Thread: Aluminium Ducting

Originally Posted by GarethR

Has anyone used rigi-flex aluminium ducting as part of their dust extraction setup?

The ducting is thin (~100micron = 0.1mm). Perforation (high velocity wood chips) and collapsing (suction pressure) risks may be high.

Any thoughts?

Thanks.

Apart from the problems you mention, take a look at the resistance it generates .


To work out the resistance, lets consider a basic 6" (150 mm) duct attached to a 2000 cfm (4000 cu m/hr) ~3HP dusty.

The figures in red are represented on the graph as the two red lines.
If these are extrapolated vertically until they cross (ie it's not even on the graph) and that point is then extrapolated horizontally this gives the final air resistance under these conditions of 350 Pa/m or about 1.6" of water/m.

Using 4 m of this ducting will use up 6.4" of pressure which is about half that available from a big dusty. This means the air will be moved along with very pressure behind it so that as soon as it strikes a junction or bag etc it will slow down.

Conversely if the DC can only generate 12" of pressure and the junctions and bags required 6" of pressure to overcome there is only 6" of pressure less so it won't move any air on a system that requires 6.4" of pressure to maintain. In practice the air speed drops so the resistance drops and reaches an equilibrium point.

Under the same conditions I would expect the resistance of smooth walled pipe to be less than a 1/3rd of most corrugated stuff.

Sure, one can go to for bigger ducting but (as I am learning) at some point the physical size of the ducting starts to really become a nuisance around machinery.

This corrugated ally stuff is designed for large ducting low flow applications such as in airconditioning.

As Bill Pentz says - nothing beats a smooth walled pipe.

Thanks BobL, I wondered as much but had trouble reading the graph .

My current thinking is to minimise the ducting lengths by having a stationary externally venting DC with separator and wheeling my machinery up to the DC. My TS and router table setup is wheeled and very easy to move around so I don't see it being too much of an issue.

For this, short lengths of flexible ducting is preferred so after flagging the Al ducting option I've come across some smooth bore flexible ducting, i.e. smooth on the inside and corrugated on the outside. This would be a better option than corrugated both in- and outside.

I'm guessing this type of ducting will lie somewhere in between straight duct and fully corrugated flexible ducting in terms of resistance?

Originally Posted by GarethR

Thanks BobL, I wondered as much but had trouble reading the graph .

Me too. It's near 2 am and I'm stuck in Melb airport at the moment but when I get back to Perth I will redraw the graph and expand the vertical scales and explain it in detail for those that are interested.

My current thinking is to minimise the ducting lengths by having a stationary externally venting DC with separator and wheeling my machinery up to the DC. My TS and router table setup is wheeled and very easy to move around so I don't see it being too much of an issue.

That is indeed one solution.

For this, short lengths of flexible ducting is preferred so after flagging the Al ducting option I've come across some smooth bore flexible ducting, i.e. smooth on the inside and corrugated on the outside. This would be a better option than corrugated both in- and outside.

I'm guessing this type of ducting will lie somewhere in between straight duct and fully corrugated flexible ducting in terms of resistance?

That is very nice stuff but it won't be as good as rigid wall pipe and expect it to be exy but if you are only using a short length it should not be too bad.

I use aluminium heating ducting to connect a thicknesser to a dust extractor. It has proved ideal for the purpose, as the following photos might indicate:
1* The thicknesser came without an extraction hood.
Attachment 183062
2* I had a surplus 'Big Gulp' lying around, and modified it to fit the thicknesser.
Attachment 183063 Attachment 183064
3* The hood winds up and down with the thicknesser, so is always in the correct position to collect shavings.
Attachment 183065 Attachment 183066
4* The aluminium ducting is about 2.5 metres long. I fitted one end with a push-on sewerage fitting.
Attachment 183067 Attachment 183068
5* One end goes directly into the PVC fitting on the hood: the other is pushed onto the fitting on the Thien-type separator which is connected to a 2hp dust extractor.
Attachment 183069 Attachment 183070
6* The rigidity of the ducting is such that it is self-supporting in use.
Attachment 183071
7* Over such a short distance, the question of 'extraction efficiency' is of less importance. Certainly very few shavings are evident around the thicknesser, with most ending up tn the blue separator container.
8* The setup is very easy to assemble, disassemble and store.

Where I last worked we ran a 7 axis robotic arm to carve out moulds from plastic resin slabs. Swarf range from soft and fluffy to chunks like smashed rock candy, hard and sharp. To reduce cleanup times and dust we ran a large dust extractor and multiple suction pipes made from aluminium air conditioning ducting (not my first or last choice but was not my call). However to my surprise it last reasonably well.

Pipe was about 140mm diameter, running a single spiral wound coil with spacing of about 40-60mm. Foil thickness, no idea but looked like very thick alfoil.

One long term problem we had was wherever there was flexing the aluminium fatigued and eventually failed. It also tended to kink at bends if not supported.

I liked the idea of the Al ducting becuase of its rigidity as you explained adeben. The less floppy ducting the better although finding a compromise between the two might not be easy.

Originally Posted by adeben

Over such a short distance, the question of 'extraction efficiency' is of less importance. Certainly very few shavings are evident around the thicknesser, with most ending up tn the blue separator container.

Just because a set up looks like it is collecting most of the chips does not mean it is efficient at collecting the fine invisible dust which is the potential cause of health problems.

Using short runs does have the advantage you indicate but it also means locating the DC inside the shed which appears to be your situation. In such a case it does not matter how efficient any setup is because all the really fine dust will go straight thru the filters and bags on DCs and fill up a shed with invisible dust. Short of using a HEPA filter on the DC the only current solution for us is to vent or place the DC outside the shed and use large smooth wall ducting to machines

What I also see in your set up is one that has been throttled down in a number of ways. Narrowing the big gulp (BG) to a small slot means the air carrying dust has to make two almost right angle turns just to get into the BG throat. Then the air carrying dust has a third right angle to negotiate even before it gets to the ducting. You would be much better off making an sheet metal or plastic adapter that goes directly in line from the thicknesser port to the metal ducting ie no bends. That corrugated dusting ducting will also have 3 times the resistance of any smooth walled pipe but seeing as it's short it's minor compared to the other problems with your setup.

I agree that metal ducting has a small advantage with it's rigidity but all it takes with plastic flexy is a couple of occky straps from a ceiling hook and it can be located more or less where one wishes as well. A disadvantage with ally ducting is it does not come off all that well when a large piece of lumber falls on it.

If all you are after is chip collection then what you have looks fine. I just don't want newbies running off and duplicating aspects of your setup in the hope they will get fine dust collection with it.

Who ya callin a newbie

Tend to agree with your observations BobL. I'm sticking with my outside venting, smooth walled and short ducting setup with separator.

Blower arrived this morning so I can start planning my separator build and trying to figure out which direction everything is setup so it matches the flow direction of my blower.

Do you have any pointers re: Thein top-hat type separator and matching direction of air flow?

Originally Posted by GarethR

Who ya callin a newbie

Tend to agree with your observations BobL. I'm sticking with my outside venting, smooth walled and short ducting setup with separator.

Blower arrived this morning so I can start planning my separator build and trying to figure out which direction everything is setup so it matches the flow direction of my blower.

Do you have any pointers re: Thein top-hat type separator and matching direction of air flow?

I have little feeling for making a Thein separator efficient.

The General principles for any DC setup are pretty simple.
- Keep the air flow as direct as possible and the ducting as straight as you can
- Try to make bends with as large a radius of curvature as possible.
- Using 2 x 45º bends to make a 90º bend is better than using a single 90º bend such as adaben uses exit from his chip collector.
- make the internals of the ducting joints as smooth as possible, avoid step or sudden changes in ducting size and direction.
- look for and eliminate leaks

Hi Bob,
You might have misunderstood a couple of points about the Big Gulp setup:
1* The slot has been narrowed so that it is an exact fit on the extraction chute of the thicknesser. That means that the chips move DIRECTLY fron the thicknesser chute across the base of the Big Gulp to the exit point, making only one rightangle turn through the PVC fitting before entering the aluminium ducting.
2* The rightangle turn is necessary to get the extraction system out of the way of timber passing through the thicknesser.
3* I understand your point about fine dust collection, but my most immediate need is to prevent the dispersal of thichnesser debris across the floor of the shed.This arrangement does that admirably, and the aluminium ducting is a useful part of the system.

Sorry BobL I was specifically referring to the spinning direction of the air in the separator versus that of the blower.

From my understanding if the blower is running in a clockwise direction then the intake in the separator needs to be setup so as to cause the air to spin in the same direction.

From Bill Pentz website:

"If the spinning air inside the cyclone hits the blower impeller going the wrong way, then the motor must do lots of extra work to reverse that spin and we lose considerable airflow. We need to make sure our cyclone, motor and impeller spins match!"

From that I take it that if the impeller is running in a clockwise direction the dust intake should sit on the lefthand side, correct?

Originally Posted by GarethR

Sorry BobL I was specifically referring to the spinning direction of the air in the separator versus that of the blower.

From my understanding if the blower is running in a clockwise direction then the intake in the separator needs to be setup so as to cause the air to spin in the same direction.

From Bill Pentz website:

"If the spinning air inside the cyclone hits the blower impeller going the wrong way, then the motor must do lots of extra work to reverse that spin and we lose considerable airflow. We need to make sure our cyclone, motor and impeller spins match!"

From that I take it that if the impeller is running in a clockwise direction the dust intake should sit on the lefthand side, correct?

Short answer is yes. The current consumption is a fair bit more trying to do it the other way. We see a 6 amp rise in cyclones that are set up with the wrong direction of rotation and they are also noisier as well as not as efficient, but BP made that point in your quote.

by christ it is bloody good to have someone like you bobl on here for us sort of like the ozzie version of bill pentz, it is just really helpful and i say that to everybody on here it is just good we can ask if we do not know properly i know my industry i have been in it 52 yrs but this dust collection is a very important part of woodworking i suppose when all said and done probaly the most important. cheers peter

Originally Posted by GarethR

Sorry BobL I was specifically referring to the spinning direction of the air in the separator versus that of the blower.

From my understanding if the blower is running in a clockwise direction then the intake in the separator needs to be setup so as to cause the air to spin in the same direction.

From Bill Pentz website:

"If the spinning air inside the cyclone hits the blower impeller going the wrong way, then the motor must do lots of extra work to reverse that spin and we lose considerable airflow. We need to make sure our cyclone, motor and impeller spins match!"

From that I take it that if the impeller is running in a clockwise direction the dust intake should sit on the lefthand side, correct?

Sounds right.