Dan,thank you for massive load of valuable information in this forum.
just got my home made indenter to the "kind of works" phase.
and it works surprisingly well.
since i have no means to calibrate a spring,i did use slightly different method of measuring force applied.
it is like this:
ball is pushed against 1 square cm of oil via rod in cylinder,
oil pressure is measured by manometer.
it measures up to 250 kgf/cm^2,so 250 kilos is maximum force i can apply.
force can be applied in very smooth controlled manner.
the whole thing looks like this
the frame is a piece of 41mm hex steel.
i gnawed out middle part of it,making it into a C frame.
some indents in cable sheath lead using 9.5mm ball and 100,200 and 250 kgs.
i will optimize distances later to make thing more compact.