The most powerful shopvac for a reasonable price I've found is a Milwaukee for about $600. It says it does 92CFM max and has a "sealed suction in water" of 134in. Does that mean it can pull a vacuum of 134 inches of water aka ~9.5inHG? Or does it mean something completely different?

Are you wanting it for a vacume chuck why not use a refrigration compressor or evac pump you can get 27"hg out of a good one I us to use ones out of pop machines for doind refg recharges With the politcal incorectness of freon now you might find an old charging station cheep they have a real nice vac pump in them. Good Luck Kevin

.. It says it does 92CFM max and has a "sealed suction in water" of 134in. Does that mean it can pull a vacuum of 134 inches of water aka ~9.5inHG? Or does it mean something completely different?

You have to be a bit careful with some of the claims for volume flow and suction. The 92 cfm probably means maximum without any hoses and it would not be surprising if the filter was not on. The 134 inches of water could be the level the water surges to; like you have the sucker running, dip the calibrated pipe into a water bucket and measure the highest point the water reaches as it has some momentum. That fact that it stabilises well below that is ignored.

I would not recommend using a shop vac for vacuum hold down. The motors that they use are a flow-thru type. They need air flow thru them to keep them cool. If you block off the air intake (suction) the motor will overheat. Using an old refrigeration compressor is a better alternative. They don't have much CFM but they have a high suction.

Thanks. I'm probably going to end up purchasing a 10hp regenerative blower for my 4x4 gantry. So far I've seen the Fuji from Grainger for $2400 and the Gast from MSC for about the same price. Any other contenders?

I wish Amazon sold this thing.

Thanks. I'm probably going to end up purchasing a 10hp regenerative blower for my 4x4 gantry. So far I've seen the Fuji from Grainger for $2400 and the Gast from MSC for about the same price. Any other contenders?

I wish Amazon sold this thing.

If you are getting into this type of horsepower and price it might be worthwhile looking at positive displacement pumps. You lose a little bit in volume but gain in negative pressure. Also they may be less noisy.

Hey Geof,

By pos displacement, are you referring to roots type blowers? Can you recommend any specific units in the 10hp range? Thanks.

The water ring pumps are good - so are the oil ring pumps - like Busch. They are higher maintenance and higher cost. They work well but I wouldn't suggest this route. They do not like moving a lot of air for a long period of time - this will blow all of the sealing oil out of the pump and cook it. They are pretty much maintenance pigs, but if you want relatively low volume and super high pressure, they are the pump you want. They can move a lot of air, but not for extended periods. They are better at building pressure.

The shop vacs aren't bad for a smaller table. I would recommend it - probably over anything else because of the economy of it. They are loud but you can dead head them all day and they will not overheat.

The regenerative blowers are probably the best option for bigger users. You can run them for extended periods dead-headed - they will get very hot but they are designed for running without air flow. Give them some ventilation and maybe a small amount of air through the pump and they will last. Maybe that depends on the manufacturer. They require good filtration but otherwise no maintenance. I have run 8HP blowers continuously with very little leakage more times than I can count while compacting pre-preg composites many years ago - only burned one up and it was brand new, so I believe it was defective. Inadequate clearance or crap built up on the impeller will send it to an early grave.

Scott

Hey Geof,

By pos displacement, are you referring to roots type blowers? Can you recommend any specific units in the 10hp range? Thanks.

I suggested positive displacement as another option but I cannot give a specific recommendation. I believe Gast makes them and Sutorbilt is another manufacturer.

Another option is to spend your money on a good compressor and then use venturi vaccum generators. This approach means you also have plenty of compressed air and you do not have to get as concerned about dust or liquids being taken into the vacuum system.

You may also want to zone your table - a 10HP pump sounds excessive for a 4'X4' area - but then again, I have no idea what the particulars are for your application. I currently operate a 6'X12' zoned table machine with an 8HP oil ring pump made by Travaini(sp?) with an Agip pump. I guess it depends on what you are doing and what your table looks like.

Hold down with vacuum depends on what you are doing - no doubt, but I think for most routing situations you won't need the super high pressures - you need more recovery potential to maintain a minimum hold down force which equals high volume, not high pressure. Having a good distribution network with minimal loss is important. With nothing on your table and the pump running, you want to see the lowest differential between the trunk line near the pump and the directly below the table. Additionally, the table surface should not be restrictive, either. A minimal gage reading under the table when the pump is running and the table surface is completely empty is a good indication of a non-restrictive surface. Hard to achieve, but something to strive for.

For 15 years I worked at a company that made ultrasonic cutting machines (in addition to other machines - including routers) up to 180 feet long that used zoned vacuum tables and the majority of what I was cutting was lofty continuous strand fibergalss mat. We would also contract cut other fibrous goods as well as sheet goods for a huge variety of companies - mainly aerospace and textile industries. We predominantly used blowers. When higher pressures were required to counter higher cutting forces, like when cutting Titanium honeycomb materials for example, we would process on a smaller table with water or oil ring pumps. Most of the pumps were made by Busch. I can't recall who makes the water rings but I am sure Google would turn up a number of potential folks making these pumps.

I can't agree with Goef this time. I can not stand using compressed air - it is not anywhere near effecient. Electrical and maintenance costs combined with initial installation costs gives it a black eye for me. It's necessary - yes, but I would not recommend using one inefficient process to drive another. Not good economy in my mind. Sorry, Geof. They have their place, but the drawbacks for this application are too numerous for the gains. Just get a pump or use a big ShopVac or two.

Scott

I can't agree with Goef this time. Scott

I would forgive you if you spelled my name correctly! :D

I agree with everything you say in terms of the negatives of compressed air; I did say it was an option to consider. Perhaps I am biased because I was lucky enough to pick up a 15hp 60 cfm rotary screw compressor for $1500 and I am located in a place with very cheap electricity.

Great info, Scott,

Geof, your comment on the venturi piqued my interest. I happen to be in the market for a new compressor to power spray guns, a line boring machine, and various pneumatic clamps around the shop. I was planning to spend about $1000-1500. I was also planning to spend 2500-3000 on my vacuum pump. If one will do both, I won't hesitate to combine the two budgets.

How much CFM are you getting out of your venturi system? I understand that a venturi is easily capable of pulling full 29inHG vacuum.

P.S. I have an extra 80 Gallon Tank sitting around that I can use as an auxiliary.

The venturi I have use 68 psi, can pull 25" Hg and consume about 6cfm of air to pull about 6cfm of vacuum flow. The volume flow numbers are out of the manufacturers spec and I have no way of confirming them. I also have not hooked up ten venturi to my compressor to see if it can handle that many. I think getting 29" falls into the category of manufacturer's optimism.

I would say if you want vacuum all the time you are operating the compressor/venturi approach is questionable but if you need air for other things and only need vacuum intermittently then it is worth considering.

Zumba If you want a root's type pump I think I still have a 5hp 3ph unit on a mount also have starters and relays you would need PM me if you are interisted

Kevin

The point of this verbosity is to explain my adventures with attempting to create a vacuum hold down system for my 4' by 8' cnc router. I had a bunch of preconceived ideas about how all this stuff worked after reading several books on the subject and watching many, many, many forums.
I have the biggest 2 speed shop vac that sears sold 7 years ago. I also have 2 vacuum pumps (Westinghouse explosion proof motors, about 5 inches in dia. and 40 lbs each) that a meter says draws 16 inches of mercury.
A friend built the system (I provided liquid refreshments and encouragement, "Go Rick, GO!!) that I am about to describe. He put both vacuum pumps in parallel sucking the vacuum chamber on the table. In this loop is the above mentioned shop vac, with a ball valve to turn the vacuum flow on and off. I have only one entry into the bottom of the chamber via a 2" vacuum pipe with a 2" stepped rubber plumbing gasket for a seal, siliconed in of course. The connection from the table to the shopvac is a 24" long 2" vacuum pipe with a ball valve near the shop vac connector. The vac can be just plugged into this pipe when needed and then moved to it's hidey hole while resting. Between the table entry and the ball valve on the 2" vacuum pipe is a 1/4" barbed plastic piece with the 1/4" rubber tube going to a tee connector which runs to each of the vacuum pumps. The idea was to use the vacuum pumps to hold the material down on the table after the shop vac had initially sucked the material down by removing the biggest volume of air out and then being shut out of the loop by closing the ball valve. Well, on to plan B or is it F! When the valve to the table is opened from the running shop vac the vacuum will pull and hold a sheet of 1/4" pvc tightly to the table. I then turn on the vacuum pumps and then turn off the shop vac. The material releases from the table. With only the shop vac running the meter shows a little less than 2" of mercury vacuum but the material holds. With both the shopvac and the two pumps running the meter shows 7 inches, so I have to assume that the pumps are working. In any case the pumps are now out of the loop as I have no idea of their history or usability, it almost seems that they draw a good vacuum until they have a load put on them. They are probably 40 years old and untraceable on the internet from Westinghouse. At this point they are just ballast as far as I'm concerned.
Plan C or is it G, there's been a lot of planning for this over the years
The vacuum chamber is a 3/4" sheet of mdf with 2 coats of primer and 4 coats of paint on all six sufaces. The outside edges of the top have two rows of 1/4" by 3/8" wide closed cell foam for the vacuum seal against whatever template that I use. Any joins or low spots in this outside seal have been gooped with silicone.
When the shop vac is used to suck the material down there is still a lot of air coming out of it - seems odd as everyone has always stated that you can't use a shop vac for a vacuum table as the incoming air must be used to cool the motor. Very odd/ Sooo... I thought, hmm this seems strange. If I put my hand over the sucking end of the shop vac hose the machines screams and cries. The same if I turn it on connected to the vacuum hold down table with the valve closed, BUT when the valve is open it sounds about the same as when it sucks a pile of mdf dust. So I left it running sucking down the pvc sheet for a few minutes and there was no temperature difference from the air flow from the top vent of the motor so I left it running for another 40 minutes, same story.
Welllll, my friend, you remeber Rick, came over and really didn't like the idea that the vacuum pumps were't working, so now we're going to use a compressor as a vacuum source in place of the vacuum pumps, but the compressor needs more ump, so we'll make the pully bigger on the motor end - not easy, have you ever tried stretching a 5" wheel to an 8" wheel and the belt, ... Anyway, after this was done we opened the drain valve on the bottom of the compressor and hooked the intake (normally the air filter) into the vacuum system. This pulled about 7 inches of mercury when running sucking from the table. Even after sucking down the sheet with the shop vac the compressor was as useless as the vacuum pumps.
" Well, it's got to be the weatherstripping" he says while adding yet more silicone to the "thin" areas. "We need that real rubber stuff with the ribs on the top, that way the sheet of pvc material could compress the weatherstripping and this or the vacuum pumps would work!" Well, as he was ranting on I went about creating a vacuum template from 1/4" hardboard with holes in it to hold 31 pvc signs that I want to cut from 1/4" material. Under each 8 by 16 inch sign are two rectangular holes that are 4 1/2" by 5 1/2" seperated by a 1" strip so the sheet is more stable. On the shiny side of the sheet I sanded and brushed on contact cement (which dried for 24 hours) and then applied a strip of 1/4" thick by 3/8" wide stick on closed cell weatherstripping around each set of holes and around the perimeter of the sheet - just to raise up the edge to the same height as the "chambers". On the rough side around the edges where the seal from the table will touch this material I ground down the edges to remove the "knurled" surface and then applied a bunch of coats of paint. I then glued a bunch of 1/4" thick hardboard pieces, shiny side up (cut from this same sheet) that I had removed the sharp edges from onto the bottom in order to bring the sheet up to the same height as the outside edge.
Meanwhile Rick was working on trying yet another compressor on the system. More power - same result. "Hey, let's try two compressors at once", he said. I said that I thought maybe we should just sit and relax and think about this.
Here's what we came up with. Vacuum pressure is a very strong force to exert on a chamber. Obviously the chamber has to be air tight and very strong. Our system is definitly not air tight and definitely not strong. If we assume that the vacuum pumps were in perfect working order, they probably only draw about 15 cubic feet per minute of air each or maybe 30 in parallel. The one compressor we tried has an output, and I assume, an input of 6 1/2 cubic feet per minute the other one has less. BUT, the shop vac has a rated output or input of 375 cubic feet per minute and on our meter only 2" of mercury. I guess cfms are way better than vacuum pull.
The thing that we seemed to fret about the most was that we didn't have a good seal. This makes sense unless you assume that all of the pumps and compressors were broken. The proof to me is that when the shop vac is used solely to hold the sheet down there is TONS of air coming through it, so of course the seals are bad, BUT this is good for me. I can run the shop vac without having to devise and tune inlets to allow more air into the motor so as not to cook the motor. I haven't tested the actual amount of air going through the leaks in the vacuum table and into the shop vac, but from the motor exhaust and the noise I think that it is probably putting out about 3/4 s of it's rated volume.
I have yet to cut the signs but I am sure that this will work, especially when I can break the seal between the pvc sheet and the first sign hole which is about 6" away from the vacuum table inlet and the PVC sheet is impossible to move sideways. I hope that I am not going to be embarrassed by having the vacuum system not hold the material. Oh well it's only been about a week of playing around!!!!!!!
Finally I have a system that will be useful for those pesky jobs that have lots of small parts that are hard to hold, that I usually have to pass on taking on as I know that they will fly loose as the bit cuts the last bit freeing the material - yes, you can use tabs but they are horrible to clean off mdf without ruining the piece. Today I test the table, cutting the pvc with a 1/4" dia. compression mortise bit on my brand new Porter Cable router - the last one's bearings are toast, which I must remember to get replaced.

When a vacuum pump is "Deadheaded"It sounds like it is hard on the pump but this is not the case as deadheading is the lowest load on the pump.Some sort of vacuum storage such as tanks can be used to store vacuum while off loading parts.Close a valve to the grid and store some CFM in the tank.Seems strange to store nothing,but the reservoir can assist at the initial pulldown.
Larry

Just an update to yesterday's entry. I finally cut the signs and the hold down worked flawlessly. When I revamped the outline of the weatherstrip around each hole in the template for each sign I neglected the two screw holes in each sign near the edges. These 62 1/4" holes cut into the vacuum chamber didn't seem to effect the vacuum hold down capacity, BUT I did stop the machine before cutting the signs out of the sheet and I put masking tape over the drill holes, I will correct this problem before cutting any more sheets. While this initial job ran I was holding the corner of the pvc sheet and trying to move it and it was as if it was welded to the table.

I have been threatening to build a vacuum hold down for years and I finally did it when my router's bearings went bad. I am a happy puppy. I am still surprized at the machine that I am using instead of the original plan of the vacuum pumps.

I will have to test some other things, such as cutting 4 or five large pieces from a 3/4" thick sheet of mdf or plywood. I think that I will put a 4' by 8' sheet of 3/4" thick sacrificial piece of plywood on the vacuum chamber and screw the mdf to it and then turn on the vacuum table, I think that this will work. The sacrificial sheet will have to have a bunch of 1/4" thick material glued to it's back in order to keep the center part of the sacrificial sheet level with the 1/4" thick weatherstrip around the perimeter of the vacuum chamber. This sure beats using two sided Intertape ( a great product by the way) for holding material to the old sacrificial sheet that was screwed down the old way.It also saves about $12 a sheet in tape costs and a bunch of time removing the used tape from the base sheet!

I guess the biggest surpize that I had was the fact that there is so much air coming through the shop vac from what I considered to be a sealed chamber, it's no wonder that the vacuum pumps and the compressor wouldn't hold the vacuum after the shop vac sucked the material down.

Unless a virtually air tight chamber is built there is no way that the pumps or the compressor could work, as they just don't draw enough cfms to keep the seal.

Anyway, I just thought that for someone looking for an easy and cheap way to hold small parts down this is a perfect idea. The only down side is the fact that a template for each job must be cut and each part's chamber must be weatherstripped. BUT if you are doing a bunch of the same pattern the time saved is enormous. The vacuum template is place on the table, the material to be cut is placed on this and the shop vac is turned on, the router is turned on and the dust collection system is turned on and then just run the cut job, no worries of debris getting into the expensive vacuum pumps or blowers! Then remove the scrap piece and the parts and blow of the table and apply the next sheet, fast and labour saving, big time.

Thanks for listening!

Hi Larry,

That's where Rick wanted to go with this, but we have no experience with vacuum pumps or these pumps in particular. We were unsure of the ability of the pumps to pull anymore vacuum than that required to make the meter register 16" of mercury. When I realized that the shop vac was easily doing the job and that it's motor wasn't overheating and that it had lots of air going through it I decided that it made more sense to just use the shop vac. I still find it hard to believe that my homemade vacuum chamber is that loose, but apparently vacuum pressure is very elusive and hard to contain. Rick was sure that this wouldn't work.

The price of the shop vacs can't be beat. I just wait for Sears to have a half price sale and then I buy their biggest for about $125 - according to the specs, they draw 375 cfms which may be wrong or exaggerated because they also rate them at 5 or 6 horsepower which is impossible from a 110-120 volt power source. I have used the my current 2 for six years in series as a dust collection system and shop cleanup so they probably both have at least 300 hours of use on each of them - it didn't work as well as a small single bag dust collector - again due to a smaller hose and less cfms than the small dust collector with the 4" intake. Gotta love those high cfms.

If I was going to continue along the vacuum pump route I would definitely get a large tank for "storing" vacuum. But it would then still be necessary to airproof the vacuum chamber and template. I figure that I have at least 6 hours into the vacuum template already (and a different one of these must be created for each job using vacuum hold down), I really wouldn't want to have to spend more time and money on it as it must be removed and stored when not in use which could easily tear the material used for the vacuum system. If I tear anything now I just hang another piece of weatherstrip on it. No special care required.

Thanks for your idea!

a company i worked for wanted to fly cut some saw guides so the boss who is an engineer on paper came up with the idea of using the shopvac , i argued till i was blue in the face it wouldn t work ,so they got one of the other guys on the job ,he was so proud to work hand and hand with the boss (one of those guys) they spent days designed a beautifully fixture ,finally they connected the shopvac and put the part down , i just watched from the background (under cover). the second the tool came in contact with the part they came to realize that a 40lb part can fly quite quickly, they launched that sucker
there were some pretty red faces on the shop floor , those two clowns and the rest of us who were trying to catch our breaths from the laughter
needless to say the part was scrapped as well as the vac idea

don't get me wrong ,i'm not trying to discourage anyone but the shopvac idea brought back some fond memories

I now know from experience that the shop vac works with 1/4" thick 4' by 8' foamed pvc sheets holding 31 parts that are an odd shape and are 8 by 16 inches. This is the type of job ( the parts are on the large side) that I have had to pass on in the past because I couldn't hold the parts down. I now know that I won't have to lose these jobs in the future. The vacuum template for this job can be used an unlimited amount of times. If I blow the shop vac motor after X amount of sheets I can just factor the cost in to each job as I must do for the Porter Cable 7518 routers (new units and rebuild costs), router bits, hydro and labour. I also save about $12 a sheet of material cut for double sided tape. For these house signs I could have just had the machine drill the holes first and then I could have pplied 62 screws with washers, but then the material being screwed into would fail after a few sheets and the labour and aggravtion level would be high.

In general I also know that the shop vac is pulling hardly any vacuum, only 2 inches of mercury. I also know that large vacuum blower pumps have a lot of cfms as well. If it isn't necessary to pull lots of cfms as well as applying vacuum why are they used?

I don't know about others but I have neither the space, the income to cover the exhorbitant cost or the need for these units.

I have proven to myself that low cfm pumps or compressors are of no use when pulling from a leaky chamber. I also know that there has to be a limit to how much stress this system can maintain. In general I cut 3/4" mdf at 1 1/2" a second or 3/4" ply at 1" a second in a single pass with a 1/4" mortice compression bit (up and down spiral 2 flute) but these pieces are usually large. There is very little side pressure exerted when a sharp bit is used. I doubt that I would ever use a specific vacuum template for these materials in large pieces as the volume is usually low (one offs).

Any time that I would use a vacuum template as I have just done would only be on small parts in thin sheets, max 3/8" foamed pvc or 1/4" ply or mdf, which, as I said earlier, I still have to test. I also know that the low vacuum pressure will not pull through the mdf as high powered blower motors do.

I just think that if I had have known of this system earlier on thin materials I would have tried it. I have definitely heard of it but there has been very little real information posted. If I can save someone else a lot of time and lost jobs I have succeeded in putting this up on this forum.

I think that it is wonderful for those of you who have a large budget, a lot of space and a keen need to purchase a surplus of technology. When a low tech, low cost and space efficient (almost every shop has a shop vacuum for clean up) alternative is available I'm on board for testing it and using it if it works for only a small volume of the work that I do.

I am so sick and tired of building and using hold down clamps, jigs, screws, t-slots and double sided tape that I am ecstatic about this system.

As I said I still have to do more testing. I am concerned that there will be a limit to the smallest size of small parts as there is the same side cutting pressure, but there is a smaller force holding the parts down. I think that when I find the failure size / shape of small parts of thin pvc or ply or mdf I will simply turn on the vacuum motors in conjunction with the shop vac see if this adds the required vacuum strength as they do pull 7 to 8 inches of mercury.

Thanks for your reply, I probably should have stressed more that this was a very specific appliction.

I must agree with you about the engineer that you mentioned. Maybe he was a train engineer!

Gary,
Here is some useful links.
http://www.shopbottools.com/vacuumholddown.htm
http://www.allstaradhesives.com./index.php
Larry

Maybe he was a train engineer!

more like a train wreck

Geof,hope you drop by and give some comments or insight.
Gast makes some serious multi stage vacuum venturi units.Check the PDF pages 14&15.
VG260-08-00 has 158CFM at 26Hg,requiring an air supply of 56CFM at68psi.A 10 to15Hp compressor can do this.
A 7Hp regen blower can do 140CFM at13"Hg for $6,000.
Don't know the cost of the Gast but assume it cannot be to pricy as there is no moving parts.My only concern is the 1 1/2" pipe. seems small for 158 CFM.Looks good to me.What do you think?
http://www.gastmfg.com/pdf/vacgen/catalog.pdf
Larry