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      Board Status   07/20/2018

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Going to test the Bondo fiberglass cloth and resin.

See if it is the right thickness of cloth for scale bodies. 1/16 1/8 1/4 and 1/2 scale.

Cloth says .20 millimeters. What is that equivalent to in ounce cloth?

Hobbylinc has 2oz and 5oz. I started at the bottom and ordered 1/2oz from them and it is too thin.

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29 minutes ago, regular guy said:

Hobbylinc has 2oz and 5oz. I started at the bottom and ordered 1/2oz from them and it is too thin.

Define "too thin".

ANYTHING correctly made from fiberglass cloth in an open mold is made of MULTIPLE LAMINATE LAYERS, not one single layer.

The Bondo brand stuff is loosely woven "boat cloth" and is appropriate for multiple layers on REAL car parts (of low to moderate quality), but not anything in scale...other than perhaps a flat bulkhead.

For some reason, newcomers to composite material fabrication seem to almost always make stuff WAY TOO THICK, ridiculously too thick.

Even a not-great fiberglass laminate is MUCH stronger than a steel part of the same weight, so the glass part can be MUCH LIGHTER than a steel part of the same strength.

An open-molded part will be in the neighborhood of 3 TIMES as strong as a steel part of the same weight, so it can be made at 1/3 the weight of steel and have the same strength.

But I STILL see people making body panels from glass on real cars that weigh almost as much as steel.

The final thickness of a model car body in 1/8 scale doesn't need to be any more than .030". This can be ideally achieved by 3 layers of fine cloth that is .010" thick.

Edited by Ace-Garageguy

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What ounce cloth is this .20 millimeter cloth equal to please?

This newcomer would like to know.Started doing this in the 60's I guess my next stop is the retirement homes

in the area to find more experienced people to answer this question.

Let me get back to making my inferior parts here.

 

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What we're doing is laying a piece of cloth on waxpaper.

Then saturating it with resin and letting it dry overnight.

That's to see what it is like by itself.

The 1/4 ounce is very thin. I will check package to see if it is 1/4 or 1/2 ounce.Think it's 1/4 ounce.

Think it's for covering model airplanes.Give them a little strength without adding too much weight.

This new cloth is about as thick as jeans fabric. Maybe a tad thinner.

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16 minutes ago, regular guy said:

Let me get back to making my inferior parts here.

Making "inferior" parts is a choice.

It often seems you ask for advice, but don't actually take it.

I'll be glad to help you, as I most probably know more about composite materials than 90% of people in the business, and most certainly more than anyone on this board.

Without knowing the weave, or having a sample of the particular cloth to weigh, I can not possibly tell you what weight it is.

YOU can weigh a square section of the stuff on a gram scale and do some simple arithmetic to see what the per-square-yard weight is.

Edited by Ace-Garageguy

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10 minutes ago, regular guy said:

What we're doing is laying a piece of cloth on waxpaper.

Then saturating it with resin and letting it dry overnight.

That's to see what it is like by itself.

The 1/4 ounce is very thin. I will check package to see if it is 1/4 or 1/2 ounce.Think it's 1/4 ounce.

Think it's for covering model airplanes.Give them a little strength without adding too much weight.

This new cloth is about as thick as jeans fabric. Maybe a tad thinner.

Properly mixed polyester resin should jell in about an hour at 60 F, and should be fully hard in a few hours.

The ratio of catalyst to resin is important, as is the ratio of mixed resin to glass.

Edited by Ace-Garageguy

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Ace Thanks

Do you have some 2 ounce or 5 ounce in the shop?

How thick is it please?

I think the two of them from Hobbylinc will get me in the ballpark.Just the 1/4 ounce was a bad move.

You do good work.If I had a budget I would send you plans and let you build it.

That's what I did in the 80's. The guy built racing catamarans.

These part just need to hold their shape for now.

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3 hours ago, regular guy said:

Ace Thanks

Do you have some 2 ounce or 5 ounce in the shop?

How thick is it please?

I think the two of them from Hobbylinc will get me in the ballpark.Just the 1/4 ounce was a bad move.

You do good work.If I had a budget I would send you plans and let you build it.

That's what I did in the 80's. The guy built racing catamarans.

These part just need to hold their shape for now.

Do an internet search for "Fiberglass Cloth Chart". You should find what you are looking for.

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Thanks!

Looking for a chart was a can of worms but it made me think to look around for info.

https://www.hobbico.com/shop/accys/hcar5000.php

That's from Hobbico website.Maker of cloth for Hobbylinc.

Apparently we have the 3/4 ounce.You don't want my memory!

It says 5 ounce is for making parts.It's probably the thickness of this Bondo cloth.

Happy Holidays!

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1 hour ago, Xingu said:

This is what i found, it gives weight and thickness.

Better than nothing, but it's only about 1% of what's available, and the only fabric listed there that's appropriate for this kind of model work is the "108 Lightweight".

Composite cloth comes in a mind-boggling array of weights, weaves and compositions. Then there's non-woven materials like surfacing veil and mat, and multiple permutations of those too. There's unidirectional knitted fabric, and 3-dimensional fabric that has fibers in all three axes. They all do some things well, some things not so well. Some drape in complex shapes easily, some just flat don't drape at all.

I've stated countless times that what folks need to get started doing glass work for models is the stuff sold by hobby shops in the RC model plane section.

It's the right weight (approximately .55 oz. and .75 oz. and  the 1.5 oz that's about what's shown as the "lightweight" cloth in the chart above), it's readily available, and it's cheap. It's a "plain weave" and follows complex shapes OK, but not wonderfully.

Nobody listens, or instead of taking the damm advice, they want to know "what about this?" and "well, what about that?"

I've also offered to write an in-depth article for the mag explaining the entire process, and apparently there's no interest...or not enough to pay for my knowledge.

I'm tired of answering questions one at a time, for people who don't seem to pay attention to what I say anyway.

I know this stuff upside down and backwards, it's complex, I made it a large part of my life's work to learn it, I've largely pioneered using high-strength epoxies and fiberglass for almost-scale-thickness panels for models,  I've pioneered repair procedures for REAL aircraft that the factory engineers said couldn't be done, I've refined and developed the processes over many years, and still...oh, never mind.

Good luck.

http://www.sigmfg.com/cgi-bin/dpsmart.exe/IndexText/FSIGGF001.html?E+Sig

https://fiberglasswarehouse.com/breakdown-of-different-fiberglass-cloths/

Edited by Ace-Garageguy

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Getting the tools and supplies together to do this.

Fiberglass cloth and resin.

Plastic cups for mixing.

Wooden tongue depressors to mix it up with.

Wax paper to do it on.

Flux brush to paint resin onto cloth.

Think it's all set.

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39 minutes ago, regular guy said:

Getting the tools and supplies together to do this.

Fiberglass cloth and resin.

Plastic cups for mixing.

Wooden tongue depressors to mix it up with.

Wax paper to do it on.

Flux brush to paint resin onto cloth.

Think it's all set.

You need an eye-dropper to properly MEASURE your catalyst. Here's a chart. Adjust for smaller quantities and hot or cold temperatures. Do NOT go outside these percentages.

http://www.fiberglasssupply.com/pdf/miscellaneous/MEKPChart.pdf

The mix ratio IS IMPORTANT, no matter what you may hear from the slop-jockeys.

You also need EYE PROTECTION AND GLOVES. Polyester catalyst is nasty stuff.

Plastic cups (styrene ones anyway) will MELT in polyester resin.

You're far better off using paper Dixie un-waxed bathroom cups for mixing small quantities.

You need acetone for cleaning you brushes or other implements.

AND...if you're doing test panels of a size appropriate for a 1/8 scale model, you'll be better off using natural-bristle paint or "chip" brushes 1" wide. "Acid" or "flux" brushes are the choice for doing small-scale layups, but if you're doing anything over about 1" on a side, you simply need a larger brush.

 

Edited by Ace-Garageguy

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Going to back up a little here.

Will mix resin and catalyst on a sheet of cardboard.

Have been doing same thing to test some glues.

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Update.

Opened up Bondo fiberglass resin and it had crystallized.

Bought it a couple years ago.

Learned something though.

It is polyester resin. The way you can tell is if it has catalyst that just takes a small amount for the resin.

Epoxy is a 1 to 1 ratio.Not even close.

Will get some epoxy resin and try this again later.

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On 5/22/2018 at 9:55 PM, regular guy said:

 

It is polyester resin. The way you can tell is if it has catalyst that just takes a small amount for the resin.

Epoxy is a 1 to 1 ratio.Not even close.

 

Polyester takes a MEASURED amount of catalyst, in the .5%-2% range IF YOU WANT IT TO WORK RIGHT.

Polyester resin cures by an exothermic (heat) reaction created by promoters (cobalt & amine) and activator Methyl Ethel Ketone Peroxide (MEKP). The reaction of polyester will occur at the thickest cross section sending out a wave of heat, which cures resin to a solid glass-like hardness. Temperature and moisture content can affect the rate of cure and the drying of part’s surface. The resin’s reaction starts with the addition of MEKP at 0.5% to 1.5 % (2 % for thin laminates). The ratio is dependant on air temperature, resin thickness, temperature of resin and mold. Fillers are added to help control peak exotherm, shrinkage, and cure rate. Unfilled resin can heat up to 300F resulting in cracking. Resins that create uncontrolled peak exotherm can exhibit wrinkles or alligator skin. Using lower levels of MEKP, preheating the mold surface, or both, can change this. In wet weather conditions, tacky surfaces may be exhibited by resin due to high humidity. Working in a controlled, dry-heated area should help resin to cure properly.

--------------------------------------------------------------------------------------------------------------------------------------------------------

EPOXY IS NOT ALWAYS 1:1. DO NOT ASSUME ALL EPOXIES MIX 1:1. THEY DO NOT.

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Thanks Ace

Will pick up some epoxy next hobby order.

Working on frame now.

Had to toss the Bondo resin but the cloth is still good of course.

So that is some progress finding the cloth that was already bought.

Will keep chipping away at this.

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