Made my own Venturi...

[Zippi]

I bought a vac-clamp to see how it would work with my X2 mill. I have a few issues with it, and decided that if I could cut a decent venturi, I'd build my own vac table. I have the venturi done, and it works as well as the venturi in the vac-clamp. It needs less air than the vac-clamp, so my compressor will run less. I don't know about suction CFM, but it seems to be capable of the job.

About the venturi:

I machined the "catch" off of two brass 1/4" NPT quick-connect air hose couplings. I used a piece of C360 brass for the jet. The couplings and jet are press-fit together, with a bit of 603 Loctite for good measure. I did this on my lathe. I adjusted the depth of the jet for best suction. I used the vac-clamp's table to test the vacuum of my venturi, blocking the vac-clamp's exit hole. Pulling off .2" acrylic, I could tell no difference in the vac-clamp venturi versus mine.

Using the quick-connect couplings made this really easy to do.

The sketch isn't quite to scale, but you get the idea.

Enjoy,
Paul

[zoltan]

Hi,

Could you, please, give more details? I do not recognize all the pices from picture into the sketch. Some more dimensions will be great. I am not very good at pneumatics as I did not work with. More than that here we use metric system and I need some references to be able to explain to a workshop what I need to be done on their lathe.

Thank you,

Zolatn

[JFettig]

How much force can be exerted on one of these vacuume clamps?

I am relatively interested in making one of these for myself if they really work that well and can be made that easily.

Do you have some dimentions of the venturi you made?


Thanks,
Jon

[miljnor]

DITTO!

what jon said!

[High Seas]

How's the noise compare to the one you bought? (Admittedly the compressor is probably - Loud anyway) It would be a great excuse to get the compressor I've been looking to get and give the wife back her shopvac!
Jim
oh - yeah - what jon said goes for me too - maybe easier to put in the downloads somewhere?

[Geof]

Originally Posted by JFettig How much force can be exerted on one of these vacuume clamps?....

The maximum force you can get is 1 atmosphere of pressure, 14.7 psi, if you are able to draw a perfect vacuum. The best vacuum you can get with a venturi is about 90% of a perfect vacuum which is about 13.2 psi. It is fairly easy to get around 60% to 80% of a perfect vacuum with venturi which is between 8 and 9 psi. This does not sound like much but if your part has a decent sort of area the total force holding it down can be large; at 60% vacuum one square foot, 144 square inches, is clamped with a force of 1152lbs. All this assumes your system does not have any leaks; venturi vacuum generators cannot overcome leaks.

[Zippi]

Hi,

There are exactly four parts to this:

Brass Jet
Two quick-connect fittings
Alumunim Body

I don't have exact dimensions. I press fit the parts, so I used ordinary drills and cut down surfaces to match the holes as drilled (except for the air inlet, I bored the hole to match the outer diameter of the quick-connect coupler in the body as a press fit).

I'll make another one, take lots of pictures, and post a step-by-step "how to".

The most critical part is positioning the jet without damaging it. I had a tight fit for mounting the jet. I tapped the jet in very slowly, checking alignment with the bit I used to drill the jet. Not very scientific, but it worked. What I noticed is that when you get it lined up and close, there's no doubt about it. You get suction.

If you build this before I get a "how to" done up, it's important to note, the maximum pressure you could possibly get from the area off the vac line quick connect fitting (mine is .350" inner diameter) is:

R^2*Pi=Area of circle
.175^2*(22/7)=.09625 square inches of are for a .350" inner diameter tube.
.09625*14.7=1.414875 lbs

Again, you will perceive an absoulte maximum (if the venturi were able to draw a PERFECT vacuum) of only 1.414875 lbs of force at a .350" diameter opening on the vac line (meaning less than two pounds would be needed to pull your finger off of it, and that's if you were able to seal the end perfectly with your finger, AND pulled your finger off of the entire circumference at the same time- not going to happen! ).

It doesn't seem like much, but that would equate to 14.7 lbs per square inch.

If you can only get 10 pounds per square inch out of a venturi, across 32 square inches, that's 320 lbs. If a vacuum only yields 10 PSI, you'd need less than a pound of force to pull your finger off the end of a vac line with a .350" diameter opening.

At first, I didn't think I quite had it right because the draw from the vac line wasn't what I expected. Then I did the math. Then I hooked it up to the vac-clamp's table. It's right.

This venturi doesn't need or want a LOT of pressure. I ran it off an air tank charged to 100 PSI. It started working it's best somewhere below 60 PSI. It held pretty tight at 20 PSI, and finally let go of a piece of acrylic on the vac-clamp table at <5 PSI. The vac-clamp product has a minimum of 80 PSI. Obviously, I need to experiment more to determine the best operating range. I need a vacuum gauge, it would help a lot.

I'll be machining a 1" thick alu slab for my table and use EPDM foam (same stuff used on the vac-clamp product) to make the seal. I plan on using this with non-porous surfaces. Using a vacuum table makes the most sense for me, even with a venturi pump (low volume draw).

Again, I'll build another one (it's easy and they're useful) and take lots of pictures and measurements.

Thanks,
Paul

[ger21]

I made a vacuum veneer press with this Harbor Freight venturi. http://www.harborfreight.com/cpi/cta...temnumber=3952

It has a resevoir and switch, so the compressor doesn't need to run constantly. I can pull about 27" Hg with it, or about 13psi.

For more info on the whole setup, see the plans at www.joewoodworker.com

[Mcgyver]

Zippi, cool idea, thanks for sharing it.

[vacpress]

"Made my own Venturi..."


rad

[shark]

Hello guys. Today I've made my own Venturi too, based on the sketch from Zippi. Thanks Zippi.

The Venturi is made from 3 brass pieces and one plastic chamber.

The first brass piece (the rightmost one) is a quick-connect air hose coupling. I adjusted the thinner end to be exactly 6.05 mm in exterior diameter, to match my 6mm drill for the plastic chamber.

The nozzle is second brass part from right. I machined the body to fit the inner diameter of the hose coupling (about 4,5 mm). The cone on the end is very important; it has an agle of 16 deg (15 to 18 seems fairly good) that allows it to extend about 18,5 mm in the vacuum chamber, covering very well the suction hole on the bottom. (~5mm)

The third brass part (the suction coupling on the botton) is somewhat too complicated for its role. Anyway, I am planning to use the vacuum pump not for a vac table (as most of you seem to) but for bleeding the brakes on my BMW. Therefore, the suction coupling matches the various tubes and connectors used in the process.

The design is very simple and also very tolerant to errors. The three most important things are the inner nozzle diameter (1mm), the output inner diameter (2.5mm) and the suction part inner diameter (2mm). I found this values by making 4 testing vacuum chambers with different parameters until the I've got the best suction. The nozzle position in the vac chamber is somewhat important too. I tried different positions until i got it right (somewhat very very close to the output hole).

If you are interested in more details, I've made a couple of photos of the parts as well as sketch, to the best of my abilities. The sketch is also in CorelDraw 13 format (the zip file), scaled 1:1 so you can actually measure on the sketch any dimension you want. In fact, Corel has a very good measuring tool.

Well tha't it. A couple of words more, for the ending, a sort of FAQ:
Spelling. I am sorry for amy spelling mistakes I may have made, but English is not my native language.
Why I did this? Well, here in Romania, things are a little bit different form other places. Tool professionals didn't even heard of Venturi before, so imagine what happens when I want to buy a redy-made venturi pump. A ... what? they ask ...
So, i needed one. Starting from Zippi's idea, I made a few testing of my own, and, "voila!".
Sketck errors. If any, remember I am only a hobbist machinist, and the spare time is little.
Well, I guess that is all. I hope you guys find it useful the few pieces on info I have shared. If you have any questions or, more important, upgrading ideas, please fell free to tell me.

Oh, I almost forgot! How does it perform? In one word: WELL! I don't have any means to measure the vacuum, but if I try to extract the air from a plastic bottle, well, let's say it becomes **very** thin. I found out that the pump is most efficient at about 5-6 bar of comressed air. Anyway, it is way to powerfull for bleeding the brakes. I generaly use it with 0,5 - 1 bar of compressed air.

[Mcgyver]

Shark good job and thanks for sharing - your English is fine - as good or better than many for whom it's their native tongue.