Replies

1. 
   stonefever | Jul 17, 2003 04:47pm | #1

   Please take the time to review the book from the Taunton Press entitled, "Woodshop Dust Control."

   In it, you'll learn about static electricity buildup within PVC pipe that can lead to explosions and fire.  Although it is used in many places, successful applications employ uncoated ground wires inside such pipes.

   You will also learn about the proper way to engineer the ductwork so as to provide the highest static pressure, thus leading to improved dust collection efforts.

   It doesn't have to be expensive.  But be fully aware of just what other conditions will affect your application.  Any turns and/or connections will introduce friction and slow your air flow.  Turns themselves require a long sweeping elbow.  Any tee's or wye's require stepping up in size downstream.

   2" pipe is insufficient to carry the amount of air necessary to remove the dust from even a small belt sander.  Anything bigger (such as a mitersaw) will overwhelm your collection efforts.

   The smallest drop I'm using in my system is a 4".  The mitersaw drop will be a 5".

   I'm sorry to rain on your parade, but the result will essentially be minimal collection and you'll have to clean up anyway with your shop vac.  Thereby saving nothing.

   I do like your thought about using caps vs gates.  Them gates can run $50 apiece!  More if they are automatically sensed and controlled.

   You can get a lot of ducting information from http://www.oneida-air.com.

   Here a just a few of the warnings found in the Oneida Dust Collector owner's manual:

   "Wood shaping and cutting processes generate wood chips, shavings, and dust.  These materials are considered combustible.  Air borne wood dust below 420 microns in size (.0017 of an inch) in certain concentration ranges when ignited can deflagrate (burn quickly)."

   "An ignition source such as a spark, or ember, can ignite a dust mixture resulting in an expanding flame front, which can cause an explosion if tightly contained.  A disturbance that raises a cloud of accumulated fine dust can raise additional dust clouds, which can cause a series of explosions that can level an entire building.  Until this type of fire has been witnessed, it is difficult to believe the devastation.  This type of fire is rare, but worth safeguarding against."

   They talk about (lots of) fire and building codes and regulations governing such applications.  So it may be worth checking out your building department to see if they have special concerns.  Mine does.

   It goes on to say:

   "Sparks can be generated in several ways:

      High speed sanders and planers can strike foreign material.   Saws and edgers may strike foreign material and create a red hot metal fragment.   Knots in hardwood can create frictional sparks.   Tramp metal when drawn into the collector can spark against ductwork.  Check woodstock for old nails and screws."

   "Electrically ground all equipment and ducting.  Static sparks can ignite wood dust.  (Avoid using PVC drainpipe.)"

   "Be especially careful with sanding units.  They can produce concentrations of dust in the combustible range.  Make certain enough air volume is at the suction point to capture all the particulate generated."

   "Don't allow accumulation of layers of fine dust on horizontal surfaces.  (Especially overhead lights, electrical boxes, and fuse panels which can ignite such dust.)"

   And it goes on and on.  These guys have much experience with collectors.  I'm respecting their opinion.

   You also mention finishing.  I, too am planning on some finishing facilities in my shop.  But any dust within the shop is counterproductive to such finishing efforts.  (You gotta get it all out.)  My finishing area will have an explosion-proof ventilation hood.

   I wish you the best.  Sorry for not supporting your concept.