Thread: New dust extraction system

I'm sorry to tell you that the 100mm clear pipe kit doesn't take advantage of what a 2HP system is capable of (see generic 2HP thread sticky to see how to make the generic 2HP DC sing).
Removing the bags won't make very much difference because even a short length of 100 mm ducting immediately limits the flow 400 cfm and any 100mm ducting system is downhill from there.
For $279 you could have purchase 12m of 150mm ducting and all the fittings you need to make up a far superior system.

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I like the idea, and had considered doing it myself with 6" ducting.

However, what was of concern to me was the potential of dust (MDF and similar toxic) getting into my drinking water tank which is connected to the shed.

I also considered that it may be, in my case, more effective for the ducting to exit the shed from a lower height so that the shavings/dust do not have to travel as great a height and possibly be more effective. In this regard, I was going to run the ducting along two (2) adjacent walls at say 1.6 mtr height with angled 'Y' connectors where required - all the machines would have to be located around the walls.

The problem here is what to do with the panel saw in the centre - your drop down connections would solve this.

Let us know how it goes.

Originally Posted by BobL

I'm sorry to tell you that the 100mm clear pipe kit doesn't take advantage of what a 2HP system is capable of (see generic 2HP thread sticky to see how to make the generic 2HP DC sing).
Removing the bags won't make very much difference because even a short length of 100 mm ducting immediately limits the flow 400 cfm and any 100mm ducting system is downhill from there.
For $279 you could have purchase 12m of 150mm ducting and all the fittings you need to make up a far superior system.

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Deep down I think I knew this, but I took the easy way out with the clear piping kit. I only ever run one machine at a time and even with a drum sander or thicknesser running it has always been sufficient. I know it could be better again but I'm sure this will be fine for my needs. If I have issues down the track I will update as necessary.
By hanging the fan on the wall it is only two angles to any machine. One from the main pipe and one to the machine outlet, I guess this is helpful. I tested it out last night at the furthest outlet and it easily picked up a big handful of chips and it was at the fan in well less than a second. So attaching it back to the bag and filter won't reduce the air flow? I would have thought as the filter fills with dust the flow would lessen? I better read the post you suggested and educate myself a bit more. I will probably regret it though as I'm sure I'll learn that everything I just set up was inferior...

Sorry to sound so negative but I just wanted to advise other newbies about the poor performance of 100 mm ducting in controlling dust.

Originally Posted by asheddie

By hanging the fan on the wall it is only two angles to any machine. One from the main pipe and one to the machine outlet, I guess this is helpful.

Yes reducing the number of bends does help but it won't help much.

I tested it out last night at the furthest outlet and it easily picked up a big handful of chips and it was at the fan in well less than a second.

This is a common test performed by users, along with feeling the suck of the air by hand at the end of a piece of ducting.
However, both tests are poor indicators of DC performance.
The chips have to be collected from a spinning machine throwing dust away from the machine, not to mention that the air used to collect the ships is not passing directly into an open duct but has to pass through a number of choke points.
Chips are one thing but to control fine invisible, dust which is what affects health,nothing beats maximum air flow and unfortunately 100mmm ducting simply cannot carry enough air to do this.

So attaching it back to the bag and filter won't reduce the air flow? I would have thought as the filter fills with dust the flow would lessen?

Yes it will reduce the air flow but not by much at the start when the bags are clean and the 100mm ducting restriction will dominate the flow.
You are right that at some point the filter fills to a point where it starts to dominate the air flow but because of the 100mm ducting the flow can never be more than 400 cfm even without the filter.

Remember not only do you have 100 mm ducting you have rather long length of it so it might only be a maximum of 300 cfm.

I guess one thing I should have pointed out is that I always wear a dust mask while wood working. The dust collection system for me is more of a house keeping apparatus than a health saver. It seems I can get more out of this dust extractor but all my machines have small outlets anyway. I think I'll need to modify them before I think of running larger pipe. I dream of the day I actually do some wood work in my shed and stop modifying the shed its self... haha, that will never happen!

PS thanks for the advice BobL, it's always very helpful.

How about general shed ventilation?
Ie doors and window location - hopefully your outdoor container is downwind from this?

I am interested in how you are going to connect to the 'outdoor container' without all the sawdust escaping.

I'm not totally sure how I'm going to do it cava!!! As for the outside tub venting dust it will be on the other side of the shed, away from any doors and I don't have any windows. I was planning on sitting it in a dense growth of bushes a few meters away from the shed. When the dust vents out the vent holes it'll become mulch for the garden. I have a strict no MDF rule in my shed so it will only be natural timber dust. Maybe if I'm going to be doing a large amount of jointing/thicknessing then I could throw a wet hessian sack loosely over it to catch excess dust? Perhaps I could have the garden sprinkler on each time I use the dust extractor, the irrigation controller is in the shed, it would only take two seconds to turn it on. I'm just thinking out loud to be honest. I might re attach the filter/bag yet? I'm just floating ideas.

The big settling tank idea is not as silly as it might seem.

If the tank is big enough and the outlet is big enough and far enough away from the inlet for the escaping air speed to drop dramatically the chips will drop out of the air flow and only the finer dust will flow out of the tank.

The trick will be to get a long slow speed path length in the tank before the air escapes out of the tank.

So B will be much better than A - remember you want the outlet MUCH bigger than the inlet or you will have introduced a chip collector into the line (it doesn't matter whether its before or after the impeller). Do not place a chip collectors of cyclone onto this system as it is only 2HP and these add MORE resistance to flow than clean filters but less than dirty ones.

In these pictures the black arrows represent the size of the chips coming out of suspension. In A you will see that if the path length is too short some small chips may still be carried out of the exit.
Whereas in B only the fine dust that stays suspended will exit the tank.

BigTank.jpg

Bob, how big does the tank have to be for a 2 HP dusty?

The reason for the question is that I have a 1000 litre IBC that 'may' be re-purposed for such a use. Emptying it may present problems though.

Originally Posted by cava

Bob, how big does the tank have to be for a 2 HP dusty?

The reason for the question is that I have a 1000 litre IBC that 'may' be re-purposed for such a use. Emptying it may present problems though.

That depends on
- the total air flow (so modified or modified 2HP DC, ducting length and size etc)
- how much escaped dust you are prepared to tolerate.
A 200L drum is prob OK for a low flow system and you are not worried about some visible sawdust escape.

1000L would probably catch all visible dust provided it was not a tall narrow shape (i.e. A above) but more of a squat shape like B.
Clean up is a PITA so a hopper style floor and underneath access would the way to go.