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Airflow restriction question

954 Views 6 Replies 5 Participants Last post by  honesttjohn
I have recently added a CNC tol my shop, and I use a Harbor Freight 1 hp dust collector that was rated at about 750 cfm when I bought it (now they only claim it has 650).

I'm wondering if reducing the 4 inch inlet pipe to the collector down to the 2 1/2" dusc shoe connection on the CNC and only connecting the CNC will overwork the motor on the dust collector if I don't provide any other intake for the collector. I have health problems and need to capture all the fine dust generated by the machine that I can.

I have run the collector with two 2 1/2" inlets on my table saw for short periods of time with no appreciable pulldown of the motor, but some of the projects on the CNC can take a long time. For example, the Vcarve software estimates it will take 50 minutes to surface the spoilboard.

I know that Desert Rat Tom and others have used the Harbor Freight collectors extensively and would like to get some advice on this. Also, i may upgrade to the 1550 cfm model and am wondering if the problem would be even worse on it. Thanks.
1 - 7 of 7 Posts
rated at 650 eh...
it's IRL it's closer to 400 more ot less... most likely.. less..
and if you neck it down it will be more like 150ish.
you can only get so much air (CFM) to move through a fixed sized pipe...
throw in some turns and that number drops...



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Lots to absorb there, Stick. Thanks!
Stick is right, and don't worry about the load on the motor the less air flow the less the motor works.
Lots to absorb there, Stick. Thanks!
yur welcome..
the best you can do is increase the size of the take off port or/and add another port
If you're going to use 2 1/2" fittings anywhere in the line, I think you would be better off hooking up to a shop vac instead of a dust collector. A dust collector doesn't make as much static pressure (suction) when restricted as a vacuum machine. Put a Dust Deputy in front of the vac to avoid clogging the filter.
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I have mine hooked to a Ridgid (the big one) vac with a dust deputy in between. With a dustshoe I just have to empty the bucket before it gets full and the vac keeps right on chugging along. I blow the filter out every few months or so. Ridgid has a lifetime warranty so I run the heck out of it. I had the small one before and it lasted 15 months before burning up - HD replaced it and I upgraded to the 14 or 16 gallon (can't remember which) and it runs sometimes 18 hours a day.
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