Technique: Laminating by Vacuum Bagging
Background:
Vacuum bagging is used all over the world to press stuff together...furniture builders use it...instrument builders use it...everywhere strange bends or smooth flat surfaces are needed, and be pressed, they use it...
I'm about to start with the thing but still have to do some work on my vacuum pump...
Again Grega from Slovenia supplied me with info and pictures on how he uses the technique in a simple straight forward way...it's still a bit more of a technical technique though...and you have to be a bit handy to get things right...
1:What is vacuum and what can it do for us: Some Physics
I'll try to explain it in a simple way...(using the metric system):

We are surrounded by air...and that air presses on-to us and everything with an average 1Kg (1000Grams) per square cm (cm²) at sea level...(the higher you go the lesser air pressure)...Imagine that you've got a open plastic bag in front of you...with the stuff mentioned above, you can understand that the pressure on the outside of the bag is the same as on the inside...
Now, if you close that bag and suck all air out of it, then that pressure on the inside is gone and you're left with 1 Kg/cm² on the outside...you can say that there's a "vacuum" (a kind of "nothing-ness" situation) in the bag now...and all that would be placed in the bag would endure 1Kg/cm² on it's surface...simple isn't it !
It's impossible to get all the air out of the bag...scientists have quite performant pumps at their disposal to nearly get there but still...it isn't possible to get a absolute vacuum

We will only need a partial vacuum...not all the air needs to be out of the bag but still quite a lot of it...If there's still some air left inside the bag then that means that there is still some force pressing against the inner side of the bag...So, the air on the outside will be pressing with something like 400Gr/cm²...so, vacuum can be rated in grams/cm² on the outside (or pounds per square inch (psi) if you are not using the metric system)
Pure scientific measurement is centimeters or inches of mercury (Cm/Hg or Inch/Hg)...but that's another story... :-)
2: The above applied:
We will need some tools...an airtight bag to keep the outer air on the outside...and a pump to pump the stuff out of the bag to get a vacuum situation...
The Bag:
This bag has to be airtight and reasonably flexible because it will have to follow the contours of our mold and anything we want to be pressed onto that mold...being plywood or veneer or even epoxy/glass fiber/wood assembly's that have to turn into decks with noses and tails or other experimental bends ;-)
A piece of vinyl sheet is a good and cheap alternative to high quality rubber to construct the bag...it can be glued easily into a bag of the right dimensions needed...and you can see through it!
Here's a nice link at www.joewoodworker.com ...the section on building a vacuum bag is fabulous! What more can I add to it...only the size of the bag would be different...
The Pump:
This is something else...like mentioned in the Physics section on this page...a good vacuum pump is expensive...but there's a alternative...yep, a fridge compressor...
I can hear you think "huh?...a compressor?...that's to compress air!"...indeed...it can do this also but it has a double function inside a refrigerator...it has to build a low pressure on the vaporizing side and it has to build a high pressure at the condensing side...Never mind this vaporizing and condensing bit, we don't need the info, but here's a simple explanation for those that want to know more
I'm also a qualified refrigeration technician, and I'll have a go at it...

A liquid vaporizes easily in a low pressure environment and to do that it needs heat...this heat is taken from the closed space where your food sits...after vaporizing it is sucked through the pump and comes into the high pressure environment created in that radiator at the back and condenses again into a liquid, giving off heat caused by being compressed and also the heat it took up from the inside of the fridge...then the cycle can start again...it is a plain heat pump system, transporting heat...the liquid used in the old days was actually a gas called Freon...The good environmental laws made us switch to a more ozone friendly substance...

The low pressure side of the pump is what we need...because it can get rid of the air inside the bag...like mentioned above...we don't need a absolute vacuum...we can do with 300 to 400 grams pressing on that bag...If you would glue something that is 1 m² (10.000cm²) then that would equal with about 3000 Kg to 4000 Kg pressing onto your stuff !!!!...
A longboard is about 120 cm by 24 cm, that's 2880 cm², not taking notice of the real shape, this still means about 1152 Kg pressing on it from the outside of the bag when using 400gr/cm² vacuum...
You can't get even near to this with the simple wooden press I've made...
The Pump: a small note on refrigerator pumps
A refrigerator pump has an oil bath to keep things running smoothly...when running, the oil is circulated by the electrical motor axel...In a fridge, the pump sits in a closed circuit and the oil drops always get back towards that oil bath at the underside of the pump...
When using the pump as a vacuum pump, we will lose that oil bit by bit through the outlet of the pump...this process will take quite some time but in the end all oil will get out of the pump...
A small modification would allow us to check the oil level and fill it up again...or capture that oil and transfer it back...but I haven't worked that one out yet...any suggestions to solve the oil problem are welcome!
As we are sucking air out of the bag, we will suck moisture along with it...this also affects the oil and its lifetime will shorten...
Joe from www.joewoodworker.com sent me an email with some solution to the oil problem:

"I did want to add one comment about using a refrigerant compressor for vacuum. I have a few customers who built vacuum systems with a refrigerator compressor. To stop the oil from spewing out, they manipulated the copper tubing upward by 10" and coiled it around a piece of pipe (just to make the coil shape). They claim that gravity keeps most of the oil in the unit."

This is indeed a plain forward way to keep oil in the system...
The Pump:how would a semi professional set look like ?
The electro valve;
Why the electro valve or solenoid valve ?...well, when that fridge pump switches off, the valve inside the pump can't hold a vacuum...it doesn't seal to well and air can be sucked back into the bag...By this you lose your vacuum and the thing keeps pumping every now and then...when placing a mechanical valve at the inlet of the bag you won't be able to gauge or switch the pump action
The differential switch;
This one is there, in the low pressure circuit, to decide when to switch on the pump again when the vacuum is disappearing by the bag or system not being airtight enough...there's always some leak problem...any material we will use is not completely airtight...this is molecular science ;-) ...it also steers the electro valve...by this you can leave the lot to harden over-night...
The gauge:
The gauge is the right thing to keep track of pressures or vacuums inside the bag...a good tool to fine tune your differential switch and to see what is going on...
Grega's setup looks a bit different...but does the same thing...
You can see the gauge, the bag and a home made vacuum switch...It's a simple and cheap setup that can be used over and over again...
This is the vacuum switch Grega made using a membrane that can be found in cars...yep,it's the one that is used to alter the ignition timing...I don't know if they are still used in modern electronic ignition cars but this is a cheap way to build a switch...just make sure it doesn't leak...
It's actuator rod is connected to a micro-switch, and this switch steers the pump...
The gauge has a scale between 0 and -1.0 Bar...straight forward to read and you see here that Grega has about -0.55 Bar on the scale (this one has steps per 4 units)...This means that he has 550 Grams pressing on every square centimeter of his vacuum bag...His pump can suck to -0,8 Bar, but this would ruin a hard foam mold...about -0,5 to -0,6 does the trick...
The inlet of the pump is connected to the bag using a plastic tube that doesn't collapse under vacuum...it can be a bit difficult to get everything sealed...
The tubing and the gauge are the expensive bits of the system...the pump and the membrane can sometimes be obtained for free at junkyards Grega says :-)