Job Start Date - How are they calculated?

Hi all,

We have an issue with our job start dates and I wondered how they are calculated.

In our test environment, I created two sales order lines each with a release with the same ship by date. However, when I raised the job through order job wizard, the start dates for the jobs were different. One of the jobs had a start date the day after the ship by date.

Each line was for a different part which had a different resource group. Our system is very simplistic in terms of production and we have not set any other criteria which I would think could influence the scheduling of jobs.

We’ve been using E10 for a couple of years but never noticed this issue before because our production team make everything to order and their custom dashboard displays the order required by date rather than the job start date. However, we are introducing materials picking for jobs, and currently the material pick requests are being sent down for the day after the job is due to be started/completed.

Any help would be much appreciated.

jDJ

Unfortunately, without knowing your exact settings, this is a very hard question to answer. Have you reviewed the MRP and Scheduling Technical Reference Guides? You should be able to figure out how yours are being calculated based off of those. Take one of the jobs and step through all of the settings for that while referencing the guides. If you have specific questions about specific settings, someone should be able to answer them here. But without specifics, it will be hard to help.

I agree with @jkane, there are dozen’s of settings (variables) that the scheduling engine uses, which makes it very flexible, but often times, with flexibility comes complexity. The Scheduling Technical Reference Guide is your friend when trying to determine how you got the result.
It’s not a simple calculation, it’s scheduling which is impacted by the scheduling mode (Forward or Backwards), the current schedule load on all the resources in the job and dozen’s of other variables. In the end, the Job Start date is the date that the first operation is scheduled to start, plus any production buffer you may have.
If a Jobs Start Date is after its Req Date, then the job was probably forward scheduled since backward scheduling starts with the Req Date and the last operation and works back to the first operation.
Another huge factor is if the resources used are marked for finite or infinite scheduling.
As with many things, it’s best to determine what type of end result you want and then configure the Method/Job, Resources, etc accordingly.

In simplest terms… the start date is calculated when scheduling the job. But now, the details get messy based on the settings.

  1. Backward scheduling… the system sets the DUE date to the required date, and schedules backwards till the start date is determined
  2. Forward Scheduling… the system sets the START date, and then schedules all the items till you get a DUE date.
    BUT if you have “No Historical dates” set (which is my recommendation), then backward scheduling can sometimes hit a wall, and will then flip and do forward scheduling from TODAY.
    Then there is another setting for "optimize schedule, which if turned on, will do another pass after forward scheduling, and backward schedule the job one more time.

Throw in all sorts of other settings such as Constrained Materials, Finite Resources, Production buffers, Receive time, resource calendars, etc… and you have lots to examine.

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Hi,

I appreciate the responses, my understanding has improved and you’ve given me some areas to investigate!

Tim,
Do you suggest to “allow dates in the past” when finite scheduling? I see you mention backward scheduling can sometimes hit a wall and will flip to do forward scheduling. This happens when dates are not allowed in the past, a company configuration setting.

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Yeah, I think scheduling is one of the most complicated areas.
Tends to be a learning marathon instead of a review sprint.
As others said, the Tech Ref Guides can be your friend.

Sometimes I still prefer showing historical dates, they are a quick reference for me that there is a “wall” involved somewhere.

Also if you have methods with a lot of levels, many manufactured sub-components?
Difference between stock and non-stock sub-components can make things interesting too.
Where their dates may or may not be factored directly into the final jobs start/due dates as you might expect. Personally, I like to use non-stock components when possible… I think you’ll get more visibility into the dates on jobs.

Job Start Date is a calculation that uses the Required-By date as a date it works backwards from.
Depending on the options you’ve selected or set up (See the Scheduling & MRP Tech Ref Manuals), the following is subtracted from the Required-By date, to calculate the start date necessary to complete on time:

The Labour standards on operations.
The Que & Move times on Resource Groups &/or Resources associated with Operations. (Hours)
The Out-Time for Sub-Con Operations. (Days)
The Production Prep Time (Days) (See Site setup & Part Record, & MRP Options to use or not)
The Kit Time (Days) (See Site setup & Part Record, & MRP Options to use or not)
The Receive Time (Days) (See Site setup & Part Record - Applies to Manufactured & Purchased)
Calendars influence all of the above. There’s a Calendar hierarchy, Scheduling & MRP uses the first one it finds in this order, Resource, Resource Group, Site, Company. (Higher levels act as default when not set at lower levels)

If you have a 5-Day-8-Hr Calendar, 8 hrs of Que & Move = 1 Day.
If you have a 5-Day-16-Hr Calendar (2 Shifts), 8 hrs of Que & Move = 1/2 Day.
If you have a 5-Day-8-Hr Calendar, Saturdays, Sundays, & Vacations, will add Days to the amount of time subtracted from the Start-Date.

If the Allow Historical Dates is not checked at the Site Level or for MRP runs, Job start dates will at some point flip from backwards to forward scheduling, you will see job start dates begin to move into the future (Start After Required-By!), & MRP Buy suggestions will be delayed. This functionality is supposedly desirable, if you’re trying to finite schedule, but if you’re Infinite Scheduling this feature will make you question your sanity & Epicor’s scheduling capabilities.

Keep in mind that, for every setting in Epicor, there are often several places for the setting, & that they will have a hierarchy as to which one will take effect. The Tech Ref Manuals are your friend to discovering where the setting are. Pay attention to the “Where Located” sections.

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