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From: Peter Fairbrother <peter@tsto.co.uk>
Newsgroups: rec.crafts.metalworking
Subject: Re: Those Cheap Diamond Inserts
Date: Tue, 20 Aug 2024 18:17:05 +0100
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On 20/08/2024 07:50, Charlie+ wrote:

[...]
> Only hobby level now..
> https://www.ebay.co.uk/itm/115334715488?_nkw=diamond+inserts+carbide+lathe&itmmeta=01J5Q723XNA0GREWTN8RFZEQK2&hash=item1ada7c1860:g:YyUAAOSwUtJiUKWN&itmprp=enc%3AAQAJAAAA4HoV3kP08IDx%2BKZ9MfhVJKnC8gu8jBQODZUzjY6nfSpuZas%2FJzGcWIYLgG5EPfxVgG0wH1c4QdrYrUHqD4z98NSE8atbz28SHAAsTTB%2FvXsdw1KSXcN7%2Bx6cwyg%2FcKXwvDq3eEqXZbpx%2Bzxtc0f0%2Fp0BsyoIUtnlZlJQI86p6TyhETkaZsGuuwYw1Ayo2CHAORe6WE1WiaDElO8xogeQY1mItmsxVxjRLhavW15vEW5hMGkyR8srWzmxrGq4dX%2B9yZ23zhsDDiiDdifsQ%2Bk8r7IRPefZ9T%2FppdLbpKF%2FwpjM%7Ctkp%3ABk9SR_S-iOetZA

Those are PCD polycrystalline diamond tipped inserts.  Diamond crystals 
in a cobalt alloy matrix. For very hard materials sometimes, but far 
more often for extreme wear resistance.

> It says for non ferrous [..]
The carbon in the diamond dissolves in iron and steel (and nickel 
alloys), so they don't last long on steel. You can use CBN cubic boron 
nitride on steel etc for longer life, about the same price.

Hobby level chaps (and most small-batch pros, indeed most pros) should 
generally stick to HSS or carbide, unless they are doing something unusual.

> Can they be touched up if/when the edge goes?  

No. Carbide inserts can sometimes be touched up with diamond (though 
it's usually not worth doing unless you want something special), but not 
PCD or CBN.

> I know its only a single but looks uncheap to me!  C+

Last time I bought any they were £20-odd each, and that was years ago.


Peter Fairbrother