As a potential replacement for soluble ABS cores over which to layup the carbon fiber bicycle, I am testing printed PVA cores. PVA is soluble in plain water. I designed a mock head tube assembly consisting of dissolvable cores and end caps and 2 bearing races which would remain in the composite part. Conceivably, the races would be machined in titanium for the final product.
Printed, assembled, layup, wrapped.
I experienced some sliding in the layup again. I am not allowing enough room on the caps to secure the wrap before spiraling down the layup. Certainly still room for improvement there. Also, resin ran into my bearing cups because the design of my caps and core did not block it properly.
But regarding a new core material, and only judging with one test, the 3D printed PVA solvable core for composite layup worked only okay. First off, PVA is a bitch to print. It takes longer than ABS or PLA, it wants to come off your bed, filament is more expensive, and parts have to be dry-bagged for storage after printing or they will absorb some water. [Although in my tests, the problem of water absorption affecting dimensions might be exaggerated. I could not measure more than a 1% increase in dimensions on test blocks left in a humid room versus control blocks which were dry bagged.]
Secondly, and more importantly, PVA is a soft and flexible material. It might print at the dimension you want, at the shape you want, but it will not stay at that dimension and shape if you apply force. It is not a rigid material. So as a core to hold hard points like bearing races and pivots in their place while wrapped with carbon fiber, PVA is not as suitable as I'd hoped.
Back to the whiteboard on soluble cores.
Printed, assembled, layup, wrapped.
Unwrapped and disassembled. The printed caps split when I pried them off.
Overnight in water and a quick rinse got me this:
I experienced some sliding in the layup again. I am not allowing enough room on the caps to secure the wrap before spiraling down the layup. Certainly still room for improvement there. Also, resin ran into my bearing cups because the design of my caps and core did not block it properly.
But regarding a new core material, and only judging with one test, the 3D printed PVA solvable core for composite layup worked only okay. First off, PVA is a bitch to print. It takes longer than ABS or PLA, it wants to come off your bed, filament is more expensive, and parts have to be dry-bagged for storage after printing or they will absorb some water. [Although in my tests, the problem of water absorption affecting dimensions might be exaggerated. I could not measure more than a 1% increase in dimensions on test blocks left in a humid room versus control blocks which were dry bagged.]
Secondly, and more importantly, PVA is a soft and flexible material. It might print at the dimension you want, at the shape you want, but it will not stay at that dimension and shape if you apply force. It is not a rigid material. So as a core to hold hard points like bearing races and pivots in their place while wrapped with carbon fiber, PVA is not as suitable as I'd hoped.
Back to the whiteboard on soluble cores.
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