Machinist

[Lawrence London <lfljvenaura@gmail.com>]

Recommendations on inserts for hard turning
http://www.practicalmachinist.com/vb/general/recommendations-inserts-hard-turning-336346/

Consensus:

CBN

Almost all hard turning is done with CBN inserts, usually CBN tipped inserts.
A CNGA will come with 1,2 or 4 usable corners.
Now the grade and edge prep is application dependent but they are a bit versatile. I'm sure many here will have favorite flavors.
Chip control is a problem as chipbreakers cut into CBN are expensive. Sometimes a clamp on breaker is a good idea.
Bob

Keep in mind that CBN likes a rigid setup and machine, if you're working with an older, looser lathe you may have some issues. Maybe make a test piece to check cutting parameters and see if the insert works before committing to the real parts.

Maybe but I cut hard steel and ball screw ends with cbn on a 70 year old 14-1/2 south bend and tight or rigid or decent surface footage are most certainly not in it's vocabulary.
But .0003 out of size full top cbns are free for me from the scrap off the grinders so tool life.... not an issue.
Bob

Exactly what are we considering "HARD". Up in the 60's on the C-scale?
mid 50's, low 50's, 40's...

I think that would make the biggest difference as to what tools to use.

Also, what material?

Be prepared for sticker shock with the CBN insert and that price is for one cutting edge/tip.

If there is any interruption in the cut its going to suck big time, they don't like to be pounded.
Been a while since I have looked at specks but ceramic inserts are capable of hard turning as well up to a certain range then CBN takes over.
Ceramic is pricey to but at least you get more than one cutting tip per insert.

Either way, don't back off much from what the manufacturer recommends, it will be normal for red hot stringers instead of chips if your turning hardened material.

Have you considered nitride coating the part? Machine, nitride and ship.

I'm Glad some one finally ask Hardness
4142can go up to mid 50's rc
How long are the bushings and how thick is the flange you will be holding on with.
some times it is good to make the head or flange extra long for chucking rigidity and cut the extra off latter. If you have a 4 inch long bushing and only a .25 thick head to hold on with you will run in to problems.
mid to low 50's 4142 can be cut nicely with a good coated carbide and using a tool with a positive geometry will reduce a lot of cutting pressure issues GNMG are negative and CBN'S have a fair amount of edge prep angle.


cermets work well for hard turning too . they are better if you don't have the RPMs to get the right SFMs you really need
for ceramics. generally W.A.O. is the way to go.

I like Sumitomo BN200 and BN250 CBN, we find them forgiving parameterwise and tolerant on interrupted cuts, 4140 in the lower 50s can be cut with Cermets if you don't have any interruptions in the cut. CBN is generally not supposed to be used below 60 Rc but we use the Sumitomos on Rc 52 w/o any problems.

And yeah, ebay is the place, I'd try anything that's cheap and fits your holders.

hard turning 4340 rc-52 . 3.5" diameter @ 1250 rpm., .012 infeed, .004 ipr .

kyocera-ceratip, VNMG cermet inserts, tn-60 grade . on a modified 1950's south bend 16" belt drive
machine.

video here:

vlc record 216 1 2 h31m7s DSCF28 AVI - YouTube

How many sleeves are you making? If you are only doing a few, Walter CNMG432 carbide grade Wkk10s with an RP5 chipbreaker should do it. Call your local Walter rep and ask for some freebies. The Wkk10s grade is one of the hardest carbide grades available.

if you are doing any quantity then Cbn inserts aren't that expensive maybe $20-$25 for a single tip insert from Kyocera or Sumitomo.

Originally Posted by IronReb

......

If there is any interruption in the cut its going to suck big time, they don't like to be pounded.
.

Yet they work fine cutting hardened splines, shafts with notches or keyways and gear teeth and are the go to tool for such in production.
Here tool, part geometry and edge prep angle are important to get right.
The actual cutting edge never sees the impact as the t-land takes the hammer blow.
A 10 degree change in land angle can mean the difference between 1 and 5000 parts.
Same deal with ceramics which chip easier than cbn.

Most don't know the difference between a 8x10 and a 20x30 hanging on the end on those insert numbers.
This is where people like Jasley73 and ex-Kenna become golden to have hanging around trying to sell you stuff.
Application guys, .....not just catalog salesmen.
Bob

Access to forums like this for free has the potential for people like us to make money if we pay attention with an open mind to post like this one quoted.
I read these forums damn near every night and have learned and will continue to learn from those who share their experience that I do not have...yet.

i've acquired a lot of CBN turning inserts, with 1 / 2 or 4 cutting edges
Before i post some pictures, i want to ask the members if they are interested
The inserts are slightly used, but still in very good condition, no wear on the cutting edges
Different types available
See pictures below
Price:
Inserts with 1 tip = US$3 marked with 1P
Inserts with 2 tips = US$5 Marked with 2P
Inserts with 4 tips = US$8 Marked with 4P ( these are negative cutting inserts)
Shipping not included!
Some other pictures in a next message

CBN is the second hardest known material in the world; the hardest being diamond. This, in addition to many other extreme properties makes it the ideal cutting tool material for hard, abrasive workpieces. CBN has greater chemical and thermal stability than diamond, which dissolves in iron and has a maximum temperature limit of approximately 700°C (1300°F).
In contrast, CBN is chemically inert in ferrous materials and retains its hardness at temperatures in excess of 1000°C (1800°F) which is typical for HPT.

Attached Thumbnails

         

Attached Thumbnails        

--

Lawrence F. London, Jr.
lfljvenaura@gmail.com

https://sites.google.com/site/avantgeared