|Dust, everyone's Problem.
We all have to put up with perhaps the most damaging bi-product of making things on the Woodturning Lathe, Dust, but we can do things to make life in the Workshop a little bit Healthier and therefore benefit our well being.
In the Hints & Tips Section of this Web Site I describe a Dust Collection System I have made and here I try and analyse its effectiveness and also highlight what I think are the key areas and situations that determine what is the best way to trap and collect the Dust generated during Turning and Sanding.
Firstly the anatomy of Woodturning is different to an other major Dust Generator in the Workshop in as much as the Workpiece, i.e. the Wood is in motion whereas with all other Woodworking Machines the the Wood is, in principle, Static and it is the Machine Cutter that rotates.
Also we have a situation where the Workpiece on a Lathe is open on all sides, there is no natural catchment chamber to which you can connect a Vacuum Extractor System as there is with most other Machines.
So what is our Objective? Primarily it has to be to protect ourselves from the Inhalation of Dust, if this is the case then surely a suitable Respirator is all we need, it must therefore also be for other reasons? in my case it is to have a near Dust Free Working Environment as possible.
I will also admit that I will often work at the Lathe without my Respirator in place, I know this is not good practice, but!!!, so therefore the best Dust Control I can achieve is desirable.
If we look at the things that are relevant and therefore perhaps understand why the Dust goes everywhere we do not want it to go we can perhaps better understand what our problem is.
Dust will dissipate through out any Workshop as a result of:
Airborne Dust carried in Air Currents whether Mechanically Generated i.e. with a Fan, or Thermally Generated due to the Draft that will be created by virtue of the fact that Hot Air rises and Cold Air falls i.e. Thermal Currents.
Dust from the Wood being Turned will be spread due to entrapment within the Shavings, Projection from the Tool, typically along the Flute of a Gouge and by Centrifugal Force directly off of the Spinning Wood.
Dust as a result of Sanding will follow a typical pattern which is primarily created by Centrifugal Force and as a result of the Coanda Effect.
And finally as we move around the Workshop or whenever we Dust ourselves down we disturb and spread some Dust.
In the illustration [Fig.1] below I show a typical situation that can be readily observed when Sanding, [ this is best done whilst someone else does the sanding and you do the observing], which is perhaps the biggest single process for the production of Dust, in this illustration there is no Dust Extractor or Fan System in use this is just Sanding in natural conditions.
The actual projection and dissipation of the Dust will be dependent on many factors:-
Speed of the Lathe.
Diameter of the Piece.
Combined these two points above will give a "Tip Speed" at the point of contact.
The Angle at which you apply the Abrasive, I tend to use the Abrasive at 8 O'clock.
The Grit Size of the Abrasive which will determine the Dust Particle Size.
The Pressure at which the Abrasive is applied.
The Density of the Wood due to its type, e.g. Oak has a higher density than Pine.
The Density of the Dust Particle due to the Wood Type and Grit Size of Abrasive.
Other factors that will play a part are, Humidity, Position of Lathe relative to other surfaces etc.
As you can see there are 8 or 9 significant factors that you may have to consider if you are going to successfully Trap and Collect the Dust, which will disperse differently as anyone of the above changes.
In my case I can create a situation where the Dust will eject itself, into the surrounding space, with a wrap around of up to 2/3rds of the circumference of a Piece, this however can be controlled, to a degree, by Sanding with not too much pressure and at low speed, but such a combination is not always convenient or practical.
So what can we do? I like many purchased a Shavings/Dust Collector , the selection of which was based on it's Price rather than any knowledge of what it was really capable of, and the Sales Guy at the Store assured me it was OK for a Lathe? I now know otherwise.
Here [Fig.2] I illustrate my observations with only the Dust Extractor System On, using my original Unit, as detailed in the Hints & Tips Section, which offers a more controlled Collector Nozzle than just the Flexible Hose that I was provided with the Unit.
You will see that the Dust Extractor has an influence on the Projection of the Dust with perhaps a maximum wrap of no more than half way around the Piece which is an improvement but it can be improved on.
Making the Nozzle larger is not necessarily the solution as you are relying on the Air Intake Velocity to draw the Dust in and by increasing the cross sectional area of the Nozzle you will reduce the Velocity and therefore pick up less Dust, although you may well catch slightly more of the Dust by virtue of the position of the larger Nozzle? it is a compromise situation.
In Fig.3 I show the results I have obtained from using the Low Level Dust Extractor Box and the Down Draft Fans above the Lathe, again see the Hints & Tips Section, this is giving me a far better Dust Catchment and although it could probably be improved by adding a more Powerful Dust Extractor and Downdraft Fans there would have to be a compromise with respect to Comfort and Noise.
The principle here is that as used in Air Curtains, typically as utilised in Clean Rooms, where the Air Curtain contains or limits the passage of a substance, in our case Dust, and forces it to change direction [downwards] to be picked up by the Dust Extractor.
If you can imagine the Fan in Fig.3 having a reversed Air Flow, as you may have with one of the Dust Filter Units, then it is obvious that a large portion of the Dust will be directed upward and away from the Extractor Nozzle and therefore in direct conflict with what you are actually attempting to do.
I feel I have a good balance with my system and would like to be able to quantify just how efficient it is, I was thinking of carrying out a series of tests based on the three scenarios above by measuring, probably by Weight, the amount of Dust deposited in and around the Workshop and the amount actually in the Dust Collection Bag of the Extractor.
This would be a worthwhile exercise, but I am not sure I have the time and the discipline to do such a study, perhaps a Student looking for a Final Year Project might take up the challenge.
|As a guess I
would say that with the system set up that I am using, when Sanding ,
then at least 75 to 80% of the Dust is caught and
ends up in the Dust Extractor Bag therefore my Respirator has only to deal with a portion of the
remainder, whilst the rest just gets everywhere.
I still strongly believe that a Good Respirator is the Best Solution for
the Personnel Protection and Health
Issues involved here and that anything additional is just a Bonus but
certainly one that is worth investigating and investing in.
LaymarCrafts Woodturning is the Web
Site of Richard & Sheila Stapley
Last update 06 January 2009
Web Site Design & Construction by Richard Stapley.