Appreciate any suggestions on where I might source a standard tapered steel lathe mandrel of 10 mm diameter. That equates to 0.393" so is under the limit for any expanding mandrel gizmo usually beginning at 1/2" and up. Anticipating the standard ground turning mandrel taper of 0.0005" per inch, even a 13/32" fractional size mandrel (beginning at approximately 0.405" dia.) would be too large to accommodate my bore diameter of 0.393". Any 3/8" nominal sized mandrel at 0.375" would need to be an entirely impractical over 3 feet of length to get to 0.394" or 10mm. I've already contacted many of the usual domestic suppliers including: McMaster-Carr, Grainger, MSC, Travers, KBC, Victor, Taig, CDC, HHIP, etc, etc...
Looks like I'll be needing to contact an overseas supplier. Needing to rework several hubs made of sintered powdered metal (alloyed steel) with precision bore diameters of 10.0mm. Correct me if you know otherwise, but doesn't all the civilized world excepting the US, UK & Australia work to SI (System International) units (millimeters, etc.)? Precision lathe mandrels are a very common workholding tool for machine turning. Shouldn't be all that difficult?..