Indexable Carbide Turning tools

I own a Chester C3 type mini lathe and use Indexable turning tools. Could somebody explain in easy terms please the advantage or disadvantage of using different size corner radius inserts. EG what difference would a 4mm corner radius make to the stock material over say a 8 mm corner radius.

Hi Garry,

The inserts I use has a nose radius of 0.4mm that I find work well for my small lathe where I use a small cutting depth. A larger nose radius will give a stronger edge and can be used for a larger depth of cut. Sandvik has some explanations here.

Thor

It's usually taken that the larger radius is for maximum metal removal... 'roughing'...where the larger radius can take more of the cutting forces without too much damage to tip.My inserts are a combination of ccmt/ccgt 060204/02 & HSS diamond tool for the majority of my turning.

George.

Many Thanks George

Many thanks Thor much appreciated

The ideal depth of cut is about 0.6 times the tip radius.

If you are the sort of person who likes to make shallow finishing cuts I suggest CCGT inserts with a small tip radius.

Neil

How does that jibe with a single step 30mm to 25mm reduction in 303 on my S7?

Ideal depth is derived from chip form and breaker geometry. Essentially at book speeds and feeds it should produce a good finish with showers of short, nicely curved, nicely blue chips that are easy to handle and don't snarl up on everything in sight. Strictly only applicable to inserts considered capable of producing a satisfactory finish on the job in question.

In industrial use conventional roughing and finishing methods may be too slow. Better to have a tool able to take decent cuts yet still leave an adequate finish.

Most tools can take far deeper cuts at the (possible) cost of surface finish. Especially ones where the leading edge is angled forward of the tip. But you may have issues in getting the chip-breaker geometry to behave.

Whole 'nother thing when you are working outside book speeds and feeds. I've found that if you don't mind stupid long unbroken chips and have a machine of sufficient strength and power you can go pretty lunatic on depth of cut. I rarely bother tho'. Saving a couple or three roughing cuts is rarely worth it. Better to wind up the speed and feeds. Especially if I have a finish cut planned.

Clive

Every insert has an ideal DOC, but that doesn't mean it can't be used at other settings. 2.5mm isn't an overly large DOC for an S7 or even a mini lathe with carbide.

I have found the larger tip radiuses work better for deep cuts.

Neil

Neil