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SS bolts and aircraft nuts locking up?

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tmhansen
Captain

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USA
397 Posts

Initially Posted - 10/04/2003 : 03:16:24

The first time it happened I was a little puzzled but thought I must have done something wrong. Then it happened again two more times. Brand new SS 3/8" bolt and new SS 3/8" aircraft nut ( the kind with the nylon insert to keep it from backing off). The nut started on fine, was turning without any undue force and then it siezed. Could not back it off. I could see the bolt rotating, about to shear but the nut will not move. I can see the exposed threads of the bolt and they are clean, the bolt was not cross threaded or a nut with a different thread installed. All I could do was cut it off. What gives? Is it me or has this happened to anyone else?

Todd Hansen
Fior Gra'
San Luis Obispo, CA

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bear
Admiral

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USA
909 Posts

Response Posted - 10/04/2003 : 09:12:47

Todd,
Having Worked with aircraft and its associated hardware, if you want to ensure good quality of the product, use AN hardware or NAS hardware. I have found when I got away from useing aircraft hardware that the quality of the threads isn't there anymore. Buying common hardware at Home Depot or any local hardware store I have found bolts and nuts mismatched [in the wrong bins] threads that don't match up and other quality and manufacturing issues. When I retired from working on aircraft and helicopters I brought with me priceless amounts of used and new hardware. This hardware is available from aircraft parts catalogues and local airport shops. Also you can run a tap or dye on suspect threads to clean them up. Just my two cents worth. "Bear"
Wayne Brown

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Bill Holcomb
Admiral

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USA
769 Posts

Response Posted - 10/04/2003 : 10:06:14

Hi Todd,

It's sure possible that you have 3/8" bolt but somehow have gotten a 10mm nut. The two are almost the same size and would be difficult to eyeball - especially out of a bin. Unfortunately, the 10mm nut would have threading in metric units while, of course, the 3/8" bolt would not. You could probably get the nut started, but soon the threads would jam. Not knowing the situation, you might continue tightening the nut until you really got it stuck.

Bill Holcomb - C25 Snickerdoodle #4839

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ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 10/04/2003 : 11:33:06

That has happened to me more than once. :>(

You could have a mismatched metric nut, but I've seen "bad" stainless coming from the hardware store bins lately. Lousy threads, lockups (like yours) and early rusting. I suspect they are getting their stainless from a cut-rate supplier in asia.

I now buy full '316' stamped stainless from a marine store. No lock-ups with their stuff... saves troubles in the long run.

Also (generically speaking), most common stainless alloys are prone to galling under load. It is good practice to lubricate a stainless bolt/nut before installing.

Currently maintaining two holes in the water...'77 Venture 23 and new to the family,
'78 Catalina 25

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 10/04/2003 : 12:55:12

Todd,

Re: "The nut started on fine, was turning without any undue force and then it siezed... What gives? Is it me or has this happened to anyone else?"

Yes. When I ordered a truckload of trailer parts from Champion Trailers, there was a tech tip sheet packed with the small hardware which said not to ever assemble stainless steel threads dry to avoid the risk of galling. It was a whole page of paper with real big lettering. I just glanced at it and figured they meant don't torque down dry threads. I knew that.

I was playing with a stainless steel 3/8"-NC bolt and nylock nut, just checking out the fit of the threads by hand (no wrenches, etc.). The threads seemed to run just fine, and then suddenly siezed. In trying to unscrew the stuck parts using a bench vise and long socket handle, I ended up wringing off the bolt. I've had this happen on at least three occasions with like new stainless steel hardware larger than 5/16" diameter. I've never seen it happen on stainless steel hardware smaller than 1/4" diameter without there being pre existing damage to the threads.

By the way, for anyone who isn't sure what we mean here by "galling", that's when the two parts pressure weld to each other on a microscopic scale. As the part surfaces are forced to continue sliding past one another, the welded molecules hold, and one of the parts fractures or tears near the weld. As this jagged metal tries to continue sliding, it results in more localized welding, with subsequent tearing and smearing of metal. A problem that was too small to see with the naked eye quickly snowballs (almost literally) into a wad of twisted metal so large that the bolt shaft shears off near the nut.

Obviously this isn't a big problem with the smaller thread diameters we are more used to working with. I'd say that as a general rule, don't dry fit stainless steel threads larger than 1/4".

-- Leon Sisson

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eric.werkowitz
Captain

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USA
283 Posts

Response Posted - 10/04/2003 : 14:04:10

Leon,

Do you think the Nyloc nuts increase the lateral loads on the threads and increase the probability of galling?

Eric Werkowitz
C25 #4969

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Oscar
Master Marine Consultant

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USA
2030 Posts

Response Posted - 10/05/2003 : 12:41:50

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>don't dry fit stainless steel threads <hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Funny, just had this very thing happen to me (1/4" threads), and was wondering what I did wrong. Thanks for the insight Leon. Learn something here every day. Question is, what do you use to lubricate?

250WB#618 Lady Kay on the Chesapeake
<img src="http://www.woodenshoemusic.com/Images/familypics/Forumshots/sunglitter.JPG" border=0>

Edited by - Oscar on 10/05/2003 12:42:30

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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 10/05/2003 : 13:16:54

I have had several seizures of 5/16" stainless Nylock nuts on Quiet Time (Catalina 25 rigging pins are all 5/16" as you know). I use bolts and nylock nuts on the furler drum to stemhead fitting connection, and on the shroud jumpers and forward lowers (Quiet Time has a Huntington Rig conversion of the uppers for single-handed mast raising). We had a Catalina 250 in our sailing club get dismasted a couple of years ago when his furler drum came loose. He was using a rigging pin and cotter ring, and somehow the ring got pulled off, probably snagged by a dock line or anchor rode, or possibly a jib sheet. The back-and-forth rotation of the drum eventually worked the pin out of the hole before he noticed the cotter ring was missing. Fortunately no one was injured. Anyway, I no longer trust those rings, having seen several of them on the lifeline turnbuckles of my own boat get snagged by jib sheets and yanked out of shape. All of the critical rigging connections on Quiet Time that don't need to be dissassembled for trailering are done with cotter pins, not rings, and the pins that need to be removed for mast-lowering are bolts with nylock nuts. I agree with the comments about lubrication. I think the best lube for a nylock nut that a boater is likely to have on hand is wheel bearing grease, preferably the "blue goop" Marine-grade grease that boat trailer bearings should be lubed with. A tiny dab of this on the bolt threads as you assemble the nut should protect the theads. I know that there are also specialty thread lubing compounds used in the aircraft industry for protecting the threads on stainless fasteners in planes and helicopters, the stuff is nickel-based I think, but I don't remember what it's called. We used to use it to assemble head bolts, spark plugs, and exhaust manifold studs on air-cooled Volkwagen engines back in the '70's. BTW - turnbuckle studs and toggles should always be lubed before every adjustment, but you knew that, right?

Larry Charlot
Catalina 25WK/TR Mk. IV #5857 "Quiet Time"
Folsom Lake, CA

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Douglas
Master Marine Consultant

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1595 Posts

Response Posted - 10/05/2003 : 13:51:24

If your going to use stainless your going to need a thread lubericant. Almost all fitting in the high pressure hydralic systems on aircraft or tbing on the engines are stainless. We use an assembly lube to prevent gauling of the threads. Butterlube we call it. Very simmilar to vasoline. Hope this helps.

Doug&Ruth
Triska (Alberg 29)
Tacoma Wa.

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tmhansen
Captain

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USA
397 Posts

Response Posted - 10/05/2003 : 14:49:15

Thanks guys! I used to use an assembly grease on my Corvair but only on the aluminum parts so I could back them out in the future. I'll grease the threads of stainless bolts from now on! Good thing my kids were in bed the other night or I think they might have heard their dad use words the he ought not to.

Todd Hansen
Fior Gra'
San Luis Obispo, CA

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Sid
Navigator

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129 Posts

Response Posted - 10/06/2003 : 14:44:57

In previous employment at a chemical plant we often used stainless for everything (1/4" nuts to 3"threaded pipe)due to it's no reactive properties with the chemicals. In industrial applications we used a product called SWAK, a paste type teflon lube that came in a tube. It prevented galling and also served as an anti-seize for later removal. I'm not sure of the cost or where to get it, but it was very effective.

Sid

77 C25 SK #21

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MattL
Admiral

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USA
990 Posts

Response Posted - 10/06/2003 : 14:54:28

Just as a quick aside. My cousin use to have a machine shop. One day he had an employee bolting some parts together with aircraft nuts. After a while he went to check up on the guy. The fellow had a torch and was melting out all the plastic. He proudly told my cousin that the plastic was making it hard to put the nuts on so he was melting it out. They guy didn't stay with the job that long.<img src=icon_smile_blackeye.gif border=0 align=middle>

Matt/Brigitte Loeffler
E.C. Rider
Cat 25 86'
FK/SR _/)
<img src="http://im1.shutterfly.com/procserv/47b2cf25b3127cce91e544e83b8c0000001010" border=0>

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ronrryan
Admiral

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USA
561 Posts

Response Posted - 10/06/2003 : 19:59:24

In the mists of the distant past when some boats still had galvanized rigging, it was recommended to use Anhydrous Lanolin to lube turnbuckle threads. You got it at your local Pharmacy (apothecary?). I doubt my local Eckerd would know what the devil I was talking about, nowadays, but I can testify that it used to work just fine, you could disassemble a turnbuckle after a year in salt environment, rain, snow, blah blah, and the stuff was still lubing the threads, ron srsk Orion #2343 SW FL

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