markz528
Hot Rolled
- Joined
- Sep 25, 2012
- Location
- Cincinnati
Did a qualification inspection on a shaft for a rotating piece of equipment. Material is 4140 and has a shaft extension (where coupling will be mounted) diameter tolerance of 6.499 to 6.500 inches. Surface finish limit is 63 microinches RA.
Shaft extension measurements and surface finish measure in spec. But............
Around 2 inches from the end of the shaft, there is a step in the shaft of around 0.0004 inches. The end of the shaft is larger than the rest of the shaft. The surface finish at the end of the shaft is around 20 RA and elsewhere is around 40 RA. Just terrible quality overall - not sure how they messed it up.
The vendor argued that the surface finish is good and measurement is good so the shaft is good. My answer to that is no - you will not have a step in the machining under an interference fit coupling.
My questions are the following:
- Machining defects/steps are not quantifiable with a profilometer to the best of my knowledge. How do I qualify what machining defects/steps are acceptable? Is there a standard that I can use? I have had cases in the past where the machining was terrible but yet the profilometer surface finish readings were fine because the machining marks were too coarse for the profilometer to pick up. In my opinion, proper machining does not allow for steps but I don't know how to quantify/qualify them.
- How would you have responded to the vendor in my situation?
BTW - they say they have corrected the shaft and that I will be happy with it during the re-inspection next week.
Shaft extension measurements and surface finish measure in spec. But............
Around 2 inches from the end of the shaft, there is a step in the shaft of around 0.0004 inches. The end of the shaft is larger than the rest of the shaft. The surface finish at the end of the shaft is around 20 RA and elsewhere is around 40 RA. Just terrible quality overall - not sure how they messed it up.
The vendor argued that the surface finish is good and measurement is good so the shaft is good. My answer to that is no - you will not have a step in the machining under an interference fit coupling.
My questions are the following:
- Machining defects/steps are not quantifiable with a profilometer to the best of my knowledge. How do I qualify what machining defects/steps are acceptable? Is there a standard that I can use? I have had cases in the past where the machining was terrible but yet the profilometer surface finish readings were fine because the machining marks were too coarse for the profilometer to pick up. In my opinion, proper machining does not allow for steps but I don't know how to quantify/qualify them.
- How would you have responded to the vendor in my situation?
BTW - they say they have corrected the shaft and that I will be happy with it during the re-inspection next week.