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Y connector to collect dust from under and from the top of the table saw using a shopvac

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Forum topic by MiniMe posted 12-06-2019 01:56 AM 2576 views 0 times favorited 34 replies Add to Favorites Watch
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MiniMe

312 posts in 658 days


12-06-2019 01:56 AM

Ok this evening I tested my adhoc dust collection system on my table saw

It consists of a 12 gallons 5HP Ridgig dry/wet vacuum with 2.5” hose that fits straight into the dust collection port of the saw underneath and another smaller vacuum with the hose attached to an articulated arm as discussed here
https://www.lumberjocks.com/topics/307061
This arm takes care of the top side of the table saw.

I noticed two deficiencies here:
-connecting the vacuum under the saw to the dedicated port does not catch all the dust, I seem some of the floor even after one cut
-the top of the table solution does not seem to have enough power -there is dust escaping the suction pressure and landing near the edge of the table close to the user

What is a recommended solution to fix these issues:
For the top side I thin the vacuum is to weak, it needs to be really close to the dust to suck it in .
I am thinking about using a Y connector or something like below. It will simplify the whole thing and it will reduce the noise The problem is that I do not know if 5HP is enough for two hoses an 1.25” one and 2.5” one


34 replies so far

View Madmark2's profile

Madmark2

716 posts in 1195 days


#1 posted 12-06-2019 02:23 AM

Y fitting available at Rockler, Grizzly, etc for $10 or so. Vac should be sufficient for two lines. Don’t get your hopes up as contractor saws are notoriously messy.

-- The hump with the stump and the pump!

View EarlS's profile

EarlS

3427 posts in 2955 days


#2 posted 12-06-2019 12:56 PM

Ultimately, both the shop vac and the 2.5” hoses are undersized for what you are trying to do.

Read this article: Dust Collection Needs by the Number

A table saw needs 350 cfm for proper chip and dust removal and a 2.5” hose can only provide 140 cfm. Similarly, the dust removal on top of the blade also needs more airflow than can be provided by a 2.5” hose.

I recently bought a Shop Vac at the local Menards. The web page shows the technical specs for it.

It can only pull 140 cfm, which is what the hose can handle. The big difference between a shop vac and a big dust collector is the amount of vacuum it can pull. A typical dust collector can only pull 11in WC, while this Shop Vac pulls 70 in WC at 0 cfm flow. That is why you can suck up heavy things with a shop vac but not a dust collector.

Ultimately, you need more airflow than a shop vac can provide if you want to pull the chips and dust into a dust collection system.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

View MiniMe's profile

MiniMe

312 posts in 658 days


#3 posted 12-06-2019 02:25 PM

Yeah seems that that article is a classic, gets referred everywhere where I read about this
I take it that I do not necessarily need a different size hose correct?

View EarlS's profile

EarlS

3427 posts in 2955 days


#4 posted 12-06-2019 03:09 PM

A 4” hose can handle the 350 cfm, but the 2.5” hose can only handle 140 cfm. As I recall from the article, the basis is an air velocity of 4000 ft/min.

Here is the math:

area of a circle = pi() x radius ^2

for 2.5” pi() x 2.5 in diameter / (2×12 ) = 0.03409 ft^2
for 4” pi() x 4.0 in diameter / (2×12 ) = 0.08727 ft^2

volumetric flow rate = cross sectional area x velocity

2.5” – 0.03409 ft^2×4,000 ft/min = 136 cfm
4.0” – 0.08727 ft^2×4,000 ft/min = 349 cfm

Since the table saw needs 350 cfm for acceptable chip and dust removal, the 2.5” hose is too small.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

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theart

154 posts in 1161 days


#5 posted 12-06-2019 05:23 PM



A 4” hose can handle the 350 cfm, but the 2.5” hose can only handle 140 cfm. As I recall from the article, the basis is an air velocity of 4000 ft/min.

Here is the math:

area of a circle = pi() x radius ^2

for 2.5” pi() x 2.5 in diameter / (2×12 ) = 0.03409 ft^2
for 4” pi() x 4.0 in diameter / (2×12 ) = 0.08727 ft^2

volumetric flow rate = cross sectional area x velocity

2.5” – 0.03409 ft^2×4,000 ft/min = 136 cfm
4.0” – 0.08727 ft^2×4,000 ft/min = 349 cfm

Since the table saw needs 350 cfm for acceptable chip and dust removal, the 2.5” hose is too small.

- EarlS

I’m not sure you’re interpreting that correctly, because the article doesn’t bother to say what the rationale for any of the numbers is. There are two conditions that need to be met for dust collection to be efficient. (Well, three if you count not having any leaks…) The volumetric flow rate at the business end needs to be high enough for the tool, and the velocity in the plumbing needs to be high enough to keep dust from settling.

4,000 fpm is the minimum velocity to keep dust moving through the hose. The smaller the hose, the less volumetric flow you need to maintain that velocity. So, based on your calculation above, 136cfm is the minimum flow rate for 2.5”, while 349cfm is the minimum for 4”. A 2.5” hose can certainly “handle” a higher flow rate (up to around 9000cfm), but as the velocity goes up so do friction losses.

So the shop vac has enough flow rate to keep dust moving through the 2.5” line, but splitting it may result in clogging. The bigger issue is that, with any size pipe, it’s not pulling enough volume from around the tool to catch all of the dust that’s being generated.

View MiniMe's profile

MiniMe

312 posts in 658 days


#6 posted 12-06-2019 05:54 PM


A 4” hose can handle the 350 cfm, but the 2.5” hose can only handle 140 cfm. As I recall from the article, the basis is an air velocity of 4000 ft/min.

Here is the math:

area of a circle = pi() x radius ^2

for 2.5” pi() x 2.5 in diameter / (2×12 ) = 0.03409 ft^2
for 4” pi() x 4.0 in diameter / (2×12 ) = 0.08727 ft^2

volumetric flow rate = cross sectional area x velocity

2.5” – 0.03409 ft^2×4,000 ft/min = 136 cfm
4.0” – 0.08727 ft^2×4,000 ft/min = 349 cfm

Since the table saw needs 350 cfm for acceptable chip and dust removal, the 2.5” hose is too small.

- EarlS

I m not sure you re interpreting that correctly, because the article doesn t bother to say what the rationale for any of the numbers is. There are two conditions that need to be met for dust collection to be efficient. (Well, three if you count not having any leaks…) The volumetric flow rate at the business end needs to be high enough for the tool, and the velocity in the plumbing needs to be high enough to keep dust from settling.

4,000 fpm is the minimum velocity to keep dust moving through the hose. The smaller the hose, the less volumetric flow you need to maintain that velocity. So, based on your calculation above, 136cfm is the minimum flow rate for 2.5”, while 349cfm is the minimum for 4”. A 2.5” hose can certainly “handle” a higher flow rate (up to around 9000cfm), but as the velocity goes up so do friction losses.

So the shop vac has enough flow rate to keep dust moving through the 2.5” line, but splitting it may result in clogging. The bigger issue is that, with any size pipe, it s not pulling enough volume from around the tool to catch all of the dust that s being generated.

- theart

the table saw collector port takes the end of a 2.5’ anyway
I could run 4” to the saw and use a Y to split to 2.5 and to what for the top/overarm?1.5’?>

View EarlS's profile

EarlS

3427 posts in 2955 days


#7 posted 12-06-2019 06:02 PM

I was using recommended design criteria that was provided in the article I referenced. Additionally, since most shop vacs can only pull ~140 cfm, the fact that the 2.5” hose theoretically can handle higher volumetric flows is irrelevant.

If I did the math correctly, sonic velocity of air is ~1125 ft/sec which equates to ~2300 cfm in a 2.5” hose. I’m guessing you meant 9000 ft/min which would be 306 cfm.

I’d like to avoid a highly technical engineering type discussion of dilute phase fluid transport. That kind of conversation feels too much like my day job, plus there are plenty of those kinds of discussions posted elsewhere on LJ.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

View controlfreak's profile

controlfreak

409 posts in 208 days


#8 posted 12-06-2019 06:06 PM

And then there are the ribs on the hose and any 90 deg bends that cause static pressure. I skip all the math and flap my hand over the end of the hose and say “yeah that should work”

View theart's profile

theart

154 posts in 1161 days


#9 posted 12-06-2019 06:57 PM


I was using recommended design criteria that was provided in the article I referenced. Additionally, since most shop vacs can only pull ~140 cfm, the fact that the 2.5” hose theoretically can handle higher volumetric flows is irrelevant.

My point was that the article did not provide clear design criteria, but rather jumped straight into calculations which all seem to assume that all air moves at 4000ft/min all the time. Without acknowledging that this is an inequality condition, it’s easy to come up with a pronouncement that a “2.5” hose is too small”, when that’s not what your calculations actually mean. It’s entirely reasonable, though not optimal, to pull 350cfm through a 2.5” line.

If anything, the fact that shop vacs only pull 140cfm makes this whole discussion irrelevant, because hooking one up to a 4” line just makes the system fail both criteria.

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EarlS

3427 posts in 2955 days


#10 posted 12-06-2019 07:42 PM

4000 ft/min is the industry standard for designing air flow velocity in a duct. Pressure loss (friction) isn’t excessive and most particles being conveyed by dilute phase fluid (air) transfer have settling velocities that are considerably lower which means they will remained entrained in the air stream while being moved along by the air.

To your point about velocity – a perfect example is the air velocity inside the table saw cabinet. Air velocity inside the cabinet is much lower than 4000 ft/min, but having a 4” DC hose that is moving 350 cfm of air means that the air velocity inside the TS will still be able to pull most of the fine dust into the hose. Additionally, the location of the DC nozzle at the bottom of the cabinet helps with the larger, heavier chips since they pile up there because their settling velocity is higher than the air velocity in the saw cabinet. The heavier chips can be drawn into the hose since the velocity is higher than the settling velocity at the inlet of the hose.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

View Andybb's profile

Andybb

2376 posts in 1210 days


#11 posted 12-06-2019 08:31 PM



I skip all the math and flap my hand over the end of the hose and say “yeah that should work”

- controlfreak


+1 My DC system is 100% shop vac with attachments to connect the hose to each machine but dust still accumulates in the bottom of my hybrid table saw even though most of it goes into the vac system. It’s just the nature of the beast. Contractors saws are not built like cabinet saws and are not designed to suck up all of the dust. Just enough to keep the job site relatively clean.

-- Andy - Seattle USA

View MiniMe's profile

MiniMe

312 posts in 658 days


#12 posted 12-06-2019 08:57 PM


I skip all the math and flap my hand over the end of the hose and say “yeah that should work”

- controlfreak

+1 My DC system is 100% shop vac with attachments to connect the hose to each machine but dust still accumulates in the bottom of my hybrid table saw even though most of it goes into the vac system. It’s just the nature of the beast. Contractors saws are not built like cabinet saws and are not designed to suck up all of the dust. Just enough to keep the job site relatively clean.

- Andybb


So am I wasting my money getting one of these?
https://www.busybeetools.com/products/craftex-mini-portable-dust-collector-3-4hp.html

I already have a 5HP Ridgid vacuum but as you said I do see dust on the floor after cutting a small board
The hose is 2.5 and it fits exactly into my Ridgid TS 3650 port

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Andybb

2376 posts in 1210 days


#13 posted 12-06-2019 09:06 PM

Remove the vac hose and cut that same board then you’ll see what the vacuum is doing. You won’t get all of the dust no matter what you do. In my opinion you’d be wasting your money. The outlet on the saw is still 2”. Just use your shop vac and let it do what it can do then vac the dust off of the floor when you’re done.

-- Andy - Seattle USA

View MiniMe's profile

MiniMe

312 posts in 658 days


#14 posted 12-07-2019 12:26 AM


Remove the vac hose and cut that same board then you’ll see what the vacuum is doing. You won’t get all of the dust no matter what you do. In my opinion you’d be wasting your money. The outlet on the saw is still 2”. Just use your shop vac and let it do what it can do then vac the dust off of the floor when you’re done.

- Andybb


Anecdotal evidence indicates that a 4” to 2.5” hose won’t make any difference due to the way the table saw is built
This guy here is saying that

ts3650 dust collection

Just one more way to do it: Before I installed my shop’s new Jet dust collection system, I used to use this ancient Sears shop vac on my ts3650. It really does suck up a storm, and the canister holds probably 20 gallons of dust and chips. So when I tried the 4” to 2-1/2” reducer trick on the ts3650, I found I ended up with more dust on the floor than than I did with the shop vac. So now I just leave the shop vac hooked up to the saw. It fits perfectly under the table extension and is on wheels, so it goes wherever the saw goes and there’s no 4” hose to trip over. A days’ work still leaves a small dustpan of sawdust on the floor right under the saw, but there’s almost no dust in the air. Whether or not I use a zci seems to make no noticeable difference.

The bottom line is that the 4” hose throttled down to 2-1/2” doesn’t pull as well as the 2-1/2” shop vac does.

Maybe one of the below could improve the situation
https://www.busybeetools.com/products/dust-hood-in-big-gulpin-12in-x-16in.html
this is 12 X 16.
the original part is here
https://www.ereplacementparts.com/dust-chute-p-1005478.html
seems to be a Ryobi/Rdgid part and the size is 20-5/8×17-3/4,

Since it is very cheap (6CAD on sale, compared with these for 32CAD). I also suspect that something like this could be build using some aluminium tin sheets but those my collapse if there is pressure (I don’t think so since the biggest problem for this saw model is that the upper part is pretty much open which probably makes the suction inefficient)

Original part installed:

These solutions might work as well but the general feedback is that they don’t improve the situation on top of what the built in adapter can do. I have also seen a modification where this adapter was removed and replaced with one that can take a 4” hose

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MiniMe

312 posts in 658 days


#15 posted 12-07-2019 12:54 AM

A very creative guy just used a bag

Just another person who admits that there is nothing you can do for these saws, the design is not great in this sense

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