After reading the issue, I'm not a whole lot further ahead. I guess that's due to not having as complete a mental picture of the situation compared to someone who has a lot more familiarity with what is going on. Rather than describe what isn't working, describe what you need to do in general/process related terms - not database terms. I gather that there is a work order table and that if the job is executed, parts will be used. IMO that requires at least a tblWO and tblWoParts. If the WO has tasks and the parts go against the task, then you'd need at least
tblWO
tblWoTask
tblWoTaskParts
if you also want to show stock adjustments because n units are used on a WO or task, then you need a way to relate the WO (or task) to the stock transaction - maybe a quantity adjustment field (+n or -n) and an adjustment type (e.g. WoTask, StockPlus, StockMinus, LoanMinus, LoanPlus, etc). Then again, you might be wanting to show WO parts and those parts come from external suppliers, thus stock transactions doesn't fit your model. Hope that helps put some context into what I'm saying - the process is more important than what you've tried at this point.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.