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fozz
29th August 2011, 11:05 PM
Gday folks,

This may be a completely crazy idea but I was wondering if ever any of you had ever considered using a kitchen rangehood over your lathe to remove the airborne dust produced from sanding.

A few months ago I fitted a new rangehood to a customers kitchen, it was about $250.00 and produced about 650CFM of air movement.

My thinking was that as the rangehood comes with its own fan and has a duct to remove the exhaust, it could also be plumbed into our dust extraction systems which should boost the performance even more.

Anyway, I'll be interested in seeing what you think of the idea.

Ross.

BobL
29th August 2011, 11:32 PM
A range hood that vents to outside a work space is better than nothing but removal of invisible dust (the stuff that causes the health problems) from wood working machines requires 1000 cfm at 4000 fpm. Anything less that this simply doesn't work. A work area might be dust and chip free but the air surrounding will be loaded with invisible dust.

mkypenturner
29th August 2011, 11:32 PM
will be watching this to see what people think

fozz
30th August 2011, 01:28 AM
Gday Bob,

Not disputing your facts, my thinking is that instead of the seemingly usual setup for woodturning where either no extracting, little extraction or one to half a dozen fans being used to blow the dust away from the turner is the norm, an overhead extraction unit that is able to pick up smoke from cooking should be able to pick up alot more of the harmfull dust than the above methods do.

fozz
31st August 2011, 05:59 PM
Anyone else wanna chime in, otherwise it can be deleted as a waste of time?

BobL
31st August 2011, 07:21 PM
Gday Bob,

Not disputing your facts, my thinking is that instead of the seemingly usual setup for woodturning where either no extracting, little extraction or one to half a dozen fans being used to blow the dust away from the turner is the norm, an overhead extraction unit that is able to pick up smoke from cooking should be able to pick up alot more of the harmfull dust than the above methods do.

I agree that some extraction is better than no or little extraction, or blowing dust away from the operator, but only if the dust ladened air is vented outside the shed/workshop. Otherwise all that happens is the fine dust is recirculated back into the shed.

Let's assume the extractor is vented externally and just look at the potential effectiveness of the range hood arrangement. The airborne emissions of lathes are quite different from those generated by cooking food which is usually heat driven slowly upwards directly into the yaw of the range hood. Whereas A lathe throws fine dust out into the air roughly in the shape of an expanding cylinder in 3 dimensions.

To capture the dust at source, as well as sheer air volume removal, the linear speed at which the air is removed is critical. 4000 fpm is the nominal air speed needed to catch the fine dust being generated and being flung out from something like a lathe. For small objects it may be better to have lower flow but higher air speed, so something a vacuum cleaner strapped close to the spinning object. For larger objects high air speed is still essential but few DC can do both high air speed and high air flow.

The biggest opening a 650 cfm fan can have and still create 4000 fpm is 0.163 sqft or 23 sq inches or a ~6" x 4" opening. Attaching this to a 12 x 24 " (2 sqft) range hood type opening will reduce the air speed of about 52 fpm which will basically only capture static airborne dust or the dust moving directly into the hood opening. If the range hood is 420 mm from the object, the most dust a range hood can grab is that dust thrown in its general direction is 25% of the dust. If the range hood is 600 mm from the object it will only be 16% of the dust. To capture 50% of the dust the object will have to sit at the opening of the range hood. The only way to capture the rest is to start cranking up the air speed.

One benefit of range hoods is that they are relatively quiet so the could be useful as supplementary shed dust evacuators and be left running for 15 - 20 minutes after dust making activity to vent the shed of harnful dust.

fozz
31st August 2011, 08:08 PM
Gday Bob,

Thanks very much for the expanded explaination, makes it alot clearer.You now have me abit worried as to extracting dust while using the lathe.

I'm left wondering just how many dust extractors are going to be capable of doing what you state is needed and I have to ask what set up you would suggest to use for extracting most if not all the dust the average woodlathe produces.

The reason I started this thread was due to abit of crazy lateral thinking and that there are a few timbers now that I just cant tolerate. Now that I've found wood turning I'd like the fun to continue as long as possible.

hughie
1st September 2011, 09:30 AM
One benefit of range hoods is that they are relatively quiet so the could be useful as supplementary shed dust evacuators and be left running for 15 - 20 minutes after dust making activity to vent the shed of harnful dust.

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Bobs on the money:2tsup:, but it still may have a positive effect, seeing that you probably have access to many of them over time.

Its true that DC on the lathe will greatly help, but the nature of the beast is that small particles will float suspended in the air.The suspended and often unseen are the danger for the lungs.

So then you could then use the rangehood fans ie a couple or what ever you have on hand to cause cross flow ventilation and I would run them the whole time I was in the shed or when turning anyway.

With my shed I intend to just that by fitting a extraction fan at one end and either making a vent/s or leave the door open at the other end. This will give me the cross flow and the removal of the suspended particles.Saving on the main DC I have, its only one HP and will do my lathe and bandsaw etc. But way to small to do the whole shed or even contemplate it.

In your case you could fit as many as required to get sufficent air movement and it would be quiet:2tsup:. In my case I have to some extra work to do, to dampen the noise.:~

BobL
1st September 2011, 11:35 AM
Gday Bob,

Thanks very much for the expanded explaination, makes it alot clearer.You now have me abit worried as to extracting dust while using the lathe.

I'm sorry if it worries you, but having worked on and off in designing dust free laboratories for the last 25 odd years I do worry that so many people buy a 1HP DC or vacuum cleaner and think that this solves their fine dust problems.


I'm left wondering just how many dust extractors are going to be capable of doing what you state is needed
The short answer to that is "not many". The reality is that that most should be called chip collectors. Even DCs with 1 micron bags or pleated filters still only typically collect 70% of the dust particles at that size and less than 50% at 0.5 microns or smaller, which means little if large amounts of dust are generated in the first place. One benefit these finer filters have is that they can scrub an air volume faster than coarser filters but unless appropriate cross flows are established and maintained in a shed, large amounts of fine dust will still hang around in te air for hours even days.


. . . and I have to ask what set up you would suggest to use for extracting most if not all the dust the average woodlathe produces.

The first suggestion I usually make is don't vent any dust extractor into a workspace. I know this does not work for folk that need to retain warm or cool air in a work place, or have location problems, but for those that can afford to vent they should. Even if you cannot put your DC outside it may be possible to put your DC inside an enclosure inside your shed and then vent the enclosure outside. This has been done by several forum members.

The next one is set up cross ventilation (openings in the walls opposite DC ports) so that the venting of any space is as effective as possible. This can be aided by the addition of exhaust fans

Then get the biggest (most efficient) HP DC setup you can afford and if possible vent it outside the workspace. Most weekend warriors don't generate enough dust to warrant expenditure on special bags or pleated filters if they vent outside - save your money and put it towards a bigger HP DC.

For a lathe I would consider building a back hood that covers the working length of the lathe bed and connect that with as short a run of ducting as possible to the DC. I would also recommend a movable baffle that can restrict the collection to the length of the piece being turned. If possible the lathe could even be placed partially or wholly inside the hood.

If the DC comes with an adapter at the intake that constricts the intake to the impeller to 4" ports, toss the adapter and use as large a diameter ducting to the machine as you can afford.

Then consider also wearing a mask or air filter.

Leave the dust extractor running for 15-20 minute after the last dust making activity.

NeilS
1st September 2011, 01:02 PM
From what I understand, Bob has summed it up.

Consider his figures the minimum requirement for effective fine dust (the dangerous sort you can't see) removal.

If you can vent outside and don't have to push your air flow through a filter then you can achieve the required air flows with a moderate sized DE fan unit.

If you vent back into your workshop through a filter you have to go to a bigger fan unit. The bigger the filter area the better. Typically pleated filters have a larger surface area for their size and will handle a larger free flowing volume.

If you run a cyclone you have to go to a bigger fan unit. Approx 1HP extra, with matching higher volume fan unit.

If you have both a cyclone and a filter you need a larger fan unit yet again.

I found I needed as a minimum a 3HP fan unit pulling 2800cfm with a minimum of 30 sq. ins. (6" diam) ducting at the inlets and the main runs at 100 sq. ins. to run my cyclone plus 1200mm x 500mm diam pleated filter.

I also run an air filter plus use use a respirator with a 100 sq. in. HEPA filter when I'm in the workshop.

I don't claim any expertise in DE but do listen to those that do.

Stay healthy.

jefferson
1st September 2011, 06:49 PM
A very interesting discussion, for me considering my last post on Allergic Reactions to Dead Finish.

I've just spent the best part of the day turning camphor laurel - without reaction. (Plus a mate turning redgum grinders). That's with the two MC 1200s running, plus the 1hp DEs at each lathe.

Dust isn't just dust it seems. Some is worse than others.

That said, the "rules" for me seem to be:

- use as much dust extraction ie volume as you can afford. The bigger the better - and then for use while you are actually turning, not just sanding.

- filter what is left over with HEPA or similar filters. I'm very impressed with my 2 MC1200s,

- if all else fails, use a dust mask or better still a respirator.

Just my thoughts. I'll probably think otherwise when I start on the Dead Finish again. (And I will not let it beat me!)

fozz
1st September 2011, 09:42 PM
Folks, gotta thankyou all for your input, its greatly appreciated.

The dust extractor with pleated cartridge and cyclone are inside the garage and while I have no room to stick them outside, they can be enclosed in their own room with vents to the outside.

The dust filter hangs above head height at the front of the garage and the exhaust from that hits the front brick wall then divides and sends the air back down the sides of the garage to the extraction fans in the back wall of the garage.

I'll make up a hood for the lathe over the weekend and if all that doesnt make it easier to breathe then i'll have to save for a powered air filter helmet.

Thanks again for all the advice.

Ross.