I am in need of nas6603-4X thru -23X bolts for the aircraft doors my shop works on. The "X" in the part number refers to the bolt being oversized. The drawings call out for these oversized bolts, but thus far I have not been able to locate them anywhere. Does anyone have any experience with and or advice on how I might be able to locate and procure these oversized bolts? Thanks in advance
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Trouble finding nas6603-x (oversized bolts)
- Thread starter TDeMoe
- Start date
TDeMoe...
NAS660X Bolts are cadmium plated LA steel, which are loosing favor due to: (a) steel tendency to corrode [rusted = busted] in long-term service, regardless of the coating system; and (b) cadmium plating [only suitable coating for LA steel fasteners] which is an environmental hazard [highly-toxic/environmentally-persistent] metal. For this reason, demand [= production volume] is falling, so any bolts already made might be the last, without special production runs 'made-to-order'.
Since You are working on doors that have a high environmental exposure, and 'probably' a high aluminum structure content, strongly suggest You consider changing to either of the following bolts which have identical dimensions and mechanical performance, but have superior corrosion resistance and an environmentally friendly 'aluminum pigmented' coating system... and are the 'fastener of choice for current production'...
NAS6703A**X Aluminum Coated A286 CRES [1OS]
NAS6803A**X Aluminum Coated Titanium alloy [1OS]
NOTE.
NAS6603, NAS6703 and NAS6803 bolts have 'long threads' which are 'less-desirable' due to excess weight/bolt in a structural installation... unless the longer thread is ABSOLUTELY necessary. IF Your configuration permits, may want to consider using identical bolts, but with a 'short-thread'... which also might be more readily available, thus...
NAS6203-**X Cadmium plated LA steel
NAS6303A**X Aluminum Coated A286 CRES [1OS]
NAS6403A**X Aluminum Coated Titanium alloy [1OS]
CAUTION.
LA Steel, CRES and Titanium alloy bolts have virtually identical mechanical allowables. HOWEVER, LA steel and CRES bolts have ~identical modulus of elasticity [~30,000,000] and can be used interchangeably/mixed with each other... but Titanium alloys have a lower modulus of elasticity [~16,000,000] and should NEVER be mixed with steel/CRES bolts unless specifically approved by a stress analyst.
NOTE.
Ti Bolts provide significant weight-savings, which can be beneficial IF certain rules-of-usage are stringently adhered-to [OK my rules learned over decades of use, but I won't mention them now].
rb1957: I suspect that the 1OS bolts are needed for a structural modification/repair.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
NAS660X Bolts are cadmium plated LA steel, which are loosing favor due to: (a) steel tendency to corrode [rusted = busted] in long-term service, regardless of the coating system; and (b) cadmium plating [only suitable coating for LA steel fasteners] which is an environmental hazard [highly-toxic/environmentally-persistent] metal. For this reason, demand [= production volume] is falling, so any bolts already made might be the last, without special production runs 'made-to-order'.
Since You are working on doors that have a high environmental exposure, and 'probably' a high aluminum structure content, strongly suggest You consider changing to either of the following bolts which have identical dimensions and mechanical performance, but have superior corrosion resistance and an environmentally friendly 'aluminum pigmented' coating system... and are the 'fastener of choice for current production'...
NAS6703A**X Aluminum Coated A286 CRES [1OS]
NAS6803A**X Aluminum Coated Titanium alloy [1OS]
NOTE.
NAS6603, NAS6703 and NAS6803 bolts have 'long threads' which are 'less-desirable' due to excess weight/bolt in a structural installation... unless the longer thread is ABSOLUTELY necessary. IF Your configuration permits, may want to consider using identical bolts, but with a 'short-thread'... which also might be more readily available, thus...
NAS6203-**X Cadmium plated LA steel
NAS6303A**X Aluminum Coated A286 CRES [1OS]
NAS6403A**X Aluminum Coated Titanium alloy [1OS]
CAUTION.
LA Steel, CRES and Titanium alloy bolts have virtually identical mechanical allowables. HOWEVER, LA steel and CRES bolts have ~identical modulus of elasticity [~30,000,000] and can be used interchangeably/mixed with each other... but Titanium alloys have a lower modulus of elasticity [~16,000,000] and should NEVER be mixed with steel/CRES bolts unless specifically approved by a stress analyst.
NOTE.
Ti Bolts provide significant weight-savings, which can be beneficial IF certain rules-of-usage are stringently adhered-to [OK my rules learned over decades of use, but I won't mention them now].
rb1957: I suspect that the 1OS bolts are needed for a structural modification/repair.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
- Thread starter
- #4
Thanks for your response rb1957. I am not an engineer, I'm a work leader in a bomb bay door shop. But, I have asked our engineers the question of "Why are the drawings calling out for oversized bolts in new parts?". And to be honest none of our engineers have given me a solid answer as to why the drawings are calling out for oversized fasteners to be installed in our end items that are being "overhauled" with new parts. So far in my requests for an engineering work around, I have been told that basically they're not sure why the drawing is calling out for oversized bolts in doors that are being overhauled either. But, since the drawings DO call for the oversized bolts the only "work around" they can authorize is to go up to the next larger diameter bolt because it will decrease the sheer strength if a nominal bolt is used. My assumption to "why" this is the case, is that the areas that the oversized bolts are called out for are areas that require stronger sheer strength than a nominal 6603 bolt. The problem we ran into with going up to a nas6604 is edge distance on the parts the bolts go through. Therefor, it appears the only option I have is to procure the oversized bolts. And so far this has proven to be a much trickier process than I would have ever suspected it would or should be... It has become a pass the buck scenario of who's job it actually is to stock list and procure the bolts.
TDeMoe...
Match drilling/reaming 'new parts to old structure' demands that (a) all-holes be oversized to ensure a 'matched fit', and also (b) to clean-up/clean-out the existing holes in old structure [wear, corrosion, ting cracks etc].
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
Match drilling/reaming 'new parts to old structure' demands that (a) all-holes be oversized to ensure a 'matched fit', and also (b) to clean-up/clean-out the existing holes in old structure [wear, corrosion, ting cracks etc].
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
hmmm...fat fingers...
'...ting cracks...' ???
DANG... meant to type '...tiny cracks...' !!!
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
'...ting cracks...' ???
DANG... meant to type '...tiny cracks...' !!!
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
- Thread starter
- #7
My best guess (as to why an original design would call up over-size fasteners) is that they were in a corner. Loads changed late in the day, or some "smarty pants" re-calc'd and got a -ve MS, or maybe a test failure. no room to go up a size (which would increase edge distance, as you've noted) and maybe 1.5ed properties insufficient. By using oversize fasteners they may squeeze a slightly higher allowable. But it is, as you've noted, what it is !
another day in paradise, or is paradise one day closer ?
another day in paradise, or is paradise one day closer ?
Rb1957...
TDeMoe [2 Feb 17 18:41]
"... .I have been told that basically they're not sure why the drawing is calling out for oversized bolts in doors that are being overhauled either. ..."
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
TDeMoe [2 Feb 17 18:41]
"... .I have been told that basically they're not sure why the drawing is calling out for oversized bolts in doors that are being overhauled either. ..."
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
TDeMoe... TAFB???
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
i guess it could be a rework instruction, but initially it sounded an original design (using oversize).
but it that case it'd be obvious ... either up-size for cause (hole damaged in removal) or standard procedure (replace removed hardware with oversize) which is good practice but if the removal was careful the original size could still work, particularly as we're talking about screws (not Hi-Loks or such)
another day in paradise, or is paradise one day closer ?
but it that case it'd be obvious ... either up-size for cause (hole damaged in removal) or standard procedure (replace removed hardware with oversize) which is good practice but if the removal was careful the original size could still work, particularly as we're talking about screws (not Hi-Loks or such)
another day in paradise, or is paradise one day closer ?
- Thread starter
- #12
- Thread starter
- #13
rb, I have asked my engineers about the callout for oversized fasteners in the drawings and at least one of them said something to the effect of, they thought it was because of the replacement of fasteners to allow for oversizing the hole during removal process. This theory makes sense to me if their are rivets needed to be drilled out but not for removal of bolts, and the nas6603-?x are bolts.
so it's the repair work that's oversizing the fasteners ... makes more sense, though I agree with you this is "just" a bolt, removing it shouldn't damage the hole. oversizing the hole "for the heck of it" will impact future repairability. but i doubt that windmill is worth tilting at ...
another day in paradise, or is paradise one day closer ?
another day in paradise, or is paradise one day closer ?
- Thread starter
- #15
Yes, in our overhaul process we do not replace all parts on the end item with new parts. We only replace parts that are beyond "allowable damage limits" per tech data. We are allowed to go up one size of fastener in the allowable limits section of our tech data without requiring an engineering work around to do so. Now as far as "tilting the windmill" is concerned, I am actually fighting that battle in the opposite direction when it comes to replacing all new parts and then going back (per tech data) with oversized Cheery Max rivets in areas that are not accessible to shoot solid rivets. But, that is a story for another day... lol
TDeMoe...
Match drilling, much less match reaming, old structure to new structure cannot be done 'to-spec' without cleaning-out the old hole. Lots of reasons 'why'.
IF the old hole is visually OK then match drilling the hole one or two-drill-bit #s larger for a solid rivet that is bucked/squeezed in a trick that works well. The crush/swell of the rivet shank overcomes a lot of hole-wall irregularities and established a fairly good installation.
NOTE. Example of rivet replacement with a blend of new/old structure.
For a 3/16 nominal rivet the hole would normally be production-drilled to 0.194[#10]+/-0.001. When a typical rivet is bucked in the hole there is a permanent swelling of the hole [cold work-swelling during the bucking process] of ~1--2% in this case the 0.194-D hole swells to about 0.196--0.198-D permanently [typical, for 2024-T4 sheet, AD or D rivet]. Most rivet specs allow [3/16-D] solid rivet holes as-large-as 0.202 for installation. In this case a #8 [0.199] or a #7 [0.201] Dia drill can be used thru the old-hole into the new structure. This cleans out the old hole [somewhat] and establishes a relatively clean hole thru the stack-up that will accept a solid rivet installation. NOTE: YES, there are oversize solid rivets available on special order.
Everything I discussed above for solid bucked rivets DOES NOT apply to non-swelling fasteners with rigidly controlled diameters. For a blind rivet, blind bolt, lock-bolt/Hi-Lok, or bolt-nut installation, hole quality and fastener fit [class x or transition fit or interference fit, etc] are essential for structural integrity/durability... especially where there is little/NO shank swelling and the effects of compressive loads during fastener set/install are subject to variances such as tail/bulb swell/pull, pin-collar compression during collar swage or nut-bolt torque-tension... etc.
Usually blind rivet and bolt holes have +/-0.002 tolerance. Special close-tolerance/high quality drills [NAS907] might suffice... but that's 'chancy at-best for meeting hole tolerance requirements. For this reason these holes probably shouldn't be drilled: they should be [step-drilled then] finish-reamed with a piloted reamer [NAS897].
For lock-bolts/Hi-Loks/etc and bolts/nuts, holes are usually specified as +/-0.0010… or even tighter tolerance [+/-0.0005]… which is only attainable with a piloted-reamer [NAS897]. For these fastener installations [typ for highly loaded fatigue-prone structure] it has been proven time-and again by industry and DoD testing of mechanics that hand-drilled/reamed holes to the original diameter simple CANNOT pass hole tolerance requirements for those fasteners. Enlarging for/installing 1OS [1/64-OS] or 2OS [2/64-OS] for rigid Pins/bolts, in tight-tolerance controlled holes, is mandatory for shear-load transfer and long-term durability of fastener joints... not to mention optimum environmental sealing.
Rb1957…
“so it's the repair work that's oversizing the fasteners ... makes more sense, though I agree with you this is "just" a bolt, removing it shouldn't damage the hole. oversizing the hole "for the heck of it" will impact future reparability. but i doubt that windmill is worth tilting at ...”
All currently active USAF bombers… B-52Hs, built in the 1960s… and all B-1Bs built in the 1980s… are fairly old/aging battlewagons… 2017 [sadly] IS THE FUTURE.
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
TDeMoe… replying to this thread has been an interesting educational challenge… HOWEVER, you said [2 Feb 17 18:41]...
“Thanks for your response rb1957. I am not an engineer, I'm a work leader in a bomb bay door shop. …”
Eng-Tips is restricted to degreed-practicing engineers ONLY. It is very clear You are NOT an engineer, and I will [very soon] be asking Eng-Tips staff to deactivate Your membership… but leave this thread intact for its educational value. You will be free to browse any thread for information, but unable to post comments to any thread.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
Match drilling, much less match reaming, old structure to new structure cannot be done 'to-spec' without cleaning-out the old hole. Lots of reasons 'why'.
IF the old hole is visually OK then match drilling the hole one or two-drill-bit #s larger for a solid rivet that is bucked/squeezed in a trick that works well. The crush/swell of the rivet shank overcomes a lot of hole-wall irregularities and established a fairly good installation.
NOTE. Example of rivet replacement with a blend of new/old structure.
For a 3/16 nominal rivet the hole would normally be production-drilled to 0.194[#10]+/-0.001. When a typical rivet is bucked in the hole there is a permanent swelling of the hole [cold work-swelling during the bucking process] of ~1--2% in this case the 0.194-D hole swells to about 0.196--0.198-D permanently [typical, for 2024-T4 sheet, AD or D rivet]. Most rivet specs allow [3/16-D] solid rivet holes as-large-as 0.202 for installation. In this case a #8 [0.199] or a #7 [0.201] Dia drill can be used thru the old-hole into the new structure. This cleans out the old hole [somewhat] and establishes a relatively clean hole thru the stack-up that will accept a solid rivet installation. NOTE: YES, there are oversize solid rivets available on special order.
Everything I discussed above for solid bucked rivets DOES NOT apply to non-swelling fasteners with rigidly controlled diameters. For a blind rivet, blind bolt, lock-bolt/Hi-Lok, or bolt-nut installation, hole quality and fastener fit [class x or transition fit or interference fit, etc] are essential for structural integrity/durability... especially where there is little/NO shank swelling and the effects of compressive loads during fastener set/install are subject to variances such as tail/bulb swell/pull, pin-collar compression during collar swage or nut-bolt torque-tension... etc.
Usually blind rivet and bolt holes have +/-0.002 tolerance. Special close-tolerance/high quality drills [NAS907] might suffice... but that's 'chancy at-best for meeting hole tolerance requirements. For this reason these holes probably shouldn't be drilled: they should be [step-drilled then] finish-reamed with a piloted reamer [NAS897].
For lock-bolts/Hi-Loks/etc and bolts/nuts, holes are usually specified as +/-0.0010… or even tighter tolerance [+/-0.0005]… which is only attainable with a piloted-reamer [NAS897]. For these fastener installations [typ for highly loaded fatigue-prone structure] it has been proven time-and again by industry and DoD testing of mechanics that hand-drilled/reamed holes to the original diameter simple CANNOT pass hole tolerance requirements for those fasteners. Enlarging for/installing 1OS [1/64-OS] or 2OS [2/64-OS] for rigid Pins/bolts, in tight-tolerance controlled holes, is mandatory for shear-load transfer and long-term durability of fastener joints... not to mention optimum environmental sealing.
Rb1957…
“so it's the repair work that's oversizing the fasteners ... makes more sense, though I agree with you this is "just" a bolt, removing it shouldn't damage the hole. oversizing the hole "for the heck of it" will impact future reparability. but i doubt that windmill is worth tilting at ...”
All currently active USAF bombers… B-52Hs, built in the 1960s… and all B-1Bs built in the 1980s… are fairly old/aging battlewagons… 2017 [sadly] IS THE FUTURE.
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
TDeMoe… replying to this thread has been an interesting educational challenge… HOWEVER, you said [2 Feb 17 18:41]...
“Thanks for your response rb1957. I am not an engineer, I'm a work leader in a bomb bay door shop. …”
Eng-Tips is restricted to degreed-practicing engineers ONLY. It is very clear You are NOT an engineer, and I will [very soon] be asking Eng-Tips staff to deactivate Your membership… but leave this thread intact for its educational value. You will be free to browse any thread for information, but unable to post comments to any thread.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
- Thread starter
- #17
rb1957...
"...Sure, if in overhaul the screw is removed and the hole checked (for wear, corrosion, etc)... ...but if it is within tolerance why not reinstall the original size fastener ? ".
Generally speaking, I have no-problem with the concept of 'reinstalling the original size fastener' for a joint that is normally intended to be removed/disassembled for maintenance [typically class 1 or 2 fit already]... or is associated with a mechanical installation or assembly. Where this get unbelievably out-of-whack is when You realize that the 'same bolt' has probably been removed and reinstalled so many times that the head recesses and/or the threads are worn-out... as well as the mating nutplate/nut threads... and self-locking torque is fundamentally non-existent... and no one cares.
The practice of 'reinstalling the original size fastener' becomes 'sketchy' for fastener installations intended to remain as permanently assembled structure [close-tolerance, transition fit or interference fit fastener-to-hole]; especially when the joint is disassembled to facilitate other maintenance or repairs; and is ill-advised if new parts are mated to the old parts using the same fastener pattern. When 'hard fasteners' [bolts, lock-bolts, blind-bolts etc] are removed from these holes, damage to a significant percentage of these precision holes is inevitable and would be hard to inspect for; and then attempts to match-drill/ream new parts to these old hole, same diameter, WILL ABSOLUTELY blow-them out... or at least that is what my experience and various durability studies have proven. Not to mention that if the NDI lower limit of crack detection is, say 0.050, and the hole NDI's clean; then durability guys will tell you that the MUST assume a 0.049 flaw still exists. However if You oversize a hole, say 0.016 [1OS], then the flaw size can be 'presumed' to be 0.041 [0.016/2 smaller size] which is somewhat better for crack growth.
BUT...
I have violated this practice on a few rare occasions where NDI/DI of the hole 'looked good'...and oversize's were simply unavailable and next size larger was inadvisable. On the other hand I have jumped thru hoops a few times for 'non-standard oversize's' such as: (a) manufacturing 2OS solid sleeves that are shrink fit on fastener shank, then finish lathe-turned to precision [sometimes odd] ODs for a tight-match with OS-reamed-out hole; or (b) using the ACRES Fastener sleeves [MIL-S-85069/* and MIL-HDBK-271/105]. Also, I have removed and reinstalled the same Taper-Lok bolts in the same tapered holes for similar reasons and necessities [except TLs are worse]... but with TL unique special 'practices/criteria'. In all these cases I 'knew the rules so I could safely break the rules'.
BTW I prefer different definitions for Bolts and Screws.
Bolts and Screws can have any head style and any size or thread type.
Bolts have bare/precision shanks with minimized thread length and are generally intended for shear and tension loads. Because they have smooth shanks the shank Dia can be anything the manufacturer intends, Nominal, 1OS, 2OS, 3OS and stepped/shouldered; and tapered shanks [Nominal, 1OS and 2OS, what a nightmare].
Screws generally have fully-threaded, or mostly-threaded, shanks and are intended for tension loads with incidental shear thru the threads [not enough shank anywhere to transfer significant shear loads]. Screws NEVER have any oversize's associated with them [standard thread sizes only].
OK there are special bolts/screws, such and 'Cap-Bolts', Cap-screws and the family of tension bolts with necked-down shanks but... these have special mechanical [not structural] uses.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
"...Sure, if in overhaul the screw is removed and the hole checked (for wear, corrosion, etc)... ...but if it is within tolerance why not reinstall the original size fastener ? ".
Generally speaking, I have no-problem with the concept of 'reinstalling the original size fastener' for a joint that is normally intended to be removed/disassembled for maintenance [typically class 1 or 2 fit already]... or is associated with a mechanical installation or assembly. Where this get unbelievably out-of-whack is when You realize that the 'same bolt' has probably been removed and reinstalled so many times that the head recesses and/or the threads are worn-out... as well as the mating nutplate/nut threads... and self-locking torque is fundamentally non-existent... and no one cares.
The practice of 'reinstalling the original size fastener' becomes 'sketchy' for fastener installations intended to remain as permanently assembled structure [close-tolerance, transition fit or interference fit fastener-to-hole]; especially when the joint is disassembled to facilitate other maintenance or repairs; and is ill-advised if new parts are mated to the old parts using the same fastener pattern. When 'hard fasteners' [bolts, lock-bolts, blind-bolts etc] are removed from these holes, damage to a significant percentage of these precision holes is inevitable and would be hard to inspect for; and then attempts to match-drill/ream new parts to these old hole, same diameter, WILL ABSOLUTELY blow-them out... or at least that is what my experience and various durability studies have proven. Not to mention that if the NDI lower limit of crack detection is, say 0.050, and the hole NDI's clean; then durability guys will tell you that the MUST assume a 0.049 flaw still exists. However if You oversize a hole, say 0.016 [1OS], then the flaw size can be 'presumed' to be 0.041 [0.016/2 smaller size] which is somewhat better for crack growth.
BUT...
I have violated this practice on a few rare occasions where NDI/DI of the hole 'looked good'...and oversize's were simply unavailable and next size larger was inadvisable. On the other hand I have jumped thru hoops a few times for 'non-standard oversize's' such as: (a) manufacturing 2OS solid sleeves that are shrink fit on fastener shank, then finish lathe-turned to precision [sometimes odd] ODs for a tight-match with OS-reamed-out hole; or (b) using the ACRES Fastener sleeves [MIL-S-85069/* and MIL-HDBK-271/105]. Also, I have removed and reinstalled the same Taper-Lok bolts in the same tapered holes for similar reasons and necessities [except TLs are worse]... but with TL unique special 'practices/criteria'. In all these cases I 'knew the rules so I could safely break the rules'.
BTW I prefer different definitions for Bolts and Screws.
Bolts and Screws can have any head style and any size or thread type.
Bolts have bare/precision shanks with minimized thread length and are generally intended for shear and tension loads. Because they have smooth shanks the shank Dia can be anything the manufacturer intends, Nominal, 1OS, 2OS, 3OS and stepped/shouldered; and tapered shanks [Nominal, 1OS and 2OS, what a nightmare].
Screws generally have fully-threaded, or mostly-threaded, shanks and are intended for tension loads with incidental shear thru the threads [not enough shank anywhere to transfer significant shear loads]. Screws NEVER have any oversize's associated with them [standard thread sizes only].
OK there are special bolts/screws, such and 'Cap-Bolts', Cap-screws and the family of tension bolts with necked-down shanks but... these have special mechanical [not structural] uses.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
"Eng-Tips is restricted to degreed-practicing engineers ONLY. It is very clear You are NOT an engineer, and I will [very soon] be asking Eng-Tips staff to deactivate Your membership… but leave this thread intact for its educational value. You will be free to browse any thread for information, but unable to post comments to any thread."
Is this a serious comment?
Is this a serious comment?
aerodsgnr... TOTALLY SERIOUS.
rb1957... Your advice???
Should I (a) shut-up or (b) give aerodsgnr a 'WKTaylor long answer' to his question?
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
rb1957... Your advice???
Should I (a) shut-up or (b) give aerodsgnr a 'WKTaylor long answer' to his question?
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
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