Tap and die problem

[Matchless]

This is why I have a drawer of hand held thread chasers, often tickle a thread at low speed in the lathe, but I am a bodger!

Looks like that Chinesium die wore out after the first thread! try cutting another, bet it is worse!

 

[Agroshield]

Would it not be BSW anyway being a 50/60s Colchester?

I do not know. All I can do is the same as you and read the words of the original posts. Here they are:

"The screw was to replace a missing one in my 4 way toolpost.
The ones in there never want to unscrew all the way but I found one that did.
It ran down the other hole which I cleaned up with a tap fine.
The screw I made won't go in either hole properly."

He has run a 1/2" UNC tap through an existing hole and an existing bolt goes into that hole no problem.

The new bolt is the problem.

While the threads on it look dreadful and are most likely the cause of the problem, there is a very small chance that the die is incorrect (slightly increased as he says it is from a cheap set) so it is worth a moment's double-checking to find out.

Perhaps try to run the die onto the existing (known good) bolt. It it screws on without removing any material, it is of the correct pitch.

If by some freak, it turns out to be wrong, the part will need to be remade as even a brand new die will not repair it.

 

[RichardM]

UNC and WW 1/2" have a different pitch. 13 v 12 TPI

 

[dan.taylor.1]

That would be great - let me know thanks.

Had a look and I don't even have one apparently... Loads of unf, but only one unc die and it's 1/4"...

 

[fizzy]

Had a look and I don't even have one apparently... Loads of unf, but only one unc die and it's 1/4"...

Thanks anyway.
Just ordered a HSS split die - made in the UK. £9.95 delivered so not too bad.

 

[grim_d]

Would it not be BSW anyway being a50/60s colchester?

50/50 I'd say

 

[fizzy]

Most definitely 1/2" UNC - cleaned up the threads with a UNC tap and one of the other screws fits perfectly.
Shame the die isn't UNC or any other thread known to man