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Author Topic: molding shells  (Read 1380 times)
Chris Belcher
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« on: April 19, 2017, 08:04:55 AM »

What do I use to seal a balsa mold buck? Next time will use foam but already have the balsa shaped. Will zpoxy work?
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Avaiojet
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« Reply #1 on: April 19, 2017, 10:57:02 AM »

What do I use to seal a balsa mold buck? Next time will use foam but already have the balsa shaped. Will zpoxy work?

Chris,

Got photos?

Sounds interesting.

CB


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« Reply #2 on: April 19, 2017, 11:07:26 AM »

Zpoxy will be overkill, but will work.  Dope will work.  If I didn't use dope I'd use the cheapest waterproof laquer or enamel from the HW store.

Foam doesn't need to be sealed unless you're going to go into production, in which case you might want to put a couple of layers of fiberglass on it for durability.
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« Reply #3 on: April 19, 2017, 11:22:58 AM »

2 coats of nitrate dope thinned 50/50 then one or two coats of minwax polycrylic.


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« Reply #4 on: April 20, 2017, 08:23:40 PM »

I use plastic wrap on both foam and carved balsa mold bucks. Something that won't adhere to the balsa sheeting while drying for a few days. I tape it down along the rear of the mold so it doesn't shift during wrapping of the wet sheet.
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« Reply #5 on: April 21, 2017, 06:13:24 AM »

I do the same as Mike, even when doing CF or glass.  The wrap is fail proof as far as releasing.  Sure you can get some wrinkles but that's why they make sandpaper.
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« Reply #6 on: April 21, 2017, 12:38:48 PM »

I do the same as Mike, even when doing CF or glass.  The wrap is fail proof as far as releasing.  Sure you can get some wrinkles but that's why they make sandpaper.

"Good" Will Hinton,

I used to make fiberglass parts for art work, but parts are parts.

I used the large black plastic bags and cut them in long endless strips 2" or so wide, just keep cutting round and around the bag, could get 20 feet or more. Eyeballed the width actually.

This would get wrapped around the mold continually from one end to the other. I once did one large fiberglass Coca Cola disk about 24" in diam. For that I applied the black bag over the entire area then just gathered the excess behind the mold tight. Second bag wrap over the glass was to pull it tight. Could also squeegee on the bag depending on the task.

Could easily use the 2" wrap thing, because as you wrap from one end to the other, you can set the skin. Un-rap for change in the sheeting then start again if necessary.

I haven't done this in years, but it could be one method that could work well for sheeting.

I have sheeted models, like one of the two Grumman F3F-1's I started years ago for R/C, but I prefer "planking."

As I just recently did on my Gee Bee R-3. The GBR3 model was planked carefully for fit, but the Mig-3 planking was rushed and I paid no attention to correct fit or detail on it.

CB
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"Nothing is easier or more pathetic than being a Critic."  Donald Trumph, 5-13-17.

I look at the Forum as a place to contribute and make friends, some view it as a Realm where they could be King."

Owner of CFC Graphics. "Model Airplane Graphics from a Model Airplane Builder."

"I'd like to build a reputation, not be given one."
X-Files quote

"Ya gotta love it when a plane comes together."

Proverb 11.9  "With his mouth the Godless destroys his neighbor..."

"So popular, they named a television series after me."

"Perhaps the greatest challenge in modeling is to build a competitive control line stunter that looks like a real airplane."
David McCellan, 1980.

"If you can't rise above, you destroy."
Rush Limbaugh, 2015.
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« Reply #7 on: April 29, 2017, 03:01:41 PM »

Another good way to get reliable release, for sure.
I've experienced way too many mold release failures that required major repairs to the sheeting to go back to anything but plastic or wrap.
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« Reply #8 on: May 17, 2017, 06:06:00 AM »

Chris in RC Groups under Molding Fabrication forum you can find all the information you will ever need and then some.
https://www.rcgroups.com/composites-fabrication-210/
Do a search on whatever topic you want and go with it. I have spent endless hours researching around RCG and found all kinds of information.
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« Reply #9 on: May 17, 2017, 06:21:04 AM »

What do I use to seal a balsa mold buck? Next time will use foam but already have the balsa shaped. Will zpoxy work?

Chris,

Are you off planet?  Layingdown

What's the project?

CB
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"Nothing is easier or more pathetic than being a Critic."  Donald Trumph, 5-13-17.

I look at the Forum as a place to contribute and make friends, some view it as a Realm where they could be King."

Owner of CFC Graphics. "Model Airplane Graphics from a Model Airplane Builder."

"I'd like to build a reputation, not be given one."
X-Files quote

"Ya gotta love it when a plane comes together."

Proverb 11.9  "With his mouth the Godless destroys his neighbor..."

"So popular, they named a television series after me."

"Perhaps the greatest challenge in modeling is to build a competitive control line stunter that looks like a real airplane."
David McCellan, 1980.

"If you can't rise above, you destroy."
Rush Limbaugh, 2015.
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« Reply #10 on: May 17, 2017, 11:14:20 AM »

I presume that Chris is referring to a mold buck over which he's going to put a wet sheet of balsa to be held in place until it dries.  There would be no adhesive to get stuck, so the problem is just waterproofing the (balsa) mold buck.  Dope or most anything would work.

Coating a balsa plug to make a casting-resin mold or an epoxy-matrix part is a different issue.  Dope reacts with some mold release agents to form a super adhesive.  I've had to chisel out the doped plug from some cowl molds. I use K&B Superpoxy to finish these plugs.  I still have some, and it still works.   No doubt Z-poxy or that stuff Brett uses would work fine, too.
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Chris Belcher
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« Reply #11 on: May 19, 2017, 12:21:28 PM »

Sorry...been away for a while. I used 2 coats of Zpoxy cuz that's what I had around. The 3/32" a grain molded shell came out great, no release issues at all. The hardest part was getting the fit right on the fuse sides. I cut 1/8" slits in the buck at points matched to the fuse formers and put balsa squares in the slits to mark , shape and sand to fit formers for the inside of the shell. The formers in the shell sit right on top of the fuse formers top edge. The part came out to 11 grams ready to glue on after wing install. Not sure what a hollowed block would have weighed but I bet more..and no busting through and having to repair those later. I'm happy with it, little bit of work but...that's fun, so....
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Avaiojet
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« Reply #12 on: May 19, 2017, 02:31:29 PM »

Sorry...been away for a while. I used 2 coats of Zpoxy cuz that's what I had around. The 3/32" a grain molded shell came out great, no release issues at all. The hardest part was getting the fit right on the fuse sides. I cut 1/8" slits in the buck at points matched to the fuse formers and put balsa squares in the slits to mark , shape and sand to fit formers for the inside of the shell. The formers in the shell sit right on top of the fuse formers top edge. The part came out to 11 grams ready to glue on after wing install. Not sure what a hollowed block would have weighed but I bet more..and no busting through and having to repair those later. I'm happy with it, little bit of work but...that's fun, so....

Chris,

Sounds like you did a great job!

Photos?

CB
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"Nothing is easier or more pathetic than being a Critic."  Donald Trumph, 5-13-17.

I look at the Forum as a place to contribute and make friends, some view it as a Realm where they could be King."

Owner of CFC Graphics. "Model Airplane Graphics from a Model Airplane Builder."

"I'd like to build a reputation, not be given one."
X-Files quote

"Ya gotta love it when a plane comes together."

Proverb 11.9  "With his mouth the Godless destroys his neighbor..."

"So popular, they named a television series after me."

"Perhaps the greatest challenge in modeling is to build a competitive control line stunter that looks like a real airplane."
David McCellan, 1980.

"If you can't rise above, you destroy."
Rush Limbaugh, 2015.

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