Twin plate fork crown?

[Jim Gourgoutis]

I have access to a water jet at work, and am thinking of using it to cut parts for a twin plate fork crown. Can anyone offer recommendations on how thick the plate steel should be? Is .125” the usual choice for this?

Thanks!

-Jim G

[Jon Norstog]

Jim, list:

I would use heavier material. and chrome-moly plate.  A twin-plate crown gets a pretty heavy torsional load.  Below is a Pacenti crown from a fork I built maybe 15 years ago that was recovered with its frame from an Albuquerque thrift store.  I'm thinking the radial cracks could be the resul of torsional stresses.  I've heard of this particular crown having "issues" but this is my first encounter with them.

If I were doing it, I would use 1/4" chrome moly plate and don't make the crown any wider than it needs to be.

Good luck!

jn

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[Colin Pinney]

Hey Jim,

I used 3/16" (~5 mm) 4130 plate when I made some plates 8 or so years ago.  It seemed to be a good compromise to me between 1/8 being too thin and 1/4 being thick and chunky looking.

The fork survived the crash where something jammed between the front wheel spokes and the fork.  The frame buckled and broke at the downtube/ headtube junction.

It was nice having my friend 3d print plastic plates to check fit and clearance tire widths.

Kindly

Colin

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