# How much CFM is Enough



## Teddytim1 (Oct 5, 2013)

I have just finished making my new router table. I'm using a Triton 3 1/4 Hp TRA001 and I'm pulling the chips out with a Porter Cable Shop Vacuum. There are three pick up points. One is in the dust extraction port in the safety guard and two pick ups built into the fence on either side of the bit cove in the back. [Hope that's the right terminology?] The vacuum has a Dust Deputy keeping the filter clear, [which works great] so the vacuum seems to have a fair CFM as vacuums go. But still, it seems wanting in this capacity so my question is this. How much CFM should it have? How much CFM is Enough CFM?


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## Stick486 (Jan 4, 2013)

Teddytim1 said:


> I have just finished making my new router table. I'm using a Triton 3 1/4 Hp TRA001 and I'm pulling the chips out with a Porter Cable Shop Vacuum. There are three pick up points. One is in the dust extraction port in the safety guard and two pick ups built into the fence on either side of the bit cove in the back. [Hope that's the right terminology?] The vacuum has a Dust Deputy keeping the filter clear, [which works great] so the vacuum seems to have a fair CFM as vacuums go. But still, it seems wanting in this capacity so my question is this. How much CFM should it have? How much CFM is Enough CFM?


A shop vac has it's limits... they have suction but not CFM...

a little reading material for ya...


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## Nickp (Dec 4, 2012)

There's no replacement for cubic displacement...(racing days)

You'll know it's enough when the dust deputy gets overpowered and the sawdust circles round n round at its top...at that point you'll need a way to break the air flow. I usually turn the shop vac off and back on and the chips will drop. I am using a Ridgid 5 gal vac with the dust deputy...2 1/4" ID hose to the table and 1 1/2" ID to the vac. I'm guessing the dust deputy will keep doing its thing but I break the vacuum just in case...

Nick


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## jw2170 (Jan 24, 2008)

IMHO;

For a router, you should not need more that a shop vac. After all, if using correctly, you are only sucking up dust.

For a thickness planer or jointer, however you will be sucking up dust and _chips_...
Probably need about 1200cfm as a minimum..

I found that out the hard way....


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## jw2170 (Jan 24, 2008)

pS, I would use a cyclone between the work and the vac....


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## PhilBa (Sep 25, 2014)

CFM depends on how much of an opening you have. If you use your hand to block the hose, you have zero CFM. For under router table DC most designs have a fresh air intake because you need to have flow. Suction doesn't move the chips, airflow does. So, if you have a 2.5" hose on your shop vac, you have about 5 square inches (4.9 actually) of opening, anything less on your table will reduce the airflow. Also, if you have too much of an opening, you will reduce the ability to pick up the chips. I like to think of it as balancing the flow though I'm sure there is some latitude. I'm wondering if the two fence ports are too much. 

Most importantly, don't get too wound up about perfect DC. Give it a try and if it works for you, don't worry. If it doesn't tweak it until it works well enough. 

For what it's worth, I use a 1.5 HP DC, 4" hose and a shop built Thein Baffle separator. I recently finished my router table top for PC7518 + Lift + Incra positioner. No RT cabinet yet (next project) so I built a shroud for under table DC. I left a good 6 sq inch opening in the shroud and use a fairly big insert in the lift plate. Amazingly good DC! The Incra LS doesn't have a dust port in the fence and I was concerned about that but it's really not necessary. I'll probably switch to the Incra inserts that have extra holes to improved my under table DC.


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## Ghidrah (Oct 21, 2008)

A agree with James, I've been using the same old Craftsman 16 gal 6 hp wet/dry vac on the RT since 98. I used to use it on my TS too but I was filling up too fast so I went with the Delta DC 50-760 for the TS, jointer and BS. The Craftsman has enough suction to hold a piece of wood up to the fence and in place like it was glued. 

If I draw from the bottom of the RT it does leave a little debris, but the cavity below the table 14"X14"X14" with a 1" X 14" suction slot at the bottom back. The only time I open the front is to change bits and lock the lift.


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## Alf Beharie (Apr 12, 2015)

FWIW, you don't need to specifically buy a "Dust Deputy" Cyclone...Other makes of Cyclone are available that do exactly the same job but for considerably less money.
For instance, the "Dust Mite" Cyclone is half the price. I bought an "Omni Dust" version because it seems to be more robust than other makes...Cost £45...£25 cheaper than a Dust Deptuty!


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## RainMan 2.0 (May 6, 2014)

I have a General dust collection unit and if I did it again I'd buy the biggest one available .
My theory now is to go with the biggest and baddest you can afford as you can have to little suction but I doubt you can have to much :no:


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## timbertailor (Oct 4, 2009)

As PhilBa pointed out, CFM is generally limited to the diameter of the hose. 4" hose is about 400cfm. A 2hp unit will get you there if you only use it on one power tool at a time.

The real key is to upgrade the filters. Very few shop vacs or even the larger systems come with anything close to adequate to remove the extremely dangerous fine particles. You really want a filter that not only removes particles down to 0.5 micron, but also, able to supply a VERY high flow rate to prevent constant clogging.

Dust collection should not be thought of as a way to keep your shop clean.
It should be approached from a safety standpoint. Fine particles can severely affect you and your families health. So, the more flow, the better.

Stick provided some good links.

Here is another site I recommend spending some time getting familiar with.

Bill Pentz


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## Alf Beharie (Apr 12, 2015)

I looked long and hard for my first dust extractor...In the end I chose the Scheppach ha1000 because of its winning combination of compact dimensions, 50 litre collection bucket, 100mm hose, relatively quiet 77dba 1100 Watt motor, lightweight, cheap price but most importantly its filters down to 0.3 microns...Its only minus is that its not rated for continuous use, say like running for several hours continuously, but then again, I dought many amateur woodworkers leave their extractors running for that long at a time anyway.









Because of its ability to filter very fine dust, its filter bags would probably clog up quite quickly (which is no doubt why it not only comes fitted with one filter but they give you four spares!), so I decided to invest in a Cyclone setup to keep the filters lasting at long as possible.
I chose the Omni Dust from Omnipole Ltd: http://www.omnipole-systems.com/guttervac/OP-ICEdustcyclone.html
To remove any possible strain from the outlet fitting on top of the Cyclone I also bought a silicon rubber curved hose end from them and they threw in a 4" length of Aluminium tube with it to join onto the hose cuff:


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