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All Forums >> RC Airplanes >> Composites Fabrication And Repair >> Need tricks on sanding down carbon fiber wing tube.
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Need tricks on sanding down carbon fiber wing tube. - 6/29/2004 6:05 AM   
Smokey


 

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From: Bronxville, NY, USA
Status: offline 		I have to sand down a carbon fiber wing tube that i bought. It is very tight on the fuselage and wont even go in on the wings. Anybody have any quick ways of reducing its diameter?
If all i can do is sand it down. What grit sand paper should i use and do i wet it?

Thanks
Smokey

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RE: Need tricks on sanding down carbon fiber wing tube. - 6/29/2004 9:03 AM   
Mike James



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Status: offline 		Well...

If you have a choice, I would trade the tube or buy another one that's the correct size. Carbon isn't fun to sand, and if you get into it much, you may weaken it. Maybe just save the tube you have, as is, for another project, and replace it with one that fits.


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RE: Need tricks on sanding down carbon fiber wing tube. - 6/29/2004 7:00 PM   
buttuh


 

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Status: offline 		Amen to Mike

Evan

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RE: Need tricks on sanding down carbon fiber wing tube. - 6/29/2004 9:44 PM   
sensei



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Status: online 		I would not even consider the idea of sanding on the wing tube, however in the past I have been faced with the same situation, so I got my hands on a 36" 3/8" dowel and slotted one end of it down the center opprox. 2.00" deep and ca glued a piece of stiff backed 80 grit sand paper doubled over on itself about 3.00" long by 2.00" wide. I then inserted the other end into a 3/8 chucked electric drill motor and slowly honed the inside of the wing tube. You must hone the inside of the tube with a constant moving motion in and out at a low to medium rpm and checking the tube fit frequently. This works very well and you only have to take off a few thousandths to achieve your objective.

Bob Sawyer

PS We did this operation with a 40 % Radiocraft Extra and with a Hanger 9 Ultimate bipe, both worked out very well and are still flying today.
quote:

ORIGINAL: Smokey

I have to sand down a carbon fiber wing tube that i bought. It is very tight on the fuselage and wont even go in on the wings. Anybody have any quick ways of reducing its diameter?
If all i can do is sand it down. What grit sand paper should i use and do i wet it?

Thanks
Smokey


< Message edited by sensei -- 6/29/2004 2:13:47 PM >

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RE: Need tricks on sanding down carbon fiber wing tube. - 6/30/2004 5:12 AM   
probligo



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From: opononi, NEW ZEALAND
Status: offline 		Again, amen to those who are saying "do not sand it..."

A thought for you, and following from Sensai above, is to sand out the wing tubes.

There are two reasons for this - one valid and one questionable...

First - it will be a lot safer all round than sanding the cf joiner(s). I presume the tubes will be ali? If glass then go carefully as well to not cut the glass threads as well. I WOULD STILL LEAVE THOSE TUBES SO THAT THE JOINERS ARE A FIRM FIT. That helps keep the wings on

The second (this is something I have tried but not proven sucessfully) is based on a comment that was made to me some while back that cf tube does not like point loads. IF THIS IS CORRECT then sanding out the tubes in the wings could be combined with relieving the tube ends just a fraction more to stop the point load at the joint. I repeat, this is to my knowledge conjectural and not fully proven and I for another would appreciate comment from those who know.

<e> One thing I haven't seen mentioned...

MEASURE FIRST, and work out how much difference you are going to have to take off the tube. It should be very little - like no more than a wipe or three with 400 grit wd paper...

Is the wing root joint to the tube "blocked" with a thin layer of epoxy?

Is there a simpler answer? as has been said - different sized tube (be careful with that as well because you do not want to under-spec it... )

< Message edited by probligo -- 6/30/2004 2:18:30 AM >

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RE: Need tricks on sanding down carbon fiber wing tube. - 6/30/2004 7:00 AM   
sensei



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Status: online 		What I have found is that you only need to remove 2 or 3 thousandths, and this will allow the wing tube to be snug, but more user friendly. If you use the 80 grit sand paper and the method I spoke of in my first post it will take you around 10 minutes a wing socket. If you are going to use a carbon wing tube there is one more step you should really do, at the root rib and the the fuselage sides where the tube penetrates the wing socket and fuselage socket, Roll the edge of the sockets with 180 grit sand paper and finish with 320 grit so you do not have a hard sharp corner. This will keep the wing tube from wearing a groove during flight, additionally it will remove some of the stress riser from having a sharp corner.

Bob Sawyer

CEO FIBER ART INC.
www.fiberartinc.com

< Message edited by sensei -- 6/30/2004 6:30:22 AM >

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RE: Need tricks on sanding down carbon fiber wing tube. - 6/30/2004 7:18 AM   
Smokey


 

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Status: offline 		I went with the 3/8" dowel, sandpaper and drill route. Worked great!!!! Thanks for everyones help.

Smokey

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RE: Need tricks on sanding down carbon fiber wing tube. - 6/30/2004 8:25 AM   
HORNETONE


 

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Status: offline 		Hi everyone .....

By looking at this post I also have a question that keeps bugging me for a while ,can CF tube to be threaded on the inside or outside .
T I A ,
Sonny !

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RE: Need tricks on sanding down carbon fiber wing tube. - 6/30/2004 10:10 AM   
buttuh


 

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Status: offline 		Sonny,

I've never done it but my guess would be no it's not possible. Carbon graphite shatters easily. Even if you could thread it I wouldn't count on it to keep anything in place.

Evan

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RE: Need tricks on sanding down carbon fiber wing tube. - 6/30/2004 1:46 PM   
davidfee



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Status: offline 		Yes, you can thread carbon rod or tube. However, you're usually better off just epoxying a concentric rod or sleeve to the end since, as Evan said, carbon is brittle. What's more, the fibers are cut in the threading process, so there isn't much holding the threads in place... they will be weak.

That all said, I have threaded the ends of carbon rod pushrods and screwed metal clevises onto them. It worked, but now I just make custom ends and epoxy them. It can be as simple as a bent piece of music wire, with the joint epoxied and wrapped with Kevlar thread.

-David

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