vacuum press - bag

zackariah · Post by **zackariah** » Wed Apr 16, 2008 3:11 pm

I'm building a pair of 99cm skiboards for my sr. project at school (on a fairly low budget), and I have two questions regarding vacuum pressing:

1) Will a shopvac provide enough pressure to press? I've heard it can, but I want to make sure.

2) My mom just got one of those "space bags", you know for compressing shirts, bedding etc., would that be sufficient to use as a bag?

Thank you in advance

Greg · Post by **Greg** » Thu Apr 17, 2008 6:50 am

I'd like to be able to answer you with experience, but I would bet that the space bags would work for the vacuum bag. As for the vacuum cleaner as a vacuum pump... I don't think anyone has tried that before. I recommend testing it out. You could have just found the "holy grail" of vacuum pressing, but you never know until you try it out.

The shop vac should be able to pull a lot of the air bubbles out of the ski layup, but, I wouldn't count on it producing enough vacuum to shape the tips or develop any significant camber. However, I haven't tested it, and don't believe that anyone else has either, so I could be totally wrong.

sammer · Post by **sammer** » Thu Apr 17, 2008 7:14 am

If you read through the posts or use search you will find the answer!

Space bags are quite expensive compared to making your own with poly.

Shop vac will work but to keep it running the entire time it takes for your epoxy to cure will burn it out pretty quick.
sam

x15man · Post by **x15man** » Thu Apr 24, 2008 9:04 am

A shop vac only gives you about 4 to 6" Hg vacuum (2 to 3 PSI). A vacuum generator will give you 28" Hg (about 14 PSI). You can get these at places like Heatcon for about $150. (Their part number is HCS2026-01. You can find them on the web, located in Seattle.

BbTahoe · Post by **BbTahoe** » Thu May 01, 2008 10:24 am

So how would you go about making your own bag out of poly? How do you ensure that there will be no leaks? Melt the edges together?

krp8128 · Post by **krp8128** » Thu May 01, 2008 11:54 am

BbTahoe wrote:So how would you go about making your own bag out of poly? How do you ensure that there will be no leaks? Melt the edges together?

Butyl sealing tape, black and sticky. Any store that sells bagging material will have it.

I've seen people put the whole mold in a bag. For my mold, the top surface is non-porous formica, and I just seal a layer of poly to the outer edges.

rockaukum · Post by **rockaukum** » Thu May 01, 2008 11:58 am

krp8128,
I have seen the same method you describe before and it works perfectly!
They just seal the top of the mold, no need to seal / bag the whole mold.
rockaukum

BbTahoe · Post by **BbTahoe** » Thu May 01, 2008 1:10 pm

Are sealing tape and bagging material available at any old hardware store? I don't have a mega-hardware store like Home Depot nearby. I'm wondering if I can make it work locally.

sammer · Post by **sammer** » Thu May 01, 2008 7:20 pm

I've done a few tests with my vac system using 6 mil vapour barrier and butyl tape. Works great
But its been suggested that you could seal it with tape. Probably tuck tape would work if you didn't have any creases. Duct and packing tape don't stick to the poly very well.
You could just order butyl from fibreglast. (sealant tape)
sam

krp8128 · Post by **krp8128** » Fri May 02, 2008 7:27 am

I thought I had a pic of my new mold all sealed up, but I guess not. Here's the original, with an aluminum flashing surface:

http://farm3.static.flickr.com/2154/156 ... _b.jpg[img][/img]

krp8128 · Post by **krp8128** » Fri May 02, 2008 7:30 am

I thought I had a pic of my new mold all sealed up, but I guess not. Here's the original, with an aluminum flashing surface:

I wouldn't recommend flashing as a mold surface, it tore it several times popping the ski loose.

BdTahoe,

I've tried duct tape and rope caulking from Home Depot. Duct tape pulls of while the bag is flexing, and the rope caulk just wasn;t sticky enough. By the time you get ready to bag the skis you will already have significant money into the project, not to mention your time. Spend the $10 and get some butyl "Tacky" tape.

http://www.jamestowndistributors.com/us ... aling+Tape

http://www.mrfiberglass.com/vacuum_bagging.html

sammer · Post by **sammer** » Fri May 02, 2008 3:48 pm

krp8128... i see you just used cardboard as a breather. did you put it directly on your topsheet and if so did it leave a corrugated pattern on your ski?
sam

krp8128 · Post by **krp8128** » Sat May 03, 2008 9:59 am

sammer wrote:krp8128... i see you just used cardboard as a breather. did you put it directly on your topsheet and if so did it leave a corrugated pattern on your ski?
sam

Yes, and yes.

After that ski I stopped using breather altogether. Now I just use a layer of 6 mil plastic then an 1/8" sheet of masonite on top. My pump pulls all the air out no problem. You can see how smooth they are in this pic:

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vacuum press - bag

vacuum press - bag

Try using a vacuum generator device