Quote:
Graham,
It goes without saying that it is important to make sure the newly drilled hole is axial with the old one.
Peter.
Well, almost. I have been thinking about that. I suspect that if I take them to a shop with the capacity to do that to high accuracy, it'll exceed the cost of replacing with good second hand ones - there're some on eBay at £7.50 each for 3/8ths and £5.00 for 7/16ths.
I've only got a vice and a black and decker. But since I'm putting a 9.9mm (25/64ths) drill into a hole already 9.5mm in the case of the stripped one, I think it should be good enough to make a nut for the spares box. Slightly less confident if I decide to do the 8.6mm id ones.
As to the capacity in the nut walls: they are 17 mm od, and we're looking at 0.468" or 11.38 mm free outer diameter of the helicoil threads - which I think must be larger than the inserted diameter, but I'm not sure by how much (I'll measure the tap to be sure when I get it).
And that's compared to an outer thread diameter of more than 11.11 for the 7/16 unf thread - if anyone has a 7/16ths bottoming tap to measure, that would be interesting. That gives a wall thickness of about 2.95mm each side with the 7/16th. So coiling at 3/8 UNF give a wall thickness that must be no more than 0.14 mm less, or 6 thou off about 118 thou.
If someone can give me the 7/16ths UNF tap diameter, and I measure the 3/8 UNF coiling tap at anything like 12 thou bigger, I think I'll be fine with that.
Graham