Bending Formable Carbon Tubes.

[BorisS]

Hi,

I want to build a new dome out of these formable carbon tubes.
http://www.carbonscout-shop.de/CFK-Carbon-Rohr-thermoplastisch-Abm-16x14x500mm.html

They should be fixed to the center-plates exactly like the booms on a AD 8 HL but than bend up over the Center plate and Electronics.

Does one of you have any experience with this formable Carbon. I am pretty sure if i try to bend it it will not stay in shape but fold and not stay round. I know of trumpet makers that they bend the cooper or brass tubes , by filling them with lead and let it cool down and than they can bend it, without the tubes folding. I dont want to heat up 200 ml of lead and deal with it hot with carbon . Can anybody think of something else ? Or is formable carbon easier to handle as i am putting it ?

Thanks

Boris

 

[jes1111]

I've been using the thermoformable sheets from them, but have not tried the tube. The problem (with sheet, but particularly with the tube) is that the material will not stretch (which is what happens to the outside of the curve when you bend metal tube or plate). This is okay with the sheet, as long as you do not attempt too small a radius on the bend (i.e. don't make the corner too tight). But, looking at the images they provide, the tube does not bend so well - you can see on the picture on their site that a very gentle curve worked okay, but on the 90 degree bend the carbon fabric is "bunching" on the inside of the bend and the tube is flattening itself on the outside (where the material would want to stretch). I therefore concluded myself that the material was of limited use (to me). However, for a cage it might work well if you "exploit its weakness". Instead of attempting a 90 degree bend, flatten one end and bend it to make the mounting foot, make a very gentle curve (like the bottom piece in the image). Then flatten the other end and bend it to make the other foot. Now heat and pinch the centre of your curve and bend that flat section at each end to create your "arch". Now just make another one exactly the same (always the most difficult part ) and drill the mounting holes in the "feet". I'd recommend joining the two flats where they cross at the top with epoxy.

EDIT: I lied! I get mine from www.carbon-team-de - same price and appears to be the same material.

EDIT2: if you do want to fill the tube with something to stop it collapsing completely, dry sand is probably the best. Commercial operations (for general pipe bending) often use candle wax melted into the tube.

 

[Crash]

EDIT2: if you do want to fill the tube with something to stop it collapsing completely, dry sand is probably the best. Commercial operations (for general pipe bending) often use candle wax melted into the tube.

I have used sand quite successfully to bend PVC tubing. Never heard of using wax. That's a good idea.

 

[RTRyder]

Or you could just get one of the Flight control crash cage now being offered, see it here... http://www.droidworx.com.au/conceptx.html

Ken

 

[BorisS]

Sand sounds like a good idea. Wax would probably also do it but warming up the finished formed tube to get the material out again is were i cant (without having worked with the material) estimate if the tube would change its form again. But maybe its the point of getting some wax with a very low melting point. I will consider both. Thanks !

Ken yes I like that one but with the prices DW has I would prefer to make my own and be proud. I think the looks of having exactly the same tubes like the booms coming from the center plate would also look good, Keeping it simple and sticking to one form.

Thanks Guys, ordering some tubes and will experiment.

 

[Droider]

Sand.. we used to sand load copper / lead pipes to bend them with out creasing.. now that going back a few years.. now we just use fittings and rarely bend pipe.. but sand hammered in tight a a VP then plugged with either a wood stopper or rammed rags.

Dave

 

[BorisS]

Would you guys be concerned to drill extra holes for screws into the center-plate ? I am not familiar with carbon would it weaken the structure ? For holding the shaped tubes i want to use the standard boom clamps, although i am shocked by the price.

http://www.kopterworx.com/Spares/Boom-clamps

Thanks

Boris

 

[ovdt]

Boris, I drilled a 4mm hole to the Droidworx carbon fiber extended landing gear which has 2 mm wall thickness.

If you hold tight and drill it with very high speed, you won't have any cracking problem. You should be fast and strong while doing this

 

[jes1111]

...and use a good drill bit, preferably tungsten tipped, or a carbide/diamond coated bit. Use light oil to lubricate (you don't want the CF or the drill to get too hot). After drilling, seal the exposed edge with CA glue. It won't weaken anything, no worries.

 

[BorisS]

tubes should arrive tomorrow or friday than i will report and show the first results. I changed my mind to use the booms clamps and to drill additional holes in the center plates. Cant deal with all the taking apart desoldering etc. I will use the existing holes for the Cover Dome fixation on the center-plates and just drill holes in the formed tubes that will become the cage. The arms will come together not over but around the GPS shield so that should give enough support.

I would like to additionally place some MTU metal to shield the gps even better. Does one of you have a source ?

Thanks for all the advice on the drilling.

 

[BorisS]

hmm must say the quality of the tubes that just arrived dont make me happy ! Maybe i expected to much. They are soft roughly cut on the edges and compared to the booms of the AD just not nicely finished. But maybe thats the sacrifice for it being formable ?

View attachment 663

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[jes1111]

Hmmm... they don't look very nice, do they? The top layer is gel-coat: you can sand it down with medium then fine wet-and-dry. After shaping you could spray with a standard gloss varnish.

 

[BorisS]

japp i will do that. I just feel a little cheated. The price is high and the end and beginning piece i will have to cut away since they are already thorn slightly. Whatever will start building some bending forms so i get them all the same shape and i will try it out.

 

[jes1111]

This is a (bad) picture of regular CF sheet (on the left) and thermoformable (on the right). Slightly different weave - but otherwise of apparently identical quality.

Second image is the legs of my Gitzo tripod (mega-quality pulwinded, with matt finish) versus 18mm pulwinded tube (second from the bottom - actually gloss finish but doesn't really show).

All from www-carbon-team.de

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[BorisS]

Strange one the Thermosheet looks a lot beter than the tube. I hate going through complaints back to companies but in this case i might just do it ! Thanks for the pics !!!!!

Boris