A Futile Chip-Vacuum Project

[grooveguy]

I believe in the importance to document failures as well as successes. We've all had our share of both, and learning from the mistakes or misunderstandings of others is a great way to expand one's knowledge.

A first disclaimer: This troll is not ashamed to admit to sleeping through the theory and math parts of classes, picking up instead the more practical aspects of physics, mechanics and electronics. The Internet is the invaluable friend to any seat-of-the-pants experimenter, and groups such as the Lathe Trolls are the perfect resource for helping one another. So please cut some slack here and don't laugh too hard at one experimenter's exercise in futility.

This forum has hosted many discussions of chip- (swarf-) removal devices, from fixed brushes to vacuum systems, the latter generally considered the better option, although somewhat more difficult and expensive to implement on a DIY basis. I'm lucky to have a good, multistage vacuum system on my own lathe, and undertook this project with the hope of helping others achieve good suction performance at a modest price. My hopes were dashed to the ground, but I'm sharing this experience anyway.

The idea here came as an 'aha!' while searching through information on cooling fans for electronics, where I saw this page:

RotronSeriesParallel.jpg

The Rotron people noted here that multiple fans may be placed in parallel to move more air, or in series for higher static pressure. Their plot shows that the static pressure (with no air moving) is about twice as high with two fans in series than just one. Now, I'm sure that there are rules and points of diminishing return and all that, but, heck, if two fans give you twice the pressure (or suction?), what would a bunch of them in parallel do?

So I went looking for a source of cheap fans that might be useful in giving this idea a try, and found these:

AllElect.jpg

A good size for the experiment and cheap! I looked up the specs:

DeltaSheet.jpg

...and these little fans seemed to have a pretty good pressure vs. volume characteristic. So I bought ten of them:

Received.jpg

[grooveguy]

And started putting them into a 'series' configuration:

PartialAssy.jpg

I'd purchased a cheap 12V power supply to run these, one intended for LED lighting systems, but with enough horsepower to drive all these motors, once they were finally assembled:

PSeBay.jpg

I did find that, sure enough, the power supply had enough guts to run all the fans, but it would not start under the full load. A 1.5-ohm resistor in series with the load allowed the power supply to reach 12 volts, and with the fans running slowly (and the resistor getting hot!), the resistor could then be shorted to apply the full 12 volts to all the fans.

Here is a shot of the complete super-vacuum system as tested:

FinalAssy.jpg

And, as you might have already guessed, the testing was a real disappointment.

There must be restrictions on placing fans in series and getting progressively more pressure. Maybe they can't simple be screwed end-to-end as I did here. I don't have any means of measuring the suction that this lashup provides, but judging by how hard it pulls on my finger, even with all ten fans running, the suction seems about the same as with just half that number, and not all that much more than just one fan.

So the experiment was a failure. However, if anyone out there wants to do any further work on this project, contact me with a private message. I will gladly donate this collection to anyone seriously interested in doing further work, for just the cost of the shipping. Projects like this, whether they work or not, provide me a reward, and if another troll can take the ball, run with it and have greater success, he's welcome to try.

[markrob]

Hi,

Interesting experiment. I wonder if the fans just don't have enough strength to make much of a difference (even at 10X). The highest pressure at no flow is stated as 10 mm of H2O. This is equal to about .7 mm Hg. Even is you got 10X performance in this configuration, you would still only be at about 7 mm Hg (with no flow). 760 mm Hg is one atmosphere. Not sure how what pressures and flow rates you need to get the chip moving.

Mark

[grooveguy]

Good points, Mark. As I said, I had no quantitative way of measuring the suction, but it sure didn't seem to multiply the way the Rotron sheet said it should. I was wondering if those axial fan blades, butted right next to one another, might be interfering somehow. Perhaps an 'expansion (or contraction) chamber' between fans might help. Once I had the whole thing assembled, I got it going and heard all sorts of sucking from the joints between the fans. You can see in the last photo that I caulked these with RTV, which stopped the leakage, but did nothing discernible to help the overall performance. But, hey, it was fun.

[SueDenim]

Hi,

Just a thought, but wouldn't you need to synchronise the fan blades on each unit to ensure that interference patterns weren't created, therefore distorting the overall effect?

Thanks.

[Gridlock]

I use a dust buster with a bunch of duct tape and a clear hose. I made a soft suede leather nozzle sewed into a "conical cylinder" on the end. You have to have the clear hose (1/5" id?) be short enough to unclog the m$##;;#!$ with a wire hanger straightened out. And the dust busters open up so you can just empty out your witch hair and impress the neighbors with the sound fireball (a good bs back story and some buildup is key( thats all for now.

[grooveguy]

SueDenim: You may be right about the interference between the adjacent blades. Either synchronizing them or a 'buffer chamber' between fans would probably take care of that.

Gridlock: A Dustbuster is cheap enough that it makes a good solution. Not sure how long one would last before self-destructing, but at that price just keep a spare on hand. I ruined my mom's full-size cannister-type vacuum cleaner in 1960, I guess it was; I think it was called the Whirlwind. Got into all kinds of trouble, had to pay to get it fixed.

[EpicenterBryan]

An interesting project!
I think what might be going on is that the fan blades are going into a stall condition because of turbulence from the previous fan stage – much like an aircraft wing.

If you have a 3D printer, I’m going to suggest making something to go between the fan stages. Although this image looks like a simple screen, it’s really more of a flow straightener. What looks like holes are actually tubes (honeycomb) which are easy to print. It also has a chamber with a pressure tap point.

flow straightener.jpg

One other thing I read is that a small portion of outlet pressure can be fed back into the inlet and may help in some instances. The pressure tap point might be useful to accomplish that from one stage to the previous stage assuming there is one of these screens between each fan.

Here are some things I looked at:
http://www.aerovent.com/docs/fan-engineering-topics/surge-stall-and-instabilities-in-fans---fe-600.pdf
http://www.zitron.com/download/FanProtection.pdf

Thoughts?

Bryan

[grooveguy]

Hi, Bryan,

And thanks very much for the suggestions. Well, first of all I don't have access to a 3D printer, and secondly I have 'exhausted' (pardon the allusion) my interest in this project. Had this turned out to be a simple, effective, easy-to-build vacuum system for chip removal, I would have written it up as such and hoped that fellow trolls would profit from my experiments.

But time (and patience) has run out at this end, hence my offer to send the entire project, kit and caboodle, to anyone interested in pursuing it, just for the cost of shipping. Hey, free fans! I'm hoping that someone picks up on this offer and makes a working vacuum pump out of this, if indeed it's possible.

There are certainly alternatives to a good, cheap vacuum; as Gridlock pointed out, a Dustbuster is about $30, and when run from an external power supply would probably do the job pretty well. I'm a bit leery of motors that run really fast; my own Lamb Electric vacuum motor is doing fine on about 85V, otherwise I'd be afraid it would run too hot and burn out. But a Dustbuster can just run its life course and be replaced quickly and easily. Doubtless there are other vacuums that could do likewise.

Anyway, YOU keep working on that cutterhead!

[Soulbear]

Hi Grooveguy,
My "TwoPennyworth" on this most interesting Project. I used to maintain "High Performance" Axial Flow Ventilation Fans, both in my earlier career in the U.K. Coal Mining Industry, and later as a Major Equipment Hire Specialist to the U.K and European Tunneling Industry. What I can tell you without equivocation, is that on all the "Tandem" or "Paired" Ventilation Fans I Maintained and Serviced, the Motors and hence the Vanes were all, without exception, set to "Contra-Rotate" That is, if the 1st Fan in the Pair ran "Clockwise" then the 2nd Fan would run Counter Clockwise" The "Aerofoil" shape of the Vanes" on each Fan being similarly Reversed or Mirrored, for each unit. I can't fully remember, the reasons for adopting this design feature, but I can remember discussing this with a "Mining Ventilation Engineer" who once gave me the Technical Lowdown about the "Significant Gains" in the Performance of these Fan Units when configured in this way. I only maintained these Fans, and could advise End Users on Power Supply Requirements, and the Specifications regarding Volumes of 1000's of C.F.M. of Free Air each Unit was capable of Delivering, but as for the reason for the "Contra-Rotation" in this Set-Up, I must admit, "I Just Don't Know" I don't think it's at all to do with the "Gyroscopic" effect of running "Tandem Fans" in the same Rotation, but suspect it has more to do with the "Vanes" grabbing more Air. Perhaps some wiser heads than mine can give the "Scientific" explanation why this is so.
Regards Soulbear

[grooveguy]

Hi, Soulbear,

Good to hear from you. Yes, without a doubt, it's not just a simple matter of ganging-up fans for more pressure (or lack thereof, which is want we want). Either turbulance, lack of space for proper expansion or compression, or something like that is obviously going on. Reversing vanes and rotation could certainly keep the adjacent fans from looking like just one big blade, but so could a chamber between them as well. The multistage Lamb Electric vacuum motors have centrifugal blades (suck at the center, discharge at the edge), and had baffles between stages to guide the air from the outer diameter of one stage to the inner of the next.

[Bahndahn]

Hi Grooveguy,
My "TwoPennyworth" on this most interesting Project. I used to maintain "High Performance" Axial Flow Ventilation Fans, both in my earlier career in the U.K. Coal Mining Industry, and later as a Major Equipment Hire Specialist to the U.K and European Tunneling Industry. What I can tell you without equivocation, is that on all the "Tandem" or "Paired" Ventilation Fans I Maintained and Serviced, the Motors and hence the Vanes were all, without exception, set to "Contra-Rotate" That is, if the 1st Fan in the Pair ran "Clockwise" then the 2nd Fan would run Counter Clockwise" The "Aerofoil" shape of the Vanes" on each Fan being similarly Reversed or Mirrored, for each unit. I can't fully remember, the reasons for adopting this design feature, but I can remember discussing this with a "Mining Ventilation Engineer" who once gave me the Technical Lowdown about the "Significant Gains" in the Performance of these Fan Units when configured in this way. I only maintained these Fans, and could advise End Users on Power Supply Requirements, and the Specifications regarding Volumes of 1000's of C.F.M. of Free Air each Unit was capable of Delivering, but as for the reason for the "Contra-Rotation" in this Set-Up, I must admit, "I Just Don't Know" I don't think it's at all to do with the "Gyroscopic" effect of running "Tandem Fans" in the same Rotation, but suspect it has more to do with the "Vanes" grabbing more Air. Perhaps some wiser heads than mine can give the "Scientific" explanation why this is so.
Regards Soulbear

Interesting!

Wouldn't this be as simple as flipping the orientation of every other fan in this fan chain shown here and reversing the polarity of the DC motor leads of said reversed units? I may be missing something...

[grooveguy]

No, I don't think that would work. Swapping the fan end-for-end would not change the angle of the blades, they'd be the same. So even if the motors could be reversed, I'm pretty sure we'd be right back to where we started. These fans are the 'brushless' DC ones with a driver circuit inside, and they just don't run with reverse polarity at all.

[Soulbear]

Hi Grooveguy,,
Mystery of the Reason for the Contra Rotation "Solved" (Sorta!!) I went a-looking for some answers and our good friends at Wiki came up Trumps in a article on Aircraft with Contra Rotating Propellers. I'm assuming the same principles applied to the "Tanden Fan Sets" I mentioned " the mass of the air flowing through the propeller disk (thrust) causes a significant amount of tangential or rotational air flow to be created by the spinning blades. The energy of this tangential air flow is wasted in a single-propeller design. To use this wasted effort the placement of a second propeller behind the first takes advantage of the disturbed airflow"

but suspect it has more to do with the "Vanes" grabbing more Air

No, I don't think that would work. Swapping the fan end-for-end would not change the angle of the blades, they'd be the same. So even if the motors could be reversed, I'm pretty sure we'd be right back to where we started

In light of your assessment, regarding the "Blade Angle and Non-Reversible Motor" I think this "Set-Up" is a Non-Runner, but Kudos to you for a most interesting and diverting Experiment.

learning from the mistakes or misunderstandings of others is a great way to expand one's knowledge.

I wholeheartedly Concur.
Regards Soulbear

[Kiss the Groove]

Grooveguy,

We love failures! How else will one find out what's possible?

I'm going to say that both Soulbear and Epicenterbryan are correct. Tandem fans need either (1) a large-ish plenum space between stages, or (2) a flow-straightening element between stages, or (3) counter-rotating blades. All three methods are in common use.

EBM-Pabst actually makes a tandem fan with a separator built in: http://www.ebmpapst.com/en/press/press_releases/pressdetail_61825.php Unlike the counter-rotation employed by other manufacturers, however, the two fans are identical and rotate in the same direction, requiring only a 4 mm thick honeycomb separator to work efficiently.

If you weren't so done with this project I might suggest removing the fan blades from every other fan in the stack, using the empty frames as convenient inter-fan plenums. That would also cut the number of active fans in half, probably eliminating the need for the start-up resistor.

[grooveguy]

Thanks, Kiss. Yeah, I'm afraid that I am 'done with it.' I have so many projects and so few years; gotta move on. Sure wish someone would pick this up and run with it. That 12V supply, alone, is worth the shipping cost. Free fans!

[Gridlock]

Trade ya for a distbuster with custom hose and leather nozzle. order now and get a free wire coat hanger!

Sorry i had to.

[EpicenterBryan]

I might suggest removing the fan blades from every other fan in the stack, using the empty frames as convenient inter-fan plenums.

You know, I have another idea. It comes from watching this video that shows the internals of a compressor. One thing to notice is that there are stater blades (don't rotate) between the rotor blades (which do rotate). It looks like the stater blades set up the air flow for subsequent rotor blades and are in the other direction.

Here is the YouTube video I found useful:

An easy test would be to reverse the fans in every other position, and either temporally jam them so they can't rotate, or perhaps short the power and ground pins so they act like a shorted generator and resist free spinning.

Sure wish someone would pick this up and run with it. That 12V supply, alone, is worth the shipping cost. Free fans!

I agree. But I hope you try that quick test above first. If you really have run out of interest and there are no other takers, I'll take you up on the offer. You should have my E-mail address (or PM me) and I'll cover postage.

Bryan

[EpicenterBryan]

Just got back from the ultimate concert weekend to find a package from Jim!
Oh, I should say something about the concert - Desert Trip... Bob Dylan, The Stones, Neil Young, Paul McCartney, The Who, and Roger Waters (Pink Floyd). Wow.

I printed up a flow straightener in black PLA plastic, and the screen was a bit too fine causing air restriction. Then I decided to make the holes larger and use NinjaFlex to kill two birds with one stone. Since it flexes, the idea was to also use the straightener as it's own gasket.

IMG_5260.JPG

And while messing with things, some how I actually sliced my finger on a plastic fan!

IMG_5259.JPG

Oh the sacrifices we trolls are willing to endure in the quest...
Anyway, looking forward to progress on about 5 project this weekend. Look for updates on all fronts.

Bryan

[grooveguy]

My word, Bryan; was that one of the fans you got from me that sliced your finger? Should I alert my attorneys, I wonder... the Law Offices of Dewey, Swindahl and Howe? Please recuperate, complete the project and report back. If something like this works, it's a relatively inexpensive way to 'suck the swarf.'