Table saws and collection

chook · #1 13th Feb 2012, 08:30 AM

In another thread I have just read the following and I quote
"Any saw that uses 4" dust ports simply does not have "good dust extraction design". If one is paying $1000 for a TS one might well expect it to come with a 4" dust port but if one is paying more than $2000 then what would it take for these saw manufacturers to provide a 6" dust port and include a 6-4" reducer for those that only have 4" ducting?"
from BobL in the thread After much searching and lurking... Another table saw choice question.

As I have gotten older I have begun to realize that decades of exposure to dust may not be something I can ignore for ever. So I have begun a process of reducing the dust levels in my shed to as close to zero as possible. The problem is that none of the saws that are commonly available for the home workshop come with anything other than a 4 inch port.

From what I have read the efficiency of a dust collection system depends upon a whole range of things including
1. The size of the dust collect ports
2. The size of the tubing
3. The design of the tubes (eg smooth PVC pipes are better than the common wrinkled flexible plastic pipes)
4. The layout and design of the pipes. The fewer bends and the fewer sharp bends the better)
5. The distance between the machine and the collector
6. The cfm rating of the collector
7. The surface area through which the air can escape after passing through the filter.
8. The type of dust collected (eg fine particles or larger chips)
9. The minimum size of the particles that can be trapped by the filter (cartridge is better than needle felt.)

Taking all these things into account and given that my table saw has a 4 inch outlet I decided that the best way to extract dust was to place a 1200 cfm machine as close as possible to the saw and connected by a straight run of flexible pipe. PVC pipe is impractical and perhaps unnecessary over the short distance involved.

This seems to work okay. But there are still some things I can do to improve the situation.

I am going to toss the needle felt bag and put on a cartridge filter which will increase the flow of air escaping from the filter and decrease the size of the particles able to be trapped. I will still be left with dust in the air and I will then hang an air filter from the ceiling. The cost of a cartridge filter and an air filter is around $600. I have been tossing away cash to various tools companies recently so this will have to wait, perhaps until the wood show in May when hopefully there may be some show specials.

I suppose I could cut a bigger outlet into the side of my saw and attach a 6 inch outlet, but surgery to the saw will be a last resort.

johnc · #2 13th Feb 2012, 09:24 AM

What you describe is pretty much my set up, 1200cfm dusty with dust dog cartridge, short run of flexible pipe, room filter. It removes most of the dust, it would be impossible to pick up all as you still get a bit flung clear of the extraction by the blade, and the room filter picks up any loose stuff moving around. The shed no longer suffers from dust build up however I suspect no matter what you do there has to remain a minor amount of dust suspended in the air and it amazing how much dust you can generate out of a sander when the hose detaches itself without being noticed

.

Mini · #3 17th Feb 2012, 04:40 PM

Quote:

Originally Posted by chook

From what I have read the efficiency of a dust collection system depends upon a whole range of things including
1. The size of the dust collect ports
2. The size of the tubing
3. The design of the tubes (eg smooth PVC pipes are better than the common wrinkled flexible plastic pipes)
4. The layout and design of the pipes. The fewer bends and the fewer sharp bends the better)
5. The distance between the machine and the collector
6. The cfm rating of the collector
7. The surface area through which the air can escape after passing through the filter.
8. The type of dust collected (eg fine particles or larger chips)
9. The minimum size of the particles that can be trapped by the filter (cartridge is better than needle felt.)

10. Any cabinet based tool must have a port equalling or greater than the extraction port to supply make up air. Without this the system will stall at lower CFM numbers.

chook · #4 18th Feb 2012, 07:56 PM

Quote:

Originally Posted by Mini

10. Any cabinet based tool must have a port equalling or greater than the extraction port to supply make up air. Without this the system will stall at lower CFM numbers.

The dust extractor and port on my table saw are both 4 inch. But there is a 2 and half inch port on the blade guard. I was going to put a y junction on the four inch dust line and run a 2 and a half inch hose up to this port. Are you saying that this will not work?

Mini · #5 18th Feb 2012, 11:31 PM

Quote:

Originally Posted by chook

The dust extractor and port on my table saw are both 4 inch. But there is a 2 and half inch port on the blade guard. I was going to put a y junction on the four inch dust line and run a 2 and a half inch hose up to this port. Are you saying that this will not work?

No not at all. What I am saying is that if you are extracting air via a port from the lower cabinet then you must have an opening equal to or greater than that extraction port to supply the air for the extractor. If you don't do this then the air stalls and the dust drops out of the airstream in the cabinet due to lack of air supply. To do this properly you must make another port in the cabinet to supply the needed air as the manufacturers haven't got their head around this concept yet and it is the greatest reason that dust extraction from cabinet based tools/machines is less than successful in a lot of cases. On my TS I left the original port in place and made another, the original supplying the needed air. My bandsaw needed an additional port as well otherwise the cabinet filled with saw dust despite the dust extractor hooked up to it.

BobL · #6 18th Feb 2012, 11:59 PM

Keeping a DC next to a machine like TS inside a shed even with a cartridge just ends up circulating the fine invisible potentially harmful dust inside the shed. Over time it increases the concentration of fine dust inside a shed. Remember the dust you can see is much less of a health issue than the dust you cannot see.

The next weakest link in your system is the 4" flexible tube between the saw and the DC. It really doesn't matter much what you do before or after the 4' flexy as it is physically impossible to pull 1200 cfm through a 4" tube of any kind using a hobby level DC. 4" PVC tube can only do about 400 cfm provided everything else is lined up so felxy will be less than this.

It terms of health the simplest thing anyone can do is place or vent the DC outside the shed. It is better to lose a couple of hundred CFM in doing this as at least the fine dust is eventually going outside. Being able to pull a bazillion CFM just to recirculate it is a complete waste of time.

BobL · #7 19th Feb 2012, 01:13 AM

Quote:

Originally Posted by chook

The dust extractor and port on my table saw are both 4 inch. But there is a 2 and half inch port on the blade guard. I was going to put a y junction on the four inch dust line and run a 2 and a half inch hose up to this port. Are you saying that this will not work?

I just looked up my pressure V air flow V duct size chart.

At the same pressure that 6" ducting pulls 1200 CFM, 4" ducting can only pull 400 CFM and 2.5" ducting can only pull 100 CFM.

Assuming the TS cabinet has sufficient air intakes so it is not restricting the ari flow, the 100 cfm from the 2.5" duct cannot add to the 400 cfm as 4" duct is already maxed out, so adding the 2.5 " ducting will actually reduce the airflow at the 4" port.

Trav · #8 19th Feb 2012, 10:25 AM

Bob

Does this mean that adding a zero-clearance insert could reduce the efficiency of the dust extraction? i.e. by reducing the air input to the cabinet? Would expanding the 4" port on a cabinet saw to 6" be pointless unless there is enough air entering the cabinet somewhere else?

Trav

BobL · #9 19th Feb 2012, 12:26 PM

Quote:

Originally Posted by Trav

Bob

Does this mean that adding a zero-clearance insert could reduce the efficiency of the dust extraction? i.e. by reducing the air input to the cabinet? Would expanding the 4" port on a cabinet saw to 6" be pointless unless there is enough air entering the cabinet somewhere else?

Trav

Yep - Mini has been trying to say this in this and it has been discussed in the dust forum.

Determining the total area of openings required in a TS cabinet is not that easy since it's not just the total area of openings but the tortuosity of the various air paths from the individual openings and the port that determines air flow. The only way to know that sufficient entry area has been provided is to measure the air flow with and without the TS.

If the air flow cannot be measured and most of the air intakes into a cabinet saw cabinet are through slits and narrow holes, the total area of these openings should approach double that of the exit port.

Mini · #10 19th Feb 2012, 01:16 PM

Quote:

Originally Posted by Trav

Bob

Does this mean that adding a zero-clearance insert could reduce the efficiency of the dust extraction? i.e. by reducing the air input to the cabinet? Would expanding the 4" port on a cabinet saw to 6" be pointless unless there is enough air entering the cabinet somewhere else?

Trav

A ZCI lowers the amount of air that can be drawn in, that is obvious. What is not obvious until you think about it is in the end the ZCI has no effect on the air flow as it or the original insert are progressively covered as you slide a piece of timber through the blade sealing off the insert and preventing any air flow through it. In fact if there was not enough air being admitted through other means such as inlet ports in the lower cabinet and the dust extractor had enough capacity it could conceivably make the timber hard to push through as it is drawn down on the table due to the lower pressure in the cabinet. Could the above happen? I guess it could though I have never experienced it myself.

The air entry scenario also applies to above the table guards, slide wood under the guard and it progressively blocks off the air supply to the extractor so the dust does not get caught in what should be a high speed air stream. With the speed of the blade being so high and the dust coming off travelling at the same speed you need the highest air speed you can get in the overhead dust hood. Mine is 100mm but I am going to change it to 150mm by reshaping the pipe entry until it is longer than wider and making it a part of the overhead hood. That idea on its own will not be any good unless I can supply the needed air flow through the hood and it will be interesting to see what the effect is after I get it finished.

This DE stuff is all about the invisible dust, the fact that it picks up the big bits is a bonus because working in a clean environment due to the fact that the big bits get collected should be regarded as a bonus. Taken to the extreme, if we could collect all the fine dust and left all the visible debris (impossible) a broom would fix the rest and we would still be a lot healthier.

I urge everyone to forget the stuff you can see, it only has nuisance value and the fact that we collect is a bonus, the stuff we do not see is what we have to go after. Because we can't see it makes the job even harder as we obviously don't see the end result until many years later when our lungs are still healthy against our compatriots who decided that because they picked up the big bits all was well but their doctor says they now need treatment due to dust ingestion in their lungs caused by woodworking. We all make choices in this life and the wood dust issue is akin to smoking as far as I am concerned.

Up until now the awareness and equipment did not exist for the hobby woodworker but nowadays we have the means to lower the dust ingestion level to safe levels allowing us to continue woodworking as long as we want and not have it cut short as some of our fellow forum members have had happen to them.

BobL · #11 19th Feb 2012, 04:49 PM

Quote:

Originally Posted by Mini

The air entry scenario also applies to above the table guards, slide wood under the guard and it progressively blocks off the air supply to the extractor so the dust does not get caught in what should be a high speed air stream. With the speed of the blade being so high and the dust coming off travelling at the same speed you need the highest air speed you can get in the overhead dust hood. Mine is 100mm but I am going to change it to 150mm by reshaping the pipe entry until it is longer than wider and making it a part of the overhead hood. That idea on its own will not be any good unless I can supply the needed air flow through the hood and it will be interesting to see what the effect is after I get it finished.

This is a fine point but if you want air speed, and I agree this is what is needed, then just going from 4" to a 6" pipe entry will increase the flow rate (CFM) but slow down the air speed (FPM).

This is what I use for an blade guard/hood - its a modified Dust Picker arm. The hood is attached by a SS wire and pulleys to a counter weight that enables me to more or less place it at any height.

The hood itself is too wide at the actual mouth so the air speed is too low, like Mini I need to narrow it down a bit more.

Mini · #12 19th Feb 2012, 07:02 PM

In my case I think the air speed is high enough to support the change. It is a trade off between the both for any given system and if the air speed in a bigger duct is high enough then the added volume is a bonus. Using a VFD and three phase motors as Clearvue does for most installations in this country you can alter the fan speed to achieve the result you want. I have been playing with this aspect lately and it gives fantastic results.

Mini · #13 19th Feb 2012, 07:25 PM

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Closer view here

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BobL · #14 19th Feb 2012, 08:01 PM

Ah ha - I see you have some bristle brushes in action. I have on my desk in front of a metre of a similar stuff I bought a while and will experiment with it WIGRTI [ when I get around to it]. I've just started making a welding table and don't want to get distracted

Mini · #15 19th Feb 2012, 08:15 PM

Where did you buy it Bob?