[Jewelry making - Article 00652] - Re: [Orchid] Compiling instruction guide for rolling mill

[Durston Rolling Mills]

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>          I have always heard that an off centered grinder is the best
>     & most accurate method of grinding rollers to keep them in round?
>     Of course this has to penetrate the deepest marring & case
>     hardening would be required afterwards. Perhaps Matthew or Sara
>     Durston might enlighten us all? 

    Dear All, Not sure what is meant by "off centered grinder". Maybe,
    you mean "centreless grinding." Centreless grinding does not
    necessarily make parts "more round" as compared to regular grinding.
    The important thing is - centreless grinding is no good for rolls as
    the bearing journals must run true with the main diameter. When
    grinding the main diameter between centres it is important that the
    bearing journals are checked to make sure they are running true. 

    Back to the hardening. Good quality rolls are not normally made from
    case-hardening steel. The "case" is relatively thin on case-harden
    parts and as already mentioned this would cause the sub surface to
    collapse under loading. If it were necessary to reharden the rolls
    they must be annealed first according to the spec of the steel. They
    can then usually be hardened again, although there is a risk that
    they will crack. However, the hardening would distort the rolls and
    they would have to have all diameters ground again. This will result
    in undersized bearing journals as well as the main diameter. 

    Conclusion: Good quality rolls can usually be reground without the
    need for rehardening. If rolls do become soft for whatever reason
    i.e.: incorrect material used or wrong hardening procedure, then the
    only answer is to buy new rolls. 

Matthew Durston

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