Thread: Dust extraction advice - wood and metal

I’ve been reading and learning lots. The plan is to mount dc outside although this will have to wait for a few months. Initially the DC will be in the workshop and will be used by belt grinder and disc grinder for wood, metal and some composite materials. Bandsaw and lathe will wait for outside mounting.

I’m looking at a budget of $1000 for the DC delivered to country NSW so really it is likely an $800 budget. I want to get best bang for buck and not feel I need to upgrade again in a years time. I also don’t want to spend valuable and rare shed time modifying DCs more than I have to. This has meant looking for units with main inlet as minimum 150mm, impeller size greater than 300mm and 3hp if possible. This search narrows the field pretty substantially. So far only three I have found meet these criteria of specs and one of those on cost. From their website at least woodfast’s DC5000 has a 200mm inlet, 330mm impeller and 3hp for price of $820. So far it is looking like best deal if these specs are what I should be looking at. Of course it often is never quite that simple and dust collection is one of those things that there is a lot to consider......

My search continues.

You need to check with BobL.

Originally Posted by rob streeper

You need to check with BobL.

Thank you Rob - yep BobL given me some advice and I he read many of his posts on the forum which has been invaluable.

Another question - how do 200mm flex versus 150m DMV pipe compare in term of ar flow?

Originally Posted by Danger Mouse

how do 200mm flex versus 150m DMV pipe compare in term of ar flow?

At the same impeller pressure a 200mm diameter smooth plastic pipe will theoretically move about 2x more than a 150mm pipe.

The effect of flex can be anywhere from about a 5 to a 25% reduction in flow depending on the actual material stiffness, depth of corrugations and curves etc of the flex.
In general the overall effect for short straightish runs of flex is that 200 mm will move more air than 150mm smooth pipe

However - this also depends whether the impeller itself can move that air much air to begin with.
This is why it is pointless putting a 200 mm pipe on a 2HP DC3 as even though it has the static pressure it does not have the swept volume to move the nominal 1250FPM it should be able to move in a 6" pipe.
An extreme example is a shop vac which even though it has 3x the pressure, because the impellers are so small they simply cannot move enough air to be used on larger sized ducting.

So if the impeller is already close to or maxed out in terms of flow, using bigger pipe will just move the same amount of air more slowly, and then in long flat sections of ducting run the risk of the sawdust falling out of suspension, and if the ducting is flex, it can be difficult or impossible to lift out of the corrugations.

In theory a 6" duct can carry 1250 CFM at nominal DC impeller pressures. This translates to an average air speed of about 6000 FPM in the duct. This is nicely above the nominal 4000 FPM required to keep sawdust in suspension. If the impeller is maxed out so the same 1250 CFM is moved through an 8" pipe, the linear air speed is now 3600 FPM.

In practice it's a more complicated than this. For a start the term "average air speed" inside a duct is somewhat meaningless because the air speed near the wall of the duct is always much lower than 4000 FPM while in the middle of the duct the speeds will be much higher. The flow is also almost always turbulent so the resulting swirling flow is usually able to scavenge any sawdust that falls out of suspension. Results are unpredictable In practice I've found airflows with so called average speeds as low as 3000 FPM able to keep 6" and 4" ducting clear in some situations but not others, especially when a long runs of straight flat ducting was involved.

One situation where sawdust fall out is less of an issue is if ducting or flex is used in a vertical orientation. Where flex is involved small amounts of sawdust may settle in corrugations but eventually it falls out of the corrugations and is dragged into the air stream. Of course if the air speed is very slow it may not be able to clear the bigger chips and they will just stay suspended in the air flow and build up in the air stream until they are either so concentrated they will choke the flow, or you turn off the DC and then the sawdust falls to the bottom of the duct and chokes the duct.

I'll address the elephant in the room; tell me to pull my head in if ya must, but as these threads are read by people of varying degrees of education, well... I just wanna state the following for the record...


I'd be concerned about using the same DC for both metal AND woodwork unless I had some very secure spark prevention in place... and even then I'd still have some concerns.

As BobL mentions, wood particles have a habit of settling in the bottom of the runs and that's not a good combo when mixed with hot metal filings.

Personally I'd also want to have two separate cyclone collector bins, one each for metal and for wood, even when venting the finer particulates directly outdoors. This not only makes for better fire hazard control but usually simplifies the disposal of the contents.

IMO you'd be better off with two separate dedicated systems rather than try to run one which can handle both materials safely.


(FWIW, I've seen a few fires in either ducts or bins now, fortunately they were caught in time before things became expensive. Can't count on luck, though... )

Originally Posted by Skew ChiDAMN!!

I'll address the elephant in the room; tell me to pull my head in if ya must, but as these threads are read by people of varying degrees of education, well... I just wanna state the following for the record...


I'd be concerned about using the same DC for both metal AND woodwork unless I had some very secure spark prevention in place... and even then I'd still have some concerns.

An understandable concern.
I have experience with both wood and metal dust and posted my setup for metal dust collection in the metal workers forum.
All that is needed is a dedicated non-flammable chip catcher that will prevent hot metal lumps from entering the Ducting of the wood dust system.
I have been in external communication with the OP about this and reckon we have it under control.

Yep very good points raised and valid concerns. I will have a system in place that I feel prevents any hot material getting caught up in the long pipe run and dc unit. As I get this setup I will post up a WIP but as with most things it will be slow.

BobL has been in touch with me for which I am very grateful and has given excellent advice as he so often does on this forum.

So so far I am leaning heavily towards the wood fast dc5000 unit which is 3hp with 13 inch impeller and 200mm inlet. I’m just waiting for the guys that sell it to get back to me (bit slow but at least they are staying in touch). The inlet will be throttled to 150mm and dc mounted outside the shed. 150mm pvc supply line and then get as close to each machine with 150mm as possible. I have grabbed a drum (on it’s way) for use as a separator for the metal grinder and am working on some 150mm Flexi. I am yet to work out how I am going to approach a bell mouth hood - ideally I’d buy one if I could but looks like I may have to have a crack at making one.

Ok so I have bitten the bullet after a long time contemplating. I bought a wood fast DC5000 which turned up this week. First impressions are that it is BIG!

I have not done much yet, started to put it together (awkward on my own as its big and heavy) and have assembled the pieces for the first version of my setup which will be my belt grinder. Whilst apart, I took a pic of the fan in this sucker for anyone who may want to see as there doesn’t seem to be many photos of these around that I have seen.

Fan is 330mm diameter



Looks like it has been balanced



Inlet is 200mm so I have a reducer to 150mm



I picked up a 150mm conduit fitting which is very heavy duty so we’ll see how it handles metal grinding dust. You can just see 150mm flex pipe but likely this will be directly attached to 150mm pvc pipe into the collection bin.



Another view



And this is the drum that will be under the grinder. I will cut holes to bring in hot metal to here and the an outlet back to the DC. There will be a smaller plastic bucket inside under the inlet filled with water so any hot material will go there. On the outlet side will be 150mm flex back to the DC.




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I should also add here that whilst I have been talking about metal dust my biggest issue really are other materials I grind -G10, micarta and wood. The metal isn’t too bad and if I am not satisfied that I am completely eliminating any chance of metal accumulation in the DC I will only turn it on on when grinding the particularly dusty materials. Next step will be to take it outside and set piping to add in my wood lathe and bandsaw.


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Originally Posted by Danger Mouse

I should also add here that whilst I have been talking about metal dust my biggest issue really are other materials I grind -G10, micarta and wood. The metal isn’t too bad and if I am not satisfied that I am completely eliminating any chance of metal accumulation in the DC I will only turn it on on when grinding the particularly dusty materials. Next step will be to take it outside and set piping to add in my wood lathe and bandsaw.


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You won't eliminate it completely - there will always be a very small amount of very fine metal dust coming through - even f you were to use HEPA filters some would still get through..