Table Saw Dust Collection
#9
  
I took apart my overhead 6" pipe only to find a large amount of small wood chips in it. Pipe is dedicated to the table saw. Chips may be from the dado cuts or when I'm shaving a piece off a board. I was thinking of making a box off the saw maybe 2'x2'x2' so that the horizontal pipe dumps in and a vertical pipe pulls it to the dusk collector. Hoping the bigger stuff will stay in it for a clean out later.  Any thoughts?
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#10
  Re: Table Saw Dust Collection by jeffss (I took apart my over...)
It sounds as if there is too low flow for the 6" pipe.  Was your filter clogged?  If so, cleaning it might up the flow to the point it cleans out the pipe on its own.  Anything you add to the flow path will decrease the flow, so if you add such a box, you'd be best off putting it where there is already a flow disturbance, like at the saw itself.  You may also be able to leave the pipes as they are, periodically flushing them by covering the inlet, letting the system pump down, and then uncovering the inlet to let a pulse of air through.  Doing this once a week might take care of the problem, and leave your system with more airflow than you'd have with a preseparator.

If you do add a preseparator, the challenge is to make it effective at capturing dust without costing too much of your already limited airflow.  I would use a round container of as large diameter as is practical.  Separation of fine dust is better at small diameters, but that costs you more in airflow.  You are spinning the air in a circle, which throws the dust to the outside, and drawing air off the center.  I suppose just using a much larger diameter pipe for the vertical path might slow the air to the point where big stuff drops out without the cyclone (spinning) action that costs more flow.
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#11
  Re: Table Saw Dust Collection by jeffss (I took apart my over...)
See above about pipes above.  You don't have the velocity to carry.  Bernoulli it with smaller pipe, or try having gravity help.  I suppose the third alternative is a "cyclone" under the saw.
Better to follow the leader than the pack. Less to step in.
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#12
  Re: Table Saw Dust Collection by jeffss (I took apart my over...)
Alternatively, as the pipe builds debris, the area will decrease, and the velocity increase, until the detritus on the bottom moves. Unfortunately, a chunk can break loose at once, but that wouldn't hurt my system at least.

The real answer is to increase blower performance, either with a different blower wheel and motor, or reducing restrictions somewhere. Or adding a preseparator to the machine making the big bits, so they never get into the ductwork in the first place. Like a Thien separator on a small can.
Tom

“This place smells like that odd combo of flop sweat, hopelessness, aaaand feet.”







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#13
  Re: Table Saw Dust Collection by jeffss (I took apart my over...)
Make a water manometer and measure the pressure drop near the inlet (6' - 8' upstream in a straight section) of your dust collector with all the ports open.  Then measure it with all the ports closed except the one to the TS.  Then go over to the TS and measure it again right near the outlet from the saw.  If you only have a couple of inches of water at the TS then you're cooked.  The question then is why is it so low?  It could be due to too many elbows, too long a run, too much flex hose, or your filter bags or canister has too much back pressure.  Smaller pipe/hose isn't going to fix a system that has too many restrictions, it will just make it worse.  If you have 4 or 5 inches of pressure drop at your TS then smaller pipe/hose would probably work.  Go measure your system and see what you have. 

John
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#14
  Re: Table Saw Dust Collection by jeffss (I took apart my over...)
It's an internet fallacy that 6" duct or larger is ideal.  You need to size the duct to the collector to ensure adequate air velocity (speed) in the duct.  The experts say you need 4,000 ft per minute to keep dust suspended.  Also most duct collectors are very optimistically rated by the manufacturer.  Commercial grade are more accurately rated but the consumer products rating are nearly worthless.

A well design 5HP collector and cyclone will pull 1100 cfm through a 6" duct with a 6" port or opening at the tool.  Connect that duct to a 4" port which is common on most tools and the cfm will drop to 350 cfm.  Run 350 cfm through a 6" duct and you will get dust settling in the horizontal ducts.

The biggest improvement you can make is to enlarge the ports on your machines wherever possible.

In my experience the smallest port you can have on a 6" duct is a 5" port.

Also you can open additional gates to get more air flowing in your main overhead duct but if you have a smallish collector that will reduce the collection at the saw.

You might well be better off with 5" ducts.
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#15
  Re: Table Saw Dust Collection by jeffss (I took apart my over...)
Here is a link to a forum where I posted a paper I wrote.
http://www.sawmillcreek.org/showthread.p...ctor/page3
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#16
  Re: Table Saw Dust Collection by jeffss (I took apart my over...)
So I checked it out some more. I have 2 six inch main lines and 11 four inch drops. I disconnected every line except the 2 for the table saw and kept them open . Put a rubber glove over each closed 9$ gate. Guess what, all leaked.
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