Rec.Woodworking - Dust FAQ
v0.06 - 5/01/00
Written by Folklore (with much assistance), HTML conversion
and butchering by Dave Castiglione (without much assistance J)
( 1999, 2000 Folklore)
Redistribution, except through rec.woodworking newsgroup
expressly prohibited
May not be duplicated or published without written permission.
Many thanks go to Gerry Glauser, Jim Thompson, John Lemmons,
Bert Robbins, Brook (Dr. Vermin), Patrick Corrigan, CanoeCedar, Gary Hyde,
Jeff Gorman, Alex Rodriquez, Daniel Shafner, Dave Castiglione (DStig) and
several others for their informative and professional posts that provided
the content for this FAQ.
Note from the "host" (Dave Castiglione):
As this document is primarily a conversion and reformatting of Folklore's
DustFaq posted regularly to the rec.woodworking newsgroup, any such references
as "me" or "my system" or the like are Folklore's words and not mine.
Introduction to Dust FAQ
For the individual who is serious about dust control and protecting
their health, I strongly recommend that you read the June 2000 issue of
American Woodworker and the book 'Woodshop Dust Control' by Sandor Nagyszalanczy
and that you visit http://www.airhand.com
and http://www.oneida-air.com as
well as http://www.jimthompson.net/family/
(and click on the dust collection link) before making any major decisions.
These sources as well as others mentioned in and at the end of this FAQ
have a wealth of good information and I did not feel it necessary to duplicate
in this FAQ the valuable information already readily available.
Legal mumbo-jumbo
This FAQ is intended as a brief overview of Dust Collection. I am not
an expert in this field and have only spent enough time researching this
to come to my own conclusion about dust control. Though the information
in the FAQ is believed to be factual and accurate, use at your own risk.
And now for the legal stuff: This article is provided as is without any
express or implied warranties. While every effort has been taken to ensure
the accuracy of the information contained in this article, the author/maintainer/host/contributors
assume(s) no responsibility for errors or omissions or for damages resulting
from the use of the information contained herein.
Disclaimer: While I have tried to be objective in the writing of this
FAQ, I am human. I started my search for dust collection thinking I would
buy a 650 CFM system, then quickly realized a 1200 CFM would be more appropriate
and made the purchase. After more research I realized that I would not
be satisfied with the 1200, back it went, and I currently have an Oneida
on order. There are many woodworkers who have purchased 650, 1200, and
2000 CFM 'big-bag' dust collectors that have been very satisfied with them
and these systems have served their needs very well. As this FAQ points
out you will need to make your own determination regarding what is best
for your situation. Though I have tried to be objective, my preferences
may sneak in occasionally. Please forgive me when this happens.
Duplicate redundant repetitive Disclaimer from the host: Ditto.
I have tried to be complete and thorough in catching errors and avoiding
them in the conversion and reformatting, however use this at your own risk
The same disclaimer from my other page applies
here.
Contents
1. Introduction and Terminology
Why should I include a dust collection system in my shop?
Types of systems
Which one should I buy?
Terms: CFM, FPM, Static Pressure, Face Velocity,
Conversions to metric
2. Building and Spec'ing
Your System
Determining CFM and SP requirements
Better filter bags (and the integrated
Oneida cyclone)
Replacing the bottom filter bag with
a trash can or plastic bag
Ductwork:
Sizing
Plastic pipe
Standard metal HVAC
ducting
Is that nice
looking clear 2" dust collection pipe OK?
Locating your dust collection system
Exhausting your DC to the outside
Building your own system
Finding plans to build your own
Cyclone
Fans for building your own DC, Cyclone,
or Air Filter
Filter media
How can I turn my DC on automatically?
3. Hooking-up Equipment
Tablesaws (especially Contractor's saws)
and equipment in the middle of the floor
Bandsaws
Mitre or Chop Saws
Scroll Saws
Sanders
Adapters
Ambient Air Filtration
Should I purchase or make one of the
ceiling mount air-filtration systems like the JDS 2000?
Miscellaneous
Once I have a dust collection system will
I still need to wear a dust mask?
How can I keep from fogging up my safety
glasses when I'm wearing a dust mask?
Toxicity of various woods/wood dusts
Clogging filters on wet/dry vacs
What to do with collected shavings
and sawdust
Other Resources on the web (links)
Introduction
and Terminology
Why should I include a
dust collection system in my shop?
There are 4 primary reasons for woodshop dust control. These are:
-
Health concerns from dust particles
- There have been numerous articles written over the years about the health
affects of breathing various kinds of wood dust, which is now a known carcinogen.
I and many others have worked in woodshops for years with no apparent ill
affects (just as many smoked for years with no apparent ill affects), however,
the mountain of evidence that breathing wood dust is harmful is growing.
Of particular concern are particles of less than 5 microns and especially
those less than 1 micron. It should be noted that adequate measures for
health may include a combination of dust collection, air filtration, and/or
dust masks.
-
Cleanliness - Cleaning up sawdust and
shavings, especially from a planer, can be a real pain and can reduce the
enjoyment of the work we are doing. (This is a big plus for becoming a
Neander. Tom Lie-Neilson will gladly provide us with a nice set of 3 planes
for what a power planer and dust collection will cost). There's really
nothing like stopping every 5 passes out of 60 through the planer to clear
away the shavings. Further, dust control may reduce the maintenance on
your tools and extend their life. In some cases a good dust control system
can also save your marriage if you are getting complaints about the beautiful
coat of fine Jarrah on everything in the house.
-
Sometimes you just need it - For instance,
on my router table there are some operations that I could not perform at
all without something to handle the dust particles, otherwise I would have
to stop numerous times during even some single operations to wipe away
the pile. First option was an air hose, an hour later option (it took me
55 minutes to go to the store) was a fence-based collector connected to
my wet/dry-vac.
-
Safety - This is a hotly debated topic,
but there is a possibility of any open flames or sparks creating an explosion,
fireball, or fire from the dust hanging in the air. At this time this appears
to be more theory than reality as there are no known (at least to the Rec.Woodworking
group) documented cases of these types of events in a small or home shop.
This may be akin to saying that sugar is bad for you because when lab rats
were fed twice their weight in sugar on a daily basis for several years,
they died. However, this is a serious problem in industrial environments
and may be a problem in some home environments so it is included here for
completeness and to encourage someone with authoritative knowledge to step
forward.
Types of systems
-
Broom and Dust Pan (or for some, just a broom)
-
Wet/Dry Vac
-
Single-Stage Big Bag (currently the most popular, such as the Jet DC1200-1)
-
Two Stage portable (E.G., a canister with a bag on the side)
-
Two Stage (Separate chip collector and filter)
-
Integral Unit (Blower on top of Cyclone with some type of filtration such
as Oneida)
This FAQ will concentrate on the last three items. It is worth noting
at this point that a dust collection system, such as the last three, operate
on High-Volume, Low-Pressure vs. a wet/dry vac or household vac that operates
on High-Pressure (vac), Low-Volume. The reason for this is based on the
application of what the product is designed for.
Which one should
I buy?
This depends on your shop and what you want to accomplish. Ask yourself
several questions before diving in:
- Is health a concern?
- Will I mind dragging a portable unit to each tool when I use them?
- Do I want this for all tools or just my planer and jointer?
- How often will I use the system?
- Will the noise bother me?
For myself I have precious little time as it is to spend in my shop
and I want to insure that what time I am there is productive, enjoyable,
safe, and does not endanger my marriage. Cleaning up debris piles, moving
a portable unit around all the time, annoyance of tripping over flex duct
on the floor, constantly having to empty bags, and a desire to use this
system on all power tools as well as cleanup from hand tools led me to
my decision that a central system was the only viable alternative.
Thus, my personal goals are:
- Reduce health problems caused by dust.
- Reduce amount of stuff tracked into house (Marriage Saver).
- Automatically collect most of the dust and shavings from my tools
so I can spend more time making sawdust and less time cleaning it up.
- Easy to empty chip/dust collector
- Quiet (I really don't want the lovely, high-pitched whine of my planer
disturbed by a loud dust collector)
Your goals may be different and will thus affect the system that you
build or purchase.
Important Terms
CFM: What
are the CFM ratings I see on the systems?
CFM stands for Cubic Feet per Minute and is a measurement of
the volume of air transferred in a given amount of time. For instance,
a home-shop planer generally requires 450 CFM of air movement to clear
away the dust, chips, and other debris. Other stationary tools need anywhere
from 300 to 600. Thus, at first blush you just need to purchase a dust
collector with a CFM rating higher than your tool with the highest requirements.
Not So, CFM by itself is almost completely useless. You also need to understand
a little about Static Pressure. The CFM ratings on the boxes are often
just the blower, these ratings can be significantly less once filter bags
and any flex or permanent ducting are attached.
FPM:
FPM stands for Feet Per Minute and is a measurement of the
velocity (speed) of the air. It is related to CFM, but is different
and important in it's own right, especially if you are installing a dedicated
duct system. You want to insure that you maintain an airspeed of approximately
4000 FPM in branch circuits and a speed of 3500 in the main duct.
Too high a velocity (too small pipe) and your static pressure will go through
the roof decreasing your CFM. Too low velocity and you can have
significant clogging. The reason for this is that the dust collection system
uses the air-flow to transport the wood chips and dust from your machine
to the collector. Too low a speed and the chips will no longer stay air-born
resulting in chip settlement in ducts and a fair amount of time on your
part un-clogging everything. For example, you need 400 CFM to clear
the debris from your bandsaw. A 4" pipe at at 400 CFM will have
a velocity of 3940 FPM. This will work well. However, if instead
you increase the pipe size to 6" your air velocity will decrease to 2800
FPM.
At this rate some heavier particles can settle causing clogs. This can
be especially important in a branch with vertical runs where the correct
air velocity is needed to lift the chips up the pipe. A good example of
changes in velocity with the same CFM is your outside water hose. With
the water turned on and nothing on the end you get a certain volume of
water per minute, usually coming out pretty slow. It wouldn't do much to
wash debris from your driveway. However, if you close down the end of the
hose with your finger or with a nozzle, you will still get the same amount
of volume per minute (CFM) as before, but the velocity or speed (FPM) at
which it comes out is much greater and thus is able to do a good job of
pushing debris from your drive.
The references at the end of this FAQ provide a more detailed description
of this and how to calculate the FPM for your ducts. Go to Air
Handling Systems webpage for more info.
Static Pressure or "Inches of Water":
Static Pressure or SP is a measurement that is married to CFM. SP
and CFM have an inverse relationship. For a given system, as SP increases
CFM decreases. Some people refer to this as the "suck power." SP is a way
of measuring and expressing the resistance of all of the components of
a dust collection system. This resistance is caused by several things including
bends in the hose or pipe that the air must move around, resistance from
filter bags, etc. Many dust collectors publish a CFM figure that is measured
at 0" of static pressure, sometimes referred to as free air flow or free
fan flow (and likewise publish a SP number directly below that is at 0
CFM). Measurements such as these are misleading. These measurements are
for a system with no resistance whatsoever (which is, BTW, impossible if
you actually use the thing). For instance, a collector might measure 1200
CFM without any pipe or filter bags connected. As soon as you install the
filter bags the CFM drops to about 1050 (for standard sized 30 micron bags,
approximately 800 CFM for 5 micron and 600 CFM for 1 micron). 4" flex hose
has a static pressure of anywhere between 0.157" to .210" per linear foot.
Thus, if you add 10' of flex hose between your dust collector and Planer
you've added approximately 2" of SP and again reduce your CFM. Now you're
down to approximately 600 CFM at your tool (assuming 5 micron bags). A
valid data point will be indicated as xx CFM @ yy" SP such as 560 CFM @
7.62" SP.
So, to know the performance of the dust collector you need to know what
the CFM is at a given static pressure. This is often referred to as the
fan
performance curve. The chart below has some averaged performance
curve numbers for a typical single-stage, big-bag system (no ducting included).
These numbers are for just the blower and do not include filter bags or
ducting, except in the case of the Oneida (and the similar PennState Tempest
system), which includes the cyclone and filter. (Disclaimer: This information
was gathered through various web sites and calls to manufacturers and was
unscientifically verified by my own testing. Though it is believed
to be correct, this cannot be guaranteed. You may use this information
as a guide but should contact specific manufacturers directl prior to making
design or purchasing decisions.)
Though most manufacturers don't openly publish their performance curve
information yet, all but one provided the information to me over the phone
once I got them to think I actually knew what I was talking about. Since
most people do not understand this information I can understand their hesitancy
in openly publishing these numbers since many people might try to compare
A's 800 CFM @ 8" SP with B's 1200 CFM at 0" SP and incorrectly determine
that B is better. OK, done with my defense of manufacturers for the year.
It is also worth noting how much duct size will impact these measurements.
All of the systems above will perform much better if only a 6" or 8" inlet
is used (remove any double 4" rigs that come with the machine).
Face Velocity
Face velocity is the speed of the air flowing through the filter media.
It is typically measured in Feet per Minute (FPM). The similarity
in units between volume flow (CFM) and velocity (FPM) is no accident.
You determine the face velocity by dividing the volume flow in CFM by the
total filter area in Square Feet to get FPM. Face velocity is important
in designing a system with respect to sizing the filter. If you have
visited Oneida's
web page, you have probably noted their references to keeping a minimum
10:1 "Air-to-Cloth" ratio, or no more than 10 CFM per square foot of filter.
This is another way of stating face velocity. Face Velocity has a
big impact on how well the filter media works. Too high a face velocity
and dust will get forced through the filters back into the air you breathe.
The lower the face velocity, the more efficient the filtration (the more
particles the filter removes from the air), so you want to keep face velocity
as low as possible. The 10:1 ratio (assuming a good quality 16oz
filter media) has been developed as a good compromise of filtration efficiency
vs. size and cost, but 8:1 or 7:1 is much better. Thus, if you have
a 1200 cfm big-bag system with an effective working cfm of 400 (after all
static pressures are calculated) then you will need at least 40 sq ft of
filter material. For a much better explaination go to to part of DStig's
page here.
Conversions to Metric Units
(As supplied by Robert MacKinnon)
Air Volume is speced in cubic meters per hour
(m^3/hr). To convert:
1
CFM = 1.699011 m^3/hr
1
m^3/hr = 0.58851667 CFM
Air speed is in meters per second (m/sec).
To convert:
1
FPM = 0.00508 m/sec
1
m/sec = 196.8 FPM
Static pressure I think is expressed in vacuum
Pascal millimeters?? (vP mm) I'm not sure of the
conversion factors for this.
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