Carbon Fiber Saddle rails

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#1

I am designing a saddle out of carbon fiber .
I have already made the shell and what is left is the rails underneath.
I was wondering if anyone has made any before me in the forum and could advise me in any mean.
The rails have to be lightest possible so they will be hollow
They have to be 7mm outer diameter
I think they will not be 1 part with the shell as there are difficulties in the mold and the demold process .
So i have come to the decision to make the shell , the rails and bond them together . - There will be a hole in the down side of the shell that the rails will be inserted in ( like other manufacturers do)

  1. I am wondering what would bee the best method to create the rails

I will take an existing rail and make make a mould out of it - but with what material?

1a)Split mold with high temp Epoxy resin combined with fiber glass ? ? - using a first layer of the resin combined with some fumed silica to play with the thixotropy of the material and give it a gel coat abilities .

1b) Split mold Epoxy casting aluminium ?

  • Thing i will with this one .

  1. Now the killer part … How do i make the 7mm tube hollow
    2a) By creating before a smaller foam tube wrapping around it with carbon fiber and then put it in the mold???
    2b) by creating before a smaller rtv silicone part that i will wrap around again put in the mold and let the thermal expansion work - but at 7 mm diameter in 120 degrees celcius of the prepreg i expect expansion of the diameter around .1 mm and i dont know if this expanion will be enough for the right cure of the prepreg and the removal of the silicon from the cured part…
    2c) With positive pressure bag inside the hole … using a hollow casted silicone tube witha valve on the one side …but haven not tried this before.

  2. I am thinking of doing 2 projects - the one with carbon fiber only and the other with combination of carbon fiber and 2mm -3mm honeycomb,my only concern with that is the possibility of delamination of the saddle after some years of use

Any thoughts would be more than welcome

#2

for part 2

why not use a extruded CF tube that you can bond in ? maybe wrap it in carbon tow on the bias first this will help it to adhere

i use a foam rod that i wrap double bias carbon to make shear webs, and it works great !

#3

[QUOTE=Blackrat;60557]for part 2

why not use a extruded CF tube that you can bond in ? maybe wrap it in carbon tow on the bias first this will help it to adhere

i use a foam rod that i wrap double bias carbon to make shear webs, and it works great ![/QUOT

I cant use ready made tubes because the shape of the rails has corners and it chances direction and thinckness

#4

A cheap way of doing it is to get styrofoam, shape by hand and wrap with 1-2 layers of light cloth, light compression and allow to cure. Then sand the cloth, apply more layers as required and as much consolidating force as possible. Can even acetone the foam afterwards to melt it out but could actually be a useful damper in there

#5

I can as well pour 2 part polyurethane cast and pour it to the mold with a spacer of aprox 1 mm and then wrap wround carbon fiber

#6

It is for a bike saddle, right?

You have to use braid carbon fiber with internal inflate bladder.
Two valve mould of course

#7

for a bicycle saddle ? how long are the rods ? 150-200mm ? to make them hollow to save what 20 -30 grams ?
i would use a soft foam core and pull a few layers of braid over the core and then pull thru the mold

you can also use PVC clear tube for the mold, cut out a shape in plywood where the tube must lay, pull the fibers thru the PVC tube and lay in the wood shape…

after cut the pvc tube off

#8

It is a bicycle saddle and i want to go below 90 grams so 10 grams without a reason at the rails is a broblem

#9

Right!

But maybe you have ti changed your point of view…

Everybody use tube rail under the bike saddle (Steel, carbon, titanium)

It should be great to change tubes with another system compatible with the seat fix system…

#10

Could you be a bit more specific?
You mean take the tube wrap around prepreg put it inside the 2 part mold and then pull out the the pvc pipe remaining only with the carbon fiber ??