Placing a 5/8 ground rod in a 5/8 chuck will work till you hit a hard rock of
dense clay and then the mushrooming will get ya. That's a been there done that
I have also seen on some hammer drill models that in the hammer mode that the
shape of the rod compared to the bits made for the hammer does not allow the
rod to contact the hammer piston follower and enable the hammer only mode. The
follower has to be pushed up about 3/16 inch to contact the hammer through the
cushion between them. That's why the rod adapters are mandatory on some models.
The clay up here in the north west is only about a 100 years short of being
rock. It chips just like it and is impermeable to water. A 16 lb sledge just
mushrooms the rod after a foot or so but the larger hammers will do the job
albeit slowly though.
I would complain to where you rented it as they instructed you as to its
usability and it was unsuitable. A rent reduction at least, or another 4 hours
on them with one that works.
Skookum clay country
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