Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

  • Congratulations KootK on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

3/8-24NF Threads Rusting in an Outdoor 0.226 wall Galvanized CS Clamp. Should I Coat Threads?

Status
Not open for further replies.

racookpe1978

Nuclear
Feb 1, 2007
5,979
I have 4x 3/8 dia carbon steel setscrews holding each of 13 CS rings in place in an outdoor setting. (Low stress, but the surface rust and subsequent streaks are irritating.)
The CS centerpost itself and the 13x rings are spray galvanized with a commercial topcoat, and the rest of the post and assembly is otherwise withstanding rust well over the past 5 years. (The setscrews are in tapped holes, each hole is appx 0.226 deep al the way through the CS ring.)
The setscrews and their threads are not "expected" to be removed or adjusted or need tightening, but each set screw point does cut into the primed surface under each screw.
When I removed the first handful of CS setscrews to replace them with SSTL setscrews, every thread was corroded. Most old screws were (are) difficult to remove.

Question: I am reluctant to spray a thread cutting lubricant or oil into the threads, then paint over the outside of the ring. But, will it help, or hurt, to prevent rusting if I spray the galvanizing paint into the tapped threads in the CS ring before tightening the replacement new SSTL screws?
 
Replies continue below

Recommended for you

Stick with carbon steel but look for set screws with an inorganic zinc coating such as Dacromet. This is the same coating used on modern automotive fasteners. It will help prevent seizing. If you are still worried about thread corrosion use a low strength thread locker such as Loctite 222. This will seal the threads.
 
Thank you. Why was my assumption that the (slightly more expensive) SSTL setscrews incorrect? Or simply not needed compared to sealing the threads chemically?
 
The threads likely won't have good galvanized coating. It's best to seal them regardless of set screw used. Loctite 577 also works very well for this. These are all anaerobic sealants so they won't cure in air. The excess will need to be washed off prior to painting.
 
Op
Phosphoric acid is bad idea.
Acid corrosion.

Option 1 mecanicly remove rust.
Drill over size and retap to the next size. Then as suggested by tug.
Zonc coated threads.
Use a bottoming tap. OK to start with a
Tapered, then bottoming.

Option 2 try to. Chase threads with
Slightly over sized tap but still in size. They sell tap slightly over sized. Like .0005 , verify with no go gage.
Lube with cutting fluid. Insert tap in increments, and back out often.
Till fully chased.


Option 3 remove and replace.
 
From McMaster-Carr.
Thread
Drill Bit
Plug Chamfer
Size Lg. Overall
Lg. Size Decimal Size
Equivalent No. of
Flutes Thread
Type Pitch
Dia. Limit Each
Uncoated High-Speed Steel
3/8"-24 1 1/4" 2 15/16" Q 0.332" 4 UNF H11 2535A35 $12.73

Ordered.
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor