Shop Vac vs Dust Collector ???

[plano_harry]

I am confused! I am using a Curtis "darn near" collector box on my lathe with a 2.5" outlet. Works great but misses a little dust out the front. I have had it connected to a Dust Deputy then into my old Craftsman shop vac (probably 160-200 cfm max). Decided I wanted to up the collection performance, so step one was to try a HF 1hp Portable dust collector that "allegedly" runs 910 cfm.

I am thinking more air means better collection in my box. Not seeing it. Actually appears to has less suction than my shop vac doing the A-B swap test, so I don't think I am inlet limited. I have searched the forum to find dust wisdom, but alas. Read about shop vacs designed for "lift" and blowers for air movement Seems to me that getting 4-5 times the air down the same inlet would equate to more suction. What am I missing? Is the HF portable THAT BAD!

I was planning to do a 4" end-to-end upgrade, but now I am wondering if a new hi-suck vac might produce better results on my existing 2.5" line at lower cost. Thanks for any light that you can shed on this.
Harry

 

[The Penguin]

to be clear...are you using the same hose and dust fitting (at the lathe) with both the shop vac and the dust collector?

 

[LL Woodworks]

Harry - I used a Shop Vac with 2.5" hose for a long time. About 4 months ago I got the HF portable and am reducing the 4" hose down to 2.5" at my mini lathe. I think the Shop Vac actually pulled more dust than the HF portable but is louder, a higher pitched noise, than the HF portable.

 

[76winger]

A dust collector is designed to move larger amounts of air, but not to generate as much suction force (vacuum if you will). Think of a window or pedestal fan that movies a lot air in terms of cubic feet per minute (CFM) but very little air pressure on the front side or vacuum on the back side.

The small hole designed for your shop vac is a bottleneck where the dust collector is concerned. The lager 4-6 holes and tubes are necessary to allow it to properly move the larger amounts of air, at which time you'll see the better performance of the DC show up.

I just went though this myself with the exception I already had the larger opening at the lathe in preparation for a future DC and adapted it DOWN to accommodate the shop vac until I could afford the upgrade.

Sent from my iPad using Forum Runner

 

[plano_harry]

to be clear...are you using the same hose and dust fitting (at the lathe) with both the shop vac and the dust collector?

Yes. I just switch the short connection from the Dust Deputy output to either device.

 

[plano_harry]

Harry - I used a Shop Vac with 2.5" hose for a long time. About 4 months ago I got the HF portable and am reducing the 4" hose down to 2.5" at my mini lathe. I think the Shop Vac actually pulled more dust than the HF portable but is louder, a higher pitched noise, than the HF portable.

Thanks Lynn, same observation, the vac is louder!

A dust collector is designed to move larger amounts of air, but not to generate as much suction force (vacuum if you will). Think of a window or pedestal fan that movies a lot air in terms of cubic feet per minute (CFM) but very little air pressure on the front side or vacuum on the back side.

The small hole designed for your shop vac is a bottleneck where the dust collector is concerned. The lager 4-6 holes and tubes are necessary to allow it to properly move the larger amounts of air, at which time you'll see the better performance of the DC show up.

I just went though this myself with the exception I already had the larger opening at the lathe in preparation for a future DC and adapted it DOWN to accommodate the shop vac until I could afford the upgrade.

Sent from my iPad using Forum Runner

Thanks Dave. Maybe I need to put a Big Gulp on my box and see how it works (will have to drop the Deputy out as as well until I get a bigger version!)

 

[The Penguin]

yep, that's your problem. you need larger diameter everything for the DC

 

[LL Woodworks]

yep, that's your problem. you need larger diameter everything for the DC

I may switch to a 4" hose from DC to lathe and see if that results in better dust collection. I start with a 4" hose at the DC then reduce to 2.5" after about 18". The 2.5" carries all the way to the mini lathe.

 

[76winger]

I just got to try mine in use yesterday (since my DC is new) and it with a four inch tube all the way to the four inch hole, it's definitely pulling more air and taking more shavings with it.

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[bradh]

Basically you need high air flow to get the small dust particals that are the biggest health hazard. As others have suggested, bigger pipes are the only way to get that.
If you want detailed info on dust extraction and are not afraid of strong opinions, try this Aussie wood forum specifically on dust extraction:
DUST EXTRACTION
On this site you are going to hear that the minimum specs should be 6" pipes, a 3hp collector with cyclone filter, and venting outdoors!
Note, this is an Australian site so much of the discussion on pipe sizes is in metric.