its only 10.7% of the mass but in terms of numbers of particles this will represent far more particles than all the other stages.
BTW not much of this dust is likely to be collected by a small chip collector.

ParticleSizeDistribution.jpg

There does not appear to be any data for Aussie timbers but given their hardness the results are likely to be skewed to finer dust.

In terms of solutions I don't usually worry about the chips - if you plan and implement for large enough flows to control fine dust the chip problem usually resolves itself.

The problem with comparing what's on a filter, with and without using a chip collector, is that newbies confuse this with efficient dust collection.

Of greater significance is, how much of the fine dust generated has been collected in the first place?

It's a bit like saying we caught 100 crooks and only one re-offended so we have a good crook management system and a safe society.
Meanwhile the 1000 crooks that were not caught keep committing crime.

I managed to obtain some more 50 mm hose so I could do the DD test again using all 50 mm hose

Setup now is
VC, 50 mm hose, DD, 50 mm hose, 100 mm test pipe.

Without the DD the flow was 102 CFM and with the DD connected the flow was 83 CFM.
So even though there is a much greater (~40%) flow using the 2" as opposed to the 30 mm hose, there is a significantly greater (~18.6%) loss of flow when the DD is used.

Now for the mass efficiency test.
The claim by DD is "over 99%"

This is quite an easy test to do if you have the gear.

I removed a few kgs of dust from my DC bags and weighed a known amount (~500g) into a small plastic drum.
To do this I have a very nice lab grade balance that can measure 1kg to 10 mg.
balance2.jpg

The dust was pretty coarse as can be seen in this photo although there is a fair bit of MDF dust there as well.
The shiny stuff is Al as I have been cutting lots of this up lately - it makes much let dust than wood ;-)
dust.jpg

Then I sucked the dust in the small plastic white drum up with the VC with DD.
Then weighed the DD bucket and determined how much had made it into that bucket.
What doesn't make it must be going into the VC.

I did three tests and got 97.89, 96.50 and 98 .75% for an average of 97.71%
My measurement error/tolerance is about 0.01%

The differences between the individual tests are almost due to the variability in the composition of the dust.
For example, I did notice the second test (96.50%) did contain a lot less coarse material and consequently more fine material.
If anyone around Perth can provide me with some really fine dust I would like to repeat this with sort of material.

The important thing with filtration efficiency is not what is collected but "what is not collected" and comparisons should be made between the escaping dust % rather than the retained dust %.
In this case the % dust not retained is 2.29%, compared to the manufacturers claim of <1%
Some might well say, who cares what the numbers are as long as the filters are kept cleaner than not using the DD.
I'll let you decide this for yourself.

Now lets explore the ~2.3% that is not captured by the DD. A near full W&D vac would have several kg of dust in it so this means around 46g (~ 6.5 table spoons) of that dust gets through the DD and should be stopped by the VC filters?

However this is not what DD users report - they report nothing or near nothing on their filters - All good eh - must be I can't see any dust in there.

A more likely scenario is that 46g of dust is the super fine dust that is so small that it almost certainly passes straight through a normal VC filter.
Its not that the DD is doing a good job , but more likely that the VC is not up to stopping the fine dust that the DD efficiently separates out.
It might even be the case that a DD makes it easier for a VC filter to let fine dust through because at least clogging filter lets even less finer dust through.

BTW 46 g of dust distributed throughout a shed that is 6x4x2.7 (64.8 m^3) = 679 mg/m^3 or 710 times above OHS levels for hardwood (1 mg/m^3).
Even if the efficiency of the DD was 1% that's still 20g of fine dust that goes straight through the VC and produces ~300x above OHS levels for the same sized shed.

To reduce the fine dust to OHS acceptable levels, a real HEPA filtered VC is needed.
This will reduce the level to around 0.2 mg/m^3.

But based on my testing of even real HEPA filtered VCs I wouldn't trust any VC to perform at this level in the long term, and it further highlights the need for all VCs and DCs to, where possible be vented outside a shed.

Originally Posted by BobL

However this is not what DD users report - they report nothing or near nothing on their filters - All good eh - must be I can't see any dust in there.

This comment sparked my interest. I hadn't actually checked the inside of my shopvac since connecting it to a cyclone because it was still sucking well enough and I know that when the bags are full, the sucking reduces badly, no different to any standard vacuum cleaner that is used to clean carpets. To be honest, I was expecting the vac bags to be partially filled, as well a fine layer of dust covered all over the inside of the shopvac.

as expected, the first thing I noticed was a layer of dust on my pre-filter protection condom bag (i don't know what it is called...). a layer of dust around the inside of the shopvac housing. a fair amount of fine dust (mostly fines, no big chunks) inside the vac bag.


101_0383.jpg101_0384.jpg101_0385.jpg101_0386.jpg

The paint bucket is collapsed in around the sides due to the vacuum pressure inside the bucket. I need to find a stronger or better shaped bucket so it doesn't collapse. I have probably emptied that paint bucket of dust/shavings about 6 times since connecting the cyclone to my shopvac. The shopvac paperbag is about (rough guesstimate) 25%-35% full of nothing but fine dust.

So a blunt review would be that the cyclone is good for separating big chunks from fine dust, which would be great if I was packaging the dust into two separate bags for sale to different clientele.....but it all goes into the garbage truck each week and I get paid SFA for it...infact it costs me about $2k/annum for the garbo to take it away