Dust extraction strategies for underneath the table saw?

[LuckyDuck]

I'm rethinking my dust extraction to the tablesaw, specifically the "below table" connection. I'm going to bring in a 160mm diameter pipe by making a port of corresponding size at the base of my saw.

I have a 1990 Delta Unisaw which is a lovely machine, but was not built for dust extraction. It has a sloped floor in the base of it, which slopes down to an existing 4" port. There is enough space for me to enlarge this port if I make a "rectangle-to-round" connection, and get it to 160mm, or just over 6".

My question, which I can't seem to find answered elsewhere, is the best way to direct the chips and dust towards the port inside the cabinet? Currently, it just sits on the sloped floor, and piles up very badly in the corners (we're talking 6" deep of chips/dust over time). Unfortunately, there is not a lot of space inside the cabinet; well, actually, there is quite a lot of space but this is needed for raising and lowering the blade (which moves the motor up and down) and changing the blade angle (which moves the motor laterally).

There is enough space to increase the angle of the sloped floor a little, and I could get rid of some of the dead space in the corners, but what I really need is a a way of making a dust "shroud" that gets rid of the dead space, and channels dust into the new port, but stays out of the way of the motor-arc as the blade is adjusted.

I'm not sure whether I could make some sort of curved structure and line it with thin ply/mdf? I was thinking about painted foam, but I'm not sure how to shape this effectively and will it be robust enough? I see that some industrial saws have internal flex that come up directly under the blade, but I don't have enough space to bring a true 6" flex inside the cabinet.

Has anyone solved this problem? Thanks for any and all replies.

[LuckyDuck]

The photos don't help much.

My Dad helped me ship this saw directly from the US so it had a 60Hz motor. In case some of you are wondering, the motor pictured is a 4HP S6 DOL Hammer motor. Considering that the saw is only a 10" machine, I would consider that a glorious motor upgrade!:D

But its the dust I'm hoping to conquer! Thanks. Sorry the photos are not the right way up.

305513305514

[BobL]

I don't think it's value for effort to do anything inside the cabinet. I would just cut a 6" hole into the cabinet in the same place as the current 4" and ensure that there is enough air flow into the cabinet as directly opposite to the outlet as possible, that means up high on the other side of the cabinet. That might mean cutting an opening in that side and putting a louvred vent. You may still end up with a few dead spaces with big dust chips in them but they are not really that much of a problem.

BTW cabinet saws with their motors inside the cabinet are problematic fine dust generators. The impeller used to cool the big electric motor will be spinning at 2850 RPM and be churning of dust into finer particles. The fact that the motor is semi contained inside a cabinet does very little for the fine dust which will leak out of the cabinet like a gas under a diffusion gradient unless high air flow rates are used.

[LuckyDuck]

Ahah, I'm making it way too hard for myself. I think I was fixated on the piles of dust not remembering that said "piles" will not gather (or mostly will not gather) once I have good flow. A grate on the opposite side is definitely doable and a lot easier than some dodgy internals...:rolleyes:

I think I understand the principle of maintaining the same cross-section to allow good airflows at 6". Are there any pointers though about how to quantify various cross-flow openings which have an impedance? For example, if I measure my throat plate opening around the blade on the tablesaw, there's not much flow potential. If I make a zero tolerance plate there would be even less. Is this why I've read that some drill holes in their throat plate? How does the saw blade rotation affect flow? And is there a generally known reduction in flow for a typical venting grate? Finally, should I bother with all the leaks in the cabinet, eg around the adjusting wheels, up underneath where the casting meets the sheet metal?

Apologies if I've missed this information in other threads. Feel free to direct me to them if that's easier. My missus is used to me reading these forums for hours on end of an evening. Almost getting in the way of actually making things in the shop!:wink:

Thanks.

[safari]

Yes, the question of what size entry for extra air is an interesting one. I modified my Laguna saw to 6" and am now trying to decide what size opening to put in the door on the opposite side of the cabinet. The door already has a small area with three or four small louvres and I find that when I hold the door open, the further open I hold it the less air is drawn through the plate which seem logical. What is less logical is it seems that when the door is fully closed the suction through the plate is at its highest. This seems to be at odds with what most people say.

[LuckyDuck]

Yes, the question of what size entry for extra air is an interesting one. I modified my Laguna saw to 6" and am now trying to decide what size opening to put in the door on the opposite side of the cabinet. The door already has a small area with three or four small louvres and I find that when I hold the door open, the further open I hold it the less air is drawn through the plate which seem logical. What is less logical is it seems that when the door is fully closed the suction through the plate is at its highest. This seems to be at odds with what most people say.

Thanks for your reply Safari. I'm not certain what you mean when you say "suction through the plate is at its highest". Do you mean by plate as in "throat plate" up at the blade? If so, I wonder whether your louvres are doing the job and you have more or less 6" of cross-sectional air-flow? Perhaps opening the door provides too much cross-sectional area which reduces speed of the air flow and therefore would reduce the CFM around the throat plate. I don't know! :(

I know I have to commit myself to attacking my machines -- and just want to make sure I do it more or less correctly!

[BobL]

I think I understand the principle of maintaining the same cross-section to allow good airflows at 6".
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.

Are there any pointers though about how to quantify various cross-flow openings which have an impedance? For example, if I measure my throat plate opening around the blade on the tablesaw, there's not much flow potential. If I make a zero tolerance plate there would be even less. Is this why I've read that some drill holes in their throat plate? How does the saw blade rotation affect flow? And is there a generally known reduction in flow for a typical venting grate?
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.

Finally, should I bother with all the leaks in the cabinet, eg around the adjusting wheels, up underneath where the casting meets the sheet metal?
Gaps up near the blade I would leave alone those down near the floor I would seal

[safari]

Sorry Lucky Duck. I didn't make it clear. I did mean the throat plate and when I put my hand over, the suction felt is definitely more with the door closed. The three louvres measure 120mmx5mm so not double the area of a 6" pipe and there are no other holes apart from the throat plate.
Another of life's mysteries!

[John Samuel]

My experience is that the recommendations already given are pretty good. I built a cabinet for my old contractor saw with nothing more than a sloped ramp leading to the 6" outlet. A small amount of dust collects in the corners either side of the outlet, but I ignore it studiously. If it is not floating around in the air in the shop and not in my lungs, and if it is not on the shop floor, I ignore it.

I did what Bob recommended. The bottom area of the cabinet is sealed. The top area is not, and dust collection is great.

Because mine is a contractor saw, there is a largish opening above the motor where air gets in. I blanked off some of the open area, but that which remains is larger than a 6" pipe, so I am confident I don't suffer restrictions that prevent enough air getting in to the cabinet.

Cheerio!

John

[John Samuel]

Yes, the question of what size entry for extra air is an interesting one. I modified my Laguna saw to 6" and am now trying to decide what size opening to put in the door on the opposite side of the cabinet. The door already has a small area with three or four small louvres and I find that when I hold the door open, the further open I hold it the less air is drawn through the plate which seem logical. What is less logical is it seems that when the door is fully closed the suction through the plate is at its highest. This seems to be at odds with what most people say.
Safari,

Maybe I am missing something here, but getting higher velocity through the throat plate with the door closed is what I would have expected. It seems that the air being drawn into and through the machine will follow the line of least resistance. If the door is open, most of the air will be drawn through the open door. If the door is closed, the cyclone will pull air from wherever it can, including the throat plate.

Could it be that when the door is closed you don't have enough air getting into the cabinet? High velocity of air through the throat plate might tell us naught about the volume of air through the machine, which is more important.

Cheerio!

John

[BobL]

What goes on at the throat plate with the blade turned off is quite different compared to when the blade is running and wood is being cut.

Whatever the air speed is at the throat plate (when the blade is static) is swamped by the spinning blade - the back of the blade easily overcomes any air drawn down through the throat plate and pulls air (and fine dust) out of the cabinet and sprays this in a circular swathe up into the shed above the blade/cut. At the front of the blade, some of the now expanded spray of dusty air is thrown down onto wood or any exposed part of table in front of the blade and onto the operator.
On top of this (at least some of) the throat plate gap is usually covered by the work being cut , so very little of the initially ejected air and dust passes down through the throat plate gap. By the time the work piece is removed exposing the throat plate gap the fine dust is too far from the gap to be captured by any air passing down through the gap. The air speed in the gap is actually not as relevant as the air speed out where the dust is hanging in the air and being swirled around by the blade.

The problem is made worse by a zero gap throat around a blade.

All this is why a throat plate gap should probably just be ignored in any dust capture possibilities and why high volume extraction hood above the blade is critical for controlling fine dust emitted by a TS.
The ideal place is as far forward on the guard as possible but this gets awkward so above the front is a reasonable compromise.

Some further info about using a blade hood is provided in this thread.
http://www.woodworkforums.com/showthread.php?t=157526&page=7 (post #98)

[John Samuel]

Hi LD,
PJT here, Based on the pics it looks like you have a similiar need for the mod I did to Roy's saw, I think I directed you to that thread? I am at John's atm so if tomorrow suits I could come over for a look, John may come as well.
Send contact details via a PM to John's PM and we can go from there.


Pete

[LuckyDuck]

My experience is that the recommendations already given are pretty good. I built a cabinet for my old contractor saw with nothing more than a sloped ramp leading to the 6" outlet. A small amount of dust collects in the corners either side of the outlet, but I ignore it studiously. If it is not floating around in the air in the shop and not in my lungs, and if it is not on the shop floor, I ignore it.

I did what Bob recommended. The bottom area of the cabinet is sealed. The top area is not, and dust collection is great.

John

Hi John:

I plan to do as you have done. I can't believe how much I've read on these forums, and yet I still have a lot to read. Have you read the Cincinnati document linked from Pentz' website? Very enlightening reading -- if a bit heavy in parts.

Thanks for your input.

[LuckyDuck]

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:

Thank you very much for this level of detail. I think for the first time I am getting a better handle of what you mean by "resistance" when it comes to machine mods. Previously, I just thought you and others were referring to the resistance from small ports (e.g. 4" instead of 6"), whereas this is only part of the picture. I've finally (I hope) got the point into my thick head that we not only need the large port, but also need large openings opposite to maintain that flow. Thanks for persevering -- I don't find a lot of this stuff very intuitive. Cheers.

[LuckyDuck]

Some further info about using a blade hood is provided in this thread.
http://www.woodworkforums.com/showthread.php?t=157526&page=7 (post #98)

Thanks for this. I've read that thread; I intend to attack my table saw above table as well. I wish all my dust mods could be done all in one day, but it is going to take me time as I still have to make some furniture. I hate the dust even more now that I know just how insidious it is.

[John Samuel]

Hi John:

I plan to do as you have done. I can't believe how much I've read on these forums, and yet I still have a lot to read. Have you read the Cincinnati document linked from Pentz' website? Very enlightening reading -- if a bit heavy in parts.

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. That's one of the things that simplified my design decisions for my new dust collection system. If we want to catch the fine dust we need 800 -1,000 CFM ... through the machine ... not at a naked impeller ... end of mission. To get that we need a certain sized impeller ... at least 6" ductwork ... well designed hoods/shrouds/ductwork to minimise losses.

So simple!

John

[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.

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.

[BobL]

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/research/reports/other/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".

[BobL]

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. :2tsup:

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. :)

[John Samuel]

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.

[John Samuel]

... 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.

[LuckyDuck]

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

[BobL]

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.

[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.

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.:rolleyes: (Sorry to hijack this thread -- stopping now).

Cheers.

[BobL]

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.:rolleyes: (Sorry to hijack this thread -- stopping now).
Johns remote start might be of some use to you?

[Chris Parks]

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.

[LuckyDuck]

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! :2tsup:

[BobL]

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.

[QC Inspector]

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. :no:

Pete

[LuckyDuck]

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!:oo:

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.

[BobL]

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?

It will probably be OK but how about front on photo of the grill. Also I'd need actual dimensions of the lengths and width of the gaps as seen directly from above (i.e. ignore the angles) in the post.

[LuckyDuck]

It will probably be OK but how about front on photo of the grill. Also I'd need actual dimensions of the lengths and width of the gaps as seen directly from above (i.e. ignore the angles) in the post.

Photo attached.
306761

Bob, I've left it in its wrapper in case it needs to be returned. The grill is on the bench, and I've taken a photo from directly above it. As you may or may not be able to see, there is no "through" gaps, where you can look straight through the louvres.

The space between each fixed louvre is exactly 10mm, each space is 135mm long (or wide), and there are 6 gaps (7 louvres).

Thanks.

[Chris Parks]

Another way to approach this but perhaps more bulky is to make a blast gate for the entry air so that the air speed can be regulated for best performance. It would be easy to build a wood frame with a sliding gate in it as big as you need. Once you have it set the excess blade sticking out could be cut off if need be and fix the blade remaining with a screw to prevent movement. Put a screen over the opening if you wished but I wouldn't bother as the entry could be used to see what is going on if required. If sited correctly it might be possible to see into the saw and watch what actually happens when something is cut, a camera could be used I suppose.

The Hammer slider I have now has the bottom half of the blade sitting in a narrow space a bit like a guard under the blade. This is hooked up to a 5" flexible line that goes straight to the extraction port. In effect it does not extract from the cabinet at all but from under the blade and is damned effective as hardly any dust goes into the cabinet. Like everything it has its drawbacks and if any larger offcuts finish up in there it can get blocked. Being a slider the top of the saw is effectively open at all times for air entry due to the construction of it.

[LuckyDuck]

Another way to approach this but perhaps more bulky is to make a blast gate for the entry air so that the air speed can be regulated for best performance. It would be easy to build a wood frame with a sliding gate in it as big as you need. Once you have it set the excess blade sticking out could be cut off if need be and fix the blade remaining with a screw to prevent movement. Put a screen over the opening if you wished but I wouldn't bother as the entry could be used to see what is going on if required. If sited correctly it might be possible to see into the saw and watch what actually happens when something is cut, a camera could be used I suppose.

The Hammer slider I have now has the bottom half of the blade sitting in a narrow space a bit like a guard under the blade. This is hooked up to a 5" flexible line that goes straight to the extraction port. In effect it does not extract from the cabinet at all but from under the blade and is damned effective as hardly any dust goes into the cabinet. Like everything it has its drawbacks and if any larger offcuts finish up in there it can get blocked. Being a slider the top of the saw is effectively open at all times for air entry due to the construction of it.

Hi Chris:

Thanks for your contribution. Your solution for making a home-made grate "sliding-gate" system sounds great. I've got some really pretty bits of New Guinea Rosewood which would do a lovely job! I've just posted about the best position of the grill -- I need all the help I can get! :rolleyes:

As for your Hammer slider, all I can say is I'm jealous. My shop is not suited to a slider of any size, so I'm "stuck" with my Delta Unisaw for the time being. I've inspected the Hammers and Felders before and yes the dust shroud system really close to the blade is fantastic. The Unisaw was just not made for such a system -- not enough space inside the cabinet. Incidentally, I've just procured a used arm guard system (the really big one) from a Felder 700 series slider. Hoping to attach it to my Unisaw for above table extraction. But that's getting beyond the parameter of this thread! :D

[BobL]

Photo attached.
Bob, I've left it in its wrapper in case it needs to be returned. The grill is on the bench, and I've taken a photo from directly above it. As you may or may not be able to see, there is no "through" gaps, where you can look straight through the louvres.

The space between each fixed louvre is exactly 10mm, each space is 135mm long (or wide), and there are 6 gaps (7 louvres).

Thanks.

Thanks for posting the picture. Now I understand what it looks like and that is important - I have these vents on the side of my sort-of-solar wood drying kiln

Long narrow angled gaps like that have a significant edge effects

I would treat the gaps as though they are only 7 mm wide. This dimension is just a ball park figure from experience.
This would then make it 6 x 7 x 135 = 5670 mm2 so you you would need 3 and abut of these to match a 160 mm duct - surprising isn't it - now this will still generate some restriction so you should use maybe five of these.

If you want to match a 100 mm duct you would just need two of them

[LuckyDuck]

Thanks for posting the picture. Now I understand what it looks like and that is important - I have these vents on the side of my sort-of-solar wood drying kiln

Long narrow angled gaps like that have a significant edge effects

I would treat the gaps as though they are only 7 mm wide. This dimension is just a ball park figure from experience.
This would then make it 6 x 7 x 135 = 5670 mm2 so you you would need 3 and abut of these to match a 160 mm duct - surprising isn't it - now this will still generate some restriction so you should use maybe five of these.

If you want to match a 100 mm duct you would just need two of them

Thank you Bob for this. This sort of detail is really helpful -- and hopefully helpful for others planning to modify their TSs like me. After this post, it is clear that the grill is going straight back to Bunnings.

I think a much cheaper and more practical option will be for me to make a timber grill -- I will double check about the danger of fingers reaching inside, but I think there is plenty of space up high on the side of the cabinet.

I'm amazed at how much venting is required -- no wonder everyone's machines are choked with low flow!

First I tried to work out how many 30mm holes would be required in a timber plate. 32 holes would be required to approximate a 160mm port, so would be looking at around 60 holes to make sure that flow is not restricted? Ridiculous!:-

Then I thought about making long narrow slits into the side of the cabinet, say all across the top of the cabinet, just under the table. Say 500mm x 27mm (making an effective 500 x 25 cross section). I would need three of these to get to 37500mm2. That would reek havoc with the strength of my cabinet's sheet metal -- so I don't think that's a very good option.

Far out -- what do you recommend!:?

[Dengue]

Was wondering when someone was going to raise the issue of weakening of the cabinet, which is required to support a few hundred kilo of cast iron table, arbor and gears, and motor!

[LuckyDuck]

Was wondering when someone was going to raise the issue of weakening of the cabinet, which is required to support a few hundred kilo of cast iron table, arbor and gears, and motor!

Well, I'm known to be a it slow at times! :rolleyes:

[BobL]

Yep - taking the angle grinder to a machine to get it to breathe is not for the faint hearted.

Most of the weight is not really taken by the flat panels but by the corners of the cabinet.
Look at how flimsy the legs are on a contractor saw - they still have to carry a similar size motor motor and a cast iron top.
The means a 150 x 300 mm section of the panel could easily be removed without compromising the strength of the cabinet

If you are at all worried about strength you could weld up a 5mm x 25 mm angle steel frame say 300 x 300 mm in size and bolt it onto the inside of the cabinet, then get an angle grinder and using the angle iron as a straight edge cit out the panel inside the frame. Then it would be just as strong as having the panel.
Then i would use a 1mm x 20 or 25 mm square mesh to keep fingers out. SS would be nice. Such a fine mesh offers so little resistance you could probably make the opening 160 x 320 and it would still work.

You did say there was a lot of other gaps and slits in the cabinet?

[pjt]

If this was my saw I'd tackle it like thus... first install dust chute/piping mods as planned, then do a flow test, ideally with an appropriate test device but for a quick and simple test device a utube manometer, due to potential edge effects at the tube end that is inserted into the pipe in this instance we are only using it as a comparitor, what we are trying to see is a difference in water colum hieght in the utube, e.g. with the door open we might have 75mm, if we close door and we get an increase in WC say 100mm then we know there is a need to allow more air into cabinet via openings. If there is no difference then we know that sufficient air is flowing into cabinet via existing gaps.
Next is whether it is an advantage to block off existing gaps and reintroduce air via new openings that promote dust pickup.

Pete

[LuckyDuck]

Pete -- the point about the order in which to make the mods is a really good one -- first the port, then the vent/grill to reduce resistance.

Bob -- agreed with your observations about sheet metal cabinets -- I was probably reacting to the extent of cuts required with the solutions so far canvassed. Your suggestion of a square/rectangle with thin wire mesh (indeed ss would be nice!) is probably the best of all.

My cabinet has a couple of holes here and there (I don't know what they served originally) near the bottom which I will plug permanently. I have had a close look at the gaps between the cabinet and the top, and I must say they are not large, perhaps 5-7mm wide, all around the top, but only intermittently on account of cast-iron ribs. Probably not much influence?

Then there is a larger curving slit where one of the adjusting wheels protrudes -- it arcs to follow the travel of the arbor/saw unit when adjusting the machine for angled cuts. I would imagine it is fairly subjective to determine the influence this slit will have on reducing resistance as the arbor/saw unit is partially blocking the slit, and the axle/wheel also helps block it.

Anyway, the slit is 37mm wide, by 250mm long, and the axle/wheel sticks out of the slit and is approximately 50mm. So effectively we have a 37-200 slit.

[Dengue]

One of your primary concerns, LD, was the amount of sawdust collecting in the corners, and not being sucked through. I have the same problem on my Carbatec THB-10 cabinet saw, so I just remove the throat plate and hit the cabinet with a blast of the compressed air hose at the end of the day, with the DC running.

More annoying is dust that gathers in the lower sloping part of the door. On opening the door it all falls on the floor. so I drilled a 10 mm hole in the side of the door and put the compressed air in there too.

I don't think there is too much wrong with the air flow on my setup, which is very similar to your Delta setup. I have a 25mm finger hole in the throat plate, and any loose sawdust I put near that gets sucked in pretty quickly, even with the motor running. The only dust control I have added is to add magnetic posters over the gap where the raise / lower wheel is to stop the sawdust coming out and spilling on to the floor.

Methinks you might be worrying a bit too much about it all, although anything you do to get better flow will be worthwhile.

[BobL]

One of your primary concerns, LD, was the amount of sawdust collecting in the corners, and not being sucked through. I have the same problem on my Carbatec THB-10 cabinet saw, so I just remove the throat plate and hit the cabinet with a blast of the compressed air hose at the end of the day, with the DC running.

More annoying is dust that gathers in the lower sloping part of the door. On opening the door it all falls on the floor. so I drilled a 10 mm hole in the side of the door and put the compressed air in there too.

I don't think there is too much wrong with the air flow on my setup, which is very similar to your Delta setup. I have a 25mm finger hole in the throat plate, and any loose sawdust I put near that gets sucked in pretty quickly, even with the motor running. The only dust control I have added is to add magnetic posters over the gap where the raise / lower wheel is to stop the sawdust coming out and spilling on to the floor.

Methinks you might be worrying a bit too much about it all, although anything you do to get better flow will be worthwhile.

These examples are understandable visual examples and apply to the visible dust, what LuckyDuck and others have realised is that these are symptomatic of poor all round (but especially very fine) dust collection while the saw is running.
If sawdust is coming out of gaps and spilling onto the floor that is a sure sign that the air flow through the cabinet is insufficient and means it will not be collecting sufficient air from the vicinity of the saw.
Don't forget that the throat plate and any holes thereon are blocked by the wood being cut will not be collecting dust while it is cutting.

[LuckyDuck]

Methinks you might be worrying a bit too much about it all, although anything you do to get better flow will be worthwhile.

No doubt! I'm a bit of a bulldog when I sink my teeth into a new idea, or become aware of a deficiency/problem!:-