Ah very good writeup David, also put on a write up on the economics of running this along with mechmate -

Vishnu, the place I purchased the pump was a very traditional machinery dealer. They don't do any business outside of Taiwan. They mostly support the local factories (of which there are many) in the Kaohsiung area which is near the southern tip of Taiwan. I'm sure you could probably source one in your neck of the woods. Taiwan is really strange as a tiny shop the size of a two car garage had this thing in stock. Their warehouse is located about 20 minutes away if I remember correctly. Not the most attractive place but they carried reasonably priced roots blowers and other types of pumps. Another shop located about 150 meters away sold the exact same pump for almost twice the price with no warranty. The primary market for roots blowers is fish farming where they have to aerate the water to keep their fish alive and these pumps run 24-7 for months on end.

Gerald thanks for the correction on the "vane" spelling. I wrote it at about 1:30 in the morning.

Irfan, the economics is quite simple. On the power consumption side of things, it draws about 30 amps from the inverter at full throttle. On the supply side of the inverter, it's only pulling about 21 amps. However, I find that there is no need to run at full power as 10-12" is more than enough to keep my parts from moving for my application. Under most operating circumstances, it's taking in about 15 amps from the inverter and about 7-8 amps from the breaker. How the inverter achieves this is a complete mystery to me but somehow, I can verify that the inverter makes a huge difference in terms of power consumption. Another big advantage is the fact that I am able to control the speed of the motor so I only use what I need.

Also, the vac hold down is a real time saver. Before, I had to make a tool path for screws which I found to be more effective at holding things down than the traditional clamp (No disrespect, Gerald;)). Also, the cut quality increased as there is less vibration as the bit cut through the material. Although I feel that vac hold down is one of best hold down methods around, I still have to agree with Gerald's earlier posts about vac not being the end all solution. It's just one more tool at your disposal when you need to get a job out quickly and don't want to play the 101 screws game. I read about massive pumps being necessary that were 20+ HP drawing a shameful amount of power. After my research, trial, and error, I can honestly say to the Mechmate community that you really don't need that much power on a 4x8 CNC router if you choose the right pump. My roots blower is still noisy (but acceptable IMHO) placed in another room and gets pretty hot, but for the price/performance ratio it's hard to beat.

I basically save about 15-20 minutes per sheet of material (compared to screws) using the vac hold down. Some people might think that's not a whole lot, but multiply that by 15 sheets and you should get the picture. How much is your time worth????? I have to squeeze every minute out of my day to balance two businesses, a very understanding wife (pregnant with our second child), and a two year old that want's daddy to play with him. Worth every penny if you ask me.

I will post more pics of the completed setup in the next week or two. I'm working on a new dust foot right now.

pardon my ignorance (for real no pun intended) how does a blower creates vacuum? a venturi?

Pablo, Roots Blowers generally have two equal sized ports. Depending on which port you use, you have either a big blower or a big vacuum. You then need to deal with designing the rest of the system. If you use it as a blower, you need a filtered source of lots of air. If you use it as a vacuum, you probably want a muffler system for the exhaust.

Thanks for all the info Dave, would you mind showing some pics of the vacuum table and manifold?

Alan, I'm planning on doing just that. However, my shop is too messy right now. To be absolutely honest, I think messy is an understatement. I'm going to clean up a bit this week and take pictures after my dust foot is finished. I should be able to get pics posted by Sunday of next week.

Good reading to on vac hold down for those interested:

http://geoteched.com/VACUUM%20INTRODUCTION.htm
http://www.techno-isel.com/cnc_route..._Hold_Down.htm

Prices like the one's mentioned on either of these links almost made me not even think about venturing into this method of hold down.

Does anyone have a source for these roots blower style vacuums here in the US?

Travis, I suggest you start with an E-Ebay search for "roots blower". That will give you a sense of the price ranges for new/rebuild/used/broken units. Then search for an industrial surplus / rebuilder in your area. These are large pieces of metal, and shipping will be significant. Note that if you don't have 30A of 3-Phase power to spare in your shop space, you probably don't want to be looking at these.

Or the money to run them... :)

The money to run them is not that significant if you pair it with an inverter and use only what you need. You will find that if you size your pump correctly with some spare overhead, often times, you'll run your pump at about 40-70% of max capacity and still maintain 11+ inches of Hg.

If anyone is interested, I'd be willing to negotiate a deal with my supplier to ship a quantity of the units here to the states. I'm sure the dealer will give me a good deal on say 10 - 15 units (fixed up, tested, and ready to go) riding piggy back on a container. Just an idea if you guys back home are interested. However, keep in mind that like Brad said, you'll need 3-phase 220 to run them. Also, I'll warn you in advanced, they are not exactly quiet either.

David, if you want to regulate the power consumption, you can just open a "leak" to reduce the holding pressure . . . . same effect as a VFD to reduce the speed, but less expensive.

Gerald, that's an interesting idea. I'll give that a try and report back as to the differences. At first I got the VFD for soft start as I got the VFD for about the same cost as a dedicated soft start circuit. I've got a release valve for removing my pieces without shutting down the blower so that will be easy to try. Thanks for the tip!

Gerald, you are correct. I bypassed the inverter and tested the "spring a leak" suggestion and indeed, the current consumed came down but not as much as using an inverter. With all valves closed, I am pulling about 22" Hg drawing about 29 amps without the inverter. To achieve the same 22" with the inverter, it's pulling about 21 amps.

Using the front four zones (half of my table size), I try to maintain about 12" Hg to make sure nothing will move. Springing a leak without the inverter the pump is pulling about 16amps without the inverter. To achieve the same hold down capacity with the inverter, I only draw about 10 amps. The "pro" to the spring a leak method is that the pump runs cooler with more air flow.

If I measure current after the inverter, I'm reading the same 16 amps but I'm only drawing 10 amps from the breaker???? Can anybody explain how this feat of magic occurs???

Here are some pics I promised.

Great setup David!

But where does that rust on the screws and plate comes from?

David,
I'm not expert but I'll have a go at the phenomena.
As we already knew, an inverter takes in AC power, rectify to DC then choop it up accordingly to make AC of desired frequency & voltage to facilitate speed variation while still maintain the torque characteristic. On the pre-text that there is a fixed relationship between the voltage & the frequency to maintain the torque characteristics, this is why inverters are more efficiency then without. From here, I presume the different current measured is due to the difference in the frequency of the input & output voltace.

Very nicely done.

I was in Taiwan over the weekend & couldn't resist to pay David & his MM a visit.
David flooded me with his warm hospitality & unselfishly sharing his knowledge.
Only had a few hours with him & I was so impressed & intrigued by his work & completely forgot about taking any picture....
I wished I had more time... but I promised I'll be back.... as soon as I can fish a good air passage bargain from AirAsia.
After seeing his rig, I am now totally convinced that a vacuum table speed reduction & vacuum table are not luxurious indulgent...
Now I have to figure out what else can I pawn to get hold of a root blower...

Ken, I am always happy to have you over. Next time, I promise I'll have the camera ready for the occasion. I've been so busy with work over the last several months that I hadn't had much time for or have been too busy to keep this magic of sharing knowledge going on this great forum. Right after you left, I completed that sign you saw leaning on the wall. After the 15mm of acrylic was cut, it turned out beautifully. I will take some pictures of my work and post it here. Stay tuned!

Hi David,

just caught up on your post the answer to the VFD reducing the current draw is that it fixes the Power Factor of the motor and draws mostly True power from the mains instead of Inductive power that is drawn by coils of wire aka inductors (like the windings of a motor)
A inductor(motor) will draw power during one part of the Alternating voltage waveform and then feed this back to the mains in another part of the waveform without it actually doing any useful work (ie: wasted current draw) Large industrial sites need to manage this load by installing capacitors at the switchboards or paying extra for there power.
Love your MM truly a well thought out layout.

Hi Andrew,

Thanks for the post. Inverters are still a mystery for me. Thank you for your compliment on my layout; however after a few years building a business (it wasn't easy in my neck of the woods) I find that there were things that could have been done better. We built this when we had minimal funding and was a part time hobby. Gerald's beast is still serving us well today. I'll do a full write-up of all that has transpired since my last post as soon as I can.

Cheers,
David