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wrote:
Hi,
I need to make some porthole liners for a barge and I was thinking of
steaming some wood strips. Size is approx 1.15m long - it is a 0.381m
diameter porthole - 60mm wide and 6 - 8 mm thick. I was thinking of
using mahogany or similar dark hard wood.

Can I bend steamed mahogany to this radius?? - or any other
suggestions??

Mahogany is not a good wood to bend. It's almost impossible to steam
bend anything close to that radius. The rig you would have to make would
be dangerous. According to my Fine Woodworking Bending Wood book the
best radius you would see for 1" thick mahogany is 32" to 36".

Even bent laminations are tricky with mahogany. If you want to attemp
this keep the strips really thin 3/32" to 1/16". Cut lots of extras,
you'll need them. Bend SLOWLY. Have both an inside and outside form. My
guess is 1/2 to 3/4 of them will break. Use epoxy if you do this. I
prefer a nice slow setting gel type.

The other choice is cutting a circle. This would be the most wasteful,
but might be your best bet.

The advantage to bending wood over cutting curved forms is tensile
strength. Grain orientation (and therefor tensile strength) is
inconsistent on a curved cut form, where a bent form will have fairly
consistent grain orientation. IMO A pothole liner would not need need
the tensile strength a bent piece of wood would give. It would be
supported on all sides, unless I'm missing something.

The other best bet option. Choose a contrasting wood that does bend well
like Ash, White Oak, or Red Oak. Walnut and Cherry will also bend well.

Christian