Re: :`( OT


gorvil
 

Tim,

I am a hobby potter as well as a hobby machinist. The ceramic slip
coat you are suggesting would shrink in the firing. Our rule of
thumb for clay shrinkage is 12.5% from greenware (soft clay) to
finished (high fired) product. Your biscuit fired slip would shrink
somewhat less, but still on the order of 5%. It would most likely
crack and fall off in the firing process.

Glen Reeser



--- In southbendlathe@yahoogroups.com, "Len Smith" <parnobal2@s...>
wrote:
Surely Tim, A) the expansion of the CI would crack off the slip
coat when firing, B) as the slip would only be on the pattern, would
it matter whether it could be removed afterward or not? and C)
assuming the spindle hole is blanked when using the "repaired" wheel
as a pattern, will some shrinkage really matter? It could only be
small fractions of an inch, and presumably the spindle bore will be
machined to correct dimensions anyway?
As an aside, cast iron repair rods are not themselves cast iron, so
the repair will be visible anyway, therefore, brazing wouldn't matter
if the only objection was the visual one.
Len


Initially, my thoughts are around using some kind of 'slip'
(liquid ceramic) . It would coat
the master easily and uniformly, by dipping . Then it could
be 'biscuit fired' at around 900
C . I think the CI inside could handle that , but please point
out if I'm wrong . That would
make it robust enough to withstand a fairly vigorous ram up .
However it would still be in
a condition to be easily broken off on completion .

Tim





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