# Experiements turning a hard SS drill bit ...



## wquiles (Oct 23, 2009)

In between my projects, I also like to "experiment" to learn the limits of my machine, and the even smaller limits of my tiny brain, so this time I was trying to reduce the diameter of a very hard, 3/4" SS spade drill bit. I tried it several times, on both sides of the insert, and I did manage "somewhat" to get the diameter down, but the insert did not fared too well - and this was with the mister going heavier than normal:






















The closeups are even more interesting:
















During one of the recent MSC specials I got two different inserts, supposed to be a good match for SS, so I will be trying again soon ...






Will


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## PhotonFanatic (Oct 24, 2009)

Will,

There are ceramic inserts for turning hardened steel, I think that they are called Cermet. Here's an interesting video for you.

And here's a link to some of the Sandvik inserts and their various grades.


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## wquiles (Oct 24, 2009)

Thanks Fred - I will order one of those soon :twothumbs

Cool video by the way 

Will


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## precisionworks (Oct 24, 2009)

> There are ceramic inserts for turning hardened steel, I think that they are called Cermet.


+1

The insert that you tried is good for non-hardened SS, or other tough materials with a Rockwell C hardness of 42 or less. You can sometimes get them to work on harder materials by reducing the sfpm by 50% to 75% less, but even then it may not work.

Cermets are useful to around 60-62 HRc, and can usually be found on eBay, especially in the CNMG-4xx size that you use. The best solution is to use either a TP grinder on the lathe, or put the drill shank in a 5C collet spinner (coffee grinder) & spin it under a surface grinder wheel. Either of the grinder methods make quick work of hardened materials. 

Some shop built TP grinders at this link, quite a few are easy to make:

http://www.thewarfields.com/cnccookbook/MTLatheTPGrinder.htm


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## scintillator (Oct 24, 2009)

Use a high speed steel bit. Ceramics don`t do well on interrupted cuts.


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## precisionworks (Oct 24, 2009)

> Ceramics don`t do well on interrupted cuts.


That was the case ten years ago. Both ceramics & cermets are available today with toughened substrates that do a good job on interrupted cuts. Iscar makes their cermet parting tool inserts (GTN3) in IC30N for specifically this purpose.

http://www.pgstools.com/servlet/the-10547/GTN3-IC30N,Iscar,Cutoff-Insert/Detail

Quite a few other manufacturers offer toughened cermets & ceramics. Even some of the inexpensive eBay cermets do a good job on interrupted cuts, depending on the substrate.


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## wquiles (Oct 24, 2009)

Ebay has these two at a fairly low price for my CNMG 43x holder:
Iscar Insert ...


Kennametal Insert ...


Which of these would work?

Will


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## precisionworks (Oct 24, 2009)

The Iscar insert is specifically made for hard turning of cast iron ... West Side Industrial sells it for $5.90 http://westsidedelivers.com/item.asp?PID=28858

The Kenna insert uses a .008" x 20° T-land edge finish (432*T*). Kenna says:



> T-lands protect the cutting edge by eliminating a sharp cutting edge, thus reducing edge chipping.





> Grade K090 offers toughness & thermal shock resistance for machining alloy steels, stainless steels & tool steels from 50 HRc to 62 HRc



The Kenna insert would probably give better results in a wider range of materials. Since this job is a continuous (non interrupted) cut, it's about as easy as hard turning gets


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## wquiles (Oct 24, 2009)

Thanks - I went ahead and bought one of the Kena inserts to play with 

Will


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## cmacclel (Oct 26, 2009)

PhotonFanatic said:


> Will,
> 
> There are ceramic inserts for turning hardened steel, I think that they are called Cermet. Here's an interesting video for you.
> 
> And here's a link to some of the Sandvik inserts and their various grades.




Cool video......I just learned how to convert a LH holder to a RH 

Mac


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## unterhausen (Oct 26, 2009)

cmacclel said:


> Cool video......I just learned how to convert a LH holder to a RH
> 
> Mac


I knew that 
Never seen a compound at that angle though.


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## KowShak (Oct 27, 2009)

unterhausen said:


> I knew that
> Never seen a compound at that angle though.



I thought that was odd as well.

Not knowing exactly what size the lathe is, the part was large diameter and he could have had the compound at that angle because he didn't have the travel on the cross slide.


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