CARTER PRECISION TOOLS
BORING BAR SELECTION
The range of boring bars is illustrated under "Boring Bars & Inserts" with a description of their individual applications. Each boring bar is available in a number of shank sizes and these are shown on the order form. Choose the largest shank size suitable for your machine to maximise rigidity.
All the inserts listed, are cermet grade T1200A featuring built in chip breakers available with two different tip radii. The larger radius provides a strong insert corner, a smoother surface finish and a longer tool life. The smaller radius produces sharper corners. On lathes used for model and other small format precision engineering, it is best to begin with a 0.2mm nose radius.
Grade T1200A is recommended for all boring bars because of it's ability to produce a good surface finish at relatively low surface speeds.
Grade A30, which is tungsten carbide, is an alternative to T1200A should the latter show any signs of edge chipping or breakage, such as on heavier or broken cut work on any steel.
SPEED AND FEEDS
Tungsten carbide tools are designed to cut at speeds typically three times faster than those for HSS, but because small machines can lack the required power or rigidity it may be necessary to work at much slower speeds. The unique properties of grade T1200A overcomes this problem as it produces excellent finishes on virtually all materials at the slower speeds associated with HSS and the higher speeds associated with Tungsten Carbide.
Choice of feed is determined not only by surface finish required, but also by the machine’s spindle power, workpiece, material, amount of tool overhang, the type and depth of cut and the insert’s nose radius. Generally speaking, for roughing, a feed rate of 50% of tip radius is correct whilst finishing cuts should be below this figure. Normally, the minimum feed should not be less than .07mm (.0025") per rev, unless you are using the smallest corner radius.
DO’S AND DON’TS
DO set the tool’s cutting edge accurately to centre height, in order to obtain optimum performance.
DO maximise rigidity by choosing the largest tool shank suitable and minimise the amount of tool overhang.
DO make sure that all gib strips, headstock bearings and screw backlash, are correctly adjusted.
DON’T ‘spot’ the tool against the workpiece. To avoid damaging the insert it must always enter and leave a moving workpiece.
DON’T overtighten the clamping screw. A light nip is adequate and heavier tightening will only reduce screw and key life.