Hi,
I’m vacuum bagging a bike frame to cure the prepreg overwrap on the joints. Some of the tubes are completely sealed and therefore full of air. For example the chainstays are sealed with adhesive where they are bonded to the frame - at both ends with no holes along the length, (whereas the headtube is open at both ends). Will this cause any issues?
Thanks
may very well be an issue with rising temperatures, but it certainly wouldn’t be an issue to drill a very tiny hole…
I am assuming you are thinking to envelope bag the whole frame?
The rear stays are probably ok or better with being sealed, the small section shape means they will likely hold true ok while cooked.
Any larger or especially oval/foil shaped tubes could be at risk of deforming under vacuum and heat, adding a hole to a sealed tube would make things worse.
I repair a lot of bikes and mostly avoid pre preg even though I use pre preg for many other jobs. It’s generally too risky for me to cook a customers valuable bike and risk the frame, the paint and any plastic parts etc.
Yes, bagging a whole frame. It’s one I’m building myself, so I know what all the Tgs of the various bits should be, and in theory should be curing at 10 degrees lower than the lowest Tg.
Yes there’s risk involved but just keep the temps as low as possible (ie low temp pre-preg say 80 deg C) and it should be ok. Support rear stays with a dummy hub and jig up as much of the frame as possible to prevent warping.
Yep, got a dummy hub in there.
Is there any rule of thumb about how low below Tg is considered safe? I haven’t found any info yet on how steep Tg transitions are.