Tapping fine over coarse threads 1

[kkeenn]

I mistakenly had a hole tapped 4-40 instead of 4-48. Normally this wouldn't be the end of the world. However, ball spring plunger only come in 4-48 in that size. Is there a remedy to this? I've attempted using a helical insert but the material is titanium and it just tore up the tap.

 

[Screwman1]

You are pretty much out of luck on that one. Since the diameters are the same, even using a solid insert and redrilling will lead to the threads unreeling in the hole. Unless you can somehow weld up the bad threads, I think that hole is not going to be able to be saved.

 

[BrianE22]

If you have the room, you could make your own solid threaded insert.

 

[racookpe1978]

Heli-coil is the best way, if the substrate is large enough for the greater diameter of the heli-coil itself. And, for a nbr 4 thread, it should be easy.

Double-tapping will not work. You will either be tapping "air" (the gaps between the original threads) or cutting and stretching criss-cross patterns through what little metal remains in the original thread.

 

[Screwman1]

Sorry, too early (not enough coffee)- I misunderstood what he was trying to do. I agree with RACook; with the correct drill diameter and tapping lube you should be able to put the 4-48 Helicoil into that location. There is nothing from the Heliciol design and installation point of view that should prevent it from working.

 

[racookpe1978]

I understand the Ti substrate, but you'll just have to change the tap. Call H-C for a different material.

And, for a nbr 4 tap in darn near anything, look also for the carbon-based-control-system-error between tap handle and floor.

 

[Tmoose]

"look also for the carbon-based-control-system-error between tap handle and floor"

It hurts my feelings when you talk about me that way. You know how sensitive I am.

Dan T

 

[racookpe1978]

See also:

http://www.cimindustry.com/article/tooling/tips-for-tapping-titanium