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In terms of personal productivity (single machine scheduling) when a task is interrupted before being done in order to switch to a different task, it incurres a 'tear down' time cost - putting tools, files, materials away etc. It also incurres a set-up cost when you pick it back up again - getting the tools, files, materials ready, reviewing the work that was previously done etc. Given a limited set of information about the task, how would one estimate the tear-down and set-up cost associated with interrupting a task?

Let's say that we have the following information:

  • Initial total estimated time to complete task.

  • Current estimated remaining time to complete task.

  • Task value (this could be an amount in $ or some other measure of importance)

Is there a good, recognized, heuristic to evaluate the time cost associated with interrupting a task? Maybe something as simple as "10% of the task's total estimated time".

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No, because the number to be produced changes the percentage ie the setting up time can be longer than the machining time for 1 piece but 3% for 100 pieces and 0.003% for 1000 pieces...

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The amount of information you specified is too limited. If you had more information, maybe you could do it, but not as stated. Machining tasks can vary greatly. I can imagine some parts where it might literally take hours to get work piece fixtured in the machine, but then the actual machining operation takes only a few minutes (e.g. a giant part for a ship or an airplane, where the part weights several tons and it takes big cranes to get it setup, but you only need to drill a few holes). But there are other parts where it might only take a few minutes to get the part fixtured, but then you need to spend 10 or 12 hours of machining. Without knowing any detail about the operation, it's impossible to estimate the overhead involved in interrupting it.

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