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Confusing ASTM B650 for plating thickness



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Q. I can't figure it out. I have a requirement to plate a rod to ASTM B650 [affil link] Class 125. Dimensions on the print are after plating. I need to make allowance for the plating thickness when machining the rod, but ASTM B650 [affil link] doesn't state what Class 125 thickness is.

ASTM B650 [affil link] (2002) states plating thickness for Class 1 and Class 2 only in section 4.1. I have a print requirement for Class 125. ASTM B650 [affil link] section 6.5 Thickness says go to "section 3 (see 7.2)", and section 3 is Terminology, and para 7.2 is Test Methods-Thickness. No specific thickness requirement for Class 125 is defined.

How is the average adult supposed to figure out what Class 125 thickness is? Was this changed in the 2002 version? Is it covered in ASTM B374 [affil link] per 3.2?

Jim Belcher
Manufacturing - Stuarts Draft, Virginia
2006


simultaneous replies

A. ASTM B650 [affil link], Class 125 thickness is 125 microns, minimum.
Changes were made in the 1995 edition of ASTM B650 [affil link]. Contact a hard chromium plater for further information. Hard chromium is often plated slightly oversize to allow grinding to precise dimension.

ASTM B374 [affil link] is a glossary of plating terms. It does not give the classes, grades, service conditions, types, etc. used to specify thicknesses in the various plating standards.

Ken Vlach [deceased]
- Goleta, California
contributor of the year Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.



A. My guess is that the specification is supposed to be "Class 1 25" meaning Class 1, 25 micrometers. This is a very common thickness for hard chrome. 2.5 micrometers is too thin for many wear applications.

Toby Padfield
Automotive module supplier - Michigan




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