Bike Frame Project Questions

Talk Composites - The Forum for Advanced Composites

Back

Bike Frame Project Questions

Author	Message
FrameFudger	FrameFudger posted 10 Years Ago HOT Topic Details
Group: Forum Members Posts: 8, Visits: 51	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... 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 Tags Bike Frame filler fillet Edited 10 Years Ago by FrameFudger
	Reply Like 2
ajb100	ajb100 posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 346, Visits: 4.4K	I personally wouldn't use 515 for tube jointing as it is very flexible so wouldn't be suitable, and will put additional stress on on the ud fibres you put on after. A rigid adhesive would be much better. As for the filtering, not sure why you would need the carbon powder. I would go for fumed silica to thicken up the resin to a paste and glass bubble to reduce the density
	Reply Like 3
FrameFudger	FrameFudger posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 8, Visits: 51	It was a suggestion from someone else, I personally haven't got a scoobie, which why I am asking here ;-) One thing I forgot to mention is once the frame has been glued together and filleted the joints will then need to be wrapped with further UD pre-preg and it will be put back in the oven at 130deg C for 2 hours...
	Reply Like 3
Warren (Staff)	Warren (Staff) posted 10 Years Ago HOT Post Details
Group: Administrators Posts: 2.5K, Visits: 7.9K	First thing i see a big problem with the fact you are looking to bond raw pre-preg onto parts - thats how it reads anyway. All of the structural adhesives are not designed for high temperature use so the pre-preg cure is likely to damage the resin bond! In my experience, bottom bracket inserts are either bonded in after the frame is made, or mechanically locked in place as the carbon is laid around it. usually bonding is preferred as it means should the bracket wear or fail it can be removed and a new one bonded into place. ET515 is not really "flexible" in the sense of you can bend the joint easily once fully cured. It has a high flexural strength ie it is able to resist flexing forces and vibration better than other adhesives. In terms of joining the tubes, again you have the heat issue damaging the glue strength. I would thoroughly recommend in your design, you have enough layers of pre-preg wrapped around so the pre-preg alone is capable of taking all the necessary expected loads. That way the bonded joint is purely there to help hold the frame in one piece during assembly and curing. ajb100 is right when it comes to making a filleting paste. The bubbles will help weight wise and the silica will thicken it to a paste/bodyfiller consistancy so you can work it where needed. Warren Penalver Easy Composites / Carbon Mods - Technical Support Assistant
	Reply Like 3
FrameFudger	FrameFudger posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 8, Visits: 51	Hi Warren, Thanks for the feedback. So modifying my plans slightly how does this plan sound? 1. Bottom Bracket: Make a CF tube using the Titanium shell as a mandrel 2. Glue the frame together, glue type not really that important as it will get damaged in the final frame curing process 3. Create fillets around joints using Fumed Silica, Glass Bubbles and Epoxy 4. Structurally wrap the joints with enough CF to guarantee joint strength 5. Cure completed frame 6. Glue in Titanium bottom bracket shell So if that sounds sensible then: - Which glue would you suggest to glue the frame together? - Which glue would you suggest to glue the titanium BB shell in? - Which epoxy would you suggest to make the fillets? - Any idea on % part quantities of Fumed Silica, Glass Bubbles and Epoxy to use for the fillets? Thanks in advance for your help. Cheers. Andy
	Reply Like 4
Warren (Staff)	Warren (Staff) posted 10 Years Ago HOT Post Details
Group: Administrators Posts: 2.5K, Visits: 7.9K	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%. Warren Penalver Easy Composites / Carbon Mods - Technical Support Assistant
	Reply Like 3