Thread: Multiple cyclones in duct runs

The first question is what dust extractor are you going to use? Assessment and comment can be made after that.

Don't think the dust extractor will make much of a difference, with a 75mm inlet the only a way a system like that would potentially work is if you had a vacuum cleaner at each cyclone, however i suspect this will throw out the notion of it being cheap.

Sadly efficient dust extraction isn't cheap, so be prepared to spend much more than what you're comfortable if youre serious about dust collection.

If you haven't done so already spend some time in the dust collection forum and you'll get a good idea of what works, the reason why something hasn't been done before is most probably because it doesn't work or there is a better way of doing it. Dust collection is all about physics and unfortunately there's no way around it.

Thanks guys - yeah realise it's not going to be cheap and dust extractor is to be decided - prob a Bill Pentz type cyclone with a 3-phase motor. Something like the clear vue 1800 but sheet metal myself - shipping kills us in NZ and have the workshops of a huge film that I can use so now they time to do the fabrication bits

Not going for the small chinese cyclone to try and make a cheap system just to put some material removal at the outlet and not move material along all the ducts - would still have a full size cyclone at the end and bigger tools would use just that.

Have done a lot of reading here and in other places and just wondering why I hadn't seen a build with cyclones and bin at the tool so you are then just shifting air after 99% of the mass is removed and not moving chip/sawdust along the lines. Esp with something like the thicknesser that's spitting out massive amounts of material. Just my non scientific idea around physics Other industries use cyclones in parallel right but that's for other reasons and means a loss of pressure - guess the answer may be that the pressure loss for the cyclone is worse than the resistance of teh material in a correctly sized system. Make sense what I'm asking?

I like innovation but what you propose is going backwards as there is no upside to it. From any machine and using a high volume low pressure design that the BP design is the ideal inlet for hobbyists is 150mm. The duct is meant to carry the dust and adding multiple collection points is only adding complications of emptying each one. The small 75mm type Asian cyclones will restrict the air so much the dust pick up would be very low as the cyclone itself is very inefficient. The inefficiencies of a cyclone such as slowing the air down are the basic reasons it works as a dust separator and adding cyclones in series as you propose + a 75mm inlet would be a disaster for good dust control.

Use a BP design in whatever material takes your fancy and I definitely don't think that is necessarily metal sheet, buy a 2nd hand three phase motor controlled by a VFD and the only problem left is the impeller and its attachment to the motor shaft and this is the point that most of these projects fall over at. BP built his first cyclone with a 14" impeller but the production 1800 has a 15" operating at 60hz. If all you had to buy was the impeller, VFD and material for the cyclone it would be a cheap answer to the problem.

Originally Posted by unitseven

Have done a lot of reading here and in other places and just wondering why I hadn't seen a build with cyclones and bin at the tool so you are then just shifting air after 99% of the mass is removed and not moving chip/sawdust along the lines. Esp with something like the thicknesser that's spitting out massive amounts of material. Just my non scientific idea around physics Other industries use cyclones in parallel right but that's for other reasons and means a loss of pressure - guess the answer may be that the pressure loss for the cyclone is worse than the resistance of teh material in a correctly sized system. Make sense what I'm asking?

It's not quite as "massive" as you might think.
This has been discussed before and here it is again.

Let's assume you are planing 1mm off a 200mm wide board that is 2.4m long.
That 1 x 200 x 2400 mm pass is equivalent to ~240 g of softwood shavings

If the DC has enough grunt, the ducting is 150mm, and the planer has been de-choaked so it is making full use of a 150mm duct it should be able to pull ~ 800 cfm or 22.7 m^3/min.

Assuming a 7m/min planning speed, that board above should pass through in ~20s during which time the DC should also move ~9.1 kg of air.

So the 240g of shavings represents ~2.6% of the mass moved.
Even going to 3mm deep passes its only 7.8% of the load.
In other words the shavings present bugger all of the load required to move the air.

If a 100 mm duct is used you can only expect ~1/3rd of the 150 mm duct air to pass through the duct.
Now a 1mm pass generates chips are 7.8% of the air load and a 3mm pass will be 23.4% of the air load.

However the health elephants in the room is not the shavings but the fine dust.
A 150mm duct will capture a lot more fine dust than a 100mm duct.

Adding a cyclone to the machine intake will rob between 25 to 40% of the air flow which means fine dust capture will be seriously compromised.

Originally Posted by unitseven

Not going for the small chinese cyclone to try and make a cheap system just to put some material removal at the outlet and not move material along all the ducts - would still have a full size cyclone at the end and bigger tools would use just that.

I see a big contradiction in your thinking here. You are making the overall system big enough to handle the heaviest load one of your machines will give it yet you want to lighten the load when using one of the lighter-load machines by putting in an intermediate small cyclone. If the overall system will handle the biggest machine it will handle the smallest with ease. Extra cyclones equals added turbulence for one thing and extra bins to remember to empty, then there's the additional footprint of the bins and cyclones taking up space in the work area.

If your workshop is big enough to seriously consider/need two cyclones, then maybe you should be considering two separate DC systems - one at each end of the shed for example - each with their own separate impeller, cyclone, bin and ducting runs.

Where in NZ are you located? Happy to help if I can. See my experiences here.