Hand Tools Archive

Lee Valley PMV11 chisel hardness

Bill Tindall, E.Tn.
David sent me the Streeper table of data. There is much about it that is suspect which would lead one to conclude the data set is unreliable for comparison purposes. In the specific case of the LV chisel the reported value is well below the LV specification. Weaver speculated that LV may have lowered their specification to make it easier to sharpen.

I asked the technical staff of LV whether the specification for PMV11 was lowered. The reply was that PMV11 hardness specification remains the published value and significantly higher than the Streeper result (more on that later). LV heat treating is monitored for quality. Every heat treat batch is measured and must meet the published standard.

The LVV11 steel was chosen because its composition enables it to be taken to high hardness while preserving toughness, both critical attributes for a chisel. It would have been silly for LV to target a lower hardness than this steel was designed to achieve.

The Streeper data is flawed because the calibration procedure and data analysis procedure used is flawed and will lead to high variance of the results obtained with different instrument calibrations (day to day) that will not show up in repeats done with the same calibration at one time. Furthermore, an expert in the machine he used stated that it is not a precise measurement, good to about +/- 2 Rc units. Streeper reports results to 2 decimal places! This fact in itself demonstrates the person dong the word lacks the experience to do it.

Reliable conclusions can not be made from the Streeper data.

It is a good bet that every company monitors the hardness of their chisels. If you want a reliable answer just call their tech service staff and ask.

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