I live about 5m from the TPtools factory/showroom.
http://www.tptools.com/VAC-40-High-Efficiency-Vacuum,3283.html?b=d*8035

Be a good sport and check their dumpster for me would ya? I'll taken a broken commercial unit and fix it.

 

A dust collector will be useless for trying to suck up fumes. (Same sort of goes for a lathe). The area of the "sucking" is just too small. You would be better off with a cheap fan blowing the air away.

I don't get it; or your first post. Maybe I will after reading more (I still haven't devoted any appreciable time to reading Bertus' link). In my layman's head it seems that if there is a distinction to be made, there are two families of suckers: High volume low pressure (dust extractor) and low volume high pressure (shopvac). So (again, in my layman's head) it seems that the dust extractor would be well suited to fume extraction (welding/painting/machining).

 

Be a good sport and check their dumpster for me would ya? I'll taken a broken commercial unit and fix it.

Thats how I got mine really they have a "scratch and dent sale" a couple of times a year for the locals. They trow out very little.

The one I linked to is just basically a large shop vac motor head, mounted on top of a couple of ~10gal grease pails. With a weighted filter bag inside. When the unit shuts off the weight causes the bag to drop, shaking the dust off of it.

Don't think a squirrel cage blower would work on the blast cabinet. Not enough speed in the air flow. But they work fine for a fume extractor or wood working dust extractor, that's what most wood dust collectors have, a squirrel cage blower. A friend made one from an old furnace blower and a plywood box and a couple of furnace filters..

 

I don't get it; or your first post. Maybe I will after reading more (I still haven't devoted any appreciable time to reading Bertus' link). In my layman's head it seems that if there is a distinction to be made, there are two families of suckers: High volume low pressure (dust extractor) and low volume high pressure (shopvac). So (again, in my layman's head) it seems that the dust extractor would be well suited to fume extraction (welding/painting/machining).

I think my English skills are letting me down here, lets try again

Imagine having wood dust on the floor. If you get a HPLV unit (vacuum cleaner) it will pick up the dust from about 100mm away and will gather a large area. If you do the same experiment with a LPHV (dust extractor) the dust will not move until you are at about 20mm from the floor. Same will go for fumes. The air around the duct (within maybe 400mm) will be moved very well, but beyond that there will be no effect. The air will still move but the radius will be much bigger. So unless you can enclose yourself in a small area and use the dust extractor to make a wind tunnel it will not work.

I guess I can also give you a real world example. After a day of woodworking, particularly with MDF, my workshop has quite a lot of dust in the air. You can see it if the sun is shining on it as you no doubt know. If I get my dust extractor out and hold it in the dust I can see, the dust around the duct is only sucked up at maybe 400mm from the duct. Dust outside this area just floats down. I guess you are thinking that the air is still moving to replace the air I have just sucked up so the dust also should be moved, but because the presser is so low (I have 8.2in form my 3HP 2400CFM dust extractor with a 150mm duct) the dust is not moved. I know this sounds wrong and I wish I could take a video of the effect to show you.
As above, a dust extractor works very well if the air is constrained. If you imagine a table saw, most of the dust exits the saw at the bottom. The dust extractor moves a heap of air out of the contained area causing a wind tunnel effect. This is also why, again against what you would think is right, you do not want to cover all the holes in you table saw to try to get move air moving around the blade. If you constrict the flow, the whole things stops working. Also interestingly, if you constrict the air flow the current draw on the motor drops too as the fan is moving less air.

I will see if I can take a video of me sanding on my lathe with the dust extractor going, just not sure how well the effect will be seen.

I hope this helps.

Mark

 

Are you closing off unused ports? Your velocity (suck power) will be higher.

The dust extractor control system needs to turn on the vac and close off ports that aren't used.

Usually there is some means to sense current of a machine and turn the extractor on + a re-triggerable delay (say 4 minutes) to turn off.
Only the dampers of the machine(s) in use will be open.

 

unless you can enclose yourself in a small area and use the dust extractor to make a wind tunnel it will not work.

I see this as an opportunity to remind you that protecting (only) a person is sometimes the right answer, compared to controlling the whole room.

 

I see this as an opportunity to remind you that protecting (only) a person is sometimes the right answer, compared to controlling the whole room.

That is what I am saying. In order for a dust extractor to work as a fume hood you will need to have the duct close to where you are working. Sometimes you can do it, most of the time it is a pain in the bum.
All I am saying is the time spent setting up the duct, putting it into the right place and keeping it there is far harder then getting this;

\

Coming back to wood dust, point is the same. Unless you can get the dust into the airflow, it will not get sucked up. On my lathe I tried to attach my dust collector to the back with a bell mouth adaptor. Yes, it caught some dust but a lot still ended up under my feet.
Am I saying dust collectors a useless - NO. they are great on machines where the dust is been made in a semi enclosed area. A table saw is a great example. (cheap ones need to be modified as they don't have input vents and choke a dust collector). a hand held sander on the other hand needs to have a vacuum cleaner, with its high pressure, attached to effectively collect the dust. again a dust collector will only collect the dust around the duct, which from my experience, is about 30% of the dust coming out of the sander.

 

Are you closing off unused ports? Your velocity (suck power) will be higher.

The dust extractor control system needs to turn on the vac and close off ports that aren't used.

Usually there is some means to sense current of a machine and turn the extractor on + a re-triggerable delay (say 4 minutes) to turn off.
Only the dampers of the machine(s) in use will be open.

The experiment above was just the duct, flexible hose really, directly to the dust extractor. I don't have a nice ducted system until recently but yes, I have blast gates install on my gear and only one is ever open at a time.

Interestingly, if you are choking the input side of the machine (a joiner is difficult to open up to the flow simply because of the design) you are better of having more then one gate open. If there is too little air been allowed into the duct the volume of are will drop by a huge amount and the dust will sit on the bottom of the duct.

 

Interestingly, if you are choking the input side of the machine you are better off having more then one gate open.

Another good reminder! You can throttle the low pressure side up to a point. Once you "break" the suction side of the squirrel and the RPMs go towards MAX, the flow rate decreases all out of proportion.

 

Just in case someone is still interested in seen what I was talking about, I took this video. As you can see, the performance in open air is not so good..

https://onedrive.live.com/redir?resid=2F201B148A757533!5983&authkey=!AB39Vi5eFA1EToI&ithint=file,avi

I would guess that it would suck smoke better the dust, but you would still need the duct very close the where you are welding.

 

Just in case someone is still interested in seen what I was talking about, I took this video. As you can see, the performance in open air is not so good..

https://onedrive.live.com/redir?resid=2F201B148A757533!5983&authkey=!AB39Vi5eFA1EToI&ithint=file,avi

I would guess that it would suck smoke better the dust, but you would still need the duct very close the where you are welding.

This is strange, i never got an alert that this thread had new replies. I just happened upon it while browsing page 2 of "new posts."

Anyway...
Thank you for taking the time to make a video.
So that was a dust collector, and you're saying that with a shop vac, the performance would have been better?

 

Yep. A high pressure unit would suck the dust up to 500mm depending on power.
Still, a fan blowing the welding fumes would be the way I would be doing it. The only problem is the air is not been replaced but I am guessing you would not be welding all day to fill the room with fumes anyway.

Have fun.

 

I'd recomend a positive displacement rotary lobe type unit or a rotary vane type like what's used on the commercial super vac trucks.
10,000+ CFM and up to around 25 inches of vacuum should clean up most anything you don't mind the 200 - 300 HP diesel clattering away in the corner of the workshop.

 

Yep. A high pressure unit would suck the dust ....

I'd recomend a positive displacement rotary lobe type ...

WTF!? Why am I not getting alerts to replies from this post?

 

Check under more options for watching the thread ans getting notifications.

 

i added an Oneida Dust Deputy to my shop vac, and I've been happy ever since. I can still use my shop vac to suck up water if necessary, but very little dust gets past the Deputy into the vac. Filter stays clean for a year or more, and performance stays high.
http://www.oneida-air.com/inventory...&CatId={6EE79B16-EB63-43E7-8F30-1E06240A24A4}

 

Thanks. I've looked into ripping off that design. How would you say it compares to a "real" dust collector?

 

I picked up a pair of 7.5 HP high capacity regenerative blowers last summer and by my estimations one of them has to be destined to become a central vac system power unit for the new house project.

 

Thanks. I've looked into ripping off that design. How would you say it compares to a "real" dust collector?

Well, suction is limited to the shop vac power, but it's a 3 HP rating, so no problems. The bucket isn't as big as an industrial unit, but I don't have shop space for the large type anyway. I'm squeezed into half a garage. I mounted the shop vac and the DD on a rolling platform, so I can move it around and plug into different machines.
Here's another cheaper option based on the same principle: http://www.rockler.com/dust-right-dust-separator
And if you google around woodworking sites, I think you'll find info on how to make one of those cyclone devices yourself.