Difference between volume and pressure -- dust control

[Jim_in_PA]

Why would anybody want to do that ?
PFlux is the wrong tool for the job when running a random orbit sander. You won't be able to hear yourself think. 6" inlet dust collector for a tool with 20mm port.

That's exactly the point Tom is making...

 

[Crazyraceguy]

Why would anybody want to do that ?
PFlux is the wrong tool for the job when running a random orbit sander. You won't be able to hear yourself think. 6" inlet dust collector for a tool with 20mm port.

That's they point, you wouldn't. One size does not fit all.

The question before anything else is to define what is meant by dust extraction. Is it to pick up the sawdust and keep the area tidy or is it to capture both the sawdust and the micro dust particles. I have always regarded vacuum cleaners as useless when it comes to connecting them to big machines unlike when they are connected to sanders. I could write pages on this subject but that seems pointless because it has already been done elsewhere with all the proof needed showing what works and what doesn't.

You're absolutely right. It really needs to be a two-step process. I think it is asking too much, to capture everything, right at the tool/source. Sure, it needs to start there, no sense in allowing it to go wild. A good extractor, rather than cheap vacuum, will at least keep from spreading the fine particles around. A big dust collector keeps messes under control, for the big machines, but that's not really the super-fine sanding dust. A shop air cleaner will take care of the rest. "Laboratory Grade" perfect? Nope, but neither is the rest of the world.
Again, "One size does not fit all"

 

[ChuckS]

I connect my SawStop PCS to a 1.5HP HEPA dust collector and the blade guard to a shop vac with a HEPA filter. My air quality monitor tells me I'm all fine with that setup. No need for overthinking.

Btw, the SawStop blade guard (when connected to a shop vac) is amazyingly effective (99.9%?), except for edge cuts. I use the spacer hack for edge cuts (99.5% in that case?).

 

[Tom the Remodeler]

Why would anybody want to do that ?
PFlux is the wrong tool for the job when running a random orbit sander. You won't be able to hear yourself think. 6" inlet dust collector for a tool with 20mm port.

Hi Steve,

That's exactly the point. You made a broad, unqualified statement to the effect of static pressure not being worthy of consideration, and that the only thing one need consider is CFM.

My point is that static pressure (and its relationship to CFM) absolutely does matter, and one would choose a HVLP or LVHP collector depending on the machinery being used. A random orbit sander demands high static pressure and relatively low CFM, whereas a 37" WBS demands enormous CFM will relatively low static pressure.

 

[Steve1]

A random orbit sander demands high static pressure

Please explain why a random orbit sander needs high static pressure vacuum ?

And what do you consider the appropriate high static pressure for a random orbit sander -- 5", 10", 20" 50", ???

I would suggest 100 cfm is plenty of airflow for a random orbit sander and don't worry about the static pressure.

Now one might take this to the extreme and pull up the specs on a muffin fan, buts lets stay realistic with commercially available dust extractors and dust collectors.

 

[ReneS]

It seems the small particles are sucked up best by high pressure air flow.

It pulls them from farther away as well, I imagine.

Probably like smoking a cigarette. You need your lips tight on the butt and some fairly high pressure.

But I am just guessing, honestly.

 

[Tom the Remodeler]

Please explain why a random orbit sander needs high static pressure vacuum ?

And what do you consider the appropriate high static pressure for a random orbit sander -- 5", 10", 20" 50", ???

I would suggest 100 cfm is plenty of airflow for a random orbit sander and don't worry about the static pressure.

Now one might take this to the extreme and pull up the specs on a muffin fan, buts lets stay realistic with commercially available dust extractors and dust collectors.

Steve,

A random orbit sander requires high static pressure for the very reason you point out: CFM is irrevocably tied to static pressure. As you acknowledge, reducing your Flux down to a 27mm hose would be a terrible idea. Why? As you state, the Flux has plenty of CFM when using a 6" duct, but it has low static pressure, so it doesn't have sufficient potential pressure differential to really pull air through the 27mm hose. This is where static pressure comes in. The smaller CT and Shop-Vac style extractors have lower rated CFM, but those lower CFM ratings are gauged at a smaller diameter hose. My suspicion is that if you put an anemometer on your PFlux necked down to 27mm you'd be getting perhaps single digit CFM. Connect that same 27mm hose to a collector rated at ~100"+ static pressure, and you're likely to see double digit CFM.

In the context of dust collection/extraction in a woodworking setting, CFM and static pressure are inexorably linked, you can't separate one from the other.

Your suggestion that 100 cfm for a random orbit sander assumes that there is sufficient static pressure to produce 100 cfm at the end of a 27mm hose.

Here's the performance curve on your PFlux1:



Reference: https://lagunatools.com/classic/dust-collectors/p-flux-1/

As you can see, there's a direct relationship between the diameter of the pipe, static pressure, and resulting CFM.

You pose a question about much static pressure is required for a random orbit sander, which is partially correct but is ultimately misunderstanding the relationship. I believe the correct question would be: "What is the optimal CFM (as measured at the end of the hose) to efficiently extract dust from a random orbit sander connected to a 27mm hose?" Once you have the answer to that question, the follow up question would necessarily have to be: "What is the static pressure necessary to produce "X" cfm at the end of a 27mm hose?"

Given that nearly all portable "dust extractors" on the market (Festool, Makita, Starmix, Nilfisk, etc....) have settled on producing portable extractors designed to extract dust from portable electric hand tools with minimum specifications of approximately 80"+ static pressure and 100+ cfm, I think we find our answer as to the minimum combination of static pressure and airflow to get the job done. Another way to state the conclusion is, the dust extractor manufacturers clearly believe that you need ~80-100" static pressure to provide sufficient CFM at the end of a 27mm hose. If it were otherwise, of course we'd be seeing a lot of machines with 20" static pressure, but we don't.

 

[Steve1]

OK.

Can we then summarize --- only cfm is going to move wood dust, but high static pressure will maintain the cfm when sucking through a straw. And a Festool 27mm hose might as well be a straw, compared to a 4" or 6" steel duct.

An accurate and concise summary ?

 

[Hipplewm]

Not to mention when you are using say a Festool dust extractor on a rotex150 I have my knob turned down to about 30% power, or the sander sticks to the board. Can do that with dust collection. Also the 27mm hose fits OVER the dust collection for the rotex, so it is even smaller - same for the Domino and other small handheld things.

 

[Jim_in_PA]

Please explain why a random orbit sander needs high static pressure vacuum ?

Since you cannot depend upon high volume air flow through a tiny port, high static pressure (vacuum) take on the extraction job. IE, it's about the law of physics.

 

[Tom the Remodeler]

OK.

Can we then summarize --- only cfm is going to move wood dust, but high static pressure will maintain the cfm when sucking through a straw. And a Festool 27mm hose might as well be a straw, compared to a 4" or 6" steel duct.

An accurate and concise summary ?

You got it Steve

CFM to move wood dust

Velocity to keep the dust suspended in the air stream

Static Pressure to ensure appropriate CFM is present at the point of collection

 

[ReneS]

You got it Steve

CFM to move wood dust

Velocity to keep the dust suspended in the air stream

Static Pressure to ensure appropriate CFM is present at the point of collection

Tom - Could you explain how velocity and pressure are related?

To me it seems like they would be closely related.

 

[MacBoy]

… Btw, the SawStop blade guard (when connected to a shop vac) is amazyingly effective (99.9%?), except for edge cuts. I use the spacer hack for edge cuts (99.5% in that case?).

Off topic — what is the Spacer Hack

 

[ChuckS]

MacBoy,

The hack is to make every edge cut a regular rip cut by adding a side piece to the board to be cut. When you use the trick on mdf, you can see how great it is. See the last photo that shows how much dust was found the table after an edge cut with my SawStop PCS (dust blade guard connected to a shop vac)...practically none.

The side strip is about 10 cm x 30 cm and the same thickness as the workpiece. I have made two, one for 1/2" and one for 3/4". If the workpiece is neither 1/2" nor 3/4", make the one-time side strip with scrap that is the same thickness as the workpiece.

 

[MacBoy]

MacBoy,

The hack is to make every edge cut a regular rip cut by adding a size piece to the board to be cut. When you use the trick on mdf, you can see how great it is. See the last photo that shows how much dust was found the table after an edge cut with my SawStop PCS (dust blade guard connected to a shop vac)...practically none.

The side strip is about 10 cm x 30 cm and the same thickness as the workpiece. I have made two, one for 1/2" and one for 3/4". If the workpiece is neither 1/2" or 3/4", make the one-time side strip with scrap that is the same thickness as the workpiece.

Ahhhh, nifty technique, especially with the magnets!

Thank you for the quick response.

 

[Tom the Remodeler]

Tom - Could you explain how velocity and pressure are related?

To me it seems like they would be closely related.

Hi Rene,

Velocity is not much of an issue in LVHP systems (small dust extractors). Where velocity really comes into consideration is in the larger HVLP systems (systems with 4"+ piping). The specifics of managing velocity are a bit above my pay grade, though many of the better dust extractor monitor velocity. For instance, my Felder RL-160 dust extractor has a warning light that illuminates if/when the velocity of the air stream drops below 20 m/s.

Bill Pentz has exhaustive writings on dust collection, and does a pretty good job of covering most of the topics: https://billpentz.com/woodworking/cyclone/staticcalc_faqs.php#AirFlowRequirements

 

[Mini Me]

The Australian information takes BP's site which is a total migraine inducing mess and gives a whole lot more. BP was involved in the early days of the Oz discussions and it was mentored by a Physics Professor who developed and built clean rooms. During the time all this information was developed we established some new guidelines, worked out that some stuff that was commonly thought to work didn't work as previously thought and this has become a huge resource to be used by everyone who wants to know this stuff.

A couple of things off the top,

Anemometers can't be used for air speed measurement

4" Duct is too small

The rest of the world's grid uses 50hz instead of 60hz as the US does and this results in a performance drop of approximately 33% which obviously means anything written based on 60hz does not apply to the ROW as far as CFM discussion goes.

We worked out how to increase the air flow at entry to the duct with the addition of bell mouth attachments.

1000 CFM is generally needed at the duct port on the machine and all machines need to be modified as no manufacturer uses a 6" port. 4" ducting can only flow about 700CFM at 60hz.

Air cannot be extracted from a closed cabinet such as a bandsaw and air entry must be allowed for. This is the single reason BS's are generally criticised and lots of people resort to adding extra pick ups under the table.


Etc Etc. There are years of work and proof of the work with all the evidence to support the findings all laid out for anyone who wants to read it. I think that a lot of people dismiss the whole idea that the information was not developed in the US so it can't be worth reading. I was in the industry, developed two businesses and took part in the discussions on the forum. In fact me selling Clearvue Cyclones in Oz most probably kick started to whole thing to a higher level and after that we developed an automatic blast gate system which is still sold today though I am no longer part of it.

All the discussion upthread has all been covered in the Oz forum along with far more as well.

 

[ReneS]

Hi Rene,

Velocity is not much of an issue in LVHP systems (small dust extractors). Where velocity really comes into consideration is in the larger HVLP systems (systems with 4"+ piping). The specifics of managing velocity are a bit above my pay grade, though many of the better dust extractor monitor velocity. For instance, my Felder RL-160 dust extractor has a warning light that illuminates if/when the velocity of the air stream drops below 20 m/s.

Bill Pentz has exhaustive writings on dust collection, and does a pretty good job of covering most of the topics: https://billpentz.com/woodworking/cyclone/staticcalc_faqs.php#AirFlowRequirements

Thanks Tom.