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How to heat treat an excavator pin
QUESTION:I have to make a new 2" pin for my excavator thumb, last time I made one, I
heat treated it by heating in cherry red with two torches and quenching in a
bucket of water, did I do it right. The pin lasted two years and when it
snapped, it didn't bend it snapped clean in the middle with out any apparent
distortion from flexing.
ANSWER: Sounds like you got a reasonable result, but it was out of sheer luck.
What material is the pin? Usual procedure is to heat the pin, but keep
heating it until a magnet won't stick to it (really!) then quench it. If
it's O1 rod then quench in oil. At this point it will be as hard as glass,
and about as brittle. Depending on the material you may need to heat it to
350 degrees or 500 degrees to temper it to the toughness you need to keep it
from shattering in use.
You are going by the seat of your pants. A proper textbook heat treat
in a temperature controlled furnace would be the proper way.
Now that we have set the BS aside you might try Mike's method with a
slight alteration. Magnet test, quench in oil, then take out quickly before
full quenching takes place. Scrape the pin to remove some oxide. Watch
the scratch marks until they start tuning blue. (purple would be better)
Quench the pin again.
The idea behind this method is to use the still red hot core of the pin
to anneal the surface that you quenched. That way you minimize the
hardening effect on the core.
This is really not the ideal method but might give you a softer core.
Some people call this "letting down" I don;t know the source of the term.
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