Copper exposed on parts that are supposed to be nickel

A. Hi Redford,
You didn't mention the configuration of the part. Do they have sharp edges where scratching could occur? If so, some things to try would be:
1) Tumble de-burr with appropriate media prior to loading the barrel.
2) Using a media in the barrel (BB shot for one example).
3) Slowing down the barrel speed.
3) Adjusting barrel load capacity if needed.
4) Make sure dangler tips are in good shape (no roughness).
5) Check Ni plated thickness, make sure it's adequate.
Regards,

A. You don't mention what kind of baths you are using, but copper plating of iron based substrates is carried out in alkaline baths (either cyanide or non-cyanide) which have much better throwing power than most (?) nickel baths. Yours could be a problem associated with part geometry and insufficient current and time for nickel to cover up recessed areas that copper did cover. Or a problem of high copper contamination in your nickel. Under certain conditions and enough level, copper present in a nickel bath will be expelled preferentially.