It's critical to get your components finished and delivered on time. But quality should not be compromised for the sake of a timely delivery. That's just daft.
The right supplier must have the capacity and capability to deliver (on time) but also the experience and expertise to complete the job to the required standard. Add a poor programmer into the mix and his insufficient experience/expertise that the skills to devise machining strategies to accommodate challenging designs is missing...
The result will be an unsatisfactory finish or deadline missed through delays. Choose the wrong supplier and this scenario, and/or similar, will be repeated, time after time... So the easiest way to improve supplier delivery performance is to choose the right one.
It's not a cop-out, honest. This post suggests 7 attributes to look for to help you get that choice right and improve supplier delivery performance.