Epoxy Filled 3D Printed Props - RC Groups
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Dec 31, 2017, 03:27 PM
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localfiend's Avatar
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Epoxy Filled 3D Printed Props


Anyone thought about doing this for oddball impossible to find props?

I've got an XF5U in need of some giant (for a foamy) 16.8" quad blade props.

Got the STL part figured. Dan Sponholz designed the profile for me so we could make a display set.

I want to go further, and have made the props thin wall printable and want to fill them with something strong enough for actual use. Any thoughts on the type if epoxy I should try for something like this?

I'd think that it would have to be thinner. Thick epoxy would be hard to fill all the voids.
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Dec 31, 2017, 04:42 PM
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Try system three clear coat. It's about 400cp. It will flow into any and all holes and cracks.
Dec 31, 2017, 04:49 PM
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localfiend's Avatar
Quote:
Originally Posted by 1freeflyer
Try system three clear coat. It's about 400cp. It will flow into any and all holes and cracks.
Cool. A little expensive, probably cause its clear. But I magine most epoxy stuff will be. Might order some if I don't find something cheaper. Being able to flow into tight spots will be perfect for the application.
Dec 31, 2017, 04:59 PM
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Rcfiddy1's Avatar
Quote:
Originally Posted by localfiend
Cool. A little expensive, probably cause its clear. But I magine most epoxy stuff will be. Might order some if I don't find something cheaper. Being able to flow into tight spots will be perfect for the application.
Why not thin the epoxy.
Dec 31, 2017, 05:18 PM
Registered User
You could go with a thicker epoxy then spin cast them. Mount them to a central block with an auto grease head filled with epoxy, then rotate the assembly at about 100 rpm.a
Dec 31, 2017, 09:19 PM
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localfiend's Avatar
Quote:
Originally Posted by Rcfiddy1
Why not thin the epoxy.
Guess it would depend on if voids are left after whatever you use to thin the epoxy evaporates. Probably worth trying though. Wonder if I have anything on hand that's got a longer that 5 minute setup time.


Quote:
Originally Posted by 1freeflyer
You could go with a thicker epoxy then spin cast them. Mount them to a central block with an auto grease head filled with epoxy, then rotate the assembly at about 100 rpm.a
Heh, that could be entertaining. I've got a vacuum chamber. Might be able to do the same without spinning if the cure time is long enough.
Jan 01, 2018, 10:36 AM
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Lnagel's Avatar
Epoxy by itself does is brittle and does not add strength. Composite materials such as carbon fiber and fiberglass get their strength from the fibers themselves. The epoxy is only used as a medium to hold the fibers together.

Larry
Jan 01, 2018, 05:11 PM
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localfiend's Avatar
Quote:
Originally Posted by Lnagel
Epoxy by itself does is brittle and does not add strength. Composite materials such as carbon fiber and fiberglass get their strength from the fibers themselves. The epoxy is only used as a medium to hold the fibers together.

Larry
I understand that, but, it just needs to be stronger than the layer adhesion on 3D printed plastic to be good enough I'm thinking. There is internal structure inside these props, as well as the outer skin itself that will be made way stronger by the addition of the epoxy.

Guess I'll just have to find out. I'll be making several different types and breaking them for analysis before putting them on a motor.

First off, some display props. These are a bit thicker than the real world use props will be, and have more room inside, which will be good for testing. You can see the supporting ribs that will be printed inside, there is room around those supports for epoxy to seep through. If I need to make more room I will do so.
Jan 08, 2018, 02:31 AM
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PaulB's Avatar
All good stuff but how about turning it around???

You are obviously all over some 3D CAD program or other to get the .STL files out so how about converting them to 3D print moulds and laminate a couple of layers of carbon in to create 'real' props??

Just food for thought,

Paul
Jan 08, 2018, 05:28 PM
wrong descision, wrong time
Quote:
Originally Posted by PaulB
All good stuff but how about turning it around???

You are obviously all over some 3D CAD program or other to get the .STL files out so how about converting them to 3D print moulds and laminate a couple of layers of carbon in to create 'real' props??

Just food for thought,

Paul
I second this suggestion. You'll get much better results. I have not had good luck with spinny 3d printed stuff.
Jan 08, 2018, 06:10 PM
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USXPAT's Avatar

Safe Props


I would third this. Using 3D printing to make molds is a great use of the tech, but I would stay away from making props. One thing I have had success with in the past is trimming/modifying existing props to look more scale. If you are careful it will probably yield a better/safer prop.
Jan 08, 2018, 06:53 PM
Registered User
localfiend
If you look at the root section of a prop it has quite substantial cross section and there is a very good reason for this. When spinning the root of the blade is under considerable tension due to the centripetal forces.
Epoxy is quite heavy so it will add to the blade wight and thus increase the radial forces still further but epoxy is brittle and weak in tension. The result is that an epoxy filled blade is more likely to fail than a hollow one!
The only way you could print a 'strong' prop would be to arrange that the printed beads ran along the blade and it would have to be solid.
Even then with the materials that can be printed it would not be as good as a proper injection moulded prop and nothing like as strong as a carbon filled one.
Jan 08, 2018, 09:23 PM
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localfiend's Avatar
Quote:
Originally Posted by Quorneng
localfiend
If you look at the root section of a prop it has quite substantial cross section and there is a very good reason for this. When spinning the root of the blade is under considerable tension due to the centripetal forces.
Epoxy is quite heavy so it will add to the blade wight and thus increase the radial forces still further but epoxy is brittle and weak in tension. The result is that an epoxy filled blade is more likely to fail than a hollow one!
The only way you could print a 'strong' prop would be to arrange that the printed beads ran along the blade and it would have to be solid.
Even then with the materials that can be printed it would not be as good as a proper injection moulded prop and nothing like as strong as a carbon filled one.
We will find out. I've got several types of epoxy on order. I understand that weight will be an issue, but I believe that can be offset to a degree. I can always include more spar material inside the prop to reduce weight, if epoxy is that much heavier than the plastic being used.

I understand it won't be as good as an injection molded prop. This is just for props that can't be easily or cheaply gotten any other way.

Of course, if it works out, making a mold from the 3D print won't be that big of a deal, and I can cast something stronger.
Jan 17, 2018, 11:38 AM
Head NEAT geek
Tom Hunt's Avatar
I have been designing and printing flyable model props for my scale and sport models since 2005. Mostly using SLS powders (nylon) but more recently in FDM machines (ABS). I have never had one fail in the air, but certainly have had them break (and quite easily) on a prop strike. 99% of the time they fail near the hub, but occasionally will fail along the length.

I have one 21" diameter 3 blade scale prop I am putting over 1800 watts into.

Occasionally I will design the prop slightly smaller (in airfoil section) and glass the outside with 2oz cloth and West Systems epoxy. I don't get that much better strength for the ground strike, but it is much less flexible in the air and a bit more efficient.

If you are using FDM process and ABS plastics, you can paint (brush) the part with acetone to make the part significantly stronger.

NEVER EVER run up a new 3d printed prop design near by. use a test stand and a ESC driven by a transmitter and stand WELL away from the prop arc. DO NOT do it inside (even if you are in the next room with the TX), unless you want a blade sticking into a nearby model or drywall!

Contrary to popular belief, the dominant load on any prop is NOT thrust! It is rotation forces trying to fling the blade out of the hub. Rotation loads are up to 100 times greater than any thrust load you can create! AND must be respected.
Jan 17, 2018, 02:17 PM
wrong descision, wrong time
Still interested in this thread. I'd like to make my own folding props for sailplanes. For whatever reason I can never find the size and pitch I need for my projects. I also need to wrap my head around now to design a prop in 3d cad ...


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