# Selecting a larger radius insert



## misfitsailor (May 10, 2018)

I would like to buy carbide turning inserts with a larger radius.  This particular holder fits a TCMT 21.50 insert.  What nomenclature would designate a cutter with more rounded tips?  

  I normally just order more of whatever size inserts came with a tool holder.


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## xpylonracer (May 10, 2018)

Check the tip spec on the linked page, you see the nose radius quoted as 008 (0.008")
You can also see the ISO number stated (TCMT 110202-PS) the last 2 numbers denote the insert nose radius, in this case the numbers are 02 which is 0.20mm radius, other rads numbers are 04 = 0.40mm, 08 = 0.80mm, 12 = 1.20mm

http://www.pts-tools.com/cgi/CGP2SR...ARTPG=CGP2SRFC&PAMENU=Content-type: text/html

xpylonracer


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## goldstar31 (May 10, 2018)

Of course, with the aid of a fine diamond file it is possible to increase the radii.

There is NOTHING new in it, people have been 'rounding off' the sharp tip of cutting tools for ever.

What is done is to improve on the  rather sharp screw cutting and obtain a mirror like finish.  It does take a bit more. horse power and possibly a lighter depth of cut-- but I digress a bit.

What can be achieved is something called 'barely perceptible swarf' which avoids the need for a cylindrical grinder( Orr should)

Hope this helps

N


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## DJP (May 10, 2018)

I have reshaped carbide inserts using a green wheel and adding radius is easy. They are no longer indexable but for my needs they work better than new.


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## petertha (May 10, 2018)

You might have to be careful about altering the nose of certain inserts. At least the ones with a lip, which are quite common. If you truncate that, I would imagine the contact geometry would be quite different & thus cutting performance. The flat style inserts might be OK. I never had much luck with a green wheel on these, it was micro-chipped along the the edge but maybe just my technique or grit or...


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## goldstar31 (May 10, 2018)

petertha said:


> You might have to be careful about altering the nose of certain inserts. At least the ones with a lip, which are quite common. If you truncate that, I would imagine the contact geometry would be quite different & thus cutting performance. The flat style inserts might be OK. I never had much luck with a green wheel on these, it was micro-chipped along the the edge but maybe just my technique or grit or...



I stopped using green grit abrasives many years ago and use, as intimated earlier, a fine diamond.

Apart from rarely using carbides, I have both fine diamond files and diamond wheels on a conventional tool and cutter grinder.

As many will testify, grinding tools is not a subject which can be dealt with adequately in 'one line ' answers.

Regards

Norm


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## mayhugh1 (May 10, 2018)

Peter,
Do you have any info on that bottom insert in your reply? It looks like it might be a nice finishing insert for steel or stainless.

Steve,
I've pretty much settled on using 21.51 inserts in both my Enco manual and Wabeco CNC lathe as these can give nice surface finishes with minimum chatter problems in my lightweight machines. I occasionally use 21.50's when I need a sharp inside corner, but the feedrate has to be slowed accordingly to get the same surface finish. As others have said if you have some 21.50 inserts you can increase their radius with a very fine manual diamond file. I've even resharpened dull inserts this way. A green silicon wheel will remove carbide but not gracefully enough for a finishing insert. - Terry


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## petertha (May 10, 2018)

Terry - I just grabbed a random image that was of appropriate visual scale to illustrate the nose. But I back-tracked & found the link from my browser, it was still warm in Google 
https://www.grainger.com/product/product/WALTER-VALENITE-Turning-Insert-53WJ60

To be honest, I have been very impressed with AliExpress/Ebay stuff. I look for this Korloy name brand which has been very consistent, particularly the uncoated ones for aluminum. Whether that is a code word for a popular 'real' brand or same thing, China direct I really don't know. But the price difference can be substantial. Also sometimes you wont get hits on NAm model descriptors so you may have to dig for equivalent model numbers. For example this one shows TNMG160404 AK H01. 
https://www.aliexpress.com/item/Lat...0006-485b-9199-2b9a7732b4ea&priceBeautifyAB=0


You might have better luck typing 'TNMG stainless'. I see a few hits with different looking coating. That's the thing about Ali, it might be there but it may take half hour of page scrolling. And when you find it, sure enough, its listed under 'cutter'.

https://www.aliexpress.com/item/Tur...2061-492a-842d-1c51b0ee23a0&priceBeautifyAB=0


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## goldstar31 (May 11, 2018)

With that warped sense of humour beloved of other members of the Atkinson clan, I re-read Conrad Hoffman's various contributions in his Messy  Basement website.

Of course, if you can't be minded to do a little research instead of using others-- Tough!

Norm


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## rlukens (May 11, 2018)

goldstar31 said:


> Of course, with the aid of a fine diamond file it is possible to increase the radii.
> 
> There is NOTHING new in it, people have been 'rounding off' the sharp tip of cutting tools for ever.
> 
> ...



I believe, with the same feed/speed, the chip load is actually decreased because it's spread over a larger surface. Could be wrong.


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## bazmak (May 11, 2018)

Chip load and cutting forces on the tool/lathe are 2 very different things


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