My point in my comment is that these tools are also used for motor armature balancing, (as they can be), and rarely can one purchase an armature with a pointed shaft, and regardless of the geometry of the axle/shaft end, the magnetic force centers the cylinder based on ferrite content [and of course our rules prevent balancing the armatures of our sealed motors].
Thus, if for some reason the tool did not come with a pointed balancing shaft/axle,the tool can still be useful for balancing a 3/32 axle and gear assembly with flat ends. In fact the axle you are planning on using, should be used with the planned crown/spur, because it is the actual part to be installed and any imbalance in the shaft itself will be resolved by the tuning of the gear or its collar.
Altho – of course- a precision pointed axle is preferred and should be provided by the vendor.
Trying to create your own pointed axle will not be useful, (the amount of ferrite at the end will be inconsistent) rather if both ends are 90-deg-Flat the balancing action *should be correct.
"... get on your bad motor scooter and ride!"
Sammy with Montrose