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Self tapping bolts into sheet metal - advice needed.

zorbazorba Senior MemberPosts: 23,659 Senior Member
edited December 2019 in Clubhouse #1
I'm reassembling my generator cabinet after replacing a rusted out bottom piece - steel sheet metal. Its held together with "thread cutting" bolts - of which I bought brand new ones. I want to rust proof it as best I can - should I:
A) Coat the threads with grease,
B ) Coat the threads with "red lead primer",
C) Coat the threads with RTV,
... before installing the bolts?
The bolts are in a protected location, but will be subject to moisture, especially on the "off side" where there could be rust induced. The off side is inaccessible. I've done B in the past with seemingly good results, but I'm wondering if A wouldn't be better. The holes in the sheet metal have a "lip" bent into them.

BTW, is there a difference between "self tapping" and "thread cutting"?
-Zorba, "The Veiled Male"

"If you get it and didn't work for it, someone else worked for it and didn't get it..."

Replies

  • LinefinderLinefinder Moderator Posts: 7,035 Senior Member
    edited December 2019 #2
    Self threading is used when the thickness of the metal itself is great enough to allow the formation of a thread. IOW, self threading is useless in 22 gauge thickness, but quite handy in 1/4" plate.

    Self tapping is used in thinner metals (22 gauge, for instance), and it simply means you don't need to drill a pilot hole.

    Mike

    edit: For self tapping screws, TEK is the gold standard brand, and they work well in 26-20 gauge and there's not much sense using any other.
    BUT, even TEKs have their drawbacks....occasionally stripping out, leaving an unfilled hole in the metal, especially in very thin metals such as stovepipe or JOVAL. In really thin metals...28-30 gauge, use pointed sheet metal screws and punch a starter hole in your material wit a hammer and icepick (or awl).

    edit edit: I'd go the grease route.
    "Walking away seems to be a lost art form."
    N454casull
  • zorbazorba Senior Member Posts: 23,659 Senior Member
    Thanx Linefinder. I think I see now, and I've used TEK before in the distant past. This is a pretty heavy gauge item, I'm guessing 10 or 12 gauge - and the pre-formed holes are - for severe lack of knowledge of the proper terminology - bent downwards around their circumferences - like a crater without a bottom. Obviously to give the thread cutting screws something to actually bite into.
    I have some really tacky waterproof grease I can use.
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
  • zorbazorba Senior Member Posts: 23,659 Senior Member
    The old one:

    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
  • jbp-ohiojbp-ohio Senior Member Posts: 10,161 Senior Member
    Buy stainless... Always called them Zip screws
    "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not." Thomas Jefferson
  • LinefinderLinefinder Moderator Posts: 7,035 Senior Member
    For  long lasting grease that is thin enough to penetrate threads fully but doesn't dry out over time, it's  gonna be pretty tough to beat tool and diemakers grease.

    "Walking away seems to be a lost art form."
    N454casull
  • JayhawkerJayhawker Moderator Posts: 16,920 Senior Member
    edited December 2019 #7
    While we're on the subject of sell-tapping screws...I put them in the vibram soles of my wading boots as cleats when fishing on rocky, slippery streambeds...a package of 12 from Orvis will run you 10 bucks plus shipping...$2.00 at the hardware store...
    Sharps Model 1874 - "The rifle that made the west safe for Winchester"
  • LinefinderLinefinder Moderator Posts: 7,035 Senior Member
    jbp-ohio said:
    Buy stainless... Always called them Zip screws

    Zip screws are actually pointed sheetmetal screws. You usually need a pilot hole or slight indentation to start them without causing undue irritation. OTOH, they provide the tightest fastening you'll get in thin sheet metal. TEK screws don't normally require any pre-prep and work well for most thin-metal applications. But, as previously mentioned, Zip screws are the thing for ultra-thin metals.

    Mike
    "Walking away seems to be a lost art form."
    N454casull
  • jbp-ohiojbp-ohio Senior Member Posts: 10,161 Senior Member
    edited December 2019 #9
    Must be regional. Any 1/4'' drive sheet metal screw under 1/2'' is a Zip screw....
    "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not." Thomas Jefferson
  • NNNN Senior Member Posts: 24,713 Senior Member
    If you use grease use lithium grease; should still come in small containers.
    Shut up-----KAREN; OK Cynthia
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