Acrylic, plastic, polycarbonate for stem top cap bolt?

Questions about bike hire abroad and everything light bike related. No off-topic chat please

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dereksmalls
Posts: 2012
Joined: Tue Aug 02, 2011 9:20 pm
Location: New Zealand

by dereksmalls

How safe and secure you think? I'm guessing ok considering in theory you don't really need one. Is acrylic the same as polycarbonate? Seems tricky finding a countersunk M6 bolt though for polycarbonate, acrylic easy as

mentok
Posts: 512
Joined: Sun Jan 01, 2012 9:58 am

by mentok

I don't see why not. Do your initial setup with a steel bolt, tighten stem bolts, remove steel bolt and replace with poly/acrylic then just hope you don't need to adjust it while you're out on the road?

spud
Posts: 635
Joined: Sat Feb 07, 2009 5:52 am

by spud

thing to look at is whether the material has creep or not. Initial elasticity is not a problem, might even be a benefit to ensure appropriate preload. But you wouldn't want it loosening up. I can tell you, for instance, that Nylon would not be a good material as it has a high coefficient of thermal expansion, as well hydro expansion.

dereksmalls
Posts: 2012
Joined: Tue Aug 02, 2011 9:20 pm
Location: New Zealand

by dereksmalls

Right so anyone know of an online source for M6 x 35mm countersunk polycarbonate bolts? Ebay is throwing out nothing

joejack951
Posts: 349
Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

Any plastic will creep over time if subjected to a constant load. There is no avoiding it, only tempering of it by using heavily filled plastics (which are extremely brittle in comparison to unfilled). Nylon does also absorb a significant amount of water (when unfilled) and will swell as a result.

If you want to save weight, do as suggested above and preload the bearings with a metal screw, tighten the stem, then just use the plastic screw to hold the cap on place. At that point, the screw material is a non-issue as you aren't requiring any significant strength from it.

Creep: https://en.m.wikipedia.org/wiki/Creep_(deformation)

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