Hi guys,
I’m thinking about building a CF saddle for my mountainbike but I can’t figure out how to make the saddle rails(6-8mm bent tubes) from CF.
The picture below shows you the underside of a commercialy available CF sadle.
http://imageshack.us/photo/my-images/132/saddleaxunderml9.jpg
The only idea I came up with is using thin walled aluminium tubes and cover them with a glass fibre sock before aplying the CF.
What do you think?
No pic, but you are new…there are rules about that 
You can do it in a few ways…female split mold, and internal bladder, or expanding core. You can use a foam core and just wrap. You can use a thin walled aluminum tube (yes, glass THEN carbon). You can maybe do a sectioned straight mold that you just pull out the pieces.
Are the tubes load bearing? If they are only 6 - 8mm then they would probably have to be solid carbon, or nearly, to bear much of a load. Making small tubes with thick walls with a bladder would be difficult. Using an expanding core wouldn’t work very well because there won’t be enough material to expand to accomplish much. Expanding cores and heated silicons are dependent upon the cross section of the core. The greater the cross section the more expanding force there is and vice-verse.
I would make them in a two piece mold with a flared entry port and pull lots carbon tow into the mold cavity. You bundle up the carbon tow and fold the bundle in half. Then you attach some cord to the fold. You then dip the bundle of carbon tow into resin to saturate and lubricate it. You then pull the bundle into the mold with the cord. The tapered entry port squeezes out the excess resin. Having a come-a-long is helpful if you want a good Vf and use a spectra cord if you will be pulling hard. You can also do this technique with a braided sleeve over the tow bundle. You make the bundle, fold in half, attach the cord, slide the braided sleeve over the bundle so the upper portion is above the chord knot. You then wrap dental floss around the braided sleeve so it is tight around the cord above the knot. This will prevent it from slipping past the knot when you pull the bundle through the mold.
It takes a little practice to learn how much carbon you can pull into the mold diameter.
Only one saddle for you? If yes buy a old Selle flite Titanium and use the titan tubes, they are light and work with carbon fibre.
Thank you all for your usefull answers!
I’ve edited the opening post and added the url tot the image of the saddle.
And in this pdf file, from page 34, you can see more pictures of cf saddles. http://ax-lightness.de/nc/infocenter/downloads/?tx_abdownloads_pi1[action]=getviewclickeddownload&tx_abdownloads_pi1[uid]=106&tx_abdownloads_pi1[cid]=486
@Riff42
A few years back I’ve tried to build some straight 6mm thin walled tubes in a female mould using a bladder, but I never got a result that satisfied me… It seemed that the fibres where floating around in the mould, which made it hard to get an even thickness of the tube.
For these tubes it even gets harder because the tubes are curved and have thick walls.
The option of building the tubes from straight pieces which are glued togeher might be the simplest option, so I will keep that in mind.
@wyowindworks
Yes the tubes are load bearing. They connect the “saddle deck” to the saddle post. Together they have to carry at least 80kg, but it will be some more when I take the dynamic loads in account.
I really like the process you describe! I think I will give that a try.
I will keep you all updated about the progress!
Oh, saddle RAILS, not the post…
Solid carbon for sure. Overlay of kevlar in case it snaps, it won’t fall completely off the post, along with clamping pressure damage. You can use braided tows, or just roll fabric. I could also say the inside is all uni, since that is the only strength you need, with just a single fabric/braid on the outside to confine the unis.