Taps (and dies)

[Hardwicke]

I want to reduce a bought part which has a turned 10BA or 12BA thread at one end down to a 14BA. I also need to make a new part and tap it to 14BA. Which is the tap I need : taper or plug and should I also buy the tap wrench/ holder. Dies: normal or HSS?

[garethashenden]

Is the hole you need to tread a through hole or a blind hole? If its a through hole, you can use a tapered tap and run it all the way through. If its a blind hole, then you will need a plug tap. But it might be easier to start the hole with a tapered tap, if there is enough depth.

What material is "normal"? In tooling generally most of the choice is between HSS and carbide, but I doubt that's the case here. It could be hardened steel I suppose, which would work, particularly in brass. What is the material?

Do the major and minor diameters work out such that a 12BA thread can be turned smooth and then treaded 14 BA? Or would some of the 12BA threads still be left when its at 14BA OD? If that's the case then trying to thread it would probably not go well.
Edit: There looks to be about 0.004" between the 12BA minor diameter and the 14 BA major diameter.

[nigelcliffe]

At 14BA, some taps and dies may be hardened carbon steel, rather than HSS. For most work the hardened steel may be a little less prone to break.

At those sizes, normal tap/die holders don't really help, they're just too big. I've made my own tiny die holders. For taps, a small pin-chuck is fine, though it helps if there is a stand to stop it tipping to one side (and breaking the tap). A small bracket over the job with a hole for the pin-chuck body is all that's needed.

And, is it easier to remake the part with the correct threads, rather than modify what you have ? Being sure its all concentric might be an issue with modification, let alone the depth of over-cutting which may have happened with the old threads.

- Nigel

[Terry Bendall]

Scalefour News 219 has some information about taps and dies that may be helpful.

Terry Bendall

[Hardwicke]

Tools have arrived...

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