Zero Timing
Zero Timing
(OP)
Okay I asked this question as part of an answer for the "Mental Challenge For Aero Engineers" Thread. But Wil Taylor who started that thread felt this was a topic of its own and therefore I am asking this as a separate question.
The question is:
If the fastener holes that are deburred are inspected with the use of HFEC (High Frequency Eddy Current) prior to installation into the aircraft, could those qualify as being zero timed?? Also a second question is how effective is the zero timing procedure as a safety precaution against crack growth? Anybody's comments on that would be great.
Cheers,
Asanga
P.S: I found out about zero timing while looking through an older (1980's) Boeing Structres Repair Document (D6-81987) so that is the extent of my knowledge of the process.
Asanga
The question is:
If the fastener holes that are deburred are inspected with the use of HFEC (High Frequency Eddy Current) prior to installation into the aircraft, could those qualify as being zero timed?? Also a second question is how effective is the zero timing procedure as a safety precaution against crack growth? Anybody's comments on that would be great.
Cheers,
Asanga
P.S: I found out about zero timing while looking through an older (1980's) Boeing Structres Repair Document (D6-81987) so that is the extent of my knowledge of the process.
Asanga





RE: Zero Timing
As for the purpose of zero timing, it removes all the fatigued material from around the hole, thus you end up with a ‘new hole’. Zero timing the hole doesn’t really act as a safety precaution against crack growth, for that you might want to also look into cold working the hole. By cold working the hole, a mandrill larger than the hole is pulled through the hole putting the material around the hole into compression.
RE: Zero Timing
After I finish with my "mental challenge question" in another thread I'll throw in my 2-cents worth here...
Regards, Wil Taylor
RE: Zero Timing
RE: Zero Timing
For the insurance cut, the 0.040" ream is performed after crack removal to ensure the hole is clean & that any fatigued material has been removed.