Old timer told me to stop chasing microns on turbine blade clearances

I was working a PT6 hot section at a shop in Wichita and spending 45 minutes getting every blade clearance to within half a thou. The lead inspector, guy named Jerry with 40 years in, watched me for a bit and said "kid, the engine doesn't care that much, just get them in the green and move on." He showed me how they used to balance blades by swapping them around instead of grinding anything. Now I focus on getting all blades within the middle of the range and checking overall balance instead of each individual gap. Has anyone else had an old hand show them a shortcut that actually improved their results?

3 comments

3 Comments

mitchell.lee15d ago

Honestly Jerry was right. I had a guy named Dave show me the same thing on a CFM56 build. Instead of chasing perfect numbers on each blade he just had me batch them by weight and then swap positions until the overall spread was tight. Cut my build time by almost an hour and the vibration readings came back better than when I was micromanaging each gap.

ivan_mason15d ago

Jumped on that same lesson with a old Pratt guy out in Phoenix. He told me the engine is a rotating assembly, not a Swiss watch, and showed me how a half thou here and there gets swallowed up once the blades heat soak and grow anyway. @mitchell.lee nailed it with the weight batching trick - I started doing it with a simple gram scale instead of a fancy rig, and my builds smoothed out way faster. Jerry knew what he was talking about, the green band is usually wider than we think.

hayden_nelson8515d ago

Brought a gram scale into the shop after reading that post from @mitchell.lee. First time I batched a set of fan blades on a CF6 it cut my trim time in half. The old timers knew this stuff, we just gotta listen.