Advice on first press

[legon22]

I'm new to building skis, and I'm thinking about building a press. I'm trying to make it as cheap as possible, so I think I've narrowed my options down to a vacuum press, or maybe a screw operated one. What would be my best bet to get a usable vacuum pump really cheaply?
I've been thinking about a modified refrigerator compressor, but would a bike pump modified to pull a vacuum also work? Also, i've read through as many of the posts regarding vacuum presses as I can, and I'm reading about bleeder cloth and other things, what exactly needs to go into the bag other than the skis and the mold? Any other advice about how best to build a cheap first press or links to a post about that stuff that I missed?
Thanks

[Idris]

legon22, search for Davide's build log (sorry I'm too lazy to look it up) and all will be reviled.

I have made many skis with refrigerator compressors, they work fine - shut off valves and vacuum reservoirs (see joe woodworker) help.

Cheap bleeder cloth is called cardboard

My early vacuum bags consisted of a sheep to polythene and packing tape.

Mold...no, pre bend the tips, vacuum against flat maisonite (with pre bent tip in the maisonite) and clamp to a flat surface, then use wedges to determine camber, rocker etc.

[NinetyFour]

Hey! Are you razors-chaz from newschoolers?

We had a huge discussion on my ski building thread over at newschoolers, basically we totally nixed the idea of a screw style press.

http://www.newschoolers.com/ns/forums/r ... 76/page/3/

It's just such a complicated setup, and by the time you've done a layup, there would be just too much to screw down to get a really good press before you're epoxy started to gel.

Vacuum pressing on the other hand is pretty simple, loads of info on here, and works well. I'd suggest it over other forms of pressing if you're looking to stay cheap.

[legon22]

thanks idris, I've never heard of shaping a ski like that, could you elaborate more please? also, what does breather cloth or cardboard do, and where should I put it. Ninety, i'm not razors from newschoolers, sorry. Thanks for the interesting thread though, and I guess you're right about a screw press. Sorry to ask another question, but I havent found the answer so far- how do you get the attachment for the hose into the vacuum bag, and what is commonly used? Thanks

[twizzstyle]

You need to get some basic education on vacuum bagging - away from the SkiBuilders forum. There are some pretty simple basics here that you need to understand first.

Here's the first link from a google search of "vacuum bagging basics", it tells you all you need to know.

http://composite.about.com/od/aboutcomp ... 000109.htm

For skis you won't have to worry about peel ply or a perforated release sheet. You can be creative for a bleeder cloth, but actual bleeder cloth is pretty cheap (I've gotten it from Aircraft Spruce in the past, as well as Fiberlay which is located in Seattle). The bleeder cloth just allows to get full vacuum everywhere. Without it the bag can suck down and seal off areas in the bag and won't pull vacuum.

As far as attaching the hose to the bag... there are expensive attachment things you can get that have two parts that clamp on two sides of the bag. They're expensive. You can use a suction cup and poke a hole in the bag, that's cheap but they never stick... I just wrap a piece of vinyl tube (hooked up to my vacuum pump) with the sealant tape, and stick it in the side where the tape is (between the bag and the mold surface, if that's what I'm taping to). Works great, no leaks, and no cost.

I don't vacuum bag my skis, but I have done a LOT of bagging for other stuff.

I think it's worth it to invest in a real vacuum pump (vs modifying refrigerator parts). Ebay is a good source, I paid $100 for mine, it's a Gast and it will run for days and days with no issue.

(and I agree, forget the screw-press... been there, it's a waste of time)

[tomcat]

@Idris: What volume did your vacuum reservoir and what did you actually use for a reservoir? Btw, I envy you so much, reading what you wrote in you r profile at "Location"

For my vacuum set-up, I was thinking about using a fridge compressor and a vacuum reservoir with a vacuum switch in order to turn on the pump in case pressure between the tank and the mold rises above a certain level.

I haven't found any vacuum switches yet, so I was thinking about trying to build my own. I messed around with an Arduino Microcontroller programer in school and I already have done a project for reading a digital pressure sensor. I want to basically do the same thing, but move the microcontroller to a separate PCB, stick the sensor itself in a A small PVC pipe that will be connected between the mold and the tank. Then use the microcontroller to trigger a relay that will start de compressor once pressure rises above a certain level (I'll have to do some experimenting with that...)

The alternative is to just buy the "small pump" from fibermaxcomposites.com here(http://www.fibermaxcomposites.com/shop/ ... 4509bf6125) considering that the parts for the switch, pressure sensor and the fridge motor, together with fittings and all that stuff will probably be around the same price as the small pump. Do you think 2.5CFM is to little?

[sammer]

tomcat,
Check out http://www.joewoodworker.com/veneering/welcome.htm
Read thru it, You'll find a ton of info.
Most of it applies to gluing veneer to a substrate but it's all the same.
You can do away with all of it 'cept the tape, bag, fitting, and vacuum pump.
All the rest will make your life easier but it will work without it.
Corrugated cardboard will work as breather, but will leave a pattern on your ski if you put it on top.
I've used it along side the ski just to make sure I get good suction along the whole bag.

2.5cfm pump is pretty small and will take a bit of time to evacuate your bag but will work.
I'd look for something used in the 5cfm range.
Vacuum works pretty good. You have to make sure all your parts fit.
If I haven't built a ski for a while I'll do a dry fit, putting it all together dry before I mix my epoxy, so I know I have all my ducks in a row.

Good luck and have fun.

sam

[tomcat]

thanks for the reply and the link sammer!

Do you think it would be an ok solution to use mastic tape on the mold surface and just sealing off the top part of the mold, so there would be a smaller volume of air to remove, instead of sticking the whole mold in a bag?
Or am I just asking for leaks by doing that?

I made a quick calculation, and for a 200x40cm press with 10cm height for the bag, it would mean about 80 liters of volume; the pump can pull about 70l/min so this means it would take a little over a minute to get all the air out.

I was thinking about ordering peel-ply and some flow fabric from fibermaxcomposites.com. I want to do this as because I am considering doing a composite topsheet. I found some really nice and not that expensive fabrics(also at fibermax ) that mimic carbon fiber with red and blue accents on some of the fibers. I was thinking that also using matching but opposite colors for the bases would look interesting so that one ski would have a blue base with red topsheet and the other one would have a red base with blue topsheet.
This way, I would also be able to make more of the excess epoxy flow out.

The only thing that scares me is that it would mean a slightly asymmetric layup and this could have bad consequences on camber. But I guess i can compensate with that when I'm designing the mold; and it shouldn't be a very dramatic chance as I don't plan on using heat for curing.

[legon22]

Yet another question, but how much epoxy should I buy for a pair or two of skis, and would this: aeromarineproducts dot com work?