Australian Wood Review – June 2019

90 Australian Wood Review

WORKSHOPS

There is a wealth of research to support these requirements.

Because we’re aspiring to collect fine dust with these systems

(not wood chips), the volume of air we need to move through

an extraction system becomes significant. Whilst 350cfm

may be adequate for wood chips, 1000cfm or more will be

required to collect fine wood dust (source billpentz.com).

There are two reasons for this. First of all, we need to

understand that fine wood dust behaves like an aerosol.

Unlike wood chips it becomes airborne immediately.

Secondly, to collect these airborne particles at the source

requires significant volumes of air to be drawn into your

ductwork. Think of it as trying to create a bubble of low

pressure air around the tool generating the dust. The science

confirms this as something that’s difficult to achieve. If

you’ve used a garden blower you’ll understand the challenge.

When used as a blower, they’re effective at blowing dust all

over the place, however, switch them to suction mode and

you’ll find that you need the inlet right on top of the material

you’re trying to vacuum. Why is this? Because blowing has

the benefit of efficiently forcing air flow in one direction.

This advantage is lost in a vacuum system as air is drawn in

from all directions at once. Once again, collecting fine dust

at the source requires large volumes of air to be drawn into

your ducting, which requires significant motor power, large

impellors and large ductwork.

Choosing a style of extractor is largely a decision between

a cyclone (photo 3) or the more conventional single stage

extractors with bags or pleated filters. Remember that both

of these systems traditionally move exhaust air through

some form of filter. As such, the performance of the system

is entirely dependent on keeping the filters clean. If you’re

like me, this rarely happens at the required frequency.

For decades the majority of large workshops have used

cyclone extraction systems for good reason. The inherent

cyclone design ensures that separation of the majority of

wood dust occurs prior to the impellor so that the exhaust

air contains only the finest dust particles.

A single stage system in comparison has all the extracted

dust passing through the impellor with subsequent impact

on performance. Cyclone systems lose out on cost and

noise, however, I chose a cyclone for my installation due to

their performance advantage and smaller physical footprint.

The choice of ducting opens up a host of options in

either rigid or flexible and metal or PVC. My choice was

PVC, purely for the convenience and flexibility, however,

there are some very professional metal ducting solutions

available. Materials aside, the first consideration should be

minimising lengths of ducting and maximising duct size.

Flexible duct should obviously be avoided wherever

possible given the significant resistance to airflow.

Recognising the research of Bill Pentz, most owners of

standard 2hp extractors nominally rated for greater than

1000cfm of flow may be horrified to recognise that this

will be reduced to something closer to 350cfm purely

through the choice of 100mm ducting.

5. Most blade guards allow for no more than 50mm ports.
   The upgrade here to 100mm is remarkably effective.


6. Modification of a big boy sander. The port is 150mm
   and the additional removable guarding allows for full
   dust collection when using the radius.


7. With the guarding removed, sanding the full length
   is possible. Note the upgraded port to the right.

57

6