View Full Version : Vacuum Hold Down Systems

Sun 03 December 2006, 22:54
Now That I have made satisfactory progress with the table. I have to start thinking of a Vac or some other Hold down system.

Gerald, by reading varous threads on this subject I have understood that the Vacuum Hold down system is the best choice but is quite expensive. Do you have any DIY Vac system in mind which could bring down the cost.

Thu 25 January 2007, 17:25
And then yesterday Fabrica asked here (http://www.mechmate.com/forums/showthread.php?p=1953&postcount=134): "If I am to do a vac hold down what should the specs be for a vacuum pump. If I know the correct specs maybe I could find a used one from a Junk yard."

Fabrica, if electricity is cheap for you, and you have a lot of spare capacity at your factory, you can look for something around 15kW or 20 HP, made of cast iron, with 75mm [3"] pipe connections. Might sound huge, but this is what the really "industrial" guys use. (We use g-clamps...I can't come to grips with using 15kW of the earth's fuels to replace 3 clamps.....)

He replied: "Gerald, Same form here electricity in this country is damn expensive. So we will just forget it for the moment. It costs around US $ 0.08 per unit.

True I too will stick to G clamps and double sided tapes for the moment. "

Thu 25 January 2007, 17:48
The size & price of buying and running a vacuum hold down is decided by the size of parts that you are cutting loose from the original boards...

Kitchen cupboard doors are big and you could manage with a cheap vacuum system. If you cut small jigsaw puzzle pieces then even the biggest vacuum pump in the world won't be big enough.

So, what a lot of people do, is to use small cheap "pumps", and when they have to cut out tiny pieces then they don't cut them loose. The small parts stay attached by bridges/tabs or skins which are broken right at the end.

The cheap "pumps" are vacuum motors (http://images.google.com/images?sourceid=navclient&ie=UTF-8&rls=GGLD%2CGGLD:2005-07%2CGGLD:en&q=vacuum+motor) or fully packaged industrial vacuum cleaners (http://images.google.com/images?sourceid=navclient&ie=UTF-8&rls=GGLD%2CGGLD:2005-07%2CGGLD:en&q=industrial+vacuum+cleaner).

Good vacuum motors: (noisy if not mounted in an enclosure)
Grainger 2M433 (http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?ItemId=1611622037)
Grainger 3HV25 (http://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId=1611764155&ccitem=)
Maybe better prices here (http://www.lighthouseenterprises.us/centralvacuummotors.htm)? Another source (http://www.imperialelectric.com/cgi-bin/wspd_cgi.sh/WService=imperial/itemdetl.html?item=122&lvl1=VM&lvl2=TBP&lvl3=&lvl4=).

Good vacuum cleaners: (high suction, low noise)
Fein Turbo III (http://www.google.com/search?sourceid=navclient&aq=t&ie=UTF-8&rls=GGLD%2CGGLD:2005-07%2CGGLD:en&q=fein+turbo+iii)

For big tables like the MechMate it is typical to use 2 vacuum motors or cleaners on 2 halves of the table.

Sheldon Dingwall
Mon 12 March 2007, 13:28
I'm gravitating toward an aluminum vacuum grid table top, but need to build a plenum to support the grid plate.

I'm thinking the plenum needs to be bolted to the table, then surfaced before mounting the grid plate.

Here's a link to a vacuum grid plate http://www.nemi.com/vacuum%20grid%20table.htm

1/2" or 3/4" alu plate might work for the plenum. Does anyone have experience using 6061 T6 plate for large areas vs cast alu jig plate?

(I've also posted this message on the Shopbot forum)

Gerald D
Sun 13 January 2008, 07:51
. . . Besides the MM, I want Dust Collection and some kind of vacuum which will require additional power.

That vacuum can use as much power as everything else put together. The really serious production people are not shy of talking 20HP just on vacuum - I cringe and think of global warming.

Sun 13 January 2008, 07:58

A few years ago, I bought a lathe and mill that run off three phase power and I was trying to get them connected. Several knowledgable people told me that the power company wouldn't just connect my house to 3 phase power because they have to install a couple of extra transformers and my power usage wouldn't justify the expense. Then I found out about VFDs. The smaller VFDs could take single phase electricity as in input and they would output enough three phase electricity to run up to a 3 hp motor. The larger VFDs required that three phase power be input. When I spoke to the salesman, he told me I could actually run a larger motor by buying a much larger VFD and derating it. I don't remember now how much larger the VFD had to be but I bet if you called one of the VFD manufacturers, they could tell you.

Sun 13 January 2008, 17:10
Doug: That is the deal with my Columbo/Delta hook-up. That's why it was a 10HP VFD for the 5HP spindle.

Nils: Even in my shop I have run a sub-panel to the area with the bot. I have it at 50 Amps and it is sufficient to run the spindle, 7.5HP regenerative blower, the 5HP dust collector and plenty for the additional 110 needs of the shop computer. My compressor is a bit of a bear and needs a lot of juice and has it's own breaker from the main. If I were to run a sub-panel from my house to my shop and needed to run all the above and also the usual additions of a table saw and other misc tools like a chop saw, drill press, lights, fans, etc. I would want to run 100 Amp Subpanel minimum.

Gerald: the 7.5 blower keeps everything in place with no problem even when taking 9 cabinet sides out of a sheet. On the other hand if I were cutting many smaller parts I know it would not be sufficient. There are times when a particular sheet of plywood has too much warp in it for the vac to hold it down. (PS-glad you had a great trip)

Sun 13 January 2008, 17:15

I am thinking of running a 100 A panel in the garage. I still have to calculate all the Amps to insure that I have enough.

I like to hear more about 7.5 Regen Blower. How you have your table set up? How many different zones? Noise level and why you went with the 7.5 HP? Tag on here or send me a private message.


Sun 13 January 2008, 17:32
Nils: Since there is no thread as of now for vacuum systems (If Gerald decides to start one he is welcome to move this reply) I'll answer here. The subject of vacuum hold is a huge part of cnc operations and with the number of MM's being completed it may be time for one. I had none for the first couple of years and then I was offered this one by a friend. It changed everything. I use 8 zones and 1"PVC to connect it all with typical valves from Home Depot. I should redo the piping to 2" for more volume. I am set up with a base of 3/4 ply and the vacuum plenum of 3/4 mdf over it. After cutting the channels and holes for the pipe I sealed it with shellac. Then it has a layer of 3/4" ultralight MDF with both sides surfaced off glued down as the bleeder. The vacuum is not quiet but then neither is a dust collector or a cutting bit.
Mike Richards who posts here regularly has a similar setup but he uses two fein vacuums and they satisfy his needs. I believe he has commented elsewhere on the need to be less aggresive in cutting to keep the vacuum from breaking loose. I also am only cutting at around 2 ips due to the flex in my current (original SB PRT) gantry. I have the MechMate parts waiting to be welded for a new gantry and when they are I expect to be cutting up around 4-6 ips and I hope my current vacuum can handle it.

Mon 14 January 2008, 06:00

More details on the Regenative Blower. Why did you decided on a 7.5 HP? Do you have additional filters? More Details.....

Gerald, Thanks for moving it to this location.

Mon 14 January 2008, 17:33
Nils: I "selected" the 7.5 because a friend had it available for a good price and was only selling it as he had acquired a larger one. He told me that he was surprised at how little difference the larger one made. I have no additional filters-Not a really good idea but I haven't busted through my spoilboard in a very long time. If I remember when I am in the shop, and can make the time, I'll post the lines for the plenum.

Mon 14 January 2008, 17:59

Yes, I would like the additional information.

Thanks for the input and you might consider adding a filter. How is the sound level?


Sat 19 January 2008, 11:26
Here's a dwg of the lines I used to create my vac. All lines were cut with a 1/2" bit 3/8" deep. The center holes in each zone were cut clear through the plenum and base board for the pipe. It was then all sealed with shellac. I used standard mdf for the plenum and I use ultralight for the bleeder. Each zone has a valve so if my part is less than full size I can shut off zones. Different people use different layouts to suit their particular needs but they are all basically the same idea. If you do not have RAR to decompress you can download it for free. a quick search will find it.

Sat 19 January 2008, 14:23
So far everything I have read here deals with high volume low pressure type systems. A typical shop vac has a max static head of 60" h2o, the Fein III is much better at 105", these figures convert to 60" = 2.2 psi and 105 = 3.8 psi.

There is another class of vacuum, the high pressure low volume which are capable of drawing 26" to 28" Hg, i.e. 12.8 psi to 13.7 psi, this is the type used for lathe vacuum chucks, milling machines and the vacuum forming people. There are different types of pumps, rotary vane, reciprocating piston, diaphragm and others, they come in different configurations, some with integral motors some as free standing pumps. Personally I use a free standing rotary vane with a 3/4 hp motor that can pull 28" hg and have used it for manual pattern routing of parts as small as 2 sq". I use Gast pumps, though there are other manufacturers this is a useful place to start. http://www.gastmfg.com/pdf/General%20catalog/FullLineCatalog.pdf

For small to medium sized templates I have used untreated MDF, but for larger work it is better to varnish the MDF or use aluminum. Sealing tape is used to form the seal, the best type is zero creep, more info can be found here: http://www.veneersupplies.com/.

I am not suggesting that this type of work holding is necessarily suitable for full size sheets of material, I can see that initial flatness can create problems with obtaining the initial seal. I have heard of systems where dual systems were used, high volume low pressure to get the initial seal then that port being sealed and the final vac being pulled down by the low volume high vac system.

Sat 19 January 2008, 17:51
Bernard: I agree that HVLP is the way to go for many applications, particularly when one is doing 3-d work on a smaller part. A good system for that is to use a hunk of UHMW with a hole bored into the side for your vac hose fitting and a hole in the middle from the top with both meeting in the center. Gasketing is important. I bought a compressor driven vac years ago to vacuum bag veneer layups and the same pump has a switch that will keep it running full time for parts hold down purposes. The only minus with it is if your compressor isn't strong enough you can lose vacuum when running another tool. The same company makes an electric version that works on the same principal as the Gast. Another good source of info on putting together your own system is: www.joewoodworker.com
It is not too hard to picture a scenario in which one cuts out parts, pre-finishes them, applies a paint mask, holds the parts down with an HVLP pump to carve them, and then finishes the exposed part differently from the blank.
The best signmakers are experts at this.

Sat 19 January 2008, 18:52
Dave, I was aware of the compressor driven vacuum pumps, but personally didn't like the idea of running a 3 to 5HP compressor to pull a vac that can be obtained from a 1/2 to 3/4 hp motor. I had similar situation when I tried using a mist system for metal cutting, a big compressor suddenly coming on to supply a mist that was not as efficient as regular flood.

I bought a Gast pump several years ago and hooked it up with a motor I already had and have never looked back.

JoeWoodworker deals mainly with veneer work and his plans are for vac units which are generally required to run for a considerable period of time to allow glues to set, as such there are reservoirs and differential vac switches. Vac chucks on the other hand are often run without anything other than an ON/OFF switch as the pump generally isn't on long enough to overheat the pump, obviously it depends on the type of pump. A quick Google search for Vacuum chucks will give information overload!!

Sun 20 January 2008, 06:20
Every day I learn more. This morning started with learning that both of the sites below (veneersupplies and joewoodworker) are run by the same guy and cross reference each other. Veneersupplies is the store and knowledge based articles are on Joewoodworker!! Look for the article on vacuum clamping. Although it is primarily aimed at short term holding it makes some good points about needs for template work.
In my shop the compressor runs regularly and additional usage usually translates to more use of on hand capacity. 99% of our work requires full sheet or large part holddown and so the blower is used most for vacuum.
Your point about short term use of the clamp and danger of overheat is a good one. Many 3-D cutting files can take quite a while to cut. For those considering the electric motor driven system, you do need to ensure your motor will take the sustained use. Since my personal experience is with an air driven pump, others will undoubtedly know more about this.

Sun 20 January 2008, 06:29

From my research, Joe's system will work great if you are not cutting complete through the board. The motor does not have to run all the time if you have a foot pedal or some thing that closes the system. I an not sold on shop vacs. I know most of the ShopBot people love them.

I am interested in a Regen system, I think. I believe I will be cutting out pieces of material. That is why I was interest in your system. These motors were built for this kind of application.

Gerald D
Sun 20 January 2008, 09:41
. . . . system will work great if you are not cutting complete through the board. .

Be careful here, the typical MDF board is rather porous, it leaks like a sieve. It doesn't matter whether you cut through or not, you have to have a High Volume vacuum system to hold porous material. And to make a high volume system affordable, it becomes a Low Pressure system.

Sun 20 January 2008, 10:06

That is true. The kind of vacuum system I was thinking of also includes zones. So that you are using a zone that is slightly smaller or the same size as the piece that you are cutting but that you are not cutting out. Which is probably not often.

Sun 20 January 2008, 12:41
Nils, There are many different vac hold down systems available and really depends on the type of work you do. If you have repeating work the simplest is a varnished sheet of MDF with each area to be cut delineated with non creep vac tape with a simple npt nipple tapped into each zone and all the zones manifolded together.
Where different patterns are constantly being used, the favorite system seems to be an aluminum plate with a grid system and a gasketing method to seal off the area of interest. Never used the method, but it looks simple enough, don't know how practical it is for large sheet products though.

Each material you are working with will have a different porosity, unfortunately I don't know anywhere where that information is published, empirically most users seem happy if the manifold pressure stays above 24" hg, this corresponds to approx 1700 lbs/sq' holding force (a FeinIII produces approx 550 lbs/sq' before losses). I noticed that the current compressed air driven vac pumps are capable of producing in the region of 26/27" hg at moderate pressures and flows.

Sun 20 January 2008, 15:40
You are correct that the vacuum puck or plate with a HPLV pump, whether compressor or electric driven is primarily used for carving the surfaces of parts without cutting through. At this point, since I went with the regen, If I have this situation (carving a part smaller than the zone) I simply cover the remaing open zone with some P-lam scrap and turn on the blower. The spoil board is glued to the plenum with glue along all zone borders. Gerald is absolutely correct about the two main points he makes:
1. The big boys run 20HP or larger.
2. MDF is porous.

Note that my main materials being cut are either particle board, mdf, or plywood that already have at least one side prelaminated with HPL and as such are not very porous, or plywood without anything laminated on it. That being said, I have cut quite a bit of bare MDF and Ultralight without losing vacuum. But if I am doing heavy carving in a larger piece of MDF (as for a sign or plaque or paint grade decorative panel, I will secure it with screws as I know its' tendancy to warp when one side is peeled will come into play. If I did large quantities of larger carved panels like that then I would build a clamp system for hold down. All info is based on my own uses and as they say "results may vary".
When processing cabinet parts I typically stick to running the sides which require so much machining and also does not result in very many small parts from one sheet. I also usually run a downcutter. Although that may cause some small amount of tearout on the bottom of a piece of plywood, our construction method makes this unimportant. I do make sure I use sharp bits, take two passes to cut out parts, and make darn sure the piece is not unduly warped.
On the affordability issue, it is certainly a question of time vs money. If you have a piece of equipment with that much invested into it combined with the software to be commercially competitive then the money becomes secondary to making production goals.

Gerald D
Sun 20 January 2008, 23:15
To get a feeling on porosity; if you use a big suction cup to lift a sheet of MDF from a stack of sheets, you are going to lift more than one sheet at a time. The guys who have tried it found about 4 sheets lifting away! :)

J.R. Hatcher
Wed 30 January 2008, 05:35
. . . .
. . . . . . .

Greg, tell me a little about your vac board?

Wed 30 January 2008, 17:12
Greg, tell me a little about your vac board?

Maybe a little less relevant to a MM.

A full table "suck through MDF spoil board" type is probably more in line with what the MM is designed for.

However on my router the one seen in the video above gets lots of use. No good for jobs that are cut through.

The main part is getting a vacuum source. Making the plenum (that's what I call it) is easy if you happen to have a CNC router available. :)

I used acrylic because I had it laying around. 1/4" sponge rubber for a gasket.

Fixed it down to a freshly surfaced table, surfaced the top and cut the grid of channels to suit the rubber.

Broadly speaking there are two types of vacuum source. Large volume - low vacuum. Typically used for "suck through MDF spoil board" type

High vacuum - low volume. Which is suitable for a low leak type device such as mine. Holding smaller items.

A cheap small air compressor was converted to a vacuum pump with some re plumbing and addition of a vac gauge and vac switch.

Once you have a vac source making custom shaped hold downs for profile cut jobs is easy.


J.R. Hatcher
Thu 31 January 2008, 06:36
Greg I could see a need for both on the MM.

This is a simple hold-down we use for sanding. It's used with the shop vac and it's incredible how strong it is.

Thu 16 October 2008, 14:09
does vacuum really holds the system down :confused:

J.R. Hatcher
Thu 16 October 2008, 18:36
Sandy the vac keeps the material from moving while it is being machined. Mine system will hold pieces about 1 sq ft or larger.

Sat 24 January 2009, 14:32
So, if I get it right, J.R. and others say that if you machine large parts, just plugging in some of the suction from a clearvue cyclone (4HP) will suffice as a vacuum holddown (or any other powerful dust collector, for that matter).
Am I right here?

Sat 24 January 2009, 15:42
I've never had success when I've tried to use a dust collector for vacuum hold-down. A shopvac type vacuum works fine for larger pieces. I use one or two FEIN vacuums, depending on the job, pulling directly through a sheet of ultra-light MDF. I would use TruPan, but it's not available here. For small pieces, I use a GAST high vacuum/low air flow vacuum pump and AllStar gasket material.

J.R. Hatcher
Sat 24 January 2009, 19:34
I'm with Mike, I don't think a dust collector will create enough suction even for large items. I also used a large shop vac with limited success.

Sat 24 January 2009, 20:18
There's a guy over on the Shopbot forums that has a lot of useful information for cnc routers. One of the things is a vacuum table. Gary Campbell is his name, I could post a link to his work, but I don't know if it's allowed, don't want to get my knockles slaped with a ruler. Last time that happened was 1958, 6th grade, Nuns you know.


Sun 25 January 2009, 13:45
From what I have heard/seen, you can use 'small' vacuum systems, but you must be careful about your expectations. One way to 'save vaccum' is by not cutting all the way through so you keep a thin membrane, or use judicious zoning, so you are not cutting a LARGE area. Using gaskets if you are doing some things helps. Not letting small pieces be 'sucked up' so they keep parts of the area covered (using tabs or keeping a thin membrane of material to be trimmed later by hand). Covering un-used table with plastic or non-permeable material.

Or break down and get a killer industrial vacuum. I saw a multi-stage multi-thou$$ vacuum motor/pump at a ShopBot conference last October in Austin TX. And it was not the largest they sold. I think it took 10A at 220V 3phase to run the vacuum only.

For special needs, using vacuum pucks seens works well.

It boils down to, determine your needs. Design for needs rather than wants (a problem I have). For many it seems that a mixture of hold down methods are 'real life'. for many folks.

For many folks it seems like the noise of the vacuum system generates is problematic. The best thing I have seen is run the motor and fans outside put have the exhaust (dust collection bags) back inside so any 'conditioned air' (heated or cooled) isn't just thrown away, but the sound stays outside (or in an adjacent 'service' building).