Ski Builders Forum

I'm having trouble with the vacuum press. I bought the Duramax 20 mil polyurethane from Joe Woodworker and built a frame similar to the one on his site. Basically the same as Sammer's - the poly won't stretch enough to mold around the tip profile of the mold. Am I missing something obvious? Not sure if my mold is too tall or if I got the wrong poly for this. My mold is about 5" above the press table at the tips. I could maybe cut an inch or so off the mold but not sure it would matter. Tried a little bit of heat from a heat gun and some weights on the frame but still can't get the frame flush with the table top. I didn't want to ruin the poly with too much heat. Seemed like OAC's membrane was way more flexible than this stuff. Any help or ideas would be great - thanks.

Balls balls balls

I don't know what Jan (OAC) used back in the day, but now he is using silicone sheet as the membrane which is way more flexible than polyurethane.

Tips on vacuum pressing and why I haven't switched to pneumatic pressing..yet :

1: Steel frame, minimize the chances of leakage around the perimeter.
2: Silicone membrane.I use 1,5mm. Not the cheapest material around but for the purpose very flexibel and durable. Can be used with fairly high heat. I use 80C.
3: Paper laminate table top, Also heat resistant up to ~150°C, And its a plastic, despite its name, so epoxi won't stick to it. I use an 8mm thick board. Not the cheapest either, but very good for the purpose.

I use one(you can have several) valve under the table to the pump.

I'm on 100+ pressed pair with this setup now! :-)

For the record: I used regular "para rubber" at first, but it didn't come in transparent and was pretty quick "dryed out" by the heat. Way cheaper than silicone thou.

Hi,

if you don't need the top inch of the tip mould, then cut it off.

The less the poly is streched, the less likely its going to tear apart somewhere. And of course, the lower the mold, the less its streched.

Had the same with my mold at the beginning, also cut away at least 2cm.

100+ pair OAC! Well done!

Thanks for the info - I looked around for some silicone sheets today and I'll go that route if I can find it in smaller quantities - just thought the poly would be more flexible. Ill try to make the poly work for now by cutting the mold down -Thanks OAC - nice journals by the way. Love the bandsaw core profiler - plan on doing the cores this week. Did you end up making a heat blanket or are you using a heater you attach to an insulated box still. I made a heat blanket like troublemakers so I'm curious how well it works with the vacuum press if you're using a blanket. Originally I was going heat from the bottom but not sure the blanket is smooth enough - may just see how it goes on top although I guess it could affect the amount of camber. Thanks again

Ya, I used a hair dryer, put clamps on the frame and slowly cranked it down until it sealed. Then pulled a vacuum and heated it up again to get it molded to my mold.
The vinyl was worse than the polyu.
IIRC the polyu just took a bit of pressure to get the frame sealed then heated up after pulling full vac.
Too much heat will blow a hole in it so be careful.

Still looking for a cheap silicone deal.
Will probably just build a proper press in the next year or so.

sam

Edited to add my molds are close to 6" at the tip and tail.

sam

falls wrote:100+ pair OAC! Well done!

I just past it! Suddenly it happens!:)
My intention from the beginning was one pair that I could ski on! But that was then...

Wvmtnbiker wrote:..Love the bandsaw core profiler - plan on doing the cores this week. Did you end up making a heat blanket or are you using a heater you attach to an insulated box still. I made a heat blanket like troublemakers so I'm curious how well it works with the vacuum press if you're using a blanket. Originally I was going heat from the bottom but not sure the blanket is smooth enough - may just see how it goes on top although I guess it could affect the amount of camber. Thanks again

Ohhh that old project! :-) I almost forgot. My bandsaw was too weeak for succeding with that. I think one need a bigger more powerful unit to get at least the blade more rigid. I'm on the planer method. Outstanding in my opinion if you don't have a CNC.
I will show how I implemented heat blanket in my press(...some day).

Cheers

You must be selling them now at that volume?

falls wrote:You must be selling them now at that volume?

Yes, I have my customers.

I have been looking around for silicone. I am currently based out of Victoria BC and its been a difficult search to find something suitable near by.

I had used regular construction poly and it worked ok, but left many wrinkles to be sanded out after pressing.

This stuff looks pretty good and is cheap but its thin...

http://shop.fiberglasssupply.com/Films- ... l_200.html



Last night I had a poke around alibaba and found many options.
Thinking about ordering from either of these folks:

http://www.alibaba.com/product-detail/2 ... 5.html?s=p

http://www.alibaba.com/product-detail/C ... 7.html?s=p

I should go for the alibaba silicone. Just remember that 2mm is pretty thick in this application. 1 - 1,5mm is enough IMHO.

Last 2 quotes I got from alibaba were around $170/sqm + $175 shipping.
Although both adds were showing around $5/kg (700% elongation)
I also got quotes for regular (300% elongation) for around $40/sqm + $175 shipping.
I've given up on silicone from china for the time being.
If somebody comes up with something let me know.

I've used the stretchlon (the green stuff) a fair bit before. It works well but gets expensive and seems quite wasteful.
Regular poly works OK but needs good pleating to avoid low pressure areas and wrinkles.

sam