vaccum or press ?

[alexisg1]

Hi everybody,

first of all, this is my first message on this forum and I'd like to say I'm sorry for my english (I'm french...) and secondly, I hope this message has not been proposed too many times I made a search on the "search engine" of the forum but did not find the info.

Well, if I'm here, it's because I'm preparing for the construction of my own pair of skis ! Youhou ! The main problem seems to glue everything together (at leat it will be one for me, because of the required materials and space). Now, one alternative to the press for skis, and mostly for a first try, is to use a vacuum system, right ?

So my question(s) would be:
- what advantages has the press compared to a vacuum system ?
- is a ski as durable if it has not been pressed ? (material cohesion)
- what pressure is required ? I know somebody who went down to - 950 millibars (relative !), is that gonna be sufficient ?


thx !



PS: First day of ski yesterday, first pow...nice

[Idris]

First welcome.

Your question is one I had to ask myself. I had started to get together the stuff for a Press. But the space, or rather the lack of it, more than anything (the expenses cab avoided or reduced by being clever with materials) made me go with vacuum.

I hope to be building my first pair of my own skis in the next day or two. I will be using vacuum. I have spent the Autumn working with PMGear (full report soon) using a heated press running at 100psi and 85C. After reading all (yes all) the posts here. But mainly Davide's posts I decided on vacuum.

After being lucky enough to meet Davide at his lab in Geneva I feel confident that I made the right choice from a simplicity point if nothing else.

I also in France (sorry I'm Welsh not French). And yes the snow was nice yesterday.

http://www.tetongravity.com/forums/show ... hp?t=70105

[alexisg1]

nice photos !

huh huh...welll, after reading buuk's description of his press (and the price : 200 euros), I was seriously thinking of building one...but now...

I am gonna try to find Davide's thread and see how he makes it work.

I guess the main problem, except the builind part, is to reach is sufficient level of vacuum...I'd like to know more about this acceptable level


damn I can fell how bad my english is...

[davide]

T'as oublie la troisième possibilité: une presse avec de serres-jointes (clamp press): c’est pas cher, mais il faut plus de travail pour la construction que un système sous vide.
En tout cas, il ne faut pas une montre pression pour coller tout ensemble: récemment on a presse sous vide une paire de miniski à -0.4 bars seulement (dans un moule alu professionnel), ça vaut dire environ 4 t/m2.

[alexisg1]

Salut et merci pour la réponse...je continue en anglais, c'est plus correct (poli).

I also have been thinking of a clamping press, but I could not find any picture or design of one, and I have no idea of the pressure you can reach with this. Anyway I trust in you saying high pressure is not required.

Another question is: is heat absolutely necessary ? With a vacuum system, people don't heat, but most people using a press do. What to think ?

[davide]

C'est pas de nouveaux trucs, alors...

Search in the forum, you will find some clamp press design (windsurfer did one). A friend of mine made a couple of skis with clamps.

Heat is needed only to go faster: actually it is more difficult to press at high
temperature (different thermal expansion of the materials).
Adding heating to a vauum system is anyway quite easy.

[Idris]

A cheap/free vacuum pump is a fridge motor. It can pull quite a high vacuum, just slowly.

[alexisg1]

yep, the guy who's motivating me is using that kind of device. Looks good, but I'm kind of perfectionnist, and like the manufacturing stuff as much as the result

I can't post links yet, but his story is quite exemplar in terms of motivation without much resources

[Skivolkl]

From my experience using both a pneumatic press and a vaccum press I would suggest that you go the route of a pneumatic press.

I started out using a vaccum press with a vaccum pump from a concrete core machine (very heavy duty). This set up worked but I was never able to achieve the amount of pressure I desired. During some events it seemed that it was even dificult to pull the core to the base of the ski at the tips and tails. There seemed to be too many source of error with this method (i.e. you have to worry about your pump giving out during pressing because it runs conituously, leaking along the vaccum tape and obtaining consistant pressure between different batches of skis. I would stay away from using an old refrigerator pump, the chances of it crapping out are high during pressing. The reason most refrigerators are discarded is because the pumps go bad.

Since I have switched over to a pneumatic system things have been like night and day. If you can seel your bladder so there are no leaks your compressor doesn't even kick on after your bladders are inflatted. As a result your don't have to monitor your pressing operation as much as with a vaccum system. If you have a regulator on your system you can also dial in the amount of pressure to exactly what is desired each time you make a ski. This comes in handy for quality control and for comparison and refining your product. The more constants you have in your operation the easier it is to determine where your sources of error came from because you will have sources of error in your first few pairs of skis. A cheap and good way to heat your pneumatic press is to build a insulation box around it. Check out hoseman's build. I built a stucture similar to his, however I heat mine via forced air with a wood stove directly piped to it. I have been pressing my skis at 130 degrees for 5 hours and then allowing them to cure for 12 hours at room temp before taking them out of the mold.

Anyway good luck with what ever method you decide to use, it is possible to make some sweet skis with both methods it just take a little trial and error to trouble shout the problems.