Talk Composites - The Forum for Advanced Composites

Bike Frame Project Questions

http://www.talkcomposites.com/Topic11902.aspx

By FrameFudger - 6/18/2014 12:05:21 PM

Hi guys,

Posted this in the projects section but didn't get a lot of love, so posted it here! 


I am making a bike frame from scratch, so far I have made all my tubes. They are made out of UD pre-preg hi-mod CF. Now I need to glue them together, wrap the titanium bottom bracket shell, fillet the joints and then wrap the joints with more UD pre-preg. 

As this will need to be put back in the oven at 130deg C all glue etc used in the joining and filleting processes needs to be able to withstand being re-heated. Obviously as its a bike frame it wont be used at temp once it is finished.


Bottom bracket Shell

Will be wrapped in pre-preg UD CF. Want to make sure the bond between the titanium and CF is stronger than the just the pre-preg resin. So which epoxy to use?



Tube joining

Tubes will be mitred and then fit flush to each other. Once they have been glued I will then be wrapped further pre-preg UD CF around the joints, so the epoxy needs to be generally strong with a little flex, however will not be the only structural element taking force and load.

I was looking at the ET515 Epoxy Adhesive, but I am not sure if this is the most suitable?


http://www.easycomposites.co.uk/products/structural-adhesives/semi-flexible-15min-epoxy-adhesive.aspx


If not what would you suggest?




Joint filleting

Prior to wrapping the joints in further UD CF I need to fillet the joint so there are no sharp acute angles which could create a void after wrapping and curing.


Similar to this...

http://applemanbicycles.com/wp-content/uploads/2013/12/KoenFilletHTP1040089.jpg



What filler \ epoxy combination would you suggest, as this isn’t structural the lighter the better.Someone on the forum suggested using a mix of carbon powder, glass bubbles and epoxy.


Which epoxy would be suitable and what ratios of each would you advise?




Look forward to your responses.


Cheers,

Andy
By Warren (Staff) - 6/19/2014 4:53:54 PM

Glue wise use ET515 throughout for simplicity.  Key reason is ET515 should give a high flexural strength to the bottom bracket joint.

EL2 is fine for making the filleting paste.

You need to experiment with filler amounts but usually 10-20% by weight bubbles is plenty and will thicken it slightly, then add fumed silica small amount at a time until you achieve the consistancy you want upto a maximum of about 3%.