Proper use of star washers.

Discussion at the hanger on star washers is as active as it is here.
Who knew there would be so many divergent opinions?
 
:) I didn't know washers were a religious topic, either.

I've only used star washers for electrical connections. I can't speak to aviation use. Outside of aviation, for things like UL and marine, general modern consensus seems to be that the star washer goes between the chassis and the lug, but as far as I know that's based on studies using high quality washers specifically designed as electrical grounding washers. I use what I think is more old school, with the lug against the chassis, then the star washer, then the nut or bolt on top. Using the star washer partly to provide low resistance connection, partly to act as a lock washer. I don't trust hardware store star washers to carry any appreciable current.

If my memory is right, it was a German aircraft company in the 30's that figured out that split lock washers don't work, but star washer do, in terms of reducing the chances of loosening under vibration. That knowledge may not have been around when your PA-17 was built, so it's possible that even if you had a manual, it would be wrong. There probably weren't any special star washers back then, either.

So if it were me, not an A&P, I try to avoid using a star washer for a mechanical assembly. I'd rather trust some sort of rated one time use nut or screw/bolt. For electrical, I'd probably do my sheet metal, lug, star washer, nut/bolt thing if it were legal. For non-airplane electrical, I like SS hardware and copper anti-seize.
 
Yep, looks like they use them to hold the crankcase halves together in the IO-540, engine mounting brackets, and a bunch of other things. From the diagrams, looks like every case is a stud, then whatever bracket/part, flat washer, internal star washer, nut. Between 1/4" and 3/8". So they must work well in that application. That's similar to how I've seen them done in old electrical installs, appliances and industrial equipment, with the lock washer on top, right under the nut. Cool so see that arrangement being mechanically sound.

There's some NASA reports suggesting free spinning lock washers are to be avoided, but referencing an old army/navy standard that could date back to ww2. Obviously the manual for the engine wins over a blanket suggestion from another group.
 
Shepherd said:
Discussion at the hanger on star washers is as active as it is here.
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FYI: this discussion has been going on since Kitty Hawk. ;)
Shepherd said:
Believe it or not, I can NOT find a repair manual specifically for the PA-17.
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Back then CAM-18/AC43.13 was the repair reference for that and similar models. Some/most airplane OEMs only provided a POH/AFM, IPC, and drawings. The rest of mx references was from various CAMs/ACs. It wasn't until the FARs required ICAs that service/maintenance showed up on the small airplane side. For example, the Super Cub has no factory service manual either --just the Owners manual with certain maintenance procedures and the drawings.
 
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Albany Tom said:
So if it were me, not an A&P, I try to avoid using a star washer for a mechanical assembly.
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FYI: Keep in mind even though you're not an AP you would still need to follow the same Part 43 rules as an AP if performing preventative mx. Which would include using those same star washers.
 
Bell206 said:
FYI: Keep in mind even though you're not an AP you would still need to follow the same Part 43 rules as an AP if performing preventative mx. Which would include using those same star washers.
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Oh of course. I tossed out the "me not an AP" to mean "everything I know about repairing an aircraft is 0", not that I'd put something together in a different way than the manufacturer advised. For a certified aircraft engine, that would be nuts. What ever is documented is proven to work, or there would be a AD to correct it. For an MTD lawnmower? I might try to re-engineer it. For a harbor freight anything? I'm *probably* going to re-engineer it.
 
Grum.Man said:
This is a common misconception about how lock washers function. They aren’t designed to “dig in” in order to prevent rotation. They are designed to apply a spring load on the fastener to prevent rotation.
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They will definitely dig in to soft sheet steel as well as provide spring load. At least the version my father invented, Everlock, but maybe not competing Shakeproof which has a different tooth design.
 
Albany Tom said:
...I use what I think is more old school, with the lug against the chassis, then the star washer, then the nut or bolt on top...
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I don't know if that's old school but if you do it that way then the terminal lug, which is normally at a tangent to the stud or bolt, is "locked" to the nut. So if you try to remove the nut you'll twist the terminal lug. If it's tied to a bundle or between guides of a block you'll be reterminating that wire with a new lug, hoping you have enough slack to do it.
 
Silvaire said:
I don't know if that's old school but if you do it that way then the terminal lug, which is normally at a tangent to the stud or bolt, is "locked" to the nut. So if you try to remove the nut you'll twist the terminal lug. If it's tied to a bundle or between guides of a block you'll be reterminating that wire with a new lug, hoping you have enough slack to do it.
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I can see how that's possible, but I haven't run into that where it causes damage. What I've seen is that you can break loose the set, with the lug typically turning as a unit with the nut and star washer for maybe 1/8 of a turn, then you can hold the lug and the nut just comes off. No damage except scraping of the tin off to the copper of the log.

edited. I used too many words.
 
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I recon on an electrical terminal lug, where the screws aren't torqued to a high tension like machine parts would be, then a star washer probably creates just enough marring to 'enhance' the electrical connection by cutting through the surface oxidation or dirt + add a little friction against a loosening rotation.
 
Timbeck2 said:
Depends on the application
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Yes. Depends on the application. If electrical, the contact point should be clear of paint and treated with a corrosion preventative. A star washer would also have a better contact into the metal for a good ground.
 
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