A finishing grade will be the hardest grade run at higher surface speed. This will not work well under vibration or heavy intermittent cuts.

CCMT (rhomboid 80 degree), DCMT (diamond 55 degree), VCMT or VBMT (diamond 35 degree) are the most popular finishing inserts.

Are you roughing, finishing or just doing some general turning? Negative inserts are strongest and the best option for roughing and general turning applications, as these will allow deeper depths of cut and higher feed rates due to strong insert shapes and thickness.

CNMG (rhomboid 80 degree), DNMG (diamond 55 degree) and WNMG (trigon 80 degree) are the most popular roughing inserts.  For heavier roughing operations, SNMGs are an excellent choice with a 45-degree approach angle allowing for larger depths of cut and reduced cutting loads.

If you are roughing, it is important to go with a roughing chip breaker (such as Korloy’s RM, HR, B25, GS & VP4 chipbreakers) to deal with the chip load and the depth of cut.

Each member brings with them their own experience and know-how to add to our growing pool of technical knowledge. That’s why our services are known for being the best in the business!

All chip breakers have a minimum depth required to get the chip breaker working.  However, instead of struggling to figure out the right chip breaker for your job, please ask our Technical Team to advise.

If you are finishing, positive inserts are always the best option as these create less cutting forces and can therefore get away with lower depths of cut, eliminating vibration.

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They can help you work out the best chipbreaker for your material and applications, whilst also recommending the minimum and maximum depth of cut you should take.

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D) The final part represents the toughness according to the ISO scale.  NC3225 ends with 25, as it is for steel it has a toughness of P25.

Top Tip for Finishing: Use a finishing chip breaker with a small enough radius to get the chip breaker working. This is a common mistake engineers make: trying to finish with an 0.8mm rad with a medium chip breaker taking a 0.1mm cut. This is just going to rub on the work piece and cause poor surface finish. Furthermore, on stainless steel you will just put heat into the job and make it unmachinable.

For finishing operations, 0.4mm or 0.2mm rad would be the best option. This allows you to take the smallest depth of cut without causing vibration.

For roughing applications, you would usually opt for a 0.8mm or 1.2mm radius depending on your machine’s horsepower and the depth of cut you plan on taking.

A chipbreaker can make a huge difference to cutting load, chip control, vibration and even prevent work hardening in materials like stainless steel or inconel.

Top tip - Lever Lock or double clamp style tool holders give higher clamping strength and stability compared to screw clamp holders.

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B) Grades beginning with P (e.g. PC8115) are PVD coated.  These grades work at lower cutting speeds than CVD grades and are more suited to shorter contact periods with the workpiece.  They are most suited for small to medium diameter workpieces and also make excellent multipurpose grades.

A) Grades beginning with N (e.g. NC3225) are CVD coated.  These grades cope with higher cutting speeds than PVD grades and can withstand longer contact periods with the workpiece.  They are most suited to medium to large diameter workpieces.

Diameter of workpiece.Material.Shape (e.g. rough, hexagon).Machine capability.From this, they can make a quick assessment of the most suitable grade of carbide for your job.

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A roughing grade is very tough and will run at slower surface speed but withstands intermittent cuts well. However, your roughing may be very different to someone else’s roughing.  For example, a turner on a VTL turning large stainless steel castings will be taking 5mm+ depth of cut, whereas a turner on a smaller lathe will be roughing with much smaller depths of cut.