Thread: Table Saw (10"Contractor's Saw) Dust Collection.

Air flow though guard will increase if rear of guard is left open like this.
ie remove section in red
TableSawGurd.jpg


Visibility would improve if curved front section is made transparent
Also adding a light into the top of the guard really helps
(ignore red circle in photo)
Guard2.jpg

Originally Posted by BobL

Air flow though guard will increase if rear of guard is left open like this.
ie remove section in red

Thanks Bob, I'll provide a full rundown in the coming days - it's a long way from perfect and I'm doing a bit of reinventing the wheel, but it's already way better than what I have! (And it will be developed over time). For now though ... I'll continue this discussion in a few days!

Cheers,

P

Bob beat me too it though I was assuming the section Bob marking in red was the front of the overhead.

Nearly every single truly effective overhead dust collection has the air flow coming up and way from the front.

A TS blade will always throw the overhead chips and dust forward on the table, meaning that to work with the airflow generated by the blade rotation and gullets in the blade ideally you would be extracting the above table stuff forward or at least straight up.

If your exit for the air is already at the front, please ignore

Thanks for pointing that out Phil, I assumed the curved exit port end was the front of the guard because if the guard was mounted a cantilevered or set of Parallelogram lifting arms then pushing most wood into the curve should force the guard up.

Originally Posted by BobL

Thanks for pointing that out Phil, I assumed the curved exit port end was the front of the guard because if the guard was mounted a cantilevered or set of Parallelogram lifting arms then pushing most wood into the curve should force the guard up.

You blokes are getting a bit ahead of me here! I am a little confused by the term "forward" @Aussiephil, BUT not to worry (both you Phil and BobL). - I noted that this was a dust control arm NOT a blade guard. That is because there are some safety bits that will definitely be missing in the short term!

I'm trying to develop something that will work for MY circumstances which are:
1) the table has to move, so the guard arm needs to be articulated to get it out of the way or relocate it in a different place. I can't use a traditional horizontal style arm in my situation for a number of reasons.

2) I almost never cut sheet material, if I do, it is usually using a sled which is problematic for most guards.
3) When I can I like to use Grrrippers - again problematic for most guards.
4) Most of my ripping stuff is thin - too thin to get a push stick between fence and guard.
4) presently when I can I use a bit of PVC angle held to the table with a magnet, which is barely better than not having anything.

Sooo... I am playing with a LIGHT WEIGHT articulated arm, and a light weight guard (above) which can be swapped out for other collector types as I think of them (or not), but I sense a simple BMH mounted a little to the right and aft of the could be useful in some circumstances where the guard won't fit.

The arm has dual ball-joints to allow infinite position adjustment - but I am a few days or a week from having it installed sufficiently to explain it - The guard above is curved so that the leading edge, (what I would call the front of the table - the one opposite where I stand which is the back) should be about 30mm or so above the work piece and the aft end where the dust connection is, can be as low as possible. If there is insufficient inlet air from this arrangement I have planned to cut semi-circular apertures in the front end of the sides rather than reduce the front (where Bob has marked in red), for structural reasons!

Note this is a prototype so of course changes are possible and these sorts of comments very welcome - however it might be better to wait till I can upload the next bit!

Thanks,

P

Originally Posted by bitingmidge

You blokes are getting a bit ahead of me here! I am a little confused by the term "forward" @Aussiephil, BUT not to worry (both you Phil and BobL). - I noted that this was a dust control arm NOT a blade guard. That is because there are some safety bits that will definitely be missing in the short term!

P

Hey mate

Can't beat the enthusiasm from us ... , the below is posted to clarify the directional info for any readers of the thread

Using an image from the web

Capture5.PNG

For me
Front is where you stand
Back is the other side
Forward is therefore towards you
A 10" blade will have around 10,000 surface feet per minute as in that is the tip speed.
this is around 120mph/190kph at the tips, this means that dust and chips get thrown from the blade rotation in the direction indicated by 1 at quite high speed, no wonder hardwood bits really hurt

Whilst the air speed of the chips and dust fall of pretty quickly unless you run your blade very high the momentum is generally straight towards you the operator.

As your goal is dust collection above the table and that was what i was thinking the first time despite calling it a guard, then working with the airflow coming off the blade itself is nearly essential.



Cheers
Phil

I can appreciate the OPs specific requirements, especially if a sled is being used, which will indeed complicate things.

My concern with the proposed hood is that it will not be very effective as it is already a constricted hood that will have to sit too high above the blade and sled. For fine dust, a 6" BMH above the blade with enough clearance for the sled is probably about as good as it's going to get. A 6" BMH has the advantage that it will at least collect much more that a 4"

However, even though BMHs have higher air speeds at greate3r distances from the hood than conventional hoods, the air speed from a TS blade will usually end up producing an air stream that is much faster than the air draw by any 6" BMH thereby defeating much of the collection ability of a BMH. This applies more to chips than fines dust but nevertheless it helps with fine dust as well.

FWIW the teeth on 12" blade moves at about 220 ft/s. I've measured the air stream coming off the blade towards the operator at ~30 ft/s. A BMH sucked on by 3HP DC connected via a 6" BMH produces about 30 ft/s at no more than about 50 mm from the hood. In other words hoods on TS will only really work if they are really close to the blade, OR the hood encapsulates the blade in a certain way

For comparisons purposes the rim of a 2" diam workpiece on a lathe turning at say 2000 rpm moves at about 9 ft/s and this can easily be achieved at about 150 mm from the hood. The nuisance factor of the lathe is that the chips are usually produced with the workpiece in the way of the hood which is why BMHs still won't collect most of the chips from turning although they will do a really good job on the fine dust.

The whole deal about having an open back and a fwd sloped hood and the main collection point directly in front the hood as shown below is that it takes advantage of the trajectory of the main high speed air stream coming off the blade as the air stream ricochets off the internally sloped inside front of the guard up into the hood carrying both chips and most fine dust along the same trajectory. The location of teh slope and the port are very significant towards efficient dust collection, especially if chip extraction is to be maximised.
TSguard4.jpg

I studied and measured the air flows in and around saw hoods for many weeks to arrive at this approach.
Here's a link to my final product
Ducting update.
I realise its not going to suit the OP but at least there might be some ideas worth pursuing.

Thanks Bob and Phil, please keep the discussion happening! I have read your thread with great interest Bob, and as I have fiddled with what I want to do and how to go about it over the past year or two, I've gone from building something similar (based on it) to eliminating all but the bare essentials. My tablesaw presently is the greatest dust creator I own (apart from routers which are operated outside), so I am deliberately starting from a compromise and working up!

PLEASE NOTE -
Before I go on - if you are considering building a blade guard - please use Bob's design not mine. We have a long way to go with this one and it will be a compromise that may or may not suit anyone but me. I am presently $5.00 or so out of pocket for a bit of PETG filament, and some scrap acrylic, so I can probably afford to keep developing this for some time!

Also - my table saw gets limited hobby use - I cannot remember the last time it was used for more than an hour in one session, nor more than twice in a week, and I have exhaust fans, air filter and vacuum cleaner to take care of the fine dust and nuisance it creates. My solution will not suit someone looking for a perfect dust collection solution.

Not yet complete is the real reason for this design compromise - the articulated arm. There are probably a host of very good reasons why you don't see lightweight arms and blade guards on the internet, I suspect that one of them is the obvious - they could be very dangerous if bumped into a moving blade and bits of stuff is flung back at the operator. However - bear with me for a few more days and it might begin to make sense.

My ordered explanation is already in disarray, so here's what I have so far

21-03- 19 at 10-54-34.jpg

The blade guard propped up into about where it would operate for sheet material - I have only a 3" overhead duct which is a little over 80mm clear diameter, and the rectangular opening (in the black part) is exactly the same area as the available minimum. When using it for sheet material it is intended to be fixed a few mm above the work, with the back (see Phil's diagram above) about thirty or so mm above the work piece. As per Bob's first comment above, I initially designed a cutout in the back (pointy) end of the sides to allow greater air flow if needed. (I've used scrappy old acrylic so I can chop it at will till I get that sorted).

The curve at the back is actually inspired by the rear plate on Bob's guard, although I think (hope) that because of my compromised width (40mm) I will have plenty of vision from the side. The guard will be moved completely out of the way when adjusting the blade.

21-03- 19 at 10-57-26.jpg

When using the sled, there's an infinite adjustment available, however I'd expect that the maximum height above the workpiece would be 50mm as shown here. Thicker work bits = closer to the guard. Note that the guard can be moved fore and aft and tilted as well to suit any given situation. (This is an effort to keep weight down and to minimise the compromise compared to a wider guard, to give more flexibility in operation).

21-03- 19 at 10-58-41.jpg

When all else fails a custom bellmouth can be mounted and positioned in the best compromise location. This one is for a 100mm outlet, so think 80% smaller. I suspect that in some operations it may well end up directly behind the sled, but we shall see. That part is many many weeks away, as I would like to see just how effective (and dangerous!) the current proposal is before going further.

There are my thoughts thus far!

I have built the ball joints for the arm, and am currently printing the mounting piece for the guard, the next few days should see the dust connection pieces produced, then I just have to wait for delivery of the magnets - perhaps I'll update daily instead of waiting for completion!

Cheers,

P

Just a general comment, but the problems i've encounted with some of the over head guards i've tried to make....

Being a newer wood worker (i'm 35 and only picked it up in the last few years) I like to be able to see what is going on between the blade and the wood. I like to know if i scribed a line i'm cutting on that line and alot of the "best practice" over head guards very much seem to obstruct the view unless standing way off to the side. Much like the OP i'm only an occasional hobbists user so there is very little exposure time.

Originally Posted by havabeer69

....... Much like the OP i'm only an occasional hobbists user so there is very little exposure time.

Please don't think less exposure time will keep you safe. It can make you more susceptible to injury because you won't know what you are doing wrong until it's too late.

Pete

Just a comment about the relative strengths of PET, Polycarbonate (PC) and Acrylic.

Acrylic, PET and PC have similar tensile strengths but for machine guards an important KPI is "impact strength".
Reported values a bit but the ones that come up most commonly are that PC has ~ 20x the impact strength off PET and PET has ~1.7X the impact strength of Acrylic.

One way around this is to use thicker pieces although this may get in the way of using the machinery.

My guard has a 20mm thick acrylic top which besides being stronger also makes it really easy to drill and tap and hold M6 screws.
The sides are 1mm PC and the front panel is 2mm PC.

Construction/joints needs to be solid otherwise failure can occur at the joints well before the material itself fails.

1mm thick PC sheets or rolls can be bought at bunnings - its not cheap but it is useful for lots of different things. My son has a shed covering his dining table so his kids can used it as an activity table paint, cutting et.I have a sheet of it covering my Jarrah slab topped study desk which I now used for electronics work.

As well as up and down, the guard also moves easily from side to side so contact with the blade sooner or later is likely so I treat the sides of my my guard as consumable although for the 3 years I IT HAS NOT made contact with blades. In previous PC guard incantations the guard has accidentally fallen on the spinning blade several times. Acrylic guards can shatter in this situation but the blade just cut a neat line through the PC and on several occasions I did not even bother to replace it.

Originally Posted by QC Inspector

Please don't think less exposure time will keep you safe. It can make you more susceptible to injury because you won't know what you are doing wrong until it's too late.

Pete

Very true Pete,

I wear a Trend Air Stealth respirator/mask whenever there is the possibility of dust in the air ie whenever I am working (including hand sanding) until the fans are off. This is a nice summary of how I feel! ;-)

Originally Posted by BobL

Just a comment about the relative strengths of PET, Polycarbonate (PC) and Acrylic.

Acrylic, PET and PC have similar tensile strengths but for machine guards an important KPI is "impact strength".
Reported values a bit but the ones that come up most commonly are that PC has ~ 20x the impact strength off PET and PET has ~1.7X the impact strength of Acrylic.

Currently the sides of my guard are 4.5mm acrylic, but once finalised I will be changing to PC. Even though they should never contact the blade (they said that about my fence too, yet one millisecond of inattention...) if it all works I plan to rebuild in Carbon reinforced Nylon, with a 1mm aluminium "impact shield" under the curved top - but that is a long way off. I suspect that when you see the completed assembly you will agree that the biggest danger will be being hit by the whole assembly rather than a series of shattered pieces! This is not being flippant - one of the benefits of building light is that it is less likely to resist catastrophic forces for long enough to break, but the disadvantage is that the whole shebang could go bang!

Cheers,

P

Originally Posted by bitingmidge

Currently the sides of my guard are 4.5mm acrylic, but once finalised I will be changing to PC. Even though they should never contact the blade (they said that about my fence too, yet one millisecond of inattention...) if it all works I plan to rebuild in Carbon reinforced Nylon, with a 1mm aluminium "impact shield" under the curved top - but that is a long way off. I suspect that when you see the completed assembly you will agree that the biggest danger will be being hit by the whole assembly rather than a series of shattered pieces! This is not being flippant - one of the benefits of building light is that it is less likely to resist catastrophic forces for long enough to break, but the disadvantage is that the whole shebang could go bang!

Cheers,

P

Destructive testing video required at the end of the build - we all know that v2 is always better

One thought back to the true purpose of dust collection is that you should look at independent pivoting sides that can pivot down to be flush with the table when you taking a shaving off.... The overhead DC on the harvey is decent enough if your doing a cut with both side equal in height with regards to the DC path.... the very second the dust can escape to the side it will and does ....
When i ripped the tongue and grooves off the hardwood flooring it was instantly noticeably to the point of grabbing a tight fitting glove to protect my left hand, it's why i'm aware just how fast those chips/dust gets propelled. That was with the overhead guard/dust collection in place.

Cheers
P