Thread: Connecting power tools to DCs and VCs - some interesting measurements.

Originally Posted by BobL

. . . . - like I need more projects

You're about to retire/retired so the need for projects multiplies to keep you in the shed and out of the way of SWMBO, plus it's all good for us as well



Pete

"The ROS pulled 42 cfm with it being turned off and 52 cfm with it being turned on - ie significantly better than the vacuum cleaner data
The Belt sander pulled only 25 cfm when it was turned off, but 57 cfm when it was turned on."

Hi Bob, would this be something to do with the tool havng inbuilt air flow? I notice with an ETS 150 sander that there is quite a significant blow out of the tool's exhaust from just it's own power (no vac).

Cheers
Brett

Originally Posted by FenceFurniture

"The ROS pulled 42 cfm with it being turned off and 52 cfm with it being turned on - ie significantly better than the vacuum cleaner data
The Belt sander pulled only 25 cfm when it was turned off, but 57 cfm when it was turned on."

Hi Bob, would this be something to do with the tool havng inbuilt air flow? I notice with an ETS 150 sander that there is quite a significant blow out of the tool's exhaust from just it's own power (no vac).

Yep that's right. I have observed that many newer power tools have much more oomph in terms of self generated airlfow and its a pity they do not have more. I'm guessing the reason they don't do this is that a bigger motor would add weight and possibly detract from the power available to the tool. On something like a big belt sander that can use weight to do the job it is less significant but on lighter tools this is not so easy. Since power tools are only intended to be hooked up to VCs they should not generate any more than about 100 cfm of air flow otherwise the dust will back up and spill out of the tool.

In addition the better designed sanders have small outlets underneath the sanding pad that deliver a slight over pressure points in between the larger outlets - this is a good example of a push-pull approach to dust collection which is supposed to be more effective than a simple pull.

Originally Posted by BobL

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I tested two sanders - a Festo ROS and a Makita 100 mm belt sander by connecting these to my test pipe using another metre of 50 mm flexy and measuring the air flow through the pipe.

The ROS pulled 42 cfm with it being turned off and 52 cfm with it being turned on - ie significantly better than the vacuum cleaner data
The Belt sander pulled only 25 cfm when it was turned off, but 57 cfm when it was turned on.

Now using 4" flexy instead of 2" flexy.
ROS: Sander off 54 cfm, Sander on 68 cfm
Belt Sander: Sander off 44 cfm, Sander on 73 cfm.
This is average of ~30% increase when using the 4" flex.

While it's not as easy to use 4" flex attached to a sander it is by no means impossible.
The way I do it is to suspend a length of dowel or metal curtain rod from the roof about above the work and then suspend the 4" flexy using several bungee cords from the curtain rod so that the flexy is about 250 mm above the work.

One thing to consider especially with sanders is that air flow is not everything.

Good suction pressure sugnificantly improves dust extraction performance on square orbitals and ROS.....to a lesser extent on belt sanders.
Any omprovement on belt snaders I put down to simple increase in flow.

I can see two reasons for this, the first is that the actual apitures in the sanding plate & abrasive media are very small and significant suction pressure is required to get flow, the second is that when the pad is flat against the work, good suction pressure pulls dust from the surface and across the face of the pad.

I have spent many hours with vac connected sanders & I can tell you that the dust collection efficiency of the samder is greatly improved by the extra suction pressure.

I can tell you it is obvious when the hose comes adrift from the vac end with the sander still running, the sander keeps pumping dust down the hose....but the amount of dust around the work increses considerably

I can also tell you that using a high suction vac with a sander improves the life of the abrasive considerably......I expect this to be because the abrasive is better cooled and less spent grit and waste remains on the surface


It would be interesting to see what the open face air flow is produced by the on machine dust fan......I expect it to be quite high...but the suction pressure will be quite low because they are only small crude single stage blowers.

I would also be interested to see what the air flow is on particularly ROS with different grades of paper and both on and off the surface.

cheers

I agree air flow is not everything especially for coarse dust and chips.
Air speed is also very important to collect chips at source and more significantly maintain suspension of chips in the airflow - which is why I am just initially working with sanders. But even then, the air speed at 52 cfm in a 50 mm duct, let alone a 100 mm duct will drop some dust out of suspension. This is one reason why VCs have such small ducting. However, with a decent DC, simply removing the sander from the ducting at the end of the job and running the DC for 30 seconds will increase the airspeed to well over 4000 fpm which will scour fine dust from even a 150 mm diam duct.

Some measure of the air flow generated by the sanders themselves can be obtained from the difference between having the tool on and off.
For the ROS the difference is 10 cfm using a 2" duct and 14 cfm using the 4" ducting ie average of 12 cfm or not much
For the BS it's 32 cfm for the 2" duct and 29 cfm (Average of 30.5 cfm) so about 2.5 times more than the ROS.
However, I will also measure these directly next time I do some testing.
It would be interesting to measure some newer power tools with the push pull technology.

using sanders and the like with 4 inch hose is completely pointless, because the entire design is worked arround a 32mm ID hose and pretty high suction pressures....yess I have tried it.

Quite righty you note that the dust falls out of the air stream......this is less of a problem than you may think.

All but the belt sander, will considerably slow its air flow when the machine is presented to the work, when the machine if lifted off the work the air flow increaeses considerably and the hose is purged.

Even then, there may be dust out of suspension, but it is not a problem untill you drop the sander off the end of the hose with the vac turned off.

If instead the vak is left going and the hose is pulled off, the hose will be purged.

If in an extream case the hose is clogged...and it wont be from dust......the high suction pressure will build up and a surge will occur purging the hose.

Anybody who has had a lot to do with vacuum cleaners and such will know the first action in a blocked hose it to remove the tool and repeated block and open the end of the hose with the hand.......this will mostly let the high suction pressure do its job.

A lot of what we think about large scale dust extraction like we have in stationary machines does not transfer to hand held power tools and shop vacs.

In large scale dust extraction, airflow in the predominating factor, in VAK type products suction pressure is the predominating factor.
With sanders especially ( not so much belt sanders) the difference is the extraction is direct at the point of generation......there is suction right where the gritt is cutting, at its best, there is suction pressure on the waste even before it is seperated from the work piece.

Where on our stationary machines, we are collecting the dust and chips some significant distance away from where they are being cut and there is less than maximum suction or airflow at the cutting edge

As for the push and pull......you do not need a modern machine to find that...any machine that comes with a dustbag will have an inbuilt dust fan.
30 year old makita belt sanders have an inbuilt dust fan.......hooking them up to a seperate vacuum machine is a relativly new idea.

Let me tell you the difference between running the any of the sanders with the dust bag and running with a good high pressure vak, results in orders of magnitude better dust capture.

I used my ROS with the dust bag ONCE for about 30 seconds........never again....the dust bag on my belt sander is as clean as the day it was stiched.

Y don't have to use instruments to see how much dust is in the air arround a machine being used with a dustbag......you can see the cloud of dust surrounding the work and you have wipe it off the face of the operator.

cheers

Would a sander attached to a 4"/100mm hose with a portion of the hose left open at the sander sucking the air around the sander, not be pulling in some of the dust that isn't being pulled through the sander at the same time?

Pete

Originally Posted by soundman

using sanders and the like with 4 inch hose is completely pointless, because the entire design is worked arround a 32mm ID hose and pretty high suction pressures....yess I have tried it.

Like many power tools out there in WWW land, none of my sanders are specifically designed to work with VC's - they have fittings that are specifically designed for those crappy dust collection bags. Some of the tools have oval or rectangular shaped outlets. I have tried using VCs on these tools but I was not satisfied with the dust collection ability of a VC so 5 years ago I started using them with a 1 Hp DC and immediately noticed an improvement, probably because my DCs have always vented outside my shed. Now with my 3HP DC the situation is better still. What I am in the process of doing is quantifying what is going on. I will eventually move onto evaluating power tools specifically designed to work with VCs but I can't see them being that much better in removing dust from a shed especially since VCs invariably vent inside a shed.

Quite righty you note that the dust falls out of the air stream......this is less of a problem than you may think.
All but the belt sander, will considerably slow its air flow when the machine is presented to the work, when the machine if lifted off the work the air flow increaeses considerably and the hose is purged.
Even then, there may be dust out of suspension, but it is not a problem untill you drop the sander off the end of the hose with the vac turned off.
If instead the vak is left going and the hose is pulled off, the hose will be purged.
If in an extream case the hose is clogged...and it wont be from dust......the high suction pressure will build up and a surge will occur purging the hose.
Anybody who has had a lot to do with vacuum cleaners and such will know the first action in a blocked hose it to remove the tool and repeated block and open the end of the hose with the hand.......this will mostly let the high suction pressure do its job.

I'm not talking about VC hose or VCs, I'm talking about using 4" ducting at 52 cfm where larger dust will fall out of suspension. The problem is, unlike VC hose, a 4" duct is so large it is much less likely to completely block but it can, over time become constricted and reduce flow below that which it is capable of achieving. The reason I mentioned this is because I know some people leave their power tools permanently connected to hoses and even if it is not blocked a 4" hose needs to be purged occasionally to restore the full 4" diam.

As for the push and pull......you do not need a modern machine to find that...any machine that comes with a dustbag will have an inbuilt dust fan.
30 year old makita belt sanders have an inbuilt dust fan.......hooking them up to a seperate vacuum machine is a relativly new idea.

I'm not talking about this simplistic approach. I'm talking about sanders like the newer Festool that actually blows a small amount of air out of some holes in its sanding pad to help sweep dust towards the suction holes. Another example would be using air jets to blow the dust off a belt towards a sucking inlet.

Let me tell you the difference between running the any of the sanders with the dust bag and running with a good high pressure vak, results in orders of magnitude better dust capture.
Y don't have to use instruments to see how much dust is in the air arround a machine being used with a dustbag......you can see the cloud of dust surrounding the work and you have wipe it off the face of the operator.

I agree, but I don't give a rats about bags - this thread is investigating the dust collection ability of VCs and DCs (not bags) from power tools.

Originally Posted by QC Inspector

Would a sander attached to a 4"/100mm hose with a portion of the hose left open at the sander sucking the air around the sander, not be pulling in some of the dust that isn't being pulled through the sander at the same time?

Pete

Yes, but the trade off is a loss of pressure/flow inside the sander. The question is then how much dust is not being captured at the sander.
I have though about doing something along the lines you suggest since my experiments show a 10% loss of flow at the sander if a second 4" (400+ cfm) port is opened up in the DC line. This second 4" line could then be placed near the The only way to test the effectiveness of this is with a particle counter while the sander is actually sanding - which is what I will do - hopefully this week.

Firstly a lot of the newer versions of the sanders ARE designed to run off dust extraction, the size and shape of the connections has more to do with selling the companies proprietary dust extraction connector, dust extraction hose and dust extraction machine.
The dust bag is still supplied because there are people out there who will persist with them because they don't know any better or simply dont care.

Running anything other than 32mm standard vac hose or the manufacturers proprietary vac hose is a pointless exercise on a portable because the size and weight of the hose make the machine unhandlable......many people are not even prepared to tolerate the standard vac hose.

If you have some sort of weird dust connector on your sander and you have not arranged a 100% seal on the suction hose you are wasting your time...because suction pressure at the machine is everything....air flow will vary dramaticaly depending on the machine and how it is being used...in these machines air flow in incedental....it is the suction that matters

There are also some sanders you will never get a high rate of dust capture simply because of the way the sander works. No sander unless it and the work is enclosed in a box will be anywhere near 100% capture.

We keep comming back to chasing the impossible and reinventing the wheel.

If you are at all worried about the dust capture of a sander, do the easy and the proven and the practical.

on small items work on a down draught table, on larger items use large scale ventilation / room extraction or use PPE.

That is what is done in industry if they give a damn....because it works.

So much of this is as simple as it seems.

The elephant in the room here is the vacuum cleaner.....as we have found most of them have poor filtration.

there are two viable silutions....

the first is, off the shelf and that is to buy a domestic inbulit vac system and install it in the shed and exhaust it outside.

the second is to modify a stock shop vak so it discharges into the 100mm ductting of your main dust extraction system....please ya self if you even have a filter in it........that will provide the high pressure suction and the main dust extraction system will deal with the "invisable Dust"

cheers

[QUOTE=soundman;1566689The elephant in the room here is the vacuum cleaner.....as we have found most of them have poor filtration.
[/QUOTE]
Your honour, I rest my case.

I will keep testing and rely on what I measure, not what is reported by companies selling a product for profit, or qualitative statements reported by others including on this forum.

I have read and heard about for some time that 4" ducting severely throttles dust extractors but despite have access to a fair range or air flow measuring equipment have not been able to measure the flow in 4" ducting all that accurately.

The main problem with measuring the flow directly with a hot wire anemometer is the flow inside in the middle of the duct is above the ranges of my hot wire anemometers (20 and 30 m/s max).
I have measured the flow with a Pitot tube but the Pitot is pretty chunky so I am worried that it interferes with the flow inside a 4" duct - as does the hotwire anemometer when the flow is too high (>10 m/s)

Recently I made up some test pipes that can be connected to the ducting/machine of interest. The test pipes have a larger diameter than the duct being tested so the air flow is reduced to low enough values for my anemometers to measure and the probes do interfere as badly with the flow.

Here are the 100 mm and 225 (actually 242 mm) mm test pipes - I also have a 150 mm test pipe but that is currently up in the rafters and I was too lazy to get it down for the photo.
The test pipes are just reasonably long sections of pipe and a set of reducers that enable the ducting to be hooked up to or between stuff and a DC.
The 100 mm pipe is what I am using to test VCs and power tools attached to VCs.

The red arrow/circle marks the test point where the anemometer is inserted. As I described in my DC setup the flow is non-uniform across the duct so a series of measurements of the air speed as a function of radius into the duct are needed to accurately determine the flow. Just to complicate matters the 225 mm test dust seems to have a resonance of some kind whereby the air speed fluctuates with about a 10 second period so one has to measure the max and min air speeds over a number of oscillations to get an average reading.

Anyway, - For the first time, today I was able to use the 225 mm test pipe to indirectly measure the flow through a 500 mm length of 4" duct going directly into a 6" duct connected to a DC capable of pulling 1250 cfm
The flow in the test pipe varies from 3 m/s at 1 cm from the wall of the duct, to ~6.5 m/s in the middle of the test pipe. Even though the air speed near the wall is less than half that of the middle of the duct the amount of air that flows in the outermost 1 cm "cylinder" is still significant.

The final result was 404 cfm. This pretty much agrees with the typical values of 400 to 430 cfm that I have read about for sorts of pressures bigger DCs generate. I also measured what flow 3m of 4" flexy can carry and that worked out to be 346 cfm confirming my understanding that 3 x 4" flexys are required on a big DC to meet the 1000 cfm spec that BP quotes.

This means I can now measure the flow rate of just about any DC with the hot wire anemometer. I'm not sure what is going to be more difficult to tote around, the Pitot tube and glass manometer, or the big test pipe and the anemometer. Given the danger of breaking the glass manometer I think the big test pipe will be safer in the long run.