Look into this thread, which has a nested thread, and see if these might hold the answer.

Are you running MRP with the Integrated with CRP option enabled? If not, the thread below explains how doing so will help get better Start Dates on your requisitions. Basically, MRP without CRP uses only the information in the routing and the Site manufacturing calendar to backward schedule the Start Date. The Shop Order, though, will use the information in the routing PLUS account for the dates on which the Work Center(s) would be available to perform the work.

Don’t have access to the 1st tread you included, but trying to get access. I did read through the 2nd one prior to submitting this, but still didn’t understand where the issue is. 

We are NOT running MRP with the Integrated CRP option enabled. If the work centers are infinite capacity AND utilize the same manufacturing calendar, I’m still not understanding why the Req start date and SO start date would differ. 

Is the Site Manufacturing Calendar the Calendar connected to each Work Center?

Also, I inserted the wrong link for the MRP with CRP post. It is here.

Yes, the site Mfg. Calendar and Work Center calendar are one in the same. 

Do any of the Work Centers have more than one Resource? If so, does the Efficiency differ between Resources?

All our WCs only have one resource at 100% efficiency. But, when setting up our part routings, we set the efficiency at 80% for each operation/s.

Have you calculated the manufacturing lead time and updated the lead times on the inventory parts?

If the lead times shown in the routing alternate do not correlate to the 80% efficiencies on the routing operations, i.e., they still reflect 100% efficiencies, MRP will use these incorrect values for calculating the start date of the SO Req. Then when converting to an order the infinite scheduler will use the data in the routing operations, the 80% efficiencies, pushing the start date of the order earlier than what was on the SO Req.

Yes. We have the Manufacturing Lead Time Calculation scheduled to run/update every night. I looked through a handful of parts and it also appears that the Inventory Part lead-time aligns with the Fixed Lead Time on the part Routing. 

I don’t think I mentioned it earlier, but if there is a discrepancy between the Shop Order Req start date and Shop Order start date, the Shop Order date is always later. 

What is the scheduling direction of the shop orders that are assigned the later start date?

We schedule all SOs Backwards. 

Are there any customizations in place regarding converting the SO Req to an order that would be moving the Need Date of the shop order to a later date? Asking as the only way I know of to move the SO Start Date to a later date with Backward Scheduling when not using CBS/APB is to adjust the Need Date to a later date.

I’m not aware of anything customized, that would effect the dates. I’ve also been unable to find any patterns to why/when it happens (i.e. it’s not part number or work center specific).

We have not tried running MRP with “Run Integrated with CRP”, I’m not familiar with what this options does. You referenced this above...Are you able to explain what this does when running MRP?

Running MRP not integrated with CRP, the start date of the requisition is determined using only the information in the routing and the Site manufacturing calendar.

Running MRP integrated with CRP, the start date of the requisition is determined using the information in the routing PLUS accounting for the dates on which the Work Center(s) would be available to perform the work.

If a Planner reviewing Shop Order Requisitions is using the Proposed Start Date as a criteria for selecting which requisitions should be converted to orders, running integrated with CRP will provide more realistic proposed Start Dates on the Requisitions.

Thanks for all the help with this Matt. I’m going to try running MRP w/ the CRP setting on tonight and see if there are any improvements on the dates tomorrow. 

This is a topic I have asked Matt and Mats lots of questions on and have learnt a lot from them :) 

One thing that might be useful to check is how you are calculating the Manufacturing Lead Time? For example are you selecting ‘Maximum Time of Machine or Labor’ ?

As Matt already explained when you run MRP without CRP, the SOR start date is calulated using the fixed & variable lead time information from the Routing.

However, the Shop Order infinite scheduler only considers Machine Time - so if you have a labor operation that is a bottleneck, this would create a difference.

Running MRP integrated with CRP will resolve this, as the scheduler logic is used to plan the individual operations.

Running MRP with CRP on has drastically improved the issue. We still have a couple anomalies each day, but are digging into those individually. Thanks for all the help!