Are lathe tool carbide inserts supposed to be sharp?

[awake]

Grinding steel on diamond disks can ruin the disks. Yes, diamonds are the hardest thing but when grinding steel the carbon in the hot diamonds can migrate to the steel and cause many problems which why you should only grind carbide on diamond wheels.

A very important word of warning. There is a caveat - as I understand it, at least one company sells a diamond grinding setup that 1) runs slowly enough not to build up a lot of heat, and 2) is water-cooled - and as a result they advertise it for use with steel or carbide.

*note that I'm going on the basis of fuzzy memory, so I may not have the details just right ...

 

[timo_gross]

there is a CBN--Cubic Boric Nitride which is used as an abrasive second inhardness to diamond. But I haven't found any tool bits made of it yet.

CBN wheels can usually be bought from the same companies that also make diamond grinding wheels or other grinding wheels.
Not as difficult to find as they are difficult to pay for.... haha.
If you want to grind HSS CBN is the way to go.

 

[SteveM]

Stefan Gotteswinter is a fine engineer who generally uses carbide for his lathe tooling and has produced some interesting videos on the subject. In one (link below) he regrinds carbide inserts, producing a sharp edge and demonstrating that the results in cutting steel, brass and aluminium are outstanding. In another he brazes used carbide endmills onto cold rolled steel for use on his small lathe.

Here's the one about the inserts: Regrinding Carbide Inserts

 

[Nerd1000]

Sorry - - - need to look a little further.
Greenleaf Crop is one name that I remember for such tooling.
Used on hardened materials and really tough as used (IIRC for the second).
Didn't use them often but when you drop an insert made of CBN into the lathe and you're turning 4140 - - - - wow - - - feels like race car time!!!!!
(That was the demo in my training.)

You can pick up Chinese CBN tipped inserts on eBay. One insert will cost you the price of an entire box of carbide tips, but on the other hand it's possible to turn heat treated HSS with them.

 

[william_b_noble]

what I will add to the carbide discussion is I have what is a "small not rigid" lathe by industrial standards, but it weighs about 1200 pounds and is massive by the standards of these little lathes you can lift with one arm. I use carbide a lot, it will cut though mill scale and surface hardning where HSS won't, I can run it making beautiful bright blue chips - and I can get a glass like finish with the right materials. But carbide is supremely brittle - I don't think I've ever worn out a carbide tip but many have failed with a broken tip - if the material is softer or you aren't taking massive cuts, then I think the recommendation to stick with HSS mostly is a good one.

 

[Bentwings]

there is nothing wrong with using carbide as long as you understand how they work. You can hone them to a razor sharp edge and they will cut nice but as soon as that edge chips even slightly everything can go down the drain in a hurry . There are some incredibly tough HSS tools that don’t dull easily and if you make proper chip breakers they cut nice and clean you can even get stringy materials the chip nice. We probably have several hundred dollars of broken carbide tools in the lathe cutter box I have a few really high quality HSS tools that are my own carefully stashed. I don’t see well or hear well and I’m not supposed to even be in the shop but I still sneak in for that special thing I need made the little lathe can’t handle heavy cutting on alloy steel like 4130 or 4150 the same with the small mill it’s not a series 2 Bridgeport or big Cincinnati . But I still can bore a hole to a pretty exact size using the right tools I don’t make much out of hot rolled anymore I don’t even like welding it

So each to their own. What ever works for you is good.
what I will add to the carbide discussion is I have what is a "small not rigid" lathe by industrial standards, but it weighs about 1200 pounds and is massive by the standards of these little lathes you can lift with one arm. I use carbide a lot, it will cut though mill scale and surface hardning where HSS won't, I can run it making beautiful bright blue chips - and I can get a glass like finish with the right materials. But carbide is supremely brittle - I don't think I've ever worn out a carbide tip but many have failed with a broken tip - if the material is softer or you aren't taking massive cuts, then I think the recommendation to stick with HSS mostly is a good one.