04-09-2015, 10:33 AM
The tool nose radius as it relates to feed rate has a profound effect upon the surface finish you get. Also, it's often critical to use at least the size of the tool nose radius as your minimum depth of cut. That's primarily true with carbide inserts because they need heat in the process to get a shiny finish in most materials, soft steels in particular.
Those inserts which have a molded-in chipbreaker (top form geometry) will have a range for depth of cut and feed rate and feed rate in the materials which a particular grade and coating were aimed at. In general terms a larger tool nose radius will get a smoother finish than a smaller radius if both are run at the same feed rate per rev. The profile shape of an insert (90º, 80º, 55º, 35º) and the approach angle of its holder have an effect too, just much less pronounced.
If you are using CNMG and WNMG negative rake inserts, tell me what materials you are turning, and the amount of stock removal you wish to get per pass. Also, the spindle power of the machine will matter with negative rake inserts. I would hope you have at least 3HP on the lathe to use negative rake inserts effectively. I can help with chipbreaker selection and grades when I learn more about what you are trying to use and what materials you are cutting.
Your machine certainly appears to be right for these inserts, I simply don't understand the bit about "keep in low"! If that's what they want, why is the lever option there at all? Perhaps they want it in low only for threading? You definitely want higher speeds and feed rates. I can't quite see the top information plate in your photo, but it appears you have a specific gear arrangement for turning feed rates. See if you can find in your machine's documentation why the notation about "Keep In Low."
Ken
Those inserts which have a molded-in chipbreaker (top form geometry) will have a range for depth of cut and feed rate and feed rate in the materials which a particular grade and coating were aimed at. In general terms a larger tool nose radius will get a smoother finish than a smaller radius if both are run at the same feed rate per rev. The profile shape of an insert (90º, 80º, 55º, 35º) and the approach angle of its holder have an effect too, just much less pronounced.
If you are using CNMG and WNMG negative rake inserts, tell me what materials you are turning, and the amount of stock removal you wish to get per pass. Also, the spindle power of the machine will matter with negative rake inserts. I would hope you have at least 3HP on the lathe to use negative rake inserts effectively. I can help with chipbreaker selection and grades when I learn more about what you are trying to use and what materials you are cutting.
Your machine certainly appears to be right for these inserts, I simply don't understand the bit about "keep in low"! If that's what they want, why is the lever option there at all? Perhaps they want it in low only for threading? You definitely want higher speeds and feed rates. I can't quite see the top information plate in your photo, but it appears you have a specific gear arrangement for turning feed rates. See if you can find in your machine's documentation why the notation about "Keep In Low."
Ken