You mention sanding on a downdraft table. Are you wanting to connect to the downdraft table or to the sander?
If connecting to the downdraft table, use a standard dust collector. More CFM is better and if this is a home-made downdraft, you can add more holes or make it larger so your collector pulls more CFM (more holes = less restriction = higher CFM from the fan).
If connecting to the sander, you want a shop-vac style because you will be using a 1-1/4" hose. I would not want to wrestle a sander with 2-1/2" hose.
I didn't know the Oneida collector filters are HEPA rated, maybe so now? The Festool vacs have HEPA 2nd stage filters. Although the vacs are expensive, they are very quiet and replacement HEPA filters in those have to be much less than a HEPA for a 3HP collector. In general, sanding dust is too fine for consumer grade cyclones anyway, a lot of it will end up in your filters, blinding them. Also, when you pull less CFM, the cyclone efficiency in drastically reduced which will allow even more carryover to the filters.
David, the language I used regarding the 2.5" port was referring to the effective cross sectional area of that opening. Take my Felder sliding saw. It has a 5" port on the back of the machine. Inside it connects directly to a 4" flex hose. That 4" flex hose connects to the cast iron blade guard which has an oval opening with an effective cross sectional area of a 3.25" diameter round port. Most machines have a smaller opening at the point of dust generation than the port on the back of the machine.
Originally Posted by David Kumm
I broke the paper into small enough files to upload.
Actually I'm right with you Joe. I was referring to the posts comparing shop vacs with a smart. If you go to the Cincinnati Fan tables and look at the RBE 9 at 3450 rpm you will see that my impeller is basically a larger version of yours. With long runs and lots of pneumatic gates, I was locked into my existing pipe at 5" reducing to 7". A typical 7.5 collector is built for 10" mains and large or multiple ports to keep the velocity up. My one machine at a time use meant I needed to use a fan that operated at higher pressure so the velocity in the mains could stay in the 3000+ range. It turned out I didn't need the speed control other than to occasionally increase hz when running the Oakley or reducing to clear the shop air with less noise. A 15.75x6.25 radial is loud. Mine is in the attic and I have accoustical blankets around the cartridges. My system was scrounged off ebay, and other finds, VFD, Torit 20-5 cyclone, RBE 9 blower and motor, blankets, muffler, and 4 Wynn nano cartridges. I use an anemometer too as I found my prior lack of testing caused me to reinvent the wheel more than once.
Even with the noise, I'm a believer in radial fans but understand why hobby systems don't use them. It is easy to burn out a motor if you don't monitor the amp draw or have a built in system to do it. Curved blade fans can be designed to top out before the motor reaches FLA so there is less chance that someone venting outside with large pipes and ports will destroy the motor. Dave
I don't know about the merits of a smart vacuum but I do think I understand shop vac setups. I use a Rigid with a filter like this:
It pulls through a dust deputy and the vac and cyclone sit on a cart based upon plans from Woodsmith. The HEPA filter is $30. A 6 gallon Rigid vac is about $50. The dust deputy is also about $50. I put an autoswitch on which was about $40 and works even with my 15A table saw. A sheet of plywood is around $30. So for about $200 you can have a very functional shop vac with HEPA filtration. It's noisy but I wear muffs in the shop anyway. Nearly all the tools are noisy. Right now, this is all I use. It won't handle the planner or jointer but works for the other tools. I need the shop vac for the tracksaw and sanders and it works as well as my little DC did for the CMS and RAS and table saw.
I'm not claiming anything about DCs. But effective shop vacs for me start about $200. Not $600.
Jim, read the Amazon reviews (especially this old one)- despite what the listing says, it is not a true HEPA filter (at least not five years ago). Also, read what people say about it loading up quickly. Also, a shopvac will not provide the CFM needed for a CMS or tablesaw.
Originally Posted by Jim Dwight
I started this thread to discuss dust collector systems and it has migrated to shop vac and for some this is quite useful.
There have been some interesting posts on shop vac systems. As much as possible, I want to use a larger system for dust collection needs. I do not want to give up space for a shop vac, dust deputy system. Also, I do not have a way to exhaust outside.
I do use a Festool CT26 for sanding. I bought it several years ago and while expensive is a HEPA vac, variable speed, quiet and has auto on off.
Joe Jensen's post and article are very useful as he has good info. I am going back to he drawing board and do some estimates of what I need given my shop layout.
Larry, sorry didn't want to hijack your thread but I guess I did.
Alan, I'll start another thread and see if anybody wants to talk about this.
Hi Everyone, I'm new here but am jumping in just to make an observation while I continue to read and learn.
My observation, specifically directed at the great looking shop pics posted by Alan Schaffter, is the need for air filtration. Vacuuming away all of the chips and dust saves cleanup time, but the really important part is getting the fine dust out of the air and keeping it out of your lungs. If you look closely at the pictures posted by Alan you can see fine dust everywhere. Look especially at plastic pieces like the vac canister, the plastic deflector behind the saw, and the extension cord reels. That is the dust that may cause health issues later in life. And that is the reason for the massive filters on the big systems like the Oneida- it takes a lot of filter media surface area to remove that dust at high CFM.
Now to go straighten up my work area. I wish it were as nice as Alans!
I cleaned the shop prior to taking those photos years ago. It hasn't been that clean since!
A "clean room" it's not! Even with a very good DC system (big blower (3 hp motor & 14" impeller), long cone cyclone, big dual filters- 600 sq ft. filter area (or bypass to outside), 6" ducting and machine triggered full autogates (so I don't have to lift a finger to turn on the DC or open a gate), my shopvac setup, and an ambient air cleaner, it still often gets a bit dirty and dusty.
LOL! I moved a few things around my "shop" and saw some countertop that hadn't seen the light of day in months. Progress...
Knowing that you have that much filtration capacity and still have the fine dust reinforces the need to wear a respirator if I am doing anything dusty. As a benefit though, maybe my wife will agree that the dust is a point in favor of a detached shop space!
Actually I am sure she would agree it is a good idea. Achieving it is a different subject.
Originally Posted by Alan Schaffter
Fan curves which plot air flow CFM as a function of static pressure are generated at the rpm the fan spins at. With a normal motor, this means there is one fan curve since there is one motor speed.
With a variable speed motor, you would have a set of fan curves for each motor speed. So you would find a reasonable low speed curve based on the motor performance (at some point, the fan on the motor may not move enough air to cool it) and the fan. You would also do a curve to find a reasonable upper speed limit for both motor and fan performance. Now you have a low speed, normal speed, and high speed fan curve.
With variable speed, you can now have a wider set of more optimal dust extraction for a wider variety of duct work suction conditions.
VFD's are getting cheaper all the time and this has allowed their use in many applications where they used to be too expensive or impractical to apply. Many air conditioners now have VFD's to allow optimized air condition based on differing cooling and humidity removal requirements.
So a smart dust extractor could certainly provide useful dust extracion for certain users depending on their tool and duct work situation
In order to know whether the extra expense is worth it, it would be useful to have more information on how the system works such as the high and low speed curves and a thorough knowledge of the resistance provided by your ductwork and tooling.
As an example of where such a system would be beneficial would probably be a shop equiped with regular machinery like table saws, drum sanders or such that has been properly ducted for extraction by more conventional practice and another machine like a cnc router which might needs more CFM than a vacuum cleaner can provide and greater performance at high static pressure loses than a sincle speed dust extractor can provide. Speeding the impeller up in a Smart cyclone may provide substantially better dust extraction in such a scenario, but it would be good to have a couple of fan curves for various speeds higher than the normal speed to see how the fan CFM and static pressure behaves as a function of rpm.
Last edited by Sean Tracey; 03-15-2016 at 1:40 PM.
That is an invalid way to asses the merits of the system because the merits of the system are determined by the CFM pulled at the tool. A fan pulls very little CFM as it approaches it's maximum static pressure and lots of air at low static pressure.
Originally Posted by Dan Friedrichs
Comparing the 3hp super dust gorilla and the 3hp smart dust collector, the Super dust collector moves 0 CFM once the static pressure is 13". The 3hp smart dust collector moves 634 CFM at 14" and 385 CFM at 23".
634 CFM and 385 CFM are substantially more than 0 CFM.
$600 dollar range vacs might pull n the 80 to 100" range and they move only 80 to 130 CFM.
Originally Posted by Alan Schaffter
A 3 hp smart collector moves 384 CFM at 23" which Oneida shows in their chart as performance through 10 feet of 2.5 inch flex duct. This might be similar to what can be applied to a CNC router.
It would be good to know the design differences in the impeller and housing that allow the 3 hp Smart to pull at 23", similar to the high vac Smart, vs the regular 5 hp smart which tops out at more like 15" sp. The high vac provides both high and low end cfm while the normal 5 hp provides more low end and the 3 hp provides more cfm at high pressure. Dave
I would think the single speed collector fan curves show only data points taken when the collector is ran at it's single speed.
Originally Posted by David Kumm
I would also think that the smart collector curves show what the unit can do in CFM at the most optimum rpm for the particular static pressure shown on the graph. For instance, at high static pressure, the CFM being moved is lower, so the hp required drops which allows the motor to be spun at higher rpm to boost the CFM while still not exceeding the hp rating of the motor at this higher rpm.
I don't think most people understand the highly non-linear relationship of CFM to static pressure at a single speed. And they really don't understand the further non-linear relationship of CFM to static pressure when you increase speed. Then you get people who don't understand how the hp required is related to the CFM moved by the fan rather than the static pressure.
The more air you try to move through a given duct, the higher the static pressure loss. A curve for the duct work can be plotted showing this static pressure vs CFM relationship. This curve will start low on the left side of the graph and curve up.
The curve for the fan can also be plotted on the same graph. This curve starts high on the left side of the graph and curves down. (Because the higher the static pressure, the lower the ability of the impeller to move air in CFM)
The system of ductwork and dust collector will pull the CFM rate that occurs at the intersection of those two curves.
When both curves are plotted on the same graph, then the way the dust collection works makes a lot more sense.
If you really want to understand what is happening in your system, you make a plot for the duct work losses to each machine all on that same graph and you would see where each duct work curve crosses the fan curve and then you could truly understand the benefit of any given single speed vs smart-variable speed collector.
Most people prefer to guess or try to reason it out in their head which is not possible since the systems perform in a highly non-linear fashion.
Last edited by Sean Tracey; 03-15-2016 at 4:23 PM.