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Discussion Starter · #1 ·
There seems to be differences of opinion on whether a router motor will overheat when enclosed in a dust collection box. Some people advocate ventilating the dust collection box so that the router motor brings in outside air that does not come in around the bit. My engineering engineering intuition says the dust collector brings in a lot more air than the router motor cooling fan. I have conducted an experiment to explore this issue and the results are attached. Let me know what you think.
 

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I don't see how a the sawdust can be removed without incoming air. My home built router table has a plexiglass front door that has 5 - 1" holes just for incoming air and that keeps the compartment almost completely dust free. Close those holes and nothing gets removed except a very little from what small amount of air infiltrates. If possible I'd add adjustable air vents. Maybe I'm missing something here.
 

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Discussion Starter · #4 ·
I am familiar with the "Venturi effect" in Fluid Mechanics but do not understand what you are referring to for a router dust collection system. Please amplify.
 

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Discussion Starter · #5 ·
I don't see how a the sawdust can be removed without incoming air. My home built router table has a plexiglass front door that has 5 - 1" holes just for incoming air and that keeps the compartment almost completely dust free. Close those holes and nothing gets removed except a very little from what small amount of air infiltrates. If possible I'd add adjustable air vents. Maybe I'm missing something here.
In my case, the air is coming into the dust collection box from above the router table. This is why it is important for the throat plate to have as much open area as possible as in the case of the Incra system that I have. The system works quite well.
 

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Ben I'll point out a few important facts about RT dust collection.
First is that not a single speck of dust is created below the table. 100% is created at the top of the table and up from there.
Second, most of us use insert rings in our table plates to keep the gap as narrow as possible. This doesn't allow much room for either the dust or the air needed to transport the dust to get through. The Clean Sweep rings help by allowing more air but the combined surface area of the openings is maybe 2 square inches of cross sectional area on average where as a 4" dust port is about 12.5 sq. in.
Third, the router is trying to blow air upwards through the router windings to cool itself. You are pulling air in the other direction. These two air flows tend to cancel each other out. You are also pulling air out at the intake end of the router.
Fourth is that cooling happens by transferring heat from the windings to the passing air molecules in the air stream. In a vacuum there are fewer molecules so cooling is reduced.

The only particles that would normally make it past the bit and go under the table are due to the randomness of the collisions between particles being ejected from the bit. Most will stay above the table if you don't try to move them somewhere else. So the logic of trying to suck all that dust down through that small hole by putting your router in a box that will probably compromise it's cooling while simultaneously making the router hard to get to for locking height, changing bits, and changing speed absolutely escapes me.

I'm considering building an extra pickup that will sit under the table at collet height that can capture the tiny fraction of dust that my fence mounted pickup misses but that also won't interfere with me getting at the router and that design will actually improve cooling. I'll probably mount it with magnets as It has to be able to attach on either side because I work from both sides of my table. I just haven't figured out what I'll make it out of and how yet.
 

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I think Ben (bfblack) has made an effort to add a real scientific evaluation here and should be commended for his sharing it with us. It shows us the importance of air flow and the huge difference there actually is when more air movement/exchanged to dissipate heat. There is no presumption here, just facts.

I also agree, that a snorkel from the end of the router to the outside of the box may help as long as you also use your DC at the same time. I presume a snorkel would cut airflow without the added DC.
 
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I think Ben (bfblack) has made an effort to add a real scientific evaluation here and should be commended for his sharing it with us.
I agree but I still have to stand by my comments. As a power engineer with a background in physics I didn't grasp what I said out of thin air.

I presume a snorkel would cut airflow without the added DC.
Only very marginally. The longer it is the more impact it would have as there is some friction between the air molecules and the side of the tube but it would be over a longer distance than anyone would need to go with the snorkel. Since the snorkel would probably be much larger than the router's intake and the distance air would have to travel to get to the intake would be very short I suspect you would need some pretty good instrumentation to see the difference.
 

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I agree but I still have to stand by my comments. As a power engineer with a background in physics I didn't grasp what I said out of thin air.

Only very marginally. The longer it is the more impact it would have as there is some friction between the air molecules and the side of the tube but it would be over a longer distance than anyone would need to go with the snorkel. Since the snorkel would probably be much larger than the router's intake and the distance air would have to travel to get to the intake would be very short I suspect you would need some pretty good instrumentation to see the difference.
two independent systems..
cooling air to the router and the DC system..
the router pulls air in through the snorkel...
it then exhausts it into the box...
the DC ''pulls'' this exhausted air away from the motor...
I see it as the DC aiding in increasing clean, cooling air flow through/to the motor...
the DC is actually a plus in removing heat from the router...

@bfblack...
I am familiar with the "Venturi effect" in Fluid Mechanics but do not understand what you are referring to for a router dust collection system. Please amplify.
the principle is the same be it liquid or air because air is fluid... motor cars use this principle..
Ben, what were your findings for the temp readings while utilizing installed independent systems and w/ the router under extended load and not under load???...
did you use a free standing router as a baseline??...

here is a pic of a non-vented router's air intake w/ DC only after extended use...
I wonder how much swarf is inside the motor...

.
 

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Ben,

Thank you for sharing that info. I have a question about the procedure; why did you not include a result for DC ON door open ???
This would be necessary to compare all facets equally ! and would show similar to what we are saying about air flow holes on the door or elsewhere. I would like to compare and see why so many people and designs use this technique.

Dan
 

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two independent systems..
cooling air to the router and the DC system..
the router pulls air in through the snorkel...
it then exhausts it into the box...
the DC ''pulls'' this exhausted air away from the motor...
I see it as the DC aiding in increasing clean, cooling air flow through/to the motor...
the DC is actually a plus in removing heat from the router...
In a case where the router intake is isolated from the DC then adding DC either near the collet area (as in a separate pickup in that area something like the bases that have a DC attachment) or across the collet area from one side of the box to the other then it would definitely aid in cooling. Either scenario would result in a pressure drop at the collet and atmospheric air would rush in to fill the void and that includes going through the router fan to get there. That situation would be comparable to having a water tank on a stand with a pump sitting on the ground under it. When you turn the pump on you not only get the pump pressure, you also get the head pressure of the water column above the pump.
 

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heres my logic;
If you run the router in the table without a cutting bit in it for a short time, and place your hand above it, you can feel the air being pushed up through the motor by the rear fan.
If you seal the router into a box and then suck the air out, then the router fan will be starved and the router will overheat.
If you seal the router in a box and do NOT remove air and dust, but allow some air in to mix then the router fan will blow dust into the router, windings, bearings, everywhere.

Therefore, if you seal the router into a box, run dust collection from it but install a tight fitting tube over the router fan entry and run that tube through the box to outside free air, you will remove the dust AND keep the router cool AND free of clogging.

Thats what I've done, and my large makita router (NOT adjustable speed) has never shown signs of overheating.
 

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I have two DC ports on my router table. One for the Incra LS fence and another for the box. Over the years I've noticed that when the DC is attached to the fence, my Milwaukee will warm up considerably during extended use. When the DC is attached to the box, no problem with the router heating up even under hard, extended use. Suction if provided by a 2 1/2" PVC run of about 25' into a dust deputy followed by a 6hp craftsman shop vac. Dust collection is quite acceptable with this setup, however, knowing what I know now, I'd probably go with a 4" line into my regular DC'r just for air flow. But after 10 years of relatively regular use, can't say I've experienced any problems relating to overheating.
 

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Stupid question: do all routers take in air from the housing-end and blow out towards the collet? Sounds like the logical flow, but I seem to remember at least one that blew the other way - perhaps the internal fan had been exchanged incorrectly.
Might account for the different observations made by members here.

Bill, I would be particularly interested to know which way your Milwaukee blows, as theoretically the top suction should increase airflow, if anything?
 

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I have two DC ports on my router table. One for the Incra LS fence and another for the box. Over the years I've noticed that when the DC is attached to the fence, my Milwaukee will warm up considerably during extended use. When the DC is attached to the box, no problem with the router heating up even under hard, extended use. Suction if provided by a 2 1/2" PVC run of about 25' into a dust deputy followed by a 6hp craftsman shop vac. Dust collection is quite acceptable with this setup, however, knowing what I know now, I'd probably go with a 4" line into my regular DC'r just for air flow. But after 10 years of relatively regular use, can't say I've experienced any problems relating to overheating.
Is the router still inside a box but with no air movement in the box? If that's the case I would expect it to get hotter than normal. My first experience with a router mounted in a cabinet was at the mantle factory I worked at for a short while. It was a big Makita and the cabinet was at least 30 inches in all 3 directions, maybe more. They had basically just boxed in the stand it was mounted in. After running the machine for 15 minutes or so I could feel the heat coming through the sides of the box. That was in about 03 or 04 so I can't remember now if there was any DC going or even hooked up to the box at the time but I was surprised at just how hot that router got and I knew after that that I never wanted to mount one in a box after that.

As I said earlier I'm looking at making a half moon shaped pickup to mount under the table and that should catch the maybe 5% that gets thrown downward without creating issues of getting to the routers controls or built up heat. The pickup design is easy enough but I still have to figure out what to use for nipples to attach the hoses to and how to Y it all together with the main pickup in my fence.
 
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@Biagio
Thank you for doing this test, However I think that this is not what concerns most of us in that you will need to do further testing with a longer duration under actual load conditions over an extended length of time. Also compare actual air flows to the Dust collector under actual full loads and with the door open and then closed. Then after a goodly length of time running continuously under load, remove the motor and dismantle to check the amount of chips and dust inside. This is one of the causes of motor failure is the chips and sawdust abraiding the field winding's insulation and shorting out the motor, from what I have read.

Herb
 
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