Thread: Vaccuum Press

I havn't tried vac pressing but read the article with interest. The fridge compressor idea seemed a bit rough but would probably work.
A mate of mine is currently treasuring the vacume punp from his old dairy with the intention of using it for wacume pressing.

With the dairy industry in turmoil could be a good place to find a serious vac pump. MMOOOO.
I would be interested to hear any experiences & comments too.

The current edition of one of the UK WW magazines has a user report on a vacuum bag kit. The kit (?? available in Oz) has all the bits to make your own vacuum press and uses a venturi valve, I believe, to create the vacuum. These little things (venturi valves that is) utilise an air compressor to force air through them at an accelerated speed. The accelerating air passes by an outlet (inlet?) in the valve which is attached to the vacuum hose. The effect of the air rushing past this outlet at high speed is to create very low pressure at the outlet and hence into the vacuum bag. Atmoshperic pressure then pushes down on the vaccuum bag to create the clamping effect.
The advantage of this setup is that the venturi has no moving parts and is virtually idestructible. You don't need a vacuum pump (expensive I believe and prone to breaking down from what I've heard), only an air compressor, which if you don't have one can also be used to run simple tools, spray guns etc. The disadvantage is that the clamping pressure is limited to atmospheric pressure, while I believe vacuum pumps can generate more suck!!

Veturis can also be used to create a whole range of clamping jigs, self clamping patterns and finger boards etc. Because a machine is not constantly sucking (I don't really know what the correct term is) venturis can be used for long periods of time without excessive strain on a machine, the compressor just keeps blowing out a stream of air. This is why the old faithful vacuum cleaner can't be used for vacuum clamping (try putting your hand over the end of the hose for more than a few minutes). Although I did read once in the Aust. WW someone suggesting drilling a small hole somewhere in the vacuum cleaner to allow a small amount of air to be sucked in constantly while the end of the hose is effectively blocked. It would be a brave male who tries this one!!

I'm no expert on venturis and such, my info comes from Mr Bill Hylton and his great book "Router Magic, tips and tricks to unleash your router's full potential". He's got whole chapters on building vacuum clamping jigs and fixtures with all the info you need. Check the Router Forum, under the topic router tables for more info on this book and its ISBN if interested.

On a side note, I've often wondered if those vacuum bags you see advertised on TV for storing winter clothes and pillows etc could be used for vacuum pressing. They're quite cheap and use a houshold vacuum to draw the air out and a one way valve to maintain the suction - no excess strain on the old vacuum cleaner this way. To release the vacuum you simply undo the ziplock on one end. Again, only atmoshperic pressure is probaly possible but for smallish, flat or slightly curved surfaces this may be a cheap way to get into vacuum pressing.

Hope this helps

Cheers, Tim

PS: soundman, whats wacuum (or is it wackuum) pressing. Is that something special you speaker box making guys do?? Or is it something you do with a heavy piece of wood, maybe one that could also be used as a doorstop??

Never used one myself for wood work but...when I was making litho printing plates we had a vacuum press to keep the film in contact with the printing plate before and during exposing the plate.
Now, there must be a few old litho printing houses or suppliers around that may have a vacuum pump going cheap.
The thing Im a but fuzzy with is .. if a vacuum press is used for say laminating and you have a bubble of air trapped in between the two surfaces, when you pull a vacuum, the air bubble will get bigger as the vacuum increases. If that don't get popped-out you would have a bigger area unstuck....or am I just getting myself unstuck ?

Regards
Sandy across the ditch

One small, rather pedantic point: the pressure holding your jig is never going to be more than atmospheric pressure (unless you live on Jupiter). The minimum possible pressure that a vacuum pump can give you is zero absolute, or minus one atmosphere gauge pressure. Of course, most vacuum cleaners won't get all that close to this.

For those uneducated a wacume is either a rapidly developing drop in air preasure or one developed in a quasi german manner such as found in the inlet manafold of a small rear engined car.

As for the houshold vac problems.
Some vac's use the suction air to cool the motor. no airflow, no cooling air, cooked motor.!

Some commercial vac's have what is known as a bypass motor where the suction air and the cooling air are seperate. a much better option. look for this when buying a industrial vac.

concerning ventury vacume devices they are easily available from most air equipment manufacturers such as norgren, festo & smc.
However their air consumption may be a concern if you have a small compressor.
A realy switched on fitter & turner should be able to whip one up prety easy.


Now. Does vonrek know wat a punp is.

Atmospheric pressure at sea level is 14.7 lbs per square inch. If the pressure in the vacuum line using a venturi could be reduced to, say 12 lbs per square inch or a differential pressure of 2.7 lbs per square inch, then a surface of twelve inches by twelve inches would provide a total sucking pressure of 388.8 pounds. Does that sound right Tristan?

Seems pretty efficient to me. Sorry about the imperial stuff – haven’t quite grasped that new fangled metric gobbledegook.

I've recently used a vacuum bag for laminating and forming, with impressive results. The bag is made from a sheet of medium weight vinyl folded and joined round the edges with yellow-tack. The pump is a small electric job that is left to run all night. Adhesive is 2 pot epoxy. There is also a fitting to join the hose to the bag. It attains about 60% of full vacuum, which, if you do the numbers, means that on a square foot of material, you have a force of about half a ton. This tends to hold the job down quite well 'til the glue dries.

Surprisingly, the bag hasn't had any punctures despite being forced around sharp corners.

I'll get details of the pump and bag and post later.

Addendum

Sorry Tristan, just having a bit of fun.

I agree that a vacuum cleaner would be hard pressed to provide the necessary suction.

The venturi requires a motive flow of air through it to generate suction. Something to do with Bernoulli’s theorem. Total pressure is the sum of dynamic and static pressure. If dynamic pressure is increased (motive flow or velocity) then static pressure within the venturi will reduce. Static pressure is ported in the wall of the venturi. The shape of the venturi is important. The rest is done with mass x velocity squared. Would be very easy to design and build.

We talk this lingo where I come from!

Thanks all for the reply's.
I've seen in the latest Australian Wood Review magazine that there is a place in W.A advertising Vaccuum press gear on his site at www.cloudmaker.net.au i'll check the site out and see what it has available


[This message has been edited by Biggles (edited 15 June 2002).]



[This message has been edited by (edited 16 June 2002).]

Sorry his / her site????

As with manual clamping do you get the same amount of "deflection or spring back" when vaccuum pressing or can you make the form exactly to the required shape.I presume the glue would determine this to a fair extent. I am thinking of making serpentine draw fronts and would'nt like them to vary too much...Any thoughts on the matter would be appeciated.Thanx

[This message has been edited by Biggles (edited 15 June 2002).]

Hi all. Have found a site which goes into making a press if you are interested. http://www.joewoodworker.com/veneering/welcome.htm

[This message has been edited by Biggles (edited 18 June 2002).]

I have never used vacum presses for woodworking however I did use them extensively for veneering model aircrafts wings (some rather big, up to 6m) and my experience may be useful to you.

- The pressure you obtain as already mentioned is rather high and it is independent of the area you press so it make is very suitable for large areas, but it works very poorly for thick pieces.

- The fridge pumps work quite well but there is a few things to take care of. They must not operate non stop for extended periods, you need some pressure switch, either commercial a one or home made with mercury (which i dont reccomend). The other thing is that if you glue with epoxy (which you may use as pva does no dry very well without air) you need some sort of filter to preserve the pump.

- The bubles of air or unequal pressure can at times be a problem but you can overcome if by inserting one or a few strings or small diameter rope in your bag trough which the air will circulate.

- To attach the hose to the bag I had a pipe with a tread and a plate to the bottom a nut and washer, a bit of clay makes wonders to make it air tight.

- I was doing the bags myself with thick packaging plastic joined with tape, as surprising as it may seem you can get something very air tight with tape and flat surfaces, again clay fixes the rest.

- You must be very carefull to not damage the bag and everything must be very clean but again tape is the best way to fix the holes.

- Another thing to be careful if you use thin veneer is that the gule can get sucked in across the veneer and it is then virtually impossible to sand it down if you use soft veneers, experimentation will tell you how much glue is optimal and generally very little glue is enough.


All this may seem like the poor's man solution but well I was around 20 when doing this and I was student so cash was a real issue, but the results were very good and my models were competing at international level. If I ever need to do veneers I guess I'd get back to this solution.

Hope that helps

Jack

Originally posted by Biggles:
Hi all. Have found a site which goes into making a press if you are interested. http://www.joewoodworker.com/veneering/welcome.htm

[This message has been edited by Biggles (edited 18 June 2002).]

Hey great site. Now I need to work out a way I could make use of a vacuum press

Cheers Ray