Insert recommendations for good chipbreaking?

[Jelly_Sheffield]

So once again this evening I dodged a faceful of fast moving turnings, as a long stringy chip of EN8 decided to wrap round the workpiece and launch itself...

I use EN8 a lot, and this birds nesting is an ongoing issue that's starting to really bug me.


For roughing I normally use CCMT 120408 MPN PC25 Carbide

Then for finishing, WNMG 080404 HQ CM20 Cermet

Both give nice smooth cutting, and good (PC25), and genuinely exceptional (CM20) finishes, but neither will break chips in EN8 for toffee.

So I'm open to recommendations for anything that works, and will fit SCLC[R/L] or MWLN[R/L] turning tools, even buying a handful of expensive proprietary inserts from the likes of Sandvik, Kennametal, Kyocera, or Mitsubishi.

I'd also consider buying a turning tool with different geometry, like CKJN[R/L] or CKNN[R/L] for KNUX inserts, or MVJN[R/L] for VNMG inserts.

 

[Erie Fred]

Have you tried increasing the feed rate ?

Also, keep a chip hook handy to remove them as soon as they get long.

 

[Jelly_Sheffield]

Have you tried increasing the feed rate ?

Also, keep a chip hook handy to remove them as soon as they get long.

I've gone through the full range of reccomended feed rates, and even tried above what's recommended up to about 0.8mm/rev (0.032"/rev)... Pretty consistently increased feed only results in thicker, hotter, angrier, metal spaghetti.

Once you get up at 0.8mm/rev (which is achievable for a finishing cut) you're into glowing chips territory, but never a sign of the chips breaking before you reach that point.

For roughing increased feed rate also massively limits the DOC, as I would rapidly hit the power limitations of the motor (5kW/6.6hp)

Typically I'll be running ar 190-400 m/min (623-1312 sfm), roughing DOC of 1-3mm (0.04"-0.12") and finishing DOC of 0.2-0.8mm (0.008"-0.032"), which are reasonably aggressive cutting parameters, and leads to the chip(s) accumulating very rapidly.

 

[northwest]

Are you able to substitute EN16T for the EN8? I have never achieved a good finish on EN8 or even EN1PB using carbide but the tempered steels are usually very good.

 

[Jelly_Sheffield]

Are you able to substitute EN16T for the EN8? I have never achieved a good finish on EN8 or even EN1PB using carbide but the tempered steels are usually very good.

Going forward that's probably a good option for a lot of applications, but I still have meters and meters of bright bar as stock to use up.

Finish wise dry cutting at very high surface speeds with a Cermet insert really does a fantastic job, but it's just the stringiness that's an issue.

 

[Kram]

I like single sided chipbreakers, the KNUX type is probably a good choice for the feed rates you mention. Single sided do seem to break chips at much more sensible feeds for a manual machine.

Have you tried turning rpms down with feedrate up as that normally works too.

I am mostly using DCET inserts with a single sided chip breaker for boring. I cant find any left handed type for OD turning but occasionally I have used by boring bar behind the work and spining in reverse.

Are you able to substitute EN16T for the EN8?

That would likely be about the same for chips, however, one of my favorite steels is 606m36/EN16M, same stuff but with sulphur added to make it very free machining, very much like brass. Supplied soft and needs heat treating after. It will spray chips at you if feed hard, instead I have learned a very deep DOC with very light feed gives nice curlers that are easy to clean up.
Its at the expense of welding - it will take a weld but perhaps not to be trusted for anything important.

 

[pressbrake1]

Are you able to substitute EN16T for the EN8? I have never achieved a good finish on EN8 or even EN1PB using carbide but the tempered steels are usually very good.

En16 in decent diameters seems to be hard to source at present. The opposite of a year ago when en16 was easy and en24 impossible to source

Modern en8 is lower in carbon hence it’s not as nice to machine as it once was and hardening contractors won’t guarantee success with it

 

[Kram]

This style is what Im using. Wish I could find some of the other handed type.

 

[8ob]

So once again this evening I dodged a faceful of fast moving turnings, as a long stringy chip of EN8 decided to wrap round the workpiece and launch itself...

I use EN8 a lot, and this birds nesting is an ongoing issue that's starting to really bug me.

I asked the same question a few years ago and was told to stop being a pussy and be a lot more brutal with the cuts.

Bob

 

[RobCox]

I use a lot of EN8 and don't have problems breaking chips. I use CCMT09T304 inserts, for 1" stock I run the lathe at 800rpm, 20 to 30thou DOC (40-60thou off the dia) with a feed rate of 8 thou/rev. Chips come off in little C's, nice and blue no problem.

 

[Hood]

Feedrate breaks the swarf, plain and simple.
Same RPM, same DOC, feedrate is the only thing that changes.

 

[Hood]

One other thing I would say, your insert geometry is erse for tit, positive (if required) for finish negative for roughing. Obviously lathe rigidity and power may determine the geometry as well but you mentioned 6hp so it must be a reasonably robust lathe.

 

[Jelly_Sheffield]

One other thing I would say, your insert geometry is erse for tit, positive (if required) for finish negative for roughing.

So the Cermet inserts have a distinct burning effect in the Negative geometry, which makes a positive difference to surface finish, compared to using the positive version.

Obviously lathe rigidity and power may determine the geometry as well but you mentioned 6hp so it must be a reasonably robust lathe.

This is part of the reason, a positive insert for roughing allows me to take a higher DOC before I over-stress the lathe.

I use a lot of EN8 and don't have problems breaking chips. I use CCMT09T304 inserts, for 1" stock I run the lathe at 800rpm, 20 to 30thou DOC (40-60thou off the dia) with a feed rate of 8 thou/rev. Chips come off in little C's, nice and blue no problem.

So I would run that at 3200rpm, 100 thou DOC, 17 thou/rev, which ought to break more easily

CCMT09T304 gives all the ISO specified details, but unfortunately doesn't give the manufacturer specific chipbreaking geometry of the inserts...

Which I would love to know as your ones do seem to work acceptably.

I asked the same question a few years ago and was told to stop being a pussy and be a lot more brutal with the cuts.

Bob

I really don't know how much further I can push that logic...

I suspect the opposite is true and the amount of heat going into the chip is softening the material so much that it's not experiencing enough stress to break.

 

[Misterg]

So I would run that at 3200rpm, 100 thou DOC, 17 thou/rev, which ought to break more easily

FWIW I would try reducing the spindle speed a lot - I think the chip is probably shooting off too hot to break.

 

[Hood]

What lathe do you have?

 

[Maker]

I usually just lean on the handwheel a bit harder to get a chip to break, it'll often be a much faster feed than the lathe's fastest power feed.

If you're into the material removal rates that warrant a separate roughing and finishing tool, your roughing should almost certainly have coolant which will eliminate the glowing chips.

 

[Jelly_Sheffield]

What lathe do you have?

TOS S32-P retrofitted with a 5kW motor (up from 3kW stock) by the previous owner.

Multifix C Toolpost with 25mm tooling.

FWIW I would try reducing the spindle speed a lot - I think the chip is probably shooting off too hot to break.

If you're into the material removal rates that warrant a separate roughing and finishing tool, your roughing should almost certainly have coolant which will eliminate the glowing chips.

I'm on the same wavelength as both of you here, and refilling the coolant system is a plan for the future once I have moved the workshop around.

But I know that there are some dry-cutting inserts which will do what I want, just not many of them.

 

[Hood]

What dia of material are you talking?

 

[Jelly_Sheffield]

What dia of material are you talking?

In this instance 30-50mm, but anything up to around 150-200mm.

I use a different set of tooling for turning small stuff <25mm and long slender shafts <50mm, where minimising tool pressure is more important than sheer MRR.

 

[Hood]

For the 30-50 use the WNMG insert, rpm about 1000, feed about 0.3mm/rev and say 1.5mm DOC (3mm overall) and see what it is like.
Personally not keen on the WNMG as swarf can get trapped in behind and mar the finish, always happens on the last cut as well