press vs vacuum

[ganipilo]

Hi people, as I'm new into this world and also a frenchspeaker I could be unclear in my posts. I apologize for this.

As I'm juggling with the idea of making ski of split board I'm searching a cheap way to achieve this goal. Of course the press is a major concern.

Clamp press seem to be instable, Due to the deformation of wood, I think that they may be irregular (different pressure on different part of ski, unreproductible results, etc). It's a cheap way to press ski but still tricky. I'm right?

Big ski press are dificult to build (welding is not accessible for me) and wood is very massive. I don't have a lot of space. It's seems to provide a good pressing quality (everyone here seem to use this kind of press). Because of the big quantity of wood and metal it needs, and the fireman hause, it's also the most expensive option. I tough it was the best way to make skis because it looked far more simple than vacuum.

BUT! Today I saw that it was possible make a vaccuum pump with a refregirator compressor for a total price of 20$!
Is this cheap enough for me? Yeah! But I'm concerned about the vacuum streght. The vacuum pressure is the good term? If someone is pressing a ski at +50 psi with a air press, is it meaning that with a vacuum press you should press at -50 psi? I really doupt that a refregirarator compressor is strong enough to suck that much pressure out of a bag...

Why everyone is using air press? (except some people) And why people like Big Kam made an air press even if they already have a vacuum press?
I understand that it's more forgiving but is it a difference in the pressing quality?

I know you'll tell me that being cheap is not compatible with ski building, but I'm just trying to find the most economic way to achieve this. University doesn't pay me for studying .

Anyway, I really enjoy your reports on ski building.
A hippie guy I met would say "so much good vibes in this forum".

En passant, bonjour à tout les québécois! (Si il y en a.)

Ganipilo

[falls]

Salut Ganipilo
You can make good skis/boards using a vacuum press. You can make better skis and boards using a pneumatic press.
The vacuum press will probably be cheaper to setup, but there are more disposable items in vacuum pressing (eg. breather fabric, vacuum tape and bags).
I think my pneumatic press (without the heater) cost $350 for the metal. Free welding by a friend. Hoses $100. Hose fittings and end clamps etc about another $100. Cat track of aluminium $250. Paint $50.
Air compressor $200. So a little over $1000 (australian). There is also additional wood in their for the top mold which you wouldn't need in a vacuum setup - so maybe add another $100.

In terms of vacuum strength.
The maximum pressure you can apply is the same as the negative of the air pressure the press is in. Normal air pressure I think is about 14.7PSI. So if you use a vacuum in normal air you will be applying 14.7 PSI to the layup. If you have an autoclave/pressure chamber you can put the vacuum press in then you can pump the pressure inside it to say 50psi. So then when the vacuum sucks the air out of the vacuum bag there will be 50PSI of force on the layup. (This is my understanding of vacuum pressing - please someone correct me if I am wrong).
Obviously attaining a pressure chamber may be much more expensive than building a pneumatic press.

Good luck.

[nrgboards]

Have you considered using a clothe press much cheaper than a steal press you still can achieve high psi with this type of press and its easy to move around. If you go on youtube you can see this type of press in action its listed under 2shopvacs.

[ganipilo]

Yes, this is my second option. Especially because I have acces to Cordura 1000 and some tubular climbing webbing... why do you use cordura tube instead of wrapping the superior mold with tubular webbing?

The main problem remain into buying a fireman hose... A vacuum setum would cost me under 100$ (with a refregirator compressor) and just the fireman hose is about this price. And I don't have a compressor... I planned to use my bike pump but I really doupt that the hose setup can confine air with a pressure of 50 psi during 24 hours...

Thank you "falls" for your explanation of vacuum pressure. Very instructive.

Why the pneumatic press offer better result than the vacuum press? Is it a matter of pressure? Is it because it's easyer to press with a bigger pressure using a pneumatic press than a vacuum press.

Is the differrence between high pressure curing and low pressure curing is that big in term of quality?

Ah, so much things to learn about composite materials!
The school of life.

Ganipilo

[chrismp]

as for the hose why not go to your local fire department and ask them if they have some used hose that fits your needs? ...thats the way i did it and i got 20m of 75mm diameter hose for free (of course i donated a couple of beers).
i'm using them in a cordura frame press and they're working like a charm.
you don't necessarily need a big diameter hose with this kind of press since you can put a couple of hoses next to each other (it's five in my case, but we're building snowboards) and you can always put some scrap wood in the press if your cordura bags are too large.

[ganipilo]

What an idea!

Why I didn't think about it before! Thank you so much for the hint!

[originskis]

ganipilo-
the reason we generally don't use webbing or straps is becuase of the pressure distribution. a wide sleeve of cordura distributes pressure more evenly than a thin strap. hope this helps.

[falls]

The cloth press is a great idea!
You would be surprised how well the hoses can hold air without a compressor topping them up. Pumping them to 40psi with a bike pump will be fine just take a bit longer than doing a bike tyre. If you think about it when you pump a bike or car tyre up to 40psi it will still be at 40psi 24 hours later. Even weeks later! There is no reason you can't seal the hoses well enough so they too hold air like a bike tyre.

In terms of quality from vacuum or pneumatic press it is a good question. Most of the information I have is just from reading this forum so I don't have practical experience with the products created by either method.

For pneumatic:
pros: makes ski conform to mold shape exactly without the need to preform the wood or plastic and edges (although you still can do this).
More pressure produces more epoxy squeeze out so a lighter end product.
Less disposable materials.
Less electricity use and noise than vac pump especially if you pump your hoses with a bike pump!

The big question about quality I don't have an answer to but have always wondered is whether pressure improves the cure or strength of the epoxy?
Heated cure will definitely improve epoxy strength but does pressure improve strength and adhesion?

[Jekul]

One other thing that hasn't been mentioned yet in this post yet is the type of ski you would like to make. You have to ask yourself if you want to make a sandwich construction ski or cap ski.

Pneumatic presses are the better choice for making a sandwich construction skis/snowboards. The pressurized tubes do not conform well laterally to the shape of the ski or snowboard. The addition of a cat track to disperse pressure basically eliminates the ability to conform to the sides of the ski.

Conversly a vacuum bagging system allows the pressurized portion of the mold to apply even pressure to all dimensions of the ski. However the pressure is significantly less than the pneumatic press.

There have been people that have incorporated capped skis in their pneumatic press, however it is significantly more involved.

[ganipilo]

People using metal part to reinforce wooden mold (to annulate de linear deflexion) apply the same force repartition than webbing would do, no?

Yes laying a hose at 50psi during 24 hours is far more easyer than trying to maintain vacuum into a bag for the same time... It's a new variable in the equation.

But what is the effect of pressure? It helps to keep a good ratio of resin vs epoxy?

Thanks everyone your helping to push my reflexion far more than I planned.

[nrgboards]

I got my hoses from the local fire dept also. I donated my time to the local girlscout troop carry tables around town to various locations to sell their cookies (they borrowed the tables from the fire dept)and the fire dept had a storage room full of old used hoses and equipment and they let me have whatever i wanted. Good luck with your build post pics so we can see your progress.

[ganipilo]

Ok, even if the pneumatic press seems more accessible I'll build a vacuum system because I want something polyvalent.I may change a lot my molds to make differents kind of skis. Actually I plan to make Telemark and cross country skis for me and my brother (who's smaller than me) so I will build different lenght of ski. I also may build a "pulka", wich is basically a sled. So the vacuum system will give me more versatility.

When I'll be comitted into ski building and when I'll find the best kind of ski that suits my needs, I'll make myself a pneumatic press.

Thank you everyone for your advices and of course I'l post a lot of pictures of my construction. I'll start the building process in fall (north america) because I have some bike travelling plans in my head.

[krp8128]

Keep in mind that for a vacuum press to work over multiple sizes, either the whole mold must fit in a vacuum bag, or the mold surface FOR EACH SIZE must be air tight.

[agiocochook]

I'm just getting started too.....after a 25 year hiatus...and figured I'd use a vacuum press to get going -- a little easier and a little more familiar as it's what I used before. Anyhow, between "bagging" the mold or "blanketing" it and using vacuum tape to seal the edges, is one better than the other?

Thanks.

[Idris]

I'm just getting started too.....after a 25 year hiatus...and figured I'd use a vacuum press to get going -- a little easier and a little more familiar as it's what I used before. Anyhow, between "bagging" the mold or "blanketing" it and using vacuum tape to seal the edges, is one better than the other?

Thanks.

Bagging is far more flexible in what you can do. While blanketing is restricted to that individual mold.

I have been using the bag method but set up in an envelope fashion rather than the common tube.

Doing this I can lay up my skis (I always make a pair not singles) and then fold the top of the bag over without disturbing my work.