# home made dust collector



## gmcooter#2 (Oct 22, 2016)

I have a home made dust collector. I used an old furnace blower housing and made my own impeller. It's made of 3/4 plywood about 14" diameter with 6 fins. It clears the air very well but won't pick up saw dust and chips very well. My question is would a larger impeller with more fins help pick up saw dust and chips?


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## Carl10 (Feb 3, 2017)

Good try with the creativity, but no (or yes until the motor burns out). You don't say, but I assume you are using the furnace motor with your own impeller? Furnace blowers are designed to gently move air without much pressure (your description of your results). What does the plate say on the motor? 1/4 or 1/3 HP You need a 3HP motor for a 14" impeller. The other issue with a furnace motor is it spins about 70% slower than a DC blower. You need a stronger design (motor, housing, impeller) to create the static pressure required to pick up dust and chips. A good blower motor will be rated Class F insulation (to accept high heat - demands of working hard). Class A or B will burn up in a blower situation. 3450 RPM is typical. Check out Bill Pentz site on motor sizing for impeller size. The other issue is a furnace blower housing is quite large/wide (good for moving air with little pressure) if you made an impeller, I assume it is a fraction of the width compared to what was in there originally. All that dead space in the housing is bad as well.

Can you explain what you are using for separation? How are you using to keep the chips and dust from hitting your impeller? Got some pics of what you did?

Good luck

Carl


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## gmcooter#2 (Oct 22, 2016)

I have a 2hp motor. I cut the housing in two and made it about half the width as it was. I made a plywood impeller about 14" diameter and with six 5"" high fins.It discharges into a 55 gallon barrel and vented to the out side. I saw a post where a guy made one with 12 fins. I think I have room to make it a little larger diameter and can add more fins. Would this help?


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## Carl10 (Feb 3, 2017)

The other issue with a furnace housing is that is made to deliver a lot of air (relatively speaking) at a low pressure. So the housing has larger inlets and outlets. For you needs you probably need smaller inlet and outlets. It is hard to understand what you have done without seeing it, but the Bill Pentz site makes both a blower with a typical DC impeller and a airfoil impeller (I assume that is what you are making). The housing design is different for both. There is also a book "How to Design and Build Centrifugal Fans for the Home Shop" that takes about all these aspects. You should definitely read it for what you are trying to do (it is not a text book and fairly short) Also what RPM is your motor? You also will want a ammeter to see how much current this motor is drawing. A metal 14" blade with only 3" blades needs a +3HP motor.

BTW If you are making a straight enclosed radial fin impeller that is a different beast as well.

Hope that helps,

Carl


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## woodnthings (Jan 24, 2009)

*why reinvent the wheel?*

I can understand that you want to make your own DC, but it's an advanced exercise in physics and fluid dynamics. Furnace blowers are "air handlers" and not really meant to move material under pressure.
A funace blower would make a great air filter and many folks have done just that. The design of a centrifugal fan is really entirely different as suggested above. The diameter of the fan, the number of fins, the shape of the fins, and the height of the fins all come into play. Then there's the aspect of making it strong enough to withstand the forces and what may happen if struck by a larger chunk of wood....? :surprise2:

The Harbor Freight DC unit can be bought for a little as $150.00 on sale and with a coupon. It's a ready made solution with all the parts you will need. Many folks have rearranged the components to better suit their shop requirements. You Tube has a bunch of the modifications. 

FYI, shop vacs move small volumes of air at very high speeds. DC units move large volumes of air at lower speeds. The 4000 FPM air speed Bill Pentz recommends to keep fine particles suspended to the filter. All sorts of factors come into play to achieve the efficiency needed. There is no need to reinvent the wheel so to speak. :wink2:


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## gmcooter#2 (Oct 22, 2016)

My motor is a heavy duty older motor. A friend that works at a paving outfit got it for me. It is 2hp 220 or 110 reversible rotation. I have it on 220. It is 3400 rpm. I have the inlet and outlet portals reduced to 4" with 4" duct work. You mentioned the volume in the housing. I my need to cut it down a little narrower. I am trying to build my own because I can't afford a store bought one right now. Also I like the challenge of trying to make it work with what I have. I have a 2hp HF dust collector hooked up to my 18" planer in the garage. It fills up a 55 gallon barrel pretty quick.I still have some that blows out the sides that I have to sweep up. I had thought of trying it in the shop an using the home made one on the planner. I have another furnace housing and I going to try it again.


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## Carl10 (Feb 3, 2017)

Well the motor could get the job done with a wood wheel, but typically you would want a 3hp motor with that size wheel. Since you already have a 2HP HF DC just use that as your template. You will notice that the wheel is not centered and it is a spiral shape. The whole housing is designed around the size of the impeller. So unless your furnace housing was also a 14" impeller, changing the width may not do what you want. There is a little flexibility in the diameter but then you start making sacrifices with performance and noise. I think if you look at your HF it has a 11" impeller (not 14") for a 2HP motor. With all the changes you are doing to this furnace housing, you might do what others have done and make the Bill Pentz housing. The default plans on his site are made for a 14" impeller (make sure your printer prints it to the right scale). Again the book mentioned above steps you through all of this. Keep us posted on your progress.

Good luck,

Carl


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## gmcooter#2 (Oct 22, 2016)

I have it about ready to hook back up. I went to 8 3"high fins and reduced the width of the housing to match the height of the fins. I have tested it on the bench and it seems to have more suction. All I like is the exhaust portal. I almost had it done when the power went off for about an hour and a half. By that time it was quitting time anyway. I'll get it Monday Lord willing. I'll let you know how it works If you are interested.


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## Carl10 (Feb 3, 2017)

Definitely would like to know how it turns out. A picture would be great. How are the proportions of this housing compared to the HF housing? Inlet/outlet/wheel placement?


Carl


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## Jig_saw (May 17, 2015)

GEMcooter#2 said:


> I have a home made dust collector. I used an old furnace blower housing and made my own impeller. It's made of 3/4 plywood about 14" diameter with 6 fins. It clears the air very well but won't pick up saw dust and chips very well. My question is would a larger impeller with more fins help pick up saw dust and chips?


You need to shape the inlet with a larger area than the duct. This would be like a convergent nozzle. Only then you can get enough airspeed to pick up chips and sawdust, like a vac.


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## gmcooter#2 (Oct 22, 2016)

I'll try to get a picture tomorrow. It is pretty close to the HF one that I have. The inlet is 4'' and outlet will be 4''. That's the way my HF one is. They are in a plywood plates attached to the housing so they can be easily changer if need be like Jig saw said. The furnace blower housing wasn't perfectly round so I put a baffle around the inside to match the impeller. It is about half the width of the first one I made. When I bench tested it yesterday I had the inlet but didn't have the outlet finished yet. I could feel the suction on my hand pretty strong. I was working the outlet when the power went off so I liked just a little getting it finished. The power was off for about 2 hours. By the time it came back on it was to late to go back to the shop. We are going To my daughters tomorrow afternoon. We'll be up there until Saturday but I'll have time to finish it before we leave. Take care and thanks for your response.


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## gmcooter#2 (Oct 22, 2016)

I got back from my daughters Sat. afternoon. I got my DC hooked back up after the changes I made. It is doing somewhat better. I have 2 runs of pipe running along 2 walls and meeting on each side of the door that leads to the room where the DC is located. They go through the wall and Y into the DC. I have a blast gate in both pipes before they go through the wall so I can close one or the other and draw through one side at a time. It picks up saw dust very well off the tables but not off the floor where it has to lift up. It will not pick up from the table saw where the pick up comes out of the bottom of the TS. Would it help if the blast gates were on each side of the Y right at the DC?


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## woodnthings (Jan 24, 2009)

*table saws are a real problem*

I have a nice Craftsman 10" hybrid with a 4" port at the very bottom and about all it collects is what slides down the inclined ramp to the port. Unless the manufacturers enclose the blade with a specific dust shroud, table saws will continue to be "gravity fed" to the DC. I have a newer Bosch Job Site saw with a shrouded blade which exits at the rear in a 2 1/2" shop vac port. It works much better than the full size table saw. 

I think that you need about 6 times the volume of air removed from the table saw cabinet that my existing DC can manage. I have the Jet 1100 a 1 1/2 HP DC advertised at 1100 CFM. The fine dust that gets airborne probably gets sucked away, but the heavier particles just fall out and down the ramp.

I have experimented with an air pressure hose to keep the dust airborne and I really can't decide if that's a solution or not. A shop vac on the "blower" function may work also.... I donno? For me it just isn't worth it. I get what I get and that's all I'm going to worry about. On my setup one Jet 1100 DC serves 3 contractor table saws on a single 4"PVC run with 3 separate blast gates. The flex hose to the DC is only about 4 ft long, so no big losses there.

I give you credit for your experiments. Keep on with it. :smile3:


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## Carl10 (Feb 3, 2017)

GEM - It is hard to say at this point why your air/flow suction is low. Without a picture of the blower it hard to comment on what we are dealing with. If your piping is 4" you are killing whatever airflow you might have had. You also don't comment on how long of a run you have how many 90s, 45's etc..

woodthings - you are right on about the table saw air gaps I have the same issue with my contractor saw. I have seen people do some patches (like water pipe foam around the table/ housing connection and custom back enclosures to seal the gaping hole in the back) to significantly improve dust collection. Also, I just sold my Jet 1100 because although it advertises 1100 CFM, with no bag filter and measuring at the 6" opening at the blower I only had ~850-900 CFM. With a bag filter and 4" rigid 10' pipe it significantly dropped to ~575 cfm. Start adding 90s and duct length and it is useless for a fixed dust collector.

I am looking at building a 3hp cyclone which I will post about when I get started.

Carl


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## gmcooter#2 (Oct 22, 2016)

*dust collector*

I took some pictures of my dust collector but can not get them into the computer. I made some changes in my gates. I put them as close to the dust collector as I could get them. The run on one wall is about 6 ft. The run on the other wall is about 8 ft There are no 90's just 2 45's in each run.They go through the wall and into a separate room and y into the collector. I can close one or the other so it draws through one run. It is now picking up from the box under the table saw. I can vacuum from the floor also. I don't know about how many cfm I have. I don't have any way to check that. All I'm going by is how it picks up and that is pretty good I think. But I'm not very much of an expert. I just do it by trial and error. I'll Keep trying to get the pictures if I can figure it out.


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## Carl10 (Feb 3, 2017)

I'll assume you have 4" PVC pipe, and although short runs, it will limit your air flow. Try opening both gates (although 2 -4" PVC pipes is still less than 1- 6") it will help with airflow. If that makes a big difference in your suction, then your blower can not produce very much static pressure (which is typical of a furnace blower).


Let us know what you find.


Camera- when connected to your PC look in the DCIM folder for the pictures.


Carl


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## woodnthings (Jan 24, 2009)

*no more furnace blower...*



GEMcooter#2 said:


> *I have a 2hp motor. I cut the housing in two and made it about half the width as it was*. *I made a plywood impeller about* 14" diameter and with six 5"" high fins.It discharges into a 55 gallon barrel and vented to the out side. I saw a post where a guy made one with 12 fins. I think I have room to make it a little larger diameter and can add more fins. Would this help?





Carl10 said:


> I'll assume you have 4" PVC pipe, and although short runs, it will limit your air flow. Try opening both gates (although 2 -4" PVC pipes is still less than 1- 6") it will help with airflow. If that makes a big difference in your suction, then your blower can not produce very much static pressure (which is typical of a furnace blower).
> Let us know what you find.
> Camera- when connected to your PC look in the DCIM folder for the pictures.
> Carl


The motor is not a typical furnace blower motor at 2 HP, and the impeller is hand built, and not like a centrifugal squirrel cage blower. Only the blower housing is left and it's been modifed.

The term furnace blower is misleading at this point, too much is not typical and has been modified.

I wouldn't be surprised if the housing gets some modification as well. As I stated in an earlier post, it like reinventing the wheel. It's great to be creative and try new ideas, but at some point the engineers who do this have sorted those issues out. As non-engineers, woodworkers will not know about air flow and fluid dynamics principles, a whole different science. Air flow is like electricity, it's difficult to watch. 

I worked in a wind tunnel when designing cars at GM and while we knew what to expect for the most part there were always some surprises. WE used little tufts of yarn to see what the air flow was doing on the various surfaces. Sometimes the yarn would lay down flat other times it would stand straight up. My greatest time was working on Richard Petty's car no. 43 which was in the tunnel under a rental agreement. There were only a few wind tunnels in the country at that time, years ago.


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