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Old 28-07-2016, 15:00   #1
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Making carbon fiber spar from chop strains

I am not very adept with working with large sheets of carbon fiber fabric.

If I want to make a quick carbon fiber spar, would the following work.

1. Stand PVC pipe vertical (one will be 4" diameter and other 6" diameter with 3" diameter hollow core)

2. Pack with chop carbon fiber strains.

3 Tamp down to pack tightly, or just let fall loosely?

3. Pour epoxy slow cure resin from the top (10 feet section at a time).

4. Let cure.

5. Use Dremel to cut away PVC pipe.



I am merely looking for a resulting spar stronger than wood and epoxy tough. I realize it won't be the strongest spar compared to working with fabric.

Questions

1. Will it work?

2. Will resin gravity flow down the pipe and air escape up... or do I need a vacuum pump at bottom? The epoxy I plan to work with takes several hours to cure. It is concrete crack filler epoxy.

Thanks
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Old 28-07-2016, 15:17   #2
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Re: Making carbon fiber spar from chop strains

Why even bother with the carbon using this method? I think for any success at all you'd need a vacuum pump at the least, but if you just fill a pipe with loosly packed strands and epoxy all you've done is make a very heavy brittle cylinder with some pretty black stuff in it.
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Old 28-07-2016, 15:35   #3
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Re: Making carbon fiber spar from chop strains

If you want to spend lots of money and weeks fiddling around with a high risk of failure, and perhaps consequential damage, then do this. Otherwise buy a used/broken spar or spinnaker pole or alloy pipe for predictable performance and minimal cost.
- M
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Old 28-07-2016, 15:35   #4
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Re: Making carbon fiber spar from chop strains

Better... spray the smaller PVC with 3M77 adhesive.
2 layers of 5 oz fiberglass cloth (to aid wicking resin down the length of tube later... it draws through the fiberglass easier than the CF TOW)
Spray again...
Layer with CF "TOW" strips covering all of the pipe.
Spray again...
Layer again with a slight spiral appx 1 turn around the pipe per 10 ft.
Spray again...
Layer again with opposing direction spiral
Spray again...
Layer with another parallel to centerline layer
Repeat alternating the straight and spirals to get desired wall thickness.
Slide your larger tube over... should be a snug but not super-tight fit.
Next use vacuum to draw slow cure resin into the CF layers.

Still not as good as a factory CF tube... and it will cost you just about as much as the factory tube.

********************

Best home made CF spar:

Layer the CF as above directly on a wood core.
Applying with poly resin., no "surfacing wax" until the final layer.
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Old 28-07-2016, 15:35   #5
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Re: Making carbon fiber spar from chop strains

I can't even imagine a practical use for this. The pole would be rife with voids, poor bonding, and weak joints. And a 3" thick carbon rod... If it's is well made would be immensely strong, stiff and light... Like lift up a mega yacht strong. To then make it out of CSM so it has a swl of almost zero because of unpredictability... I just can't see it.


If for some reason you really want to do this, you need to be able to put the entire stack under a high vaccume, use infusion epoxy, and you will get a decent monolithic structure. But it still won't be very strong.
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Old 28-07-2016, 15:37   #6
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Re: Making carbon fiber spar from chop strains

Why use carbon for a hand layup? Complete waste of money.

By chopped carbon fibre strains are you referring to filament.

Concrete crack filler epoxy. Wtf.

This post must be a joke.

The correct approach is as follows:

1) determine spar dimensions, space claim and attachment
2) calculate the axial compression load it is to carry
3) determine first harmonic
4) chose material, define laminate schedule, build process so that it will meet and exceed the static and dynamic design loads
5) build the mold
6) build it
7) finish it
8.) fit it.

Your approach will be ugly, expensive and fail possibly before you even attach it to the mast.

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Old 28-07-2016, 17:33   #7
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Re: Making carbon fiber spar from chop strains

I guess I should mention I am in the Philippines. It is difficult to follow even simple standard recommendations. Like using radiator fluid. Nearly everyone here uses water, in a city of nearly 1 million people it took me roughly 12 trips to different stores to find one that carried it. Stores sell epoxy paint but no epoxy primer. No one sells short nap rollers here. No plastic drop cloths, No painters tape.

The standard answer is maybe in Manila.

Regarding concrete crack epoxy, it is actually very neat stuff. The extremely slow cure time means it gets into all the voids. Example use I made of it was to restore interior floor boards made from closed cell foam and fiberglass. The foam didn't survive all the foot traffic and compressed. As a result my floor boards had too much give. I simply turned the boards over, drilled holes in the boards and poured in epoxy. After few hours I could pour more. Over a period of two days I just kept pouring it in. My floor boards gained some weight true, however now feel like brand new solid steel.

I checked the compression and tensile strength against West Systems epoxy. They are similar.

There is also an epoxy I can order from Manila. I await their quote.

.....

Regarding voids I can help avoid that by only filling pipes a few inches at a time instead of filling full ten foot sections.

Also I can add chopped Dyneema to the mix.

Thanks Turning Turtle for details I doubt I can find 3M but may find something.
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Old 28-07-2016, 17:40   #8
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Re: Making carbon fiber spar from chop strains

Scrap the idea of "casting" the tube using 2 PVC pipes...

I can't recommend the concrete patch as your epoxy, but I can't say it won't work.

Shredded glass and/or CF will result in a weak spar. You need paralleled strands the full spar length. Not some random disorganized mass stuffed into the mold.

Far simpler to get Carbon "TOW" which is kind of like ribbon on a reel. and layer that onto a wooden core.

We've been using similar process to what I described to build extreme performance RC aircraft wings and fuselages from the start of Carbon Fiber becoming available. Our home made tubes have always been weaker and/or heavier than the factory made, but until recently the cost difference was worth the effort to make our own.

**************

3M formula 77 spray adhesive doesn't interfere with epoxy or poly resin layups. The resin dissolves the spray glue and it becomes part of the matrix.

I am not sure of good substitutes. The purpose of the spray is to keep good control of the cloth and TOW as you apply them, then you infuse the layup with the resin.

The slight spiral is pretty easy to control and you could tack the ends of the TOW over the ends of the wood core with Cyano-Acrylate, (Crazy Glue) then cut off the ends when the spar is complete. That means setting up to make the spar appx 4 to 6 inches longer than needed, and cutting the 2 to 3 inches off each end.
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Old 28-07-2016, 18:21   #9
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Re: Making carbon fiber spar from chop strains

A lighter one is built like this:

- pvc pipe wrapped in polyethylene or similar wrap,
- carbon ribbon (2 incher) wrapped in the spiral way, one inch overlap,
- epoxy,
- optionally more layers as above, epoxy, (wet on wet),

Now either dry-cloth and tight wrap (to remove excess epoxy) or vacuum bag and pump.

Let cure.

Post cure (bake) if you care (a lamp oven will do).

Less epoxy, possibly stronger and definitely lighter.

NOTE: A wooden stake is the better mold as is stiffer and can be tapered. With pvc you end up with a mis-shaped pole, unless you are building a very short one.

Or just buy a carbon pipe or rod and cut to length. Done. ;-)

Cheers,
b.
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Old 28-07-2016, 20:08   #10
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Re: Making carbon fiber spar from chop strains

I think that if I wanted to do this I'd start at sollercomposites.com where you can get CF sleeve and heat shrink (goes up to 10" dia). Slide the sleeve over any suitable core (PVC and ABS might have a bend), wet with epoxy, slip the heat shrink over and get your heat gun out. No vacuum needed, comes out with a pretty good surface after cutting off the heat shrink but polishes up nicely. Repeat if necessary.

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Old 28-07-2016, 20:16   #11
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Re: Making carbon fiber spar from chop strains

chopped strand is definitely not a good idea to make a spar.
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Old 28-07-2016, 20:50   #12
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Re: Making carbon fiber spar from chop strains

Chopped fibers is only good for making surface structures such as paneling or hulls, but need additional reinforcement from bulkheads or braces/structs.

For a spar, you need to make a female mold that's two halves, laysheets of resin impregnated cf fabric and later until you have desired strength. Then inflate a high temp bladder and bake.

IOW, you're better off with wood.
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Old 28-07-2016, 21:54   #13
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Re: Making carbon fiber spar from chop strains

Some of these ideas are too heavy. You don't need a tube if you have side stays. The Voyager aircraft used an I beam for a wing spar mold. They used blue boat dock foam covered in glass for shape.
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Old 28-07-2016, 23:14   #14
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Re: Making carbon fiber spar from chop strains

Quote:
Originally Posted by pbmaise View Post
I am not very adept with working with large sheets of carbon fiber fabric.

If I want to make a quick carbon fiber spar, would the following work.

1. Stand PVC pipe vertical (one will be 4" diameter and other 6" diameter with 3" diameter hollow core)

2. Pack with chop carbon fiber strains.

3 Tamp down to pack tightly, or just let fall loosely?

3. Pour epoxy slow cure resin from the top (10 feet section at a time).

4. Let cure.

5. Use Dremel to cut away PVC pipe.



I am merely looking for a resulting spar stronger than wood and epoxy tough. I realize it won't be the strongest spar compared to working with fabric.

Questions

1. Will it work?

2. Will resin gravity flow down the pipe and air escape up... or do I need a vacuum pump at bottom? The epoxy I plan to work with takes several hours to cure. It is concrete crack filler epoxy.

Thanks
Seems like a bad idea for all the reasons above plus, if I did the math right, at a weight of .62 oz per cubic inch for the resin alone, your 6"OD x 3"ID spar will displace 254 cubic inches per foot, which works out to 9.84 lbs per foot. So a ten foot spar would weigh close on to 100 lbs.

Why not use the materials available in your part of the world to make a composite spar that is lighter, stronger, prettier and probably longer lived?

There are likely dozens of species of strong, (relatively) light, rot resistant hardwoods available in the tropics that wood (haha) make a good spar, especially when coupled with an appropriate construction method such as this one, called a 'birdsmouth spar'.




Combined with epoxy and a layer of glass on the outside (for protection, though considered properly it could also add considerable strength to an already very strong structure), these are strong and very light for their dimensions. And they're surprisingly easy to build, all you need is a table saw (or router though that is more difficult), some hose clamps, and a method of rounding the spar off after it's built. For the oar shafts I've built using this method I just use a hand plane and a DA for the rounding.

So you can use things that are readily available, labor and lumber, and get something that might better serve your needs. Obviously just a suggestion...

Another look at how it's done.

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Old 29-07-2016, 04:07   #15
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Re: Making carbon fiber spar from chop strains

Quote:
Originally Posted by jimbunyard View Post
Seems like a bad idea for all the reasons above plus, if I did the math right, at a weight of .62 oz per cubic inch for the resin alone, your 6"OD x 3"ID spar will displace 254 cubic inches per foot, which works out to 9.84 lbs per foot. So a ten foot spar would weigh close on to 100 lbs.

Why not use the materials available in your part of the world to make a composite spar that is lighter, stronger, prettier and probably longer lived?

There are likely dozens of species of strong, (relatively) light, rot resistant hardwoods available in the tropics that wood (haha) make a good spar, especially when coupled with an appropriate construction method such as this one, called a 'birdsmouth spar'.




Combined with epoxy and a layer of glass on the outside (for protection, though considered properly it could also add considerable strength to an already very strong structure), these are strong and very light for their dimensions. And they're surprisingly easy to build, all you need is a table saw (or router though that is more difficult), some hose clamps, and a method of rounding the spar off after it's built. For the oar shafts I've built using this method I just use a hand plane and a DA for the rounding.

So you can use things that are readily available, labor and lumber, and get something that might better serve your needs. Obviously just a suggestion...

Another look at how it's done.

I am getting a quote for hollow wooden spars made in Philippines. I am thinking of having two sets made and carry the second set flat on supports at deck level. Having one of these spars break 1/3rd of way between Japan and Hawaii would likely force me to turn back. So two sets of spars or one set vastly over capacity sounds good to me.

A 100 lb spar sounds light to me. I don't know the exact weight of my sail but it is around 225 lbs. If a crew member is on top installing the cover that is even more weight. Most of that weight must free span across my pilot house. Another task for the upper spar is lifting the dinghy on board. I have a solid fiberglass sailing dinghy and it weighs a lot.

The lower smaller spar replaces the original boom that was about 14 inches tall, and 5 inches wide. That boom weighed around 200 lbs.

I requested the spare builder quote me a solid wood smaller spar. I have Dyneema filament that I can epoxy onto the wood to make it even stronger.
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