Blow n Go

I've been working with molds and glass for years, but I am finally going to try vacuum bagging. Here is the question...........

I'll be using a single layer of 5.6 oz carbon cloth with easy-lam epoxy to lay up a large cowel. In the past (no vacuum), I would have to lay down a layer of epoxy and let it partially cure before laying the cloth. This was necessary to prevent getting pinholes on the surface of the part.....or worse, the epoxy between the weave would pull free and stick to the mold, leaving dots all over the mold (very tough to clean up!)

Is this initial layer of epoxy still necessary when bagging?

Thanks, CJ

buttuh

You can, but you don't have to wait for the first coat of resin to tack up.

rpike

My Feedback: (1)

I have all the bagging supplies to do anything I could imagine...however I have never used them( except the vac). I still layup by hand. Question? are you using PVA before you layup? I use nothing but(no wax), and have never had a part stick to the mold( watch, I just cursed myself). I never had any luck spraying it in or on the mold. so I just use a 1" fine hair artists brush to paint it on.
If you intend to bag properly, remember to put the absorbing pad and the release membrane in there or you'll have an interesting mess when you're done. As far as the first layer of epoxy goes, I think I would still do it, followed by one layer of thin cloth, let it almost set up then apply the thick cloth/resin and bag it. My rationale is as follows...if you just put the large or heavy cloth in only, then there's a chance for the weave of the cloth to show through sooner or later. Bagging is meant to achieve the ideal mix of 50/50 resin to cloth(as well as perfectly mating to the mold). Therefore, you theoretically have half cloth and half resin on the surface. Like I said before, I have the stuff, but ain't done it, so I might just be speaking out the other end. I have quite extensive theoretical and a little practical knowlege of doing this stuff. If I can help I will.
Good luck,
Rob

Blow n Go

Thanks guys,

I can handle a little cloth show-through on the finished part. It's just the pinholes I can't afford. By the time you fill all the holes, the part gets twice the weight. On the other hand, 6 ounces of "buffer" epoxy is a lot to add too, if I can get by without it.

CJ

KevinSheen

Why not put in a single layer of 1 or 1.5 oz. glass cloth before you put down the CF? It will help eliminate the pinholes and it disappears in the epoxy, you won't even know it is there.

Kevin

Magne

CJ,
You can also spray paint in the mold and let this dry before you lay up your fiberglass/carbon. The coat of paint will prevent pinholes, and give a nice, shiny surface. Epoxy based paints, such as the old K&B epoxy paint, work well. Acrylic based paints will also work, but you need to apply a second, thin, coat just before you lay up the fiberglass, as epoxy does not stick very well to dryed acrylic. (But acrylic sticks to itself.) With carbon, you can of course use a clear paint, to show off. I have used two component K&B paints, as well as one component acrylic spray-cans from the car accessory shop. Two component gives best result, and is fuel-proof. I also think some people apply primer instead of paint, but I have not done this.
Regards,
Magne

HenrikJohansson

When you make parts using vacuum with absorbing tissue, without clear gelcoate or some sort of 2k clear cote you get the worst surface you have ever seen, FULL of pinholes. This happens because the laminate gets VERY dry. A very fine fiberglass surface layer won't cure the problem. All you get is even MORE pinholes...
Solution: get some clear gelcote, apply it to the mould and let it cure to the point that it wont stick to your finger if when you touch it. Using a brush, apply epoxy to the gelcote BEFORE you lay down the cloth, or the cloth will stick to the tacky gelcote and you will have a mess...

Using vacuum can be a bit tricky before you learn it, but be patient, it will improve your lay-ups a lot!!

rajul

My Feedback: (58)

Hi CJ, there's a video by Phil Barnes http://www.paonline.com/hayman/PAGE2.htm on vac bagging but I have not seen it to make any comment. Just thought you might want to have a look at it.

Blow n Go

Good tips.............thanks guys!

CJ

Mike James

I've just vacuum bagged a test part, (canopy) as follows:

I used West Systems (#105) epoxy resin with slow hardener. After waxing and PVA-ing the mold, I brushed in a light coat of epoxy, but did NOT let it cure at all. I simply applied a layer of 2 oz. cloth, followed by a layer of 6 oz. cloth, and bagged it at 20 inches.

We pulled the part this morning, to find no pinholes at all. After cleaning it up with lukewarm water and drying it, I sprayed a little white primer on it, just to be sure. No pinholes, and no fabric weave. (image attached)

Blow n Go

Looks good. Did you use the West pigment to get the white?

HenrikJohansson

If you got no pinholes, I assume that you diden't use any absorbing cloth att all, just the vacuum bag?

buttuh

I'm guessing that it was the white primer that he used.

Mike James

No tricks...

I used wax and PVA in the mold, followed by the cloth, then the nylon peel-ply, followed by the breather felt. The breather felt soaked up 1.1 ounces of excess resin, in this case. In my post above, you'll note that the white color was only applied after the part was inspected and cleaned. (primer) I couldn't see any pinholes in the part, and the white primer was just to make it easier to see any that might have existed, against the cloth pattern.

HenrikJohansson

Very strange that you didn’t get any pinholes (Were you using 5min epoxy? ). I often cure my parts in an "oven" at about 50C. That may be why I’m getting all those pinholes when not using gelcote?
When I make parts without the gelcote, I get pinholes in every "pocket" of the surface cloth.

Mike James

West Systems #105, as in my post above. (room temperature cure)

RAPPTOR

My Feedback: (41)

HI LOOKS GREAT.. DID THE WEST SYSTEM DRY TO A ,[img][/img]GOOD STIFF PRODUCT?? I FOUND IT TO BE TOO FLEXABLE.. THANKS RD

BFoote

Pinholes are caused usually by air bubbles. Air bubbles you say? Its in a vacuum.... Well not really. If you want excellent vacuumed parts you have to have a very good vacuum AT ALLLLLL parts of the vacuumed part, not just at the gauge on the pump! Using breather cloth to give air a route to the vacuum is important. Number of pinholes is lessened to almost nothing the better the vacuum that you have. Ok that was a horrid gramatical sentance. Anyways, if your vacuum is anything lower than say 24 in Hg your work will not be as good. Also, make sure your epoxy is THIN. Reason vacuum works so well is that it moves the resin like a squeege but with more pressure than you can do in a traditional wet layup.

Cheers
Brian

Mike James

RAPPTOR,

I can't say what is "too flexible" for others. In my case, I try and build the lightest, strongest parts I can, and use different methods to do it. For example...

I did several tests on the canopy part, to determine what would give me the combination I wanted. First, I made a strictly fiberglass part, including the flanges. I thought it was too flexible. It was about 2 ounces. Next I made just the "bubble" part of the canopy, and instead of a fiberglass flange, I epoxied a lite ply frame to the bottom of the piece, while still in the mold. This part, at the SAME weight, cannot be twisted or bent, until enough force is applied that would break the frame. In this case, that would be "crash force", and nothing like you'd encounter in normal flight.

Danger... Personal opinions ahead...

Using a fiberglass fuselage as an example:
Some people think that the fuselage should be it's own structure, (with few or no formers) and that it has to take all the loads. I don't build that way. Instead, I try and plan out a sensible, light internal structure to take most of the loads (in combination with the skin, of course) and think of the fuselage primarily as a fairing around this structure.

Take either full-size or model aircraft as an example. You can walk up to most general aviation planes, and deflect the skin with your finger. It doesn't have to be super strong on it's own. Same goes for most fiberglass models. If you build it rigidly enough to resist flexing, you not only have a heavy structure, but it becomes brittle. A small amount of "give" can actually make the part last longer, and absorb loads better. If you need local stiffness in a part, it can be done more lightly by adding a bit of internal framework, and/or by adding a bit of extra glass, or Kevlar between the fiberglass laminations. (or inexpensive carbon tow)

One other thing, regarding "high-tech"...
If you are building a 40 pound jet, intended to go 200+ MPH and pull 10 Gs, or a glider intended for dynamic soaring, pulling up to 30 or 40 Gs, then yes, it would be wise to use a lot of carbon. For the vast majority of our models though, that is structural overkill, and a huge waste of money.

Magne

Henrik,
Just to clarify one point regarding your pinhole problem. In your post above (#7) you say that when you use gelcoat, you "apply epoxy to the gelcote BEFORE you lay down the cloth, or the cloth will stick to the tacky gelcote and you will have a mess... "
I assume you also apply the epoxy to the mold first when you are NOT using a gel coat?? (Otherwise you will definitely end up with pinholes, I think)
Magne

Magne

Hello Mike,
In post #14 above you wrote: "I used wax and PVA in the mold, followed by the cloth, then the nylon peel-ply, followed by the breather felt."
I am going to lay up a new fuselage for an F3A pattern model, using glass/balsa/glass sandwich. I know some people use a perforated release film on top of the last layer of glass, followed by the breather felt. Do you just use peel ply instead of release film? Do you not use a perforated release film on top of the peel-ply? The fuselage halves will be joined with glass tape, I assume the peel ply will give a good surface finish for this, in addition to gluing internal formers etc. to?
Regards,
Magne

Mike James

The peel-ply is the perforated release film. We're using room temperature cure West Systems stuff, so we're using the 2 oz. (#01-14820) from Aircraft Spruce ( http://www.aircraftspruce.com/catalo...es/vacbag1.php ) Combined with breather felt, it leaves a rough, dry surface, suitable for "secondary adhesion". (gluing formers in)

Ed Smith

Just to clarify.

Use the perforated release film or the peel ply. It is not necessary to use both.

Ed S

buttuh

Peel ply is NOT perforated release film. They are BOTH release films but not the same material and characteristic. Peel ply is a soft cloth (nylon or polyester based) that allows 100% bleed through of the resin to the breather cloth. Perforated release film is a plastic film that has holes evenly spaced approx. 1/4" - 1/2" a part to allow for some resin bleed through but not all.

Mike James

I should've used quotation marks, as in ...

The peel-ply is the "perforated release film". I know they're two different products, but we're only using the peel-ply. Actually, Aircraft Spruce's name for it is "Nylon Release Ply". It reminds me of parachute material.