David,
Regarding your lapidary arbor, I use the same type of drum/belt
combination as you and have found that:
-
There are significant variations in supposedly "identical"
belt sizes between manufacturers. Given the same dimensions of 6
inch diameter belts, one from manufacturer A will fit much more
snugly than one from manufacturer B. -
The same holds true of expandable drums. Some brands will
increase diameter at a given RPM much more than others, due to
the type and quality of rubber composition. -
If used infrequently, all rubber compounds (including car
tires) will lose elasticity over time. Your drum, if left idle
for a period of years, could well have succumbed to this
tendancy. -
The most outstanding values today in diamond belts, in terms
of quality/longevity versus price, are the metal belts by 3M.
They cut superbly. I use mine regularily, and they last a long,
long time. (No connection with the company, etc., etc.). Good
luck.