Bending CF rods and no tying of the joints - RC Groups
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Feb 02, 2016, 04:25 PM
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Ampbomber's Avatar
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Bending CF rods and no tying of the joints


Hi ,
With all the talk about bending of the CF rods I decided to start a new plane using bent rods and using a method of connecting the rods that eliminates tying all the joints.

Attached is a picture of the rods to be used in the build. The rods are made with 3K CF tow that is wetted with epoxy and pulled thru heat shrink tubing. The best hint I can give about shrinking the tubing with a heat gun is to be sure to glue down the ends of the tow before shrinking. Also, do not attempt to roll the tubing while shrinking it because that will twist up the tow inside and give a lumpy rod. Just heat it up and let it shrink around the tow. I used a 1:1 mix (weighed) of Z-poxy finishing resin. I have not experimented with any other epoxy (this is where you guys can have some fun and get back about different epoxies). After shrinking with a heat gun (takes less than 30 seconds), cut off the ends where it is glued down and pin (or whatever) the tubing to your form. Let the epoxy cure over night and then strip the tubing from the rod with a #11 blade held at a shallow angle. Stripping seems to be quite easy after the rod sets up completely ( in other words- no carbon is taken off the rod).
The rods in the picture are about 0.20 in diameter (.5mm). How strong are they..? What do they weigh..? I guess we will just have to play with this method and see what happens. The longest rod in the picture was 46 inches long and was not difficult to pull thru the tubing.
As for not tying any joints Iíll address that as I build the fuse and wings.
Enjoy,
George
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Feb 02, 2016, 05:23 PM
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MikeKucera's Avatar
If you don't mind me asking, what size of heat shrink tubing did you use?
Feb 02, 2016, 05:59 PM
A.K.A sir Crashalot
methuso's Avatar
I have ordered shrinktubing for this experiment. I think i will also try vaccum-equipment to suck out excess epoxy. My planes is small enough thati cpld fit it in my oven too to strengthen iteven further

Do someone know what could be used to dissolve the shrinktubing without affecting the carbon/epoxy?

/Ulf
Feb 02, 2016, 07:33 PM
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Ampbomber's Avatar
Quote:
Originally Posted by MikeKucera
If you don't mind me asking, what size of heat shrink tubing did you use?
tubing from eBay :
http://www.ebay.com/itm/201299881295...%3AMEBIDX%3AIT

It says 3/64 but measured 1/16. Have asked vendor about this. Vendor does list a 1 mm ID and I would probably have gotten that if I had known. Order white and it will be easy to distinguish rod from tubing.
Feb 02, 2016, 07:35 PM
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Ampbomber's Avatar
Quote:
Originally Posted by methuso
I

Do someone know what could be used to dissolve the shrinktubing without affecting the carbon/epoxy?

/Ulf
I think that would be a mess if possible. It is extremely easy to cut a slice off the top of the tubing without cutting the rod.
Feb 02, 2016, 07:48 PM
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Ampbomber's Avatar
More info: I did a test with 6K tow with the same tubing and the resulting rod was 0.026 or so. I'll be building with the 0.020 3K tow and see how it goes. Seems sort of flimsy to me but Alexey uses .5 and .3 mm rod on his plane so we will see.
Feb 02, 2016, 10:10 PM
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Ampbomber's Avatar
More info as I think of it :

When you wet the tow have it stretched out flat on the wax paper without any twists and tied down (glued) at both ends. Warm the epoxy mix a little to have it flow into the tow easier. I use my finger to work the epoxy into the tow. Next, squeggie out as much of the epoxy from the tow with a piece of card stock and then wipe the tow with a paper towel before pulling it into the tubing. The object is to totally wet the tow and then remove as much of the epoxy as you can before pulling it into the tube.
Feb 03, 2016, 12:03 AM
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MikeKucera's Avatar
Quote:
Originally Posted by Ampbomber
More info: I did a test with 6K tow with the same tubing and the resulting rod was 0.026 or so. I'll be building with the 0.020 3K tow and see how it goes. Seems sort of flimsy to me but Alexey uses .5 and .3 mm rod on his plane so we will see.
Assuming a filament diameter of 7.1 microns I calculate the fiber content to be:

Filament Count ......... Resultant Diameter ......... Fiber Content
6K .......................... 0.026" (0.660 mm) ......... 69.35%
3K .......................... 0.020" (0.508 mm) ......... 58.60%
Feb 03, 2016, 03:41 AM
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Quote:
Originally Posted by MikeKucera
Assuming a filament diameter of 7.1 microns I calculate the fiber content to be:

Filament Count ......... Resultant Diameter ......... Fiber Content
6K .......................... 0.026" (0.660 mm) ......... 69.35%
3K .......................... 0.020" (0.508 mm) ......... 58.60%
Mike,
Try and remember that I'm the low tech guy on the totem pole. What are you trying to tell me with this info?
Feb 03, 2016, 07:36 AM
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MikeKucera's Avatar
Those are excellent numbers, too much resin just adds weight.
Feb 03, 2016, 01:17 PM
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Speaking of numbers/data, MikeKucera's last post remeinds me - have you compared the weight of your rods with the commercial variety?
Feb 03, 2016, 01:22 PM
Registered User
.....and another thing!! Ampbomber, would vertically suspending the freshly wetted out tow and "squeegied" with a short (several inches) of shrink tubing was run down the entire length and then left to cure, be an alternate approach?

It seems that if the entire length of each fabbed rod needed a full-length heatshrink, you'd have spent a bunch that could have been avoided.

Just wondering, based on your approach.
Feb 03, 2016, 01:37 PM
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Hanging vertical is how he makes his straight rods. The heat shrink is for making formed to shape pieces.
Feb 03, 2016, 01:59 PM
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Quote:
Originally Posted by 3Dreaming
Hanging vertical is how he makes his straight rods. The heat shrink is for making formed to shape pieces.
AHA!!! Thanks for the reply. I just went out and fiddled a bit with some un-shrunk 1/16th heat shrink. It does make fairly small radius bends.
Feb 03, 2016, 02:01 PM
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Ampbomber's Avatar
Quote:
Originally Posted by 356Jim
.....and another thing!! Ampbomber, would vertically suspending the freshly wetted out tow and "squeegied" with a short (several inches) of shrink tubing was run down the entire length and then left to cure, be an alternate approach?

It seems that if the entire length of each fabbed rod needed a full-length heatshrink, you'd have spent a bunch that could have been avoided.

Just wondering, based on your approach.
Jim,

go here for rod info : https://www.rcgroups.com/forums/show...9#post20983768 post #285

This is how I began rod making. Since then I have changed to 25 turns and added a step that requires rolling the hung rods between the palms of my hands after the epoxy has "semi" cured. This will "cleanup" the rod and make the OD smoother. Also, I have used 12, 9 and 3 K tow for different diameter rods.
Bending the rods with the shrink tubing is inexpensive. 100 foot of the tubing is only $10. Can't bend without the tubing. Weight and strength have not been compaired.


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