fig1 and 3 illustrate one application for the method of the present invention . fig . i depicts embossing roller 10 . centrally located on circumferential surface 11 of roller 10 is working zone 12 . fig2 shows embossing roller 10 installed and operating at a roll embossing station in a heat exchanger tube manufacturing line . working zone 12 comprises a number of parallel circumferential grooves 13 as depicted in cross section in fig3 . copper strip 30 from a strip supply ( not shown ) passes between embossing wheel 10 and backing roller 20 . rollers 10 and 20 have a tangential distance between them that is less than the thickness of strip 30 , so that metal in the strip is forced into grooves 13 in working zone 12 as the strip passes between the rollers . this produces a pattern of longitudinal ribs in enhancement region 31 on strip 30 . further steps in the tube manufacturing process ( not shown ) include roll forming the strip into a tubular configuration and welding the seam formed between the two joined edges of the strip . in one example of a strip roll embossed in the manner described above , there are over 70 ribs in the approximately three centimeter wide enhancement region . each groove 13 is therefore very narrow and the grooves are very closely spaced . walls 14 between adjacent grooves are therefore also very narrow . strip rolling operations impose very high lateral stresses in the metal of walls 14 . the possibility of stress cracking in the groove walls is reduced if radius r of the base of the groove is as large as other desired dimensions of the groove will permit . the prior art method of forming very small grooves in a metal turning blank , i . e . by abrasive grinding , is not capable of forming grooves having completely rounded groove bottoms . fig4 depicts the cross section of grooves 12 &# 39 ; formed by grinding and shows that the bottom of the groove is flattened with smaller radii r &# 39 ; of curvature on each side of the groove bottom . because of these smaller radii , the areas at the edges of the base of the groove serve as stress raisers and increase in the possibility of failure by cracking in walls 14 &# 39 ;. the prior art grinding method is also not capable of producing a sharply defined shoulder but rather only a chamfered or rounded shoulder 15 &# 39 ; at the top of the groove . furthermore , the grinding wheel used in grinding the grooves is subject to loss of its shape due to wear . as the wheel wears , the shape of the grooves it cuts changes unless the operator dresses up the wheel frequently . the practice of the method of the invention requires the use of the precision or ultraprecision lathes that are now available . a precision lathe is capable of accuracies in setting up the work and positioning a cutting tool to accuracies of on the order of five to ten microns and a spindle runout accuracy on the order of less than one micron . an ultraprecision lathe has the capability of similar accuracies on the order of less than one half micron and less than a tenth of a micron . an ordinary metal tool making lathe , by comparison , has a runout accuracy of five to eight microns respectively . runouts in this latter range can cause changes in cutting forces sufficient to cause failure of the cutting tool . only with the higher precision lathes can spindle runout be sufficiently minimized and the cutting tool be positioned with respect to the work with sufficient accuracy to allow the practice of the invention . there are a number of lathes available that have sufficient precision to turn grooves according to the teaching of the present invention . precision and ultraprecision lathes have the same basic features as conventional lathes and differ from such conventional lathes primarily in the accuracy with which they are able to control the various lathe functions . fig8 and 9 , in partial semi - schematic side elevation and top views , show a grove being cut in circumferential surface 11 of roller 10 by cutting tool 40 . roller 10 is mounted on chuck 72 of lathe 70 . chuck 72 is rotated by a drive ( not shown ) in headstock 71 . cutting tool 40 is mounted in tool holder 75 , which is in turn mounted on crossfeed 74 . crossfeed 74 is mounted on carriage 73 . the position and movement of cutting tool 40 with respect to roller 10 are determined by the positions and movements of carriage 73 and crossfeed 74 . these positions and movements , in a precision or ultraprecision lathe , are controlled by a computer ( not shown ). the work must be precisely positioned on the lathe spindle , then the circumferential surface ( 12 in fig1 ) dressed by turning to ensure that the axis of the work is precisely coincident with the axis of rotation of the spindle and that all points on the circumferential surface are equidistant from those axes . the cutting tool used in the practice of the invention should have a very hard cutting tip . a good choice for the application is a tool having a cubic boron nitride ( cbn ) tip . fig5 and 6 respectively show a top and side elevation view of a suitable tool . fig7 shows a detailed view of a portion , denoted by vii in fig5 of the tip of the tool . tool 40 is prepared from an iso ( international organization for standardization ) tool vnma 16048 having a 35 ° angle ( angle β in fig7 ). base 45 of tool 40 is comprised of a cemented carbide material . cutting region 41 is comprised of a layer of cbn material 42 affixed to base 45 by a layer of cemented carbide material 43 and a layer of silver brazing material 44 . tip 46 is prepared by a suitable process such as grinding to produce a configuration appropriate to the groove to be turned ( cf . groove 13 in fig3 ). the dimensions of tip 46 can be very small . one cutting tool successfully used to cut grooves on an embossing wheel has a tip radius ( r in fig7 ) of about 40 microns , an included angle ( α ) of 15 ° and a cutting depth ( d ) of about 300 microns . it is important that , in manufacturing the cutting tool , the tool be precisely symmetrical about axis a . any asymmetry present can cause side forces during turning that can lead to fracture of the cutting tip . the properties of the cbn cutting tip must be selected for optimum performance based on the composition of the steel into which the grooves will be turned . a suitable steel for use as an embossing wheel is aisi ( american iron and steel institute ) d2 tool steel . d2 is a high carbon , high chromium steel having a rockwell c hardness in the range of 50 to 60 . the extremely hard carbide particles in d2 steel are , relatively , very large ( on the order of 25 to 500 microns ). some carbide particles thus are larger than the diameter of the tip of the cutting tool . during turning , the force on the tool is very high when it is passing through a carbide particle . the force on the tool is much lower when the tool is passing through the non - carbide matrix of the steel . the variation in cutting forces on the tool subjects it to the possibility of fatigue failure . on steels of this type , the cbn cutting material must have high fracture toughness , at the expense of hardness and wear resistance . on the other hand , turning when a steel having a relatively fine grained carbide content presents a different problem . an example of this type of steel is cpm ® ( crucible particle metallurgy ) 9v , which has carbide particles of less than 25 microns and a rockwell c hardness in the range of 53 to 58 . when such a steel is turned , the total force required to cut the steel is greater than for a steel such as d2 but the variation in force on the tool as it is cutting is much less . resistance to fatigue failure is therefore not so significant a consideration but the tool used for cutting in this case should be harder and more wear resistance . a suitable cbn material for cutting grooves in steels such as d2 is general electric ® b6500 . a suitable cbn material for use with cpm ® 9v is debeers dbc50 . critical to the ability to cut grooves of such small dimensions into hard tool steels is the alignment of the cutting tool with respect to the work . the axis ( a in fig7 ) of the tool must be positioned precisely perpendicularly to circumferential surface 12 as the tool is advanced into the work . if the tool axis is not perpendicular to the work during turning , side forces will be present that can easily cause the tool tip to fracture . finally , the cutting speed and cutting tool feed rate must be held within limits for success in practicing the method of the invention . cutting speed , the linear speed of any point on cylindrical surface 12 , must be between 80 and 200 meters per minute and preferably about 160 meters per minute . if the speed is less than this range , the wear rate on the cutting tool is excessively high . if the speed exceeds this range , the cutting operation overheats the steel of the work piece , damaging the structure of the steel and altering its strength and other properties . the cutting tool feed rate must be within the range ten to 20 microns per revolution and preferably about 20 microns per revolution . feed rates less than this range approach the lower limit of the capability of the cutting tool control apparatus and precise control of feed rate is difficult or impossible , leading to sticking or slipping of the tool positioner and an irregular feed of the tool into the work , leading to the possibility of fracture of the tool . feed rates greater than this range impose loads on the tool that may lead to fracture . fig1 is a flow diagram showing he steps necessary to practice the method of the present invention . in steps 101 and 102 , the workpiece is prepared by mounting it on the lathe chuck and predressing it by turning to remove runout . in steps 201 and 202 , a cutting tool having physical properties appropriate to the composition of the workpiece is selected and the tip of the tool is prepared by forming it to the shape necessary to cut the desired groove . in step 301 , the cutting tool is aligned so that the longitudinal axis of the tool is precisely perpendicular to the surface into which the groove will be cut . in step 302 , the lathe rotational speed is set to the proper speed . finally , in step 303 , the cutting tool is advanced into the workpiece at the proper feed rate to cut the groove . if more than one groove is to be cut into the workpiece , the cutting tool would be moved to the new location and steps 301 through 303 repeated for each groove cut . the method of the invention offers significant time , and therefore cost , advantages over prior art methods of forming small grooves in a work piece . for example , to lathe turn the grooves in an embossing roller as described in this disclosure , requires about 15 minutes . to accomplish the same task by a grinding method can require up to eight to 10 hours . further , the grinding process may not be capable of forming grooves of the desired configuration .