Thread: Extraction Outlet size?

As you say it's better to put the larger outlet on and reduce it as an interim measure.

Where a larger (150mm) outlet will not work as well at picking up chips, is if say the 2HP is connected with smaller (100 mm) ducting - then the lower flow rate will result in a lower airspeed at the outlet.

Thanks Bobl. So if I used 150 duct with the a 2hp DE connected to cupboard recess with the 150 outlet I should still get reasonable extraction at top of table with a bit of 100mm flex connected to the 150 duct?

Originally Posted by SuperB15

Thanks Bobl. So if I used 150 duct with the a 2hp DE connected to cupboard recess with the 150 outlet I should still get reasonable extraction at top of table with a bit of 100mm flex connected to the 150 duct?

Reasonable extraction is a relative term.
I've yet to see an extraction system that does a complete chip removal for all modes of cutting from the top of a router table

Have you fully modified the 2HP DC?
What filter do you have i.e. pleated filter or needle felt filter?
What sort in inlet air vent have you go going into the cupboard, if its fully sealed off or only had thin slit type air inlets you wont get much air out of it.

I have no DE at present and when I do it will be either a modified 2hp or a 3hp if I can get 15amp in shed. So I guess the question is more theory as to whether a 2hp can or cannot handle a 150mm outlet as well as a 100 outlet on a machine. Maybe there too many variables to even answer in theory.

When I add a door to the cupboard sawdust collection recess (still to do that), I understand it will need air inlet hole/s to allow flow of air in and out of the cupboard as there are only a couple of very small holes in router plate - might as well call that no air flow.

Originally Posted by SuperB15

I have no DE at present and when I do it will be either a modified 2hp or a 3hp if I can get 15amp in shed. So I guess the question is more theory as to whether a 2hp can or cannot handle a 150mm outlet as well as a 100 outlet on a machine. Maybe there too many variables to even answer in theory.

OK I will cover as many options as I can
A fully modified 2HP will draw a max of about 840 CFM with a needlefelt filter, and about 935 CFM with a PF.

This assumes no more than about 3m of straight ducting. As soon as you add more ducting, clogged filters, junctions, flex and a throttled machine it will drop off rapidly.
If the limitations to flow (restrictions) are about the same for the 150mm and 100 mm sections of ducting, the flow will split ~3:1
So the very best possible with a 2HP will be ~ 600 CFM though the 150 mm and 200 CFM through the 100 mm.
In practice it will be much less than this also because router table setups usually involved significant restrictions and we know the 2HP does not handle restrictions all that well.
The typical sorts of flows I have seem are then around half (300 - 100 CFM) the max.

If you have a 3HP or bigger DC and 6" ducting all the way to the DC the max flow can hit the theoretical max of 1200+ CFM.
This means a max of 900 CFM though the 150 mm, and 300 through the 100 mm ducting.
BUT the restrictions also won't impact as significantly on the flow so you might even get 2/3rd of the max flow (so 600 - 200 CFM).

In some ways it makes sense to reverse the 150 and 100 mm ducting positions.

My router table is attached to my TS table.
The above router table dust collection uses the same 100mm piece of flex as the overhead guard on the TS - I just pull it off the TS guard and pop it onto the router fence.

Even though I have a 150mm duct extracting dust from under my TS I don't use a full 150 mm ducting for the router enclosure simply because I don't think its needed and the space under my TS and router table is VERY crowded.
The under table dust scatter is well constrained by the smallish router enclosure and the flow from a 100 mm ducting with good air inlet flow seems to be enough.

Where nearly all router tables struggle (including mine) is above the table dust extraction where the flow from a 100 mm duct is not usually enough to catch the usually unconstrained fine dust.
It also does not catch all the chips but remember they are far less dangerous than the dust you cannot see.

As I said above it makes sone sense to then use 150 mm above the table and 100 mm below BUT manipulating and feeding the flow of a 150 mm duct directly above a router table is very awkward.

To get around this problem, immediately above the router at the ceiling I also have an additional 1200 CFM ventilation fan that fair rips any escaping fine dust straight out of the shed.
This is far easier than than trying to mess around with a 150 mm ducting above the router table.

When I add a door to the cupboard sawdust collection recess (still to do that), I understand it will need air inlet hole/s to allow flow of air in and out of the cupboard as there are only a couple of very small holes in router plate - might as well call that no air flow.

OK you got it.

Great thanks Bobl that covers what I needed - many thanks.