Thread: Air Filter units

Originally Posted by Redbeard

I'm a seeing up a woodturning workshop in half my garage (6x6x2.4) and want to minimise dust. I have a dust collector which made a significant improvement in the garden shed but as the garage is connected to the house I really want to knock the dust down hard.

I've been looking at various air filters (W326 - AP-12 Two Stage Air Filtration Unit | Hare & Forbes Machineryhouse for example) and wondered about their effectiveness. The house is a rental so hanging from the ceiling is out. How would these types of units work in an under bench arrangement? Especially if right under the main culprit, the lathe?

What size/specs is the DC and the ducting? If the dust collector is powerful enough and you are using 6" ducting and Bell Mouth Hood collection there should be no need to use a room air filter.
Rather than spend more money on a room air filter (RAF) it's usually better to fix the problem at the DC and ducting level.

In terms of a room RAF under a bench this does not work very well as fine dust coming off the lathe is warmed by the turning process so will drift upwards.
The better arrangements I have see are;
A) a stand that sits the RAF directly above the lathe, or
B) second best has the the RAF on its side or horizontal with the air intake level with the the spindle.
B works really well provided the turner is highly skilled and knows how to
- sharpen tools to a pro level.
- keeps the tools sharp
- minimises the used of sandpaper.

I have measured the dust levels in a room with a master turner demoing turning techniques using setup B and over about an hour the dust levels in the room air went down. The turner used no sandpaper and maintained sharp tools.

On these units H&F say that it is an 85% 1micron unit. Is there any way to improve that filtration, or does anyone make 99% PM2 filters for these?

I am looking at one of these for clearing the workshop after welding and painting (as well as dust)

Originally Posted by takai

On these units H&F say that it is an 85% 1micron unit. Is there any way to improve that filtration, or does anyone make 99% PM2 filters for these?

I am looking at one of these for clearing the workshop after welding and painting (as well as dust)

PM2 filters are by definition >95%, to be sure of getting 99% you will need a P3 type filter.

The 85% will be with the "unconditioned" filter, as the filter picks up dust its filter efficiency will improve.
As to how much it improves and how long this takes depends on what sort of wood dust you are making and how sharp the tools/machines are. If its fine dust like that produced by power sanding it will take maybe hours to get to say 95%. If it's from machines mainly making chips it could take days.

The problem with these filter units is their motor/fans (eg 1/4HP) have very little grunt so fitting finer filters is problematic as they find it difficult to push enough air through finer and finer and ultimately clogged filters. This is one reason why at least a 3HP motor is needed to drag enough air through needle felt filter bags and cyclones, to be effective in a workshop.

The way around this is to use deeply (150mm) pleated HEPA filters, then even an 80W fan can push 800 CFM through a super fine filter (I have one that is 99.99% efficient at 0.3 microns) even when it is partially clogged. Problem is these cost an arm and leg and one the filter is clogged - its replacement cost is in the many hundreds of $ range.

I would not recommend these room air filter (especially with say a P2 filter fitter) or any DC for painting or welding as both types fumes are sticky and will gum up the filters very quickly and there's no cleaning possible so they will need replacement. If you wish to proceed I would invest in some cheap prefilter media that will help protect the main filters. I have used the polyester stuffing from pillows as a prefilters for HEPA filters. Its far from perfect but its better than nothing and very cheap so it can be readily replaced.

Originally Posted by BobL

PM2 filters are by definition >95%, to be sure of getting 99% you will need a P3 type filter.

The 85% will be with the "unconditioned" filter, as the filter picks up dust its filter efficiency will improve.
As to how much it improves and how long this takes depends on what sort of wood dust you are making and how sharp the tools/machines are. If its fine dust like that produced by power sanding it will take maybe hours to get to say 95%. If it's from machines mainly making chips it could take days.

The problem with these filter units is their motor/fans (eg 1/4HP) have very little grunt so fitting finer filters is problematic as they find it difficult to push enough air through finer and finer and ultimately clogged filters. This is one reason why at least a 3HP motor is needed to drag enough air through needle felt filter bags and cyclones, to be effective in a workshop.

The way around this is to use deeply (150mm) pleated HEPA filters, then even an 80W fan can push 800 CFM through a super fine filter (I have one that is 99.99% efficient at 0.3 microns) even when it is partially clogged. Problem is these cost an arm and leg and one the filter is clogged - its replacement cost is in the many hundreds of $ range.

I would not recommend these room air filter (especially with say a P2 filter fitter) or any DC for painting or welding as both types fumes are sticky and will gum up the filters very quickly and there's no cleaning possible so they will need replacement. If you wish to proceed I would invest in some cheap prefilter media that will help protect the main filters. I have used the polyester stuffing from pillows as a prefilters for HEPA filters. Its far from perfect but its better than nothing and very cheap so it can be readily replaced.

I was planning on using a HEPA filter designed for gas heating intakes with a polycloth pre-filter which should keep the HEPA relatively clean, but ultimately all of it will need replacement sooner rather than later.

Originally Posted by takai

I was planning on using a HEPA filter designed for gas heating intakes with a polycloth pre-filter which should keep the HEPA relatively clean, but ultimately all of it will need replacement sooner rather than later.

That will work for the dust and paint particles but as long as you are aware that this will not work for paint solvents in gaseous form and noxious gasses that welding generates which will go straight through even HEPA filters. Welding generates loads of CO2, CO, NOx and also CrO if welding SS, and these are much better off outside your shed than repeatedly being recycled inside a shed where they can eventually build up.