Thread: Choosing a Generic 3 HP Dust Extractor

Are you able to vent the dusty outside?

I have a similar set of machines to yourself and went with a "generic" 3HP dusty attached to a Thien-type top hat separator made for a large outside bin. The fines are vented externally through a length of flexible 6in AC ducting. I have a short (1.5m) piece of flexi (6in) that attaches the separator directly to the tool. The separator is on wheels and I've laid my shed out such that each of the heavy users (PT, BS, TS) are within a couple feet of the separator, so it's not too onerous to shift the flexi from one machine to the next.

Some of the machines have had and still need modifications to accept the 6in hose. The setup works well for me and I've not had any issues with clogged pipes. For me the limiting factor appears to be the inadequacy of the machines to efficiently extract dust (e.g. 4in rather than 6in connectors).

If you're wanting to go the ducted route 3HP might be on the small side.

Dont forget to look at the woodfast single phase 3 hp dusty. It comes with a 13"impeller and i will be reducing the suction port from 200mm to 150. Its $810 from memory. I take delivery of mine mid to late jan

Originally Posted by delbs

Dont forget to look at the woodfast single phase 3 hp dusty. It comes with a 13"impeller and i will be reducing the suction port from 200mm to 150. Its $810 from memory. I take delivery of mine mid to late jan

Thanks for that suggestion Delbs. The Woodfast DC5000 Dust Extractor 3HP Single Phase (2800 CFM) at $820.00 does look like a decent unit. Unfortunately, it seems that currently there is no one in Brisbane who sells them, so I'd have to pay freight from Adelaide (I'm waiting for a quote). At 2800 CFM, this machine has the highest flow rate (by a big margin) that I've seen quoted for a 3HP Dust Extractor so far.

One alternative that also looks interesting is the Woodman DE1900 which is stocked by Gregory Machinery in Brisbane. (http://www.gregmach.com/product/de19...ust-extractor/) it has an even bigger 355mm (close enough to 14 inches) impeller, but the CFM rating on the Woodman is 1900 CFM, which is the lowest of all of the 3HP Dust Extractors that I've looked at so far. Largest impeller - but lowest flow rate ? Doesn't make sense.

So - over to the Dust Extractor Technical Experts.

1. What effect does the diameter of the impeller make on the performance of a Dust Extractor, assuming all machines supposedly use 3HP motors ?
2. Quoted CFM Flow Rates ?
   
   • Can we believe the CFM flow rates quoted for these machines ? (For the four 3HP Dust Extractors mentioned in this post, we have quoted flow rates ranging from a low of 1,900 CFM up to a high of 2,800 CFM.)
   • Are these CFM ratings relevant, seeing we don't know the conditions under which the measurements were made ?
   • If the quoted CFM specs are misleading, is there another way to evaluate the machines ?
   
   
3. Woodman quote a "Max. static pressure of 18 In H2O". Is a "static pressure" specification relevant, and if it relevant, is a maximum of 18 inches of water pressure good, bad or indifferent ?

Regards,

Roy

Just to add to your mix http://www.garypye.com/Dust-Collecte...cter-p261.html

Originally Posted by AussieRoy

What effect does the diameter of the impeller make on the performance of a Dust Extractor, assuming all machines supposedly use 3HP motors ?

The bigger the impeller the more air it can move provided the motor can actually turn the impeller. If the impeller is too large the motor will overheat and burn out.
But it's not just the diameter of the impeller that matters, the impeller and housing has to be designed appropriately so it can hold and push the air it grabs. It's too difficult to explain what is required in a few lines but it is sufficient to say that not all impellers are the same and some are sloppy joes so they don't work very well.

• Quoted CFM Flow Rates ?Can we believe the CFM flow rates quoted for these machines ? (For the four 3HP Dust Extractors mentioned in this post, we have quoted flow rates ranging from a low of 1,900 CFM up to a high of 2,800 CFM.)
• Are these CFM ratings relevant, seeing we don't know the conditions under which the measurements were made ?
• If the quoted CFM specs are misleading, is there another way to evaluate the machines ?

The manufacturers CFM ratings are basically useless as these flows rates are usually done according to an industry standard which bear little resemblance to reality.
Reality is what happens when the impellers are used with clogged filtes, choked machines, cyclones and chip collectors, and small diameter ducting, all of which which generate significant back pressure and reduce flow dramatically.
Just because something moves a heap of air according to the standard may not translate to moving air under back pressure. Think of a simple axial (propeller) type fan. They can move lots of air at zero back pressure but are near useless unser a very slight back pressure.
The way to evaluate an impeller is using a fan curve. These provide the CFM under different back pressures

Woodman quote a "Max. static pressure of 18 In H2O". Is a "static pressure" specification relevant, and if it relevant, is a maximum of 18 inches of water pressure good, bad or indifferent?

I seriously doubt this is the case.

An appropriate size, half reasonably designed impeller can with a
1HP motor produce ~6" of SP
2HP motor produce ~8" of SP
3HP can produce about 10" of SP
4/5HP can produce ~12" of SP

To generate 18" of SP requires a large compressor like impeller similar to what a vacuum cleaner uses (Vaccum cleaners typically have 25 - 30" SP but can only maintain this for small CFMs

If you read up Bill Pentz's website you will see that it is very say to use up about 4-5" of SP using filters, bags, cyclones, just short lengths of ducting and because machines are so badly choked. In the case of a 1HP DC this leaves bugger all to move air.

Originally Posted by BobL

The bigger the impeller the more air it can move provided the motor can actually turn the impeller. If the impeller is too large the motor will overheat and burn out.
But it's not just the diameter of the impeller that matters, the impeller and housing has to be designed appropriately so it can hold and push the air it grabs. It's too difficult to explain what is required in a few lines but it is sufficient to say that not all impellers are the same and some are sloppy joes so they don't work very well.............................................................If you read up Bill Pentz's website you will see that it is very easy to use up about 4-5" of SP using filters, bags, cyclones, just short lengths of ducting and because machines are so badly choked. In the case of a 1HP DC this leaves bugger all to move air.

Many thanks Bob. That's exactly the sort of information that I was looking for. I'll have another read of Bill Pentz's web site today - it's been a while since I was last there, so it's time for a refresher. I'm still not sure how to decide which of these machines is better than another - but then that's my problem.

Regards,

Roy

I have the CT model and have played around a bit with the H&F model. The CT model is made in Taiwan and was slightly better made that the H&F model and at the time the CT was on special for $1k - it was then advertised as a 3100 CFM!

My concern with the H&F model is the bendy Y connection between the impeller and the bags. Without doing any air flow measurements that just seems like it would restrict the flow.
The advertised slow rates ares meaningless. In practice if 6" ducting is used, both will pull 1250 CFM through an unrestricted 6" duct and its downhill from there.
To get a greater air flow 8" ducting would be needed but this is overkill for DIY machines and I doubt whether the standard 3HP motors will cope with this and they would probably have a much shorter life. This is where 4 & 5HP motors are needed.

I'm about to order one of those generic 3 hp dust extractors with the bendy Y connection, and was wondering if it is possible to rotate the bendy Y bit 90 degrees to mount the motor off to the side. The reason I was thinking of trying this would be to have the bags outside, and the motor inside, with the bendy bit going through the wall. It seems easier to do that than to have to build an enclosure to protect the motor from the elements.

Or am I barking up the wrong tree here?

Originally Posted by Colin62

I'm about to order one of those generic 3 hp dust extractors with the bendy Y connection, and was wondering if it is possible to rotate the bendy Y bit 90 degrees to mount the motor off to the side. The reason I was thinking of trying this would be to have the bags outside, and the motor inside, with the bendy bit going through the wall. It seems easier to do that than to have to build an enclosure to protect the motor from the elements.

Or am I barking up the wrong tree here?

One of the last things you want to do is constantly get the bags wet. The fine sawdust on the inside of the bag will form a mud and block the bags completely so that they will have to be removed at washed.

The motors make an awful noise so getting the whole thing outside the shed is a double bonus for noise and dust.

Don't know about the bendy Y - I don't think the cross section of the square ducting is symmetrical anyway.

Bugger. There goes the budget for that job...

I suppose I could stick it under the carport, but then it's right outside the only real source of ventilation. On the other hand, I don't work with the garage door open in summer because of the mosquitoes and in winter because it's cold, so maybe that's a temporary (read very-long-term) solution.

Thanks for the feedback Bob, as always you get to the core of the issue and give solid advice.

Well, I've bit the bullet and placed the order. With luck it'll be here by the weekend. I'm getti one of these (not from that supplier though) at a cost of a shade under 600 AUD. I've now got to start finding a supplier of 150mm pipes, which is going to delay things even further. At this stage I'm just worried about the lathes - I'll have to look at the bandsaw later, but that will mean deciding on a permanent spot for it, so will take longer. I need to re-read the thread on shaping the bell mouth and find something to make it out of...

I got a phonecall on Thursday afternoon to tell me the dust extractor had arrived, and I went into town to fetch it. I had a few moments spare and bought the PVC pipe couplings too, but couldn't get the pipe because I need the other car which has roof racks. I'll get that over the weekend.

I got home at 11pm (went out for dinner with a friend while I was in town), and it was all unloaded, assembled and running by 1am, in the lounge. The 160mm pipe coupling fits directly onto the inlet (in place of that thing with the three 100mm inlets), which makes it dead simple to setup. I might still change that later to try to get more air through it, but for now I'm glad it fits straight out of the box. I also found a bell shaped fitting which is used to connect the PVC pipe to the old ceramic pipe, and with a little flaring, it should work well behind the lathe.

It's got no dust in it yet, but I'm pretty chuffed so far. I'll post some pics later, when I've had some sleep (it's about 1:20 over here).

Originally Posted by Colin62

. . . . I also found a bell shaped fitting which is used to connect the PVC pipe to the old ceramic pipe, and with a little flaring, it should work well behind the lathe. .

Any flaring is better than nothing but the flaring with near zero back pressure is one that has a flare radius of curvature ~ 1/2 the radius of the pipe.
That's 37.5mm for a 150 mm diameter pipe

Originally Posted by Colin62

I'm about to order one of those generic 3 hp dust extractors with the bendy Y connection, and was wondering if it is possible to rotate the bendy Y bit 90 degrees to mount the motor off to the side. The reason I was thinking of trying this would be to have the bags outside, and the motor inside, with the bendy bit going through the wall. It seems easier to do that than to have to build an enclosure to protect the motor from the elements.

Or am I barking up the wrong tree here?

Just did it yesterday... see pic https://www.woodworkforums.com/f200/modifying-3hp-dc-7-dust-extractor-193697

Instructions on how to do it on the H&F DC-7
Remove the Phillips head screws holding the inlet panel
There is a metric hex head screw holding the impeller on. NOTE The screw has a reverse thread, clockwise to undo.
Small puller required to remove fan, but has a lip machined in to catch on for removal
4 x 10mm bolts (14mm socket and extension)
Rotate 90 degrees
bolts back in and tighten
Make sure keyway is in place and gently tap fan back on squarely
put front plate back on