Re: buying a cappings spinner?
I don't think there is a definitive number. The heavier the flow, the heavier the wax secretion instinct becomes.
This time of year I do a lot of driving the area on evenings and week ends, spot checking bee yards to determine where our time is best spent in the coming days.
Here's an observation that I have noticed through the years. You can usually get a real good idea for how full the top box is by knocking on the lid just like you would knock on a door (we use a non-recessed lid). The fuller hives build burr comb up under the lid resulting in a solid "knock" while the emptier ones sound hollow......EXCEPT on boxes which contain a number of sheets of foundation. Many of those sound hollow yet are nearly full as all the bees comb making energy goes into drawing out foundation with little energy spent making additional, relatively useless, burr comb on the top bars. My conclusion is that when a flow is in progress that wax secretions are instinctively tuned to building new comb and not filling out drawn comb where the needs are much less. More drawn comb = more burr comb.
"People will generally accept facts as truth only if the facts agree with what they already believe."- Andy Rooney