[JerryBurks]

I have been looking for a suitable vacuum pump for my CNC machine for a while. I do have a small 2-piston high vacuum oil-less pump similar to this one, but the air flow is not that great:


So I thought a Supercharger from the scrappy may do the job and found the one below eBay for $59 (Eaton M62 for a Buick 3.8 V6, free shipping ).

Received it today and it is in pretty good shape. The plan is to power it with a 1 or 2 hp induction motor and pulleys to make 6000 rpm. According to the chart from Eaton it should pump about 500 m^3/hr or 300 cubic ft/min at that speed.

Did anybody try this before? I mean I will find out soon but it would be nice to know before I go to Harborfreight to shell out another $150 for the motor. Thanks.....

[kevincnc]

Good thinking out of the box but I'm guessing it will take more HP than you will want to put on it. Look at the HP of a vacuum pump that would do what what you want..there's no freee lunch. Congrats if I'm wrong though :cheers:

By the way does it need oil flowing through it?

[parsifaldruddle]

Also, if this is for hold-down, will it like having a vacuum on the inlet? perhaps a vacuum sensor and speed control to mitigate? my limited understanding of SCs is that they are essentially air pumps, and most pumps dislike blocked inlets. just pondering - i ponder too much instead of experiment - good on you for being hands on.

As a hold down, you may have bypass some air to provide cooling.

At any rate - i like the idea.

[arizonavideo]

At 14" of mercury at 6000 RPM that blower might take 100HP or more.

You might look at the Roots style blower for a example of HP draw.

45 URAI Roots Style Blower | REP Inc

The PDF will show the HP curves. The flow verses vacuum is about the same for all rotary lobe pumps.

You can still use the pump you have but I would think you may only be able to drive it at 500 RPM or so depending on the vacuum pressure you need.

I do have a extra Roots 33 blower that has been sitting out for a few years. I don't plan on using it and it is rusted inside so it wont be good for hi vacuum but I would take $30.00 for it.
I'm in Phoenix.
Good luck.

Dave

[JerryBurks]

At 14" of mercury at 6000 RPM that blower might take 100HP or more.

You might look at the Roots style blower for a example of HP draw.

45 URAI Roots Style Blower | REP Inc

The PDF will show the HP curves. The flow verses vacuum is about the same for all rotary lobe pumps.

You can still use the pump you have but I would think you may only be able to drive it at 500 RPM or so depending on the vacuum pressure you need.

I do have a extra Roots 33 blower that has been sitting out for a few years. I don't plan on using it and it is rusted inside so it wont be good for hi vacuum but I would take $30.00 for it.
I'm in Phoenix.
Good luck.

Dave

Thanks for the link! I was looking for such charts. The info from Eaton has only the efficiency and volume chart but lacks the power info for vacuum operation. I compared a similar size from that company to my Eaton blower and it looks indeed like I would need about 6-7 hp to run at 6000 rpm. Unfortunately I do not have that much electric power available in the shop. But I could get a 3hp motor and run it at lower speed. I will give it a try. So far I only spun it with a 1 hp hand drill for testing.

.......As a hold down, you may have bypass some air to provide cooling.......

Yes, that is surely necessary. I may also have to route the motor fan air flow across the supercharger for additional cooling. Fortunately they are built to survive running hot on top of an automotive engine. But that is just part of the experiment.

.......By the way does it need oil flowing through it?

.
No, it has a built-in oil reservoir for the bearings and gears. The blower rotors run dry.

[ger21]

For what you're going to spend, you'd probably be better off buying two of these.
ShopBot Vacuum Motors

[JerryBurks]

For what you're going to spend, you'd probably be better off buying two of these.
ShopBot Vacuum Motors

These would probably do the job (although the motors do not look very heavy duty). But I am always in favor of the unconventional. Sometimes I even get it to work Sometimes I don't and learn something :idea:

[kevincnc]

I say bolt that thing onto a Grand National and go drag racing.

[arizonavideo]

I ran a roots RAI-45 for a carpet cleaning for years and it took all of a 25HP motor to pull 13 inches of vacuum at about 220 CFM.

The amount of vacuum you need is the real HP problem. If you only want 5 or 10 inches then a regenerative blower will work but if you want 10 inches or more you will need a positive displacement pump which is what you have.

This place looks like they have a bunch of pumps and good info.

Techno CNC Router Systems | Vacuum Pumps

Your pump will do the job but you need put the right pulley on it for the amount of RPM needed to give you 2HP of vacuum.

I don't really know how much vacuum the router table or mill might need. The ratio of CFM to inches of mercury is what you need to know.

You also must have a vacuum break on a postive displacement pump. You can make one fairly easy.

How many inches of vacuum pressure at what CFM do you need?

[JerryBurks]

I say bolt that thing onto a Grand National and go drag racing.

In its day (early 90's) I believe the supercharged 3.8l engine made a whopping 220 hp. I am not going to find much success in drag racing with that......

[JerryBurks]

........How many inches of vacuum pressure at what CFM do you need?

I am not looking for large sheets to clamp. My machine is midsize (34"x31" range) and I machine normally smaller parts. Therefore I want to have rather higher vacuum and can live with less air flow.

However, I never used a vacuum hold-down and would have to experiment with the optimum pulley sizes. At the end I have to live with the power that I can run in my shop and see if it is of practical use. I understand I may have to spend a bit more effort on sealing and a bigger reservoir.

[JerryBurks]

Aha, somebody moved this thread to the hold-down section.

Makes sense, thanks to whoever that did. I don't think I have been here before.

Anyway, I hooked up a 3 hp motor today with the supercharger and that seems to go quite well. Right now it is running 1:1 with a 3400 rpm motor. I have not yet measured the vacuum level when the motor stalls but I suspect I must eventually fabricate a smaller motor pulley to get higher vacuum and less flow. This gadget is pretty noisy and for practical use I will probably need some kind of muffler.

[ame=http://www.youtube.com/watch?v=Hbm-L9fB6Ck]SuperChargerVac.avi - YouTube[/ame]

[JerryBurks]

Well, good results and bad results.

The good one is with a smaller motor pulley I can get about 15"Hg Vacuum before the motor stalls and maybe 10"Hg for continuous operation. I guess that is quite reasonable for many hold-down uses.

The bad news is the deafening noise this thing makes. I suppose all roots blowers are like that but it sounds like a thickness planer at full load and I am sure it can be heard 3 blocks from my home. I have a handheld meter that showed 100 to 105 dBA measured from 10 feet away. I will see what a muffler does but If I don't get that a bit quieter the neighbors will come for me with pitch forks and burn down my shop.

How do other roots blower users deal with the hellish noise?

But after all, I think a 3hp roots vacuum pump for a total of $250 (blower $59, motor $159, belt $12 and some small stuff) is a pretty good deal.

[ame="http://www.youtube.com/watch?v=1qAS88-hKIs"]http://www.youtube.com/watch?v=1qAS88-hKIs[/ame]

[JerryBurks]

I pretty much finished my vacuum pump system today and added a vacuum reservoir (total 10 feet of 4" pipe), a vacuum regulator, intake filter and exhaust muffler. Much less noise (about 80 dBA) with the muffler, which is a baffled sandwich plate, packed with rags under the supercharger mounting plate. With the garage door closed I should be O.K.

Next step would be making a few vacuum pods and the connection plumbing.

Complete Vacuum System:


"Muffler Plate":


Vacuum bypass regulator and intake filter:

[dodger889]

Jerry you will want to add some sort of filtering system. To keep the trash out of the blower.

[JerryBurks]

Jerry you will want to add some sort of filtering system. To keep the trash out of the blower.

Yes, that for sure. But that is what the yellow condom on the last picture is for. It is a vacuum cleaner filter bag that will go into the first black tube. I hope not suck up too much dust and chips and don't need to replace it too often.

[kevincnc]

In its day (early 90's) I believe the supercharged 3.8l engine made a whopping 220 hp. I am not going to find much success in drag racing with that......

Oh, I guess you would need a turbo or two. Looks good, I'm glad it's working out for you!

[JerryBurks]

I am still fine tuning the motor pulley diameter and vacuum regulator setting. The 3 hp motor is about as low as one can go with that type of roots blower. I found running the blower under 3000 rpm is very inefficient, maybe because it needs a certain speed to overcome the internal leakage. On the other hand, running it much faster with a bigger motor pulley will increase air flow significantly but stall the motor at vacuum pressures that are too low for practical use.

This automotive blower would probably run best with a 6-7 hp motor at 4-5000 rpm, but my 3hp system works quite well. It will achieve about 80 cfm and 12" vacuum.

[diyengineer]

Do you really need 80CFM? If you use proper gasketing, and sealing off of non used surfaces id trade lower CFM for more vacuum.

Awesome build though! This reminds me of something i'd do haha.

[JerryBurks]

Do you really need 80CFM?.....

Good question. I think for large and porous sheets that is probably a minimum from what I read. Obviously some pro machines run vacuum pumps of 25+ hp.

Thing is only I don't do large sheets and I found that for my one-off projects the vacuum setup may take much longer than some creative clamping. So I have not used it much but it was fabulous fun to play with