Rod is to blame; more (a)musings on the problem of hand held small port collection

[Bruce Seidner]

Hi Bruce, I often used my cyclone for dust collection from a random orbital sander and it worked great because the sander fan already picked up the dust and ejected it at a positive pressure.

The extremely low negative pressure from the cyclone could then pull the dust through to the cyclone.

The same is definetley not true of the router where you will need a large neagative pressure to create enough airflow for chip collection. You will need a vacuum for that task.

As for a filter to discharge the air from a sanding operation into your shop, you need a HEPA filter, not a bag filter.

Regards, Rod.
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Taking this truth as self evident I have gone back to the drawing board.

This has gotten interesting because as I was looking into replacing my 25 year old Craftsman shop vac I have run across a whole industry of commercial vacuum motor replacements for carpet cleaner extractors, Car wash interior vacuum cleaners and yes, the redoubtable and venerable wet/dry shop vac design. But there are a limited number of companies that sell the same motors to these very expensive commercial units with similar specs and costs that are very reasonable. You don't get the hoses, vacuum body, filters, etc. But for a hundred bucks +/- twenty bucks what would you say to a Triple Stage vacuum unit (meaning 3 internal to the motor cooling fans), Rated at 104 CFM, with 137" water lift drawing 12.5A?

Now THIS is a vacuum cleaner! And would suck the chrome off a trailer hitch. Since the intent is to use 2" hose to a hand tool over a relatively short distance I am thinking of a modification of the Thien separator that would make the separator tall enough to replace the body of the shop vac, do just enough filtration around the motor inlet (and easily cleanable) so the vacuum impeller did not clog and then exhaust into my central dust system where a 2" duct pushing only 105 CFM would not be all that disruptive. Or if this would be disruptive to a central dust system that discharged to the outdoors with no intervening cyclone or filters, I could install a Wynn filter that returned the air to the room. http://www.wynnenv.com/c14.htm

Is this mad scientist or is there something to pursue here?

[Anthony Whitesell]

Using it attached to a ROS, I would be afraid of too much suction. I would be afraid of the ROS getting stuck due to the high vacuum. The high pressure may also cause increased pressure on the sanding disk and not allow the sandpaper to work correctly or cause scratches in the work piece. Other than that I think it would make an excellent vacuum.

[Van Huskey]

Using it attached to a ROS, I would be afraid of too much suction. I would be afraid of the ROS getting stuck due to the high vacuum. The high pressure may also cause increased pressure on the sanding disk and not allow the sandpaper to work correctly or cause scratches in the work piece. Other than that I think it would make an excellent vacuum.

You can always bleed some of the suction. Would be interested in the sources, I would be interested in something with twice the volume at about the same static pressure.

[Bruce Seidner]

So more is not necessarily better. Hmmm. I do hope people have the continence to keep from wetting themselves as they review this idea for a powered Thien top hat that empties into a bottom bin. The exhaust has not been fully worked out in my head and will no doubt be driven by facts contributed by people who are fact and not fancy driven. Since I have very few facts, mine is mostly speculation. But what sets me down these Alice in Engineeringland rabbit holes is a review of options on Grainger and McMaster-Carr. When I was a kid we actually had schools and stores and residences in a neighborhood. People lived above their stores and we walked by them to and from school. The hardware store was the best place to hang out and dig through bins of parts and fasteners. It was great to sit and listen to the tradespeople give each other advice or curse about some world event. So going online to these sites is the browsing that gets these Rube Goldberg things going in my head. My current shop vac does great for cleaning up the floor, etc. So I started looking at shop vacs and then found the repair parts for the shop vacs and then got onto the rug extractors, etc.

What would be the optimal CFM and Static Pressure (water lift inches is the term they use for these vacuums) using a 2" duct to a router or to a belt sander. These are the worst hand held offenders. Then there are the orbital sanders that are fairly tame. Come to think of it circular saws are a real mess but I tend to use them outside and a miter saw inside. But all that aside, take a gander at these links and lets ponder this project some more if you are game and posses good bladder control.

http://www.grainger.com/Grainger/wwg...n_dim_search=1
http://www.mcmaster.com/#vacuum-cleaners/=gkqo3n

From here a trip to Ebay looking for these motors yields lots more options.

[Anthony Whitesell]

For a 2" hose, under suction, the optimum flow rate will be around 100CFM. When speaking in inches of water column, air is not compressable and thus there's a limit on how fast air will flow when you suck. For a 2" duct that limit is around 100CFM. The differential pressure (SP reading) can keep increasing but it will not result in a proportionally high flow rate. It is not a coincidence the flow rate you listed is 100CMF. The same 2" hose could flow 100CFM at 15"WC SP and perhaps even lower. The flow rate will reach a limit even though the differential pressure increases. When you start working with psi in pressurized systems then you can start working with the compression factors of air and vary the flow rate with pressure. In the case of your ROS, the trick will be to reduce the SP developed, to keep the ROS from being sucked tight to the work piece.

[Bruce Seidner]

I see, that is enormously helpful. Thanx.

One of the ways that I would search for this Holy Grail of parameters is to see what machines are spec'd closer to this. The people at www.Powr-Flite.com have a good site with a bunch of specific application machines and I will spend some time there tonight. All the machines have manuals, specs, and schematics. But I think something in the shop vac department gives less issue with excess vacuum and the CFM looks about right. From a design perspective the tangential exhaust motors would be easier to deal with than the thru-flo and peripheral discharge vacuum motors for a powered Thien top hat. But I don't think it would be too hard to have the top of the peripheral discharge vacuum motor outside the tophat and then build an enclosure to manage the exhaust.

http://search.powr-flite.com/?pageNa...or&sp_cs=UTF-8
http://search.powr-flite.com/?pageNa...otor&sp_cs=UTF

[Jim Andrew]

Bruce, why don't you look at using the smaller hose? The 2" is kindof difficult to use on a small tool where you are dragging the hose along. for example the skil saw. My Bosch ROS has a fitting to connect to the smaller hose on a vac, and I have a router with a fitting that also uses the smaller hose, both work very well as long as the vac doesn't have an inch of dust built up on the filter.

[Bruce Seidner]

You can always bleed some of the suction. Would be interested in the sources, I would be interested in something with twice the volume at about the same static pressure.

Van, how do you reduce suction and not loose cfm? There is the rpm of the motor, the size of the duct, the volume of the separator, a venturi on the duct, I am juggling some parameters and wondering what you were thinking because I am not finding higher CFM and significantly lower static pressure among these vacuum motors. I imagine if I were looking at the pass-thru units for shop vacs I could find less static pressure. But if an adjustable venturi in the duct to the router would reduce static pressure without reducing CFM that would be great. I just don't know that it does. I may be using the wrong term. By venturi I mean a way to open the duct to allow more air to enter the duct between the tool and the separator. I would want such a valve or slide opening near the router so it could adjust dependent on how it was feeling. If the router stuck to the wood because of the vacuum, opening a venturi, allowing air to enter the duct would significantly reduce the vacuum at the tool. But would this not also reduce the CFM?