Epoxy squeeze out in a vacuum - does it happen

[numpty]

Hi,
I just layed up and vacuum pressed my first ski. Apart from being like juggling cats it went OKish.
The result was a very fat ski with a lumpy surface, really bad in the binding area.
I did not have a lot of room around the ski before the vacuum seal and I may have used too much epoxy. I also used a topsheet that got pushed down around the ski and trapped the epoxy.
Now that I have seen this happen, I wonder if a vacuum press will force epoxy out of the ski lamination since the pressure in the ski body is the same as the pressure around it in the bag? Why would epoxy not just get evenly distributed throughout the whole bag. Should I have used a lot more breather fabric at the sides of the ski to allow space for the epoxy?
Curious if I am alone in this problem. I did pull -22"Hg with my pump so I don't think it is a vacuum pressure thing.
Thanks for the help.

[twizzstyle]

You won't get nearly the squeeze out with a vacuum, just because there isn't the same amount of force you get with a firehose.

At ~22" Hg, that means you only had about 10psi pushing on the ski, vs 50-80psi or more that people typically press with using a firehose.

It shouldn't turn out lumpy and uneven though, it just might be a bit heavy. To help this, when you do the layup, wet out the fiberglass seperate from the ski, and squeegee out as much excess epoxy as you can. That way there isn't much epoxy to be squeezed out, and it should turn out nice and flat.

When vacuum bagging, the force doesn't happen inside the bag... its the atmosphere OUTSIDE the bag pushing on everything inside the bag. That's where the force comes from.

[numpty]

Thanks, I understand the presssure is outside the bag, so the pressure is the same around the ski as it is on the top surface so there is no pressure difference to squeeze epoxy out as far as I can tell. In a hose type surface press the pressure on the ski is much higher than the pressure at the edge so the epoxy flows to the point of low pressure, i.e. out of the laminate.
I just looked at the 333 guys video and he uses 'just enough' epoxy as you suggest and cardboard as a soaker for the epoxy (and no top sheet).

Has anyone vacuum bagged a ski on a sheet of thin alum and then bent it around the mold like the 333 guy does, is this a good method? It makes the bagging much simpler.

[twizzstyle]

Thanks, I understand the pressure is outside the bag, so the pressure is the same around the ski as it is on the top surface so there is no pressure difference to squeeze epoxy out as far as I can tell.

Not quite, you still have pressure pushing on the top, and sides of the ski... the only place for the epoxy to go is out from under the top sheet and into the breather cloth.

The breather cloth soaks up the excess resin, but if you squeegee the fiberglass out well, you shouldn't get a ton coming out. Should be some, just not tons and tons.

[numpty]

I will give it try with ski number 2, I think your method will improve the result. Any suggestions on how to soak and squeegee the glass with mixing buckets of epoxy (it goes off fast when there is any volume of it around).
Thank you for the help. Wife suggested I make 3 skis for every pair I want to account for the learning curve.

[Head Monkey]

Twizzstyle’s right on here: it’s the much lower pressure you get with vacuum bagging yielding poor squeeze out that’s your biggest problem, so you need to be much, much more careful about where you put your epoxy. A capped top sheet doesn’t help matters, either, since you are correct that there is pressure being applied to that cap from the side, making it even harder for your epoxy to get out. One thing I used to do when I vacuum bagged was I would cut long, thin strips of breather fabric and fit them closely along the edge of the board. When I put the top sheet on, I would make sure that the portion beyond the edges would sit on top of the strips of breather fabric. This gave resin getting squeezed out from underneath the top sheet a better place to go, and helped a bit. You can see what I mean here in the pics linked below.

Also, try to get better draw from your vacuum. At -22”HG, assuming you’re at sea level on an average day, that only yields 10.81psi on your board. I used to consider -24.5” my minimum good draw, with a goal of -25.5”, which is 12.04-12.53psi.

I’ve put up some of the only pictures I still have from the vacuum bagging days (2003) here: http://www.happymonkeysnowboards.com/mi ... umBagging/

There’s a .zip file there of all the pictures as well as the individual pics. I hope these can help you and others who are bagging. Note the date/time stamp on these pics is accurate so you can see how long it took me to get through that layup.

Good luck,

Mike

[numpty]

Head Monkey, thanks for the pic's they helped a lot. Two questions,
1. The top sheet of glass looks almost dry in the picture, is that true or you added a lot more after the pic?
2. The alignment inserts on the base, are they superglued to the base and then you have holes in the core to match?

In thinking about the quantity of epoxy I used I referenced a message on this site but I am now begining to think it was for TWO ski's and I layed up one, that's why I used numpty as my user name!

I guess it gets faster if you build a lot of skis but it is a bummer to go through all the process and get dud first time.
I have seen that it is possible to sand a ski, can this be done right through the top sheet and glass? I may try to rip the top sheet off tonight then sand it.

[numpty]

One more question (today), my pump starts to struggle at 21Hg so I set the cut off just above that (used Joe Woodworker design). Should the pump struggle on to get to 24 - 25Hg or should it get there quite easily and I am not being patient? My guess is that it would be 10 secs to 21Hg and another 20 minutes to get anywhere near 24 if it ever made it and that is just working against the tanks not a leaky bag.
My pump is a used industial unit rated for constant use but the spec says 150mBar (it is a Pico VLT10).

[twizzstyle]

The reason epoxy will speed up its cure in a large bucket is that large volume is creating a lot of heat, which speeds up the cure, which creates MORE heat, which speeds it up more, etc etc. Chain reaction, as the polymerization of the epoxy is an exothermic reaction

If you mix the epoxy in a bunch of smaller cups instead of one big one, or you can pour it into a paint tray (or similar). This will keep it from heating up too much and speeding up the cure while you lay it up.

What I did on my last pair, which worked out great, was have a seperate wet-out area, which was just some big plastic sheet I laid on the work table. I laid the fiberglass down, poured some epoxy over the fiberglass and spread it around with a squeegee. Then I flipped the fiberglass over and did it on the other side. This was just to make sure it got completely wetted out. Then I squeegeed quite hard (but not hard enough to mess up the fibers... have to be careful with that) to squeeze out as much epoxy as I can. You can never ever squeeze out too much epoxy, trust me. Assume there are no dry spots, you less epoxy the stronger/lighter a ski will be. THEN I picked that up and laid that onto the ski. I like this method much better than laying dry fiberglass into the ski and wetting it out then, in the mold.

Don't worry about dud skis, thats all part of the process. I just finished my 4th pair, and although they're pretty damn good, there are still minor issues. You will iron out one detail or maybe two which each ski you make, and they'll progressively get better and more "professional" quality. Just don't let the duds frustrate you, all lessons.

[Head Monkey]

Numpty,

On your first question, it’s been a long, long time since that picture was taken. I don’t actually know whether I was done with wetting the top glass, or had simply stepped back briefly to let the picture be taken in the middle of wetting it. You’d like to see your glass go translucent when it’s properly wet out, however that can take some time depending the viscosity of your epoxy and the thickness of your glass. You may find that if you spread a reasonable amount of epoxy, then simply wait, it will go translucent.

Yes to your second question. It’s a very simple alignment method that’s quite effective.

On your pump: is the pump actually struggling at 21hg, or are there leaks in your tanks? (You said that’s 21” against only the tanks, right?) Test the pump connected only to your vacuum gauge first. If you can’t draw 24-25” with it, get a better pump. If you can, then you have leaks in your tanks and you need to work to seal it more. If you have a small leak and you’re stuck at 21”, when you fix that leak you’ll jump to 25” within seconds. I recommend this pump: http://www.gastmfg.com/pdf/diaphragm/specsht/moa.pdf. It’s quiet, reliable, and easily serviced with a small kit and a few hand tools. Although the manual says max draw is 24”, I found both of mind drew 25.5” consistently against just the gauge.

Good luck.

[Steevner]

1 piece of advice to minimize bubbling and lumps in your topsheet is to add another layer of "something" above your layup. What I mean by that is adding the equivalent of a cat-track on the very top of your layup. I would suggest using a cross-grain piece of veneer (1/8" maybe, but wrap it in saran wrap to prevent it from sticking to anything!). This really helps distribute the force of the vacuum across the topsheet.

This is how I laminate veneers to longboards. It really keeps the laminate free of lumps, and helps squeeze the epoxy out.

[davide]

Here you can find few pictures about vacuum pressing:
http://www.skibuilders.com/cpg/thumbnails.php?album=8
http://www.skibuilders.com/cpg/thumbnails.php?album=6

I used a MDF mold; I used no topsheet, but I put a plastic film above the last glass layer (I will remove the film after curing) and a layer of reusable breathing tissue above it. Then I insert everything in the bag.

[sammer]

Once your ski is in the bag (under vacuum) roll it out with a j-roller or a piece of abs pipe, I've even used a nalgene bottle.
You can push out a lot of resin.
The trick is having somewhere for it to go.
The bag kinda closes its egress.
A little extra glass off to the side perhaps?

hard to explain (beer and forums don't mix)


sam