Thread: Dust extraction strategies for underneath the table saw?

I have just been in the workshop doing a few experiments with airflow through the saw. If I prop the door open 4" and rip some wood I find virtually no dust left on the table so clearly the airflow is doing its job. My next job will be to cut an opening in the door equal to twice the area of a 6" pipe.

I feel for people like BobL who have to continually reply to idiots like me who can't seem to grasp the principles of dust collection because my initial thought was that I needed maximum flow at the throat plate to clear the dust from the blade.

I must say that with the help of everyone on this forum I have been able to put together a pretty effective dust collection system compared to the days when I had had mostly triton gear and there used to be a thick layer of dust over everything in the workshop.

Originally Posted by John Samuel

David,

Yes ... at least I skimmed over the Cincinnati stuff and read the more interesting parts in detail. The nice thing is that the engineering theory behind dust extraction is well understood, so we have no need to reinvent the wheel. . . .

One of my brothers is a mech eng in the mining arena where they have a lot of dust and when I discussed dust with him he said dust control was considered by them as important but a solvable problem. The BIG difference between the mining industry, and a DIYer, being the level of resources required to meet some sort of minimum spec and the acceptance that engineering solutions are far better than just using PPE.

The cost issue is a major one for DIYer. To safely use the tool most likely to cause a DIYer to need medical attention (eye injury from an angle grinder) requires the investment of a small fraction of of the cost of the tool on some PPE, but to use a $500 table saw safely in terms of dust control requires at least the same level of investment and more if it is professionally installed rather that done by the DIYer.

The second issue is that DIYers are often physically constrained by their work environment, renters, dual use sheds, etc limit what engineering solutions can be employed (e.g. venting a DC outside, installing a bigger window, or cannot easily install 15A line etc) so they tend to be limited to using PPE or inefficient solutions to safety problems.

The third problem is DIYers can only realistically solve safety problems they can see and as the most injurious dust is invisible, acts long term, and requires testing gear beyond the cost and skill level of most DIYers it is difficult to convince them that dust control can realistically only be solved using engineering solution

Another reason why that there has been little attention paid to high volume dust control is the medical focus on immediate or emergency level injuries. As dust rarely results in a hospital admission you won't see it even mentioned in DIY safety info and if it is mentioned it will be at the often inadequate level of "use a mask".
For example this web page (http://www.monash.edu.au/miri/resear.../diyfacts.html) provides links to 3 (quite good) pamphlets for DIY safety but none even mention dust and the focus in very much on PPE rather than on engineering solutions. This just reflects the three issues I mentioned above.

Where I think engineering dust solutions could be MUCH better handled is before new sheds are constructed. If dust control infrastructure is treated more like electrical wiring and included in the cost of the shed then it is easier on the pocket. If a DIYer has a budget to work it it may mean the DIYer cannot afford quiet as big a shed as they wanted but that applies to everything (cars and houses). Considering dust control during the building stage can lead to some overall savings like only getting the sparky out once to instal that extra 15A line. Installing ducting under a concrete floor declutters the ceiling and forces users to think about their shed design compared to the all too often "build the biggest thing I can and worry about everything else later".

Originally Posted by safari

I have just been in the workshop doing a few experiments with airflow through the saw. If I prop the door open 4" and rip some wood I find virtually no dust left on the table so clearly the airflow is doing its job. My next job will be to cut an opening in the door equal to twice the area of a 6" pipe.

I feel for people like BobL who have to continually reply to idiots like me who can't seem to grasp the principles of dust collection because my initial thought was that I needed maximum flow at the throat plate to clear the dust from the blade..

No need to apologise - you can only see what you can see.

BTW you are only observing the visible dust which doesn't have anywhere near the health implications that the superfine dust has.
In general where there is visible dust there is also invisible dust but the reverse is not always the case.

Originally Posted by safari

I feel for people like BobL who have to continually reply to idiots like me who can't seem to grasp the principles of dust collection because my initial thought was that I needed maximum flow at the throat plate to clear the dust from the blade.

I must say that with the help of everyone on this forum I have been able to put together a pretty effective dust collection system compared to the days when I had had mostly triton gear and there used to be a thick layer of dust over everything in the workshop.

AMEN! I'd rather not think about what my shop would look like without this forum and folk like BobL.

Originally Posted by BobL

... it is difficult to convince them that dust control can realistically only be solved using engineering solution ...

Ain't it the truth. I have spent thirty years trying to convince managers to engineer their problems out rather than the mix of band-aids they tend to use all too often.

+1 on being thankful for this forum and for Bob's input. Thank you!

The other problem, that I recognise even within myself, is laziness.

The following is a typical scenario.
I have to undertake a low level fine dust generating activity (i.e. drill a couple of small holes in a piece of wood or use some hand tools) and knowing what I know about these activity (i.e. not much fine dust generated at the time of activity) so I don't bother to turn the DC on. This happens a number of times over a few days, the shavings lay on the floor I walk back and forth all over them and at the end of the week, there's that patina of fine dust all over the shed. . . . . .

Eventually it all gets too much and there's a major clean up and vowing to be more rigorous about using the DC and cleaning up immediately afterwards but inevitable I forget and I end up going through the whole cycle again.

All good points.

Before I got the auto-start vacuum cleaner on my SCMS I often would just do "one cut" with no dust management. Instant cloud of dust in my face.

You've answered another question I have about the accumulative effect of hand-tool work (hand sawing dovetails, for example); there is a real need to clean up after each day of work.

I currently have all my big machines (table saw, band saw and thicknesser/planer) hooked up to an automatic start relay system which turns on my dusty automatically. These machines typically are turned on and stay on for a while (resawing, or lots of ripping, or machining a bunch of boards). But I don't want to use the auto-start system for the SCMS or the lathe, as both are on-and-off (repeatedly) machines. I'm assuming the ideal solution is to have a switch in close proximity to these machines...and leave the dusty on for a more extended length of time, but it all comes down to eleccy costs. (Sorry to hijack this thread -- stopping now).

Cheers.

Originally Posted by LuckyDuck

All good points.
Before I got the auto-start vacuum cleaner on my SCMS I often would just do "one cut" with no dust management. Instant cloud of dust in my face.

Auto start does have some advantages, I would however like a simple solution to a delayed "stop" without having to build a delay circuit myself

You've answered another question I have about the accumulative effect of hand-tool work (hand sawing dovetails, for example); there is a real need to clean up after each day of work.

yep all sorts of benefits accrue from this, reduced fire risk, less danger of slipping and harder to lose stuff amongst the sawdust.

I currently have all my big machines (table saw, band saw and thicknesser/planer) hooked up to an automatic start relay system which turns on my dusty automatically. These machines typically are turned on and stay on for a while (resawing, or lots of ripping, or machining a bunch of boards). But I don't want to use the auto-start system for the SCMS or the lathe, as both are on-and-off (repeatedly) machines. I'm assuming the ideal solution is to have a switch in close proximity to these machines...and leave the dusty on for a more extended length of time, but it all comes down to eleccy costs. (Sorry to hijack this thread -- stopping now).

Johns remote start might be of some use to you?

Originally Posted by BobL

Where I think engineering dust solutions could be MUCH better handled is before new sheds are constructed.

The average tin shed is a dust trap, end of story. If more thought was given to building the shed so it performed better at not trapping the dust it would require less emphasis on dust capture as the dust would be moved out of the shed by cross ventilation and the shed would be far cooler to work in. The problem with that is no one seems interested in the issue when I have raised it before. All sides should open up under wide eaves and the slab should extend out to the end of the eaves, the shed would then be completely open to cross ventilation but could be completely locked up for good security. I doubt it would be a lot more expensive, it would save on windows and be a far more pleasant place to work in. Pre made trusses and frames with cladding and colourbond roof and you would knock it up PDQ and it would be a far more substantial structure to boot.

Originally Posted by Chris Parks

The average tin shed is a dust trap, end of story. If more thought was given to building the shed so it performed better at not trapping the dust it would require less emphasis on dust capture as the dust would be moved out of the shed by cross ventilation and the shed would be far cooler to work in. The problem with that is no one seems interested in the issue when I have raised it before. All sides should open up under wide eaves and the slab should extend out to the end of the eaves, the shed would then be completely open to cross ventilation but could be completely locked up for good security. I doubt it would be a lot more expensive, it would save on windows and be a far more pleasant place to work in. Pre made trusses and frames with cladding and colourbond roof and you would knock it up PDQ and it would be a far more substantial structure to boot.

Hi Chris:

I think your idea is a good one. Who wouldn't want to work out of a shed which is virtually open to the elements on all sides!

I think, perhaps, there are a couple of practical impediments to the implementation of your design:

1. Most of us work with sound-constraints, in that we have near neighbours...
2. Most of us work from existing sheds, or garages, or corners of basements, and don't have the luxury of designing and building our own sheds.

But hey, if I had oodles of land, and no neighbours, and enough dosh to build from scratch...I like it!

Noise is a major issue for me too - my neighbour over the back has his pool and entertainment area just a few meters from the back fence and my shed is just a metre away from the shed.

A third constraint is for those (few?) of us who have air-conditioning. Since mid November here in Perth the heat has been oppressive most days from mid morning until late evening with very few visits from the Freo Doctor. I probably wouldn't even go into the shed if it was not for the air con. Because I vent outside I do lose my cool air when I run my DC, but whenever I can I try to do all my dusty work in the morning. This summer I have been doing very little WW, mostly maintenance and a bit of MW. If I'm welding I have the same problem as WW as I run a fairly serious exhaust fan although it is variable speed and I can back it off to a minimum. If I do need to run my DC or exhaust for short bursts the air con recovers fairly quickly because it's not like everything inside the shed heats up quickly when some hot air is drawn in.

I'm not convinced that full flow ventilation is a substitute for proper dust collection. I 2002 I lost my sense of smell for 6 weeks after working with MDF outside for just a few days.

In addition to what has already been said. In most parts of Canada snowdrifts make it hard to pick wood from the lumber rack and the safety glasses frost up making those cut lines hard to see.

Pete

Originally Posted by BobL

Nope - if you maintain the same cross section you will still add resistance to flow - to effectively wipe out this resistance you need at least double the cross sectional area - this assumes no grids or mesh.

Gaps narrower than a 2 mm can be ignored in any cross sectional contribution calculations and for all others subtract 2 mm from that dimension.Drilling holes in a throat plate is better than nothing but they must be bigger than 2 mm to add to the cross section and even then when you do the sums, holes will end up contributing very little to the overall flow.Blade rotation pushes air into the cabinet at the front and pulls it out at the back so there is no net contribution.While gaps of ~2mm or less can be ignored gratings or grids have to be much smaller than 2mm before thy can be ignored. There is no way to calculate it easily because it depend on a heap of stuff like the angle of the air entry and the shape and smoothness of the actual edges of the grate/grid. Fine meshes block too easily - remember all you have to do is keep fingers out so 5mm wide slots or holes will be fine. If there is sufficient distance inside the cabinet so that even if a long finger is poked into the grid that it won't contact anything then 10 mm holes with a 1 mm mesh will be effective. If a finger looks like it make contact then using a standoff box mounted to the side of the cabinet is easily enough done.

Gaps up near the blade I would leave alone those down near the floor I would seal

Hi Bob:

I've procured an alu "door grill" which has an open area of 280mm x 135mm = ~37000mm2. I'm trying to account for the louvres; there are 7 horizontal "louvres" which are about 20mm wide, fixed at the typical 45 degrees, with approx. 10mm between each.

A 160mm diameter dust port is ~20000mm2. Keeping in mind your rule of thumb about using double the cross-sectional area of my 160mm port, I was thinking of cutting out a window high up on my saw cabinet, opposite the dust port which is situated at the floor of cabinet, and installing said grill... I know you have said "at least double the cross sectional area" to wipe out any resistance to flow, but there are quite a few "leaks" in my cabinet, up under where the cabinet meets the cast iron top, and also for the slits where hand-wheels poke through for blade adjustments, which will hopefully be about right?

I just wanted to double check that I haven't missed anything before I cut into my beloved saw with the angle grinder!

Mind you, I have just vaccuumed out the saw and my shop as I'm always anxious about grinding sparks amongst so much wood and dust!
Thanks.