Sizing Vacuum Lines

I would make all the valves and piping/tubing one size larger than the vacuum pump inlet, with one connection per zone.

Simple mind is correct. Id focus more on getting a good seal or you'll have nothing

Thank you all for the good answers

When I was working with large CNC routers and their vacuum clamping systems, the seal was the biggest issue. You can run it through a 10 mm tubing header and then to a 6 mm valve and zone manifold. We rarely had larger than 12 mm tubing in our vacuum systems.

I know about the problems with the seal and will try to do my best to avoid any leaks.

Pipe sizing sound good, just about the same as quoted earlier

Thank you

pwr2thepeople,
Good answer!
As for the wait to achieve proper vacuum then oskar can add a reservoir and keep the vacuum running to evacuate that first so that the clamping process will be sped up. Some people have re-purposed old propane cylinders for vacuum reservoirs.

I agree with Jimmyjoejetter, but because of experiences I earned with vacuum forming. My solution would be two vacuum pumps and two tanks. The first to evacuate the void quickly and that does not need to be much better than an industrial vacuum cleaner, high volume and low inches, and the second pump that can pull a lower CFM but at a minimum of 28"(look at "Gast" pumps). Another concern that would bother me about this setup though is the form and composition of the seal. If this is a CNC mill then you presumably need the base of the material being milled to have a close flatness tolerance so the material will need to come to rest on the vacuum table before the seal is fully compressed(assuming a perimeter seal). Alternatively I would zone the 1" squares and cover the whole vacuum table with a self adhesive silicone or urethane film. Ensuring consistent film thickness, and good surface pliability, ergo good vacuum seal, easy clean up and no appreciable flatness issues. Plot the perimeter of the vacuum channels with a swivel blade first, peel out the unwanted silicone, then rout the channels. I have seen this done successfully on a couple of larger CNC routers.

Usually the only thing of critical importance with vacuum systems is to guarantee that there are no leaks >> good seals.

I'm sure that oskar27 is referring to the vacuum as a clamping solution and not dust extraction.

Clamping with vacuum takes very little CFM to hold a part down to his CNC table, though if you are able to achieve 20 in. Hg or more you will be fine with the vacuum you have.

Watch the gauge and if you can, incorporate a vacuum cut out switch that will send a signal to your CNC controller that will stop any travel if you lose vacuum.

Once again, the better your seal is the better it will clamp!

Also, Do take a few minutes to think about a dust extraction solution, your machine is going to be running at a high RPM and throwing dust all over your shop. A shop vac works but will be almost as noisy as your router spindle.

Good luck with your project

Here is a good resource for hobby CNC.

http://www.cnczone.com/

I'm not an expert on vacuum systems but from what I read vacuum sometimes defies the imagination because it works in conjunction with the atmospheric pressure which at sea level is 15 PSI.

Vacuum clamping is calculated by the hold down force; Force = (area of being held in sq.in) x (vacuum in PSI). So for example if I'm using a 3" round suction cup to hold a part down and my vacuum system applies 24"Hg then: 7.069 X 11.8 = 83 Lbs of holding force. That is a heck of a holding force from one 3" hole. (3" = 7.069 sq.in and 11.8 PSI is 24" Hg)

Regarding the CFM, in vacuum clamping CFM is not important and lets look at it why; so I put a piece on my work table and I open the vacuum valve which allows the vacuum to flow and clamp my piece to the table. Assuming that we have no leaks, as soon as the piece is pulled down the pump will stop and therefore no more CFM are needed for the pump. It may take a few minutes for the pump to stop but this depends on several variables which are not important for this example.

I don't know anything about vacuum forming; perhaps on that system CFM is important.

As for the rubber seal I was told the best seal is rubber type shaped like a rope about 1/4" diameter. This rope will be squeezed into a 1/4" groove and only about 1/16" will protrude above the table surface so when you put your work piece on top, it will sit on the rubber rope and make the seal.

Perhaps other knowledgeable forum members may chime in and correct me if the above are not correct

And yes I will have a dust extraction system and interlock with the CNC to stop if vacuum falls behind an adjustable level

oskar27
Are you using solid rubber or sponge rubber.
In all of our clamps that were designed like yours we used sponge rubber because it seals and compresses and won't hold the part above the Z = 0 or your Z Datum point. I can tell you've done a lot of research and you're headed in the right direction. I think the forum would love to see pictures of your CNC creation, I know I would!
Here is a picture of one that goes on a Biesse Rover CNC router. As you can see the groove is sized to accept 1/4" x 5/16" D-shaped or round SPONGE rubber.

Macgyver thanks for the picture; it is not clear to me what gasket to use but now your saying sponge rubber I could try to use it if I knew what sponge rubber is. My local Home Depot have a foam type rope gasket which is used to seal windows but I think that's too porous and vacuum may leak. I have not been able to find anything else locally so I'm looking at eBay but it's difficult from a picture to understand the material. In any case I will try various materials and see which one will do the job.

I just started designing my 4th CNC (I build them as a hobby and after I work on them a bit I sell them to recover my cost and if I can make a few extra $$$ why not?). My 1st was made out of wood, the 2nd wood and aluminum, the 3rd and present CNC with 1/2" thick aluminum plate. The 1st item to build now is an experimental table top approx 2'x4' to test the vacuum system performance. To build a CNC I always make a model out of plywood / MDF and then cut the aluminum pieces accordingly. I don't expect to have any pictures available before December but I certainly could post some of the vacuum experiment and my wooden model when available.

Attached is a picture of my last CNC

Nicolas

1. VERY NICE!!!
2. That looks better than MOST of the other hobby gantry style CNC I have ever seen!!

OK. Sponge rubber is a closed cell foam type rubber that is more dense than typical weather seal foam and it usually has a skin on it so it is smooth yet compressible.

There is a company that sells it here in the USA. not sure if they ship to Canada. Give them a try?

Keep up the good work!!

http://www.mcmaster.com/#standard-foam-cords/=nyp4wm

If you are doing perimeter sealing then I have found Surgical Latex Tubing to be easy to work with, inexpensive, and readily available. Good luck!

The things some folks do in their "spare" time!

Oskar, that is one sweet set up. Hell I'd buy it. That looks better than some of the commercially available models I have seen in use.

Good old McMaster, an excellent source of almost anything you want but they only ship to commercial accounts in Canada.

So the only choice left is eBay where I buy a lot of items for my CNC. Eventually I will get it

Expanded Neoprene rope is available in Canada from Spaeneur, page K-20 click here

rcDesign that looks pretty good, thank you. I will call tomorrow to find out if they ship to individuals because looks like they are distributors

and any standard old heating guy's unused refrigeration hoses work fine for still 29 inches hg

1 cfm over the air volume lost in the number of exposed holes (which will have an air- CV "rating" one could quickly calculate) for say 22" Hg is likely to show a 2 CFM pump is fine for with initial leakage, as you have described the layout

Have squashed couch pillows down quite flat with common 3 stage/rotor vacuum cleaners, like a Rainbow Rexair, or other compacts... (that suck a Kirby flat, as it is one-stage which depends on flow, not static air movement) and if some high speed approach is required, well then.../ and close that 1" valve when you turn on the standard better regular pump-downer, on already-set-up for 1/4" hoses (id's) and related flairs and hubs common on RFG hose sets, if applicable...

I should be getting my vacuum pump kit next week and in the mean time I try to build the required 2 gallons reservoir tank which will prevent the pump to cycle on / off too often in case of small leaks.

The vendor recommends to build the reservoir from 4" solid core SCH 40 or 80 PVC pipe as per ASTM D1785 and in my area I can only locate 4"cellular core PVC pipe which is used in drainage.

However 2" solid core PVC pipe is available and if I use 4 pcs of 36" long each and interconnect them together I can get the required volume at a cost of approx. $60.

But I also found locally 2 portable compressed air tanks. One is for 7 gallons, 125PSI max ($70) and the other is 5 gallons, 100PSI max ($35)

I'm not sure if a compressed air tank can be used as a vacuum reservoir; what is your opinion?

Would the 5 gallons / 100PSI max be ok?

Thank you

Nicolas

Go with the cheaper of the compressed air tanks. They will work great!

Bryan

Very happy with your answer Bryan, thanks

The item is on line order from my local Home Depo store with free delivery. I will place the order right now

Got the vac pump setup in a plywood base which will be bolted to the bottom of the cnc table. Connect it temporarily to power and she sounds good and not noisy.

The pump is a reconditioned one and arrived with no guards at the front and rear impellers and so I had to make what you see.

Next step is to make the vac distribution header which will connect to the reservoir and the temporary table I will make for my experiment.

Not bad for a Gatling gun, eh?

Well, I think it sucks.

Are you using the PVC pipe as a reservoir instead of the compressor tank?

Nicolas,

Let me know if you're looking for other equipment. I have an abundance of industrial controls and instrumentation.

I know you're in Canada but I would be happy to sell / gift you my excess equipment for a great price to help you in your projects.

Send me an e-mail with what you are looking for and I will let you know if I have it. I have tons of stuff that is just wasting away in storage.

BA

No, I'm using the compressed air tank as the main reservoir; the PVC pipe reservoir (sub reservoir) on the picture is needed for the 3-way Mac valve which controls the air flow in the sub reservoir and unloads pressure from the pump when the system cycles on/off.

Nicolas

22" is a good number for vacuum. At the last shop I worked at, anything over 18" was good vacuum.

My 1st vac table experiment did not turn out well. What you see in the pics is the vac table top which is a 1/2" MDF with the top surface painted with 1/3 white glue & 2/3 water. The hole at the left was an experiment with a different nozzle which was not a good idea and sealed the hole with plywood and caulk. The hole at the right is 1/4" brass threaded coupling and the other end underneath is 1/4" barbed fitting. The grooves are free hand made with a 3/8 router bit and are 1/4" deep at the perimeter and 1/8" deep in between

To seal the perimeter I use 3/8" x 1/8" vacuum gasket tape or 3/8" rope type foam gasket; I noticed no difference between the two

I put on top another a similar size 1/2" MDF (not painted), open the zone valve, and I see the top board sucked in but then there is a big leak somewhere and the entire vacuum is depleted. Can't pinpoint at this time where the leak is

Any ideas?

Nicolas,

We always had issues with the vacuum actually sucking right through the MDF because of the thickness.

1/2" is kind of thin and then you cut 1/4" deep with a 3/8" router bit. I would suggest trying this:

• Seal the entire piece of MDF with a good lacquer based clear finish 2 times. Top, sides and bottom making sure to apply a heavy coat in the router grooves.
• For now, try a smaller area to be vacuum clamped. If your first part was 3' square, try a 1' square part. This may help you diagnose the issue.
• I'm fairly certain that the vacuum is leaking through the MDF.

Good luck
BA

A ventilation smoke tube generates a puff of powder resembling smoke. By blowing toward suspected leak areas, you can see the "smoke" disappear into actual leaks. These are available at HVAC and/or safety equipment suppliers.

Getting some good experience here with this vac system. I was suspecting that the MDF used was leaking through and today I got a 5/8" melamine piece and the results were finally good

It's a very simple setup and the foam rope gasket is stuck to melamine with masking tape. Now if I put a 1/2" MDF on top and open the vac valve all vac is depleted but when I put on top a 5/8" melamine it holds rock solid.

If I fully open the valve (22"Hg) the rope gasket is squished to hell and the top part almost touching the bottom part and the pump is going steady but if I open the valve at about 5% open the top part is held rock solid again, the gauge reads 18"Hg, the pump cycles to fill the lost vac and then the pump stops and cycles on/off every about 5 minutes for 1 minute.

Now I got to think how the above translates to what I want to achieve for my needs

I have no problem with the bottom part which in my case will be the top of my cnc table and I plan to make it from 3/8" aluminum plate and cut on it some kind of 1"x 1" waffle shapes as I have seen and it will also be zoned into 3 sections

But what I don't grasp is the top part which I will do all the cutting. What I read is that top part should be MDF (so its replaceable) and it seals to my aluminum table top with a rope gasket on the perimeter.

But with my current experience, the vac is going to go right through this MDF piece and if I use lacquer to seal it then the top of it will have no vac to hold any workpiece.

Got to think this part cause I don't get it

You can try using 3/4" MDF and seal the bottom and edges with lacquer. After you cut your groove for the gasket material, seal the routed groove with lacquer. That may work?

BA

I dont get the idea BA, if I seal the bottom and groove I would not get any vac on the top surface, would I?

Then how the part to be cut will hold?

Perhaps I'm missing something?

It was just a miscommunication

If my top MDF piece (which is called spoilboard) is as an example 20"x 20", my work piece must also be 20"x 20" to cover all the area otherwise I will loose my entire vacuum

If my workpiece is 10"x 10", then I can use pieces of Melamine to cover the unused area to prevent vacuum leaks

Nicolas,

Try making your spoil board / vacuum table with multiple grooves so that you can move the sealing foam to just under the size of the work piece.

Here is a sketch of a basic table with a few grooves.

Use the grooves to re-arrange the sealing foam.

I didn't put in too many grooves in the above picture as to confuse you.

You can put the grooves an inch apart and move the foam sealing cord to a position that is slightly smaller than your part like this.

Good luck

BA

Thank you BA for the tip, I'm aware of this method but for now I have decided to head for a Podz vacuum clamping jig.

I remember from my last cnc when I was cutting aluminum (see attached pic), the table top was getting quite messy and the cooling fluid was making the cleaning process even more difficult. Now if I was going to add slots and vacuum outlets to the top of my table, the cleaning process after each cut will be much more difficult and time consuming.

With the Podz, my table top will have no holes / grooves and it will be much easier to clean. I will make the Podz myself in any shape / size I want

Another reason to go for the Podz is that my pump is a low CFM high vacuum pump and more suitable for a Podz system. I don't complain for my pump because I find it very quite and more suitable for a hobby / small commercial applications. I assume that high CFM pump will be noisy

You're right on with the vacuum pods. And yes. The larger vacuum pumps are very noisy, and expensive. BA

Got some brass barb fittings (1/4" ID Hose x 1/8" MIP) to make my 1/2" thick aluminum podz and was sure that I have the required drill / tap but when I went home I don't have anything for 1/8" MIP

What size drill / tap I need for 1/8" MIP and what is IP ?

MIP = male iron pipe. By eyeball, 23/64 is probably the correct drill size, with some leeway. For tapping the pipe thread, you'll need an actual tap. It's 27 tpi, which does not match any usual screw pitches.

Thank you for the help

For 1/8" - 27 pipe threads the Starrett Tap and Drill chart suggests 11/32" drill size. When you thread the holes with a pipe tap, only insert the tap about halfway. This gives you an option to customize how deep the mating threaded part will go into your pod.

Thank you BA for the tip, I did get a 11/32" drill and all went fine.

Here is the revised vacuum header I did for the podz. The podz shown is a 1/2" thick aluminum 4"x 6" plate with two 1/8" tapped holes at the bottom and top. The top hole is plugged now but it will be used for other pods in the future. On the surface of the podz I have two 1/8" holes through the plate for the vacuum distribution.

The small valve on the left is for releasing the vacuum so I can remove the podz when I wanted but it looks like that I don't need it because when I shut the main valve on the right looks like that there is no vacuum left and the podz is free.

The self adhesive gasket on the top and bottom of the podz is 1/4" wide by 1/8". Tomorrow I will try a 3/8" rope gasket (baker rod) I have to see if there is any difference

The vinyl tube is 1/8" ID at $0.22 per foot rated for 55 PSI. I was hesitant to buy it because of the low rating but the stronger ones were too stiff and so I gave it a chance and it works

Putting a piece of aluminum on top of the podz it holds rock solid and the pump did not cycle on my test

Don't know if its worth to spend the time to make some grooves on the surface of the podz for better vac distribution

Look at these pod covers, they have small areas that stand up and actually support the part so you always get a good Z 0 on your part.

I would suggest you cut some grooves in your pods, and they only need to be 1/16" deep and 1/8" wide.

Your project is coming along nicely. Keep up the good work!

BA

Nice collection of pod covers you got BA, I will do the grooves you suggest

One problem I encounter with my pod is that when I put an MDF piece on top the vacuum depletes quite fast and with a piece of plywood not as fast

Before I do a final cut in aluminum I always do a run on MDF to assure all is ok (cheep insurance)

I wonder if there is a fix for that; perhaps paint the underside of my MDF?

One thing we did to combat the vacuum leaks through the wood was to use clear 2" packing tape on the underside of the part where the pods line up on the tape like this sketch.

The tape stops the vacuum leaks and is easy enough to remove after you're done routing.

BA

Great idea BA and so easy, thanks

I'm very happy and will try it soon I have a chance

Got 3 more pods made and now I have a total of 4. Did an experiment to see how an MDF piece hold but it looks like that I have to dress the MDF completely with wrapping clear tape otherwise the vacuum depletes rapidly.

Putting the palm of my hand on top of the MDF and turning ON the vacuum it's amazing to sense the force of the pull thru the1/2" MDF

Perhaps it may be better to seal the MDF with clear plastic poly because it's PITA to cover it with wrapping tape including the edges

In addition, lets say that I do seal the MDF with whatever method but when I start to do any cut on it with the cnc, the vacuum will start to leak rapidly. So it looks like that the pods are no practical for MDF.

I will wait now next month when I order my 1/2" aluminum plates to give a try with them

If the MDF is that porous, it should soak up any paint applied to it. Once the paint dries, the MDF should have no more vacuum leakage. The thinner the paint, the more of it will soak in, but it also might swell more also.

Thank you Bob but I decided MDF is not practical to hold with vacuum because if every time I want to cut an MDF piece I have to paint it first its PITA

So when I want to cut MDF I will use conventional holding methods and I will use the Podz when I cut aluminum