TURRET LATHE

TURRET LATHE

TURRET LATHE IS A FORM OF METALWORKING LATHE THAT IS USED FOR REPETITIVE PRODUCTION OF DUPLICATE PARTS (WHICH BY THE NATURE OF THEIR CUTTING PROCESS ARE USUALLY INTERCHANGEABLE). IT EVOLVED FROM EARLIER LATHES WITH THE ADDITION OF THE TURRET, WHICH IS AN INDEXABLE TOOL HOLDER THAT ALLOWS MULTIPLE CUTTING OPERATIONS TO BE PERFORMED, EACH WITH A DIFFERENT CUTTING TOOL, IN EASY, RAPID SUCCESSION, WITH NO NEED FOR THE OPERATOR TO PERFORM SETUP TASKS IN BETWEEN (SUCH AS INSTALLING OR UNINSTALLING TOOLS) NOR TO CONTROL THE TOOL PATH. (THE LATTER IS DUE TO THE TOOL PATH'S BEING CONTROLLED BY THE MACHINE, EITHER IN JIG-LIKE FASHION [VIA THE MECHANICAL LIMITS PLACED ON IT BY THE TURRET'S SLIDE AND STOPS] OR VIA IT-DIRECTED SERVOMECHANISMS

TYPES OF TURRET LATHES

THE ARCHETYPICAL TURRET LATHE, AND THE FIRST IN ORDER OF HISTORICAL APPEARANCE, IS THE HORIZONTAL-BED, MANUAL TURRET LATHE. IN MACHINE-SHOP JARGON, THE TERM TURRET LATHE WITHOUT FURTHER QUALIFICATION IS STILL USUALLY UNDERSTOOD IN CONTEXT TO REFER TO THIS TYPE. THE FORMATIVE DECADES FOR THIS CLASS OF MACHINE WERE THE 1840S THROUGH 1860S, WHEN THE BASIC IDEA OF MOUNTING AN INDEXABLE TURRET ON A BENCH LATHE OR ENGINE LATHE WAS ELABORATED UPON, DEVELOPED, AND DISSEMINATED INTO FACTORIES. SOME IMPORTANT TOOL-BUILDERS IN THIS DEVELOPMENT WERE STEPHEN FITCH; GAY, SILVER & CO.; ELISHA K. ROOT OF COLT; J.D. ALVORD OF THE SHARPS ARMORY; FREDERICK W. HOWE, RICHARD S. LAWRENCE, AND HENRY D. STONE OF ROBBINS & LAWRENCE; J.R. BROWN OF BROWN & SHARPE; PRATT & WHITNEY; AND LATER VARIOUS DESIGNERS AT THESE AND OTHER FIRMS.

SEMI-AUTOMATIC TURRET LATHES

SOMETIMES MACHINES SIMILAR TO THOSE ABOVE BUT WITH POWER FEEDS AND AUTOMATIC TURRET-INDEXING AT THE END OF THE RETURN STROKE ARE CALLED SEMI-AUTOMATIC TURRET LATHES. THIS NOMENCLATURE DISTINCTION IS BLURRY AND NOT CONSISTENTLY OBSERVED. THE TERM TURRET LATHE ENCOMPASSES THEM ALL.

DURING THE 1860S, WHEN SEMI-AUTOMATIC TURRET LATHES WERE DEVELOPED, THEY WERE SOMETIMES CALLED AUTOMATIC (WHAT WE TODAY WOULD CALL AUTOMATICS, THAT IS, FULLY AUTOMATIC MACHINES, HAD NOT BEEN DEVELOPED YET). DURING THAT ERA BOTH MANUAL AND SEMI-AUTOMATIC TURRET LATHES WERE SOMETIMES CALLED SCREW MACHINES, ALTHOUGH WE TODAY RESERVE THAT TERM FOR FULLY AUTOMATIC MACHINES.

AUTOMATIC TURRET LATHES (MECHANICALLY AUTOMATED)

DURING THE 1870S THROUGH 1890S, THE AUTOMATIC TURRET LATHE WAS DEVELOPED AND DISSEMINATED. THESE MACHINES CAN EXECUTE MANY PART-CUTTING CYCLES WITHOUT HUMAN INTERVENTION. THUS THE DUTIES OF THE OPERATOR (WHICH WERE ALREADY GREATLY REDUCED BY THE MANUAL TURRET LATHE) WERE EVEN FURTHER REDUCED, AND PRODUCTIVITY INCREASED. THESE MACHINES USE CAMS TO AUTOMATE THE SLIDING AND INDEXING OF THE TURRET AND THE OPENING AND CLOSING OF THE CHUCK. THUS, THEY EXECUTE THE PART-CUTTING CYCLE SOMEWHAT ANALOGOUSLY TO THE WAY IN WHICH AN ELABORATE CUCKOO CLOCK PERFORMS AN AUTOMATED THEATER SHOW. CHRISTOPHER MINER SPENCER BUILT THE FIRST ONE, WHICH HE PATENTED IN 1873. UNFORTUNATELY HIS PATENT ATTORNEY FAILED TO PROTECT THE MOST SIGNIFICANT PART, THE CAM DRUM (WHICH SPENCER CALLED THE "BRAIN WHEEL"). THEREFORE MANY OTHER PEOPLE QUICKLY TOOK UP THE IDEA. LATER IMPORTANT DEVELOPERS OF FULLY AUTOMATIC MACHINES WERE S. L. WORSLEY (WHO DEVELOPED A SINGLE-SPINDLE MACHINE FOR BROWN & SHARPE), AND REINHOLD HAKEWESSEL (WHO EVENTUALLY JOINED NATIONAL-ACME) AND GEORGE O. GRIDLEY (OF ACME-GRIDLEY AND NEW BRITAIN-GRIDLEY), WHO DEVELOPED MULTIPLE-SPINDLE VARIANTS.^[4] SMALL- TO MEDIUM-SIZED AUTOMATIC TURRET LATHES ARE USUALLY CALLED SCREW MACHINES (AKA AUTOMATIC SCREW MACHINES), WHILE LARGER ONES ARE USUALLY CALLED AUTOMATIC CHUCKING LATHES, AUTOMATIC CHUCKERS, OR CHUCKERS.

AT THE SAME TIME THAT FULLY AUTOMATIC SCREW MACHINES WERE BEING DEVELOPED IN NEW ENGLAND, GROWING OUT OF THE MANUAL TURRET LATHE, THEY WERE ALSO BEING INDEPENDENTLY DEVELOPED IN SWITZERLAND, WITH SOME DIFFERING INFLUENCES. THE DIFFERENCES AND SIMILARITIES BETWEEN THE AMERICAN AND SWISS MACHINES ARE INTERESTING TO COMPARE.

MACHINE TOOLS OF THE "AUTOMATIC" VARIETY ("AUTOMATIC" IN THAT PRE-IT ERA MEANING MECHANICALLY AUTOMATED) HAD ALREADY REACHED A HIGHLY ADVANCED STATE BY THE WORLD WAR I ERA.

CNC LATHES AND SECOND-OPERATION LATHES

WHEN WORLD WAR II ENDED, THE DIGITAL COMPUTER WAS POISED TO DEVELOP FROM A COLOSSAL LABORATORY CURIOSITY INTO A PRACTICAL TECHNOLOGY THAT COULD BEGIN TO DISSEMINATE INTO BUSINESS AND INDUSTRY. THE ADVENT OF IT-BASED AUTOMATION IN MACHINE TOOLS (VIA NC AND THEN CNC) DISPLACED TO A LARGE EXTENT (BUT NOT AT ALL COMPLETELY) THE PREVIOUSLY EXISTING MANUAL AND MECHANICALLY AUTOMATED MACHINES. TODAY, MOST CNC LATHES HAVE TURRETS, AND SO COULD LOGICALLY BE CALLED TURRET LATHES, BUT THE TERMINOLOGY IS USUALLY NOT USED THAT WAY. HORIZONTAL CNC LATHES, WITH OR WITHOUT TURRETS, ARE GENERALLY CALLED CNC LATHES OR CNC TURNING CENTERS OR TURNING CENTERS, AND THE TERM TURRET LATHE BY ITSELF IS STILL USUALLY UNDERSTOOD IN CONTEXT TO REFER TO HORIZONTAL, MANUAL TURRET LATHES. THE CHANGED ROLE IN THE PRODUCTION PROCESS THAT SUCH MACHINES NOW PLAY IS REFLECTED IN ANOTHER NAME FOR THEM, WHICH IS SECOND-OPERATION LATHE (OR SECOND OPERATION LATHE TO CAREFREE HYPHENATORS), AS EXPLAINED LATER.

VERTICAL TURRET LATHES

THE TERM VERTICAL TURRET LATHE (VTL) IS APPLIED TO MACHINES WHEREIN THE SAME ESSENTIAL DESIGN OF THE HORIZONTAL VERSION IS UPENDED, WHICH ALLOWS THE HEADSTOCK TO SIT ON THE FLOOR AND THE FACEPLATE TO BECOME A HORIZONTAL ROTATING TABLE (ANALOGOUS TO A HUGE POTTER'S WHEEL). THIS IS USEFUL FOR THE HANDLING OF VERY LARGE, HEAVY, SHORT WORKPIECES. VERTICAL LATHES IN GENERAL ARE ALSO CALLED VERTICAL BORING MILLS OR OFTEN SIMPLY BORING MILLS; THEREFORE A VERTICAL TURRET LATHE IS A VERTICAL BORING MILL EQUIPPED WITH A TURRET. TODAY'S CNC VERSIONS ARE CALLED CNC VTLS.

CAPSTAN VERSUS TURRET

THE TERM CAPSTAN LATHE OVERLAPS IN SENSE WITH THE TERM TURRET LATHE TO A LARGE EXTENT. IT HAS IN MANY TIMES AND PLACES BEEN UNDERSTOOD TO BE SYNONYMOUS WITH TURRET LATHE. IN OTHER TIMES AND PLACES IT HAS BEEN HELD IN TECHNICAL CONTRADISTINCTION TO TURRET LATHE, WITH THE DIFFERENCE BEING IN WHETHER THE TURRET'S SLIDE IS FIXED TO THE BED (AKA RAM-TYPE TURRET) OR SLIDES ON THE BED'S WAYS (AKA SADDLE-TYPE TURRET). THE DIFFERENCE IN TERMINOLOGY IS MOSTLY A MATTER OF UK AND COMMONWEALTH USAGE VERSUS AMERICAN USAGE. AMERICAN USAGE TENDS TO CALL THEM ALL TURRET LATHES.

THE WORD CAPSTAN COULD LOGICALLY SEEM TO REFER TO THE TURRET ITSELF, AND TO HAVE BEEN INSPIRED BY THE NAUTICAL CAPSTAN. A LATHE TURRET WITH TOOLS MOUNTED IN IT CAN VERY MUCH RESEMBLE A NAUTICAL CAPSTAN FULL OF HANDSPIKES. THIS INTERPRETATION WOULD LEAD AMERICANS TO TREAT CAPSTAN AS A SYNONYM OF TURRET AND CAPSTAN LATHE AS A SYNONYM OF TURRET LATHE. HOWEVER, THE MULTI-SPOKED HANDLES THAT THE OPERATOR USES TO ADVANCE THE SLIDE ARE ALSO CALLED CAPSTANS, AND THEY THEMSELVES ALSO RESEMBLE THE NAUTICAL CAPSTAN.

NO DISTINCTION BETWEEN TURRET LATHE AND CAPSTAN LATHE PERSISTS UPON TRANSLATION FROM ENGLISH INTO OTHER LANGUAGES. MOST TRANSLATIONS INVOLVE THE TERM "REVOLVER", AND SERVE TO TRANSLATE EITHER OF THE ENGLISH TERMS.

THE WORDS TURRET AND TOWER (THE FORMER BEING A DIMINUTIVE OF THE LATTER) COME ULTIMATELY FROM LATIN TURRIS, "TOWER", AND THE USE OF TURRET BOTH TO REFER TO LATHE TURRETS AND TO REFER TO GUN TURRETS SEEMS CERTAINLY TO HAVE BEEN INSPIRED BY ITS EARLIER CONNECTION TO THE TURRETS OF FORTIFIED BUILDINGS AND TO SIEGE TOWERS. THE HISTORY OF THE ROOK IN CHESS IS CONNECTED TO THE SAME HISTORY (AND THE FRENCH WORD FOR "ROOK" IS TOUR, "TOWER").

IT IS AN INTERESTING COINCIDENCE THAT THE WORD TOUR IN FRENCH CAN MEAN BOTH "LATHE" AND "TOWER", WITH THE FIRST SENSE COMING ULTIMATELY FROM LATIN TORNUS, "LATHE", AND THE SECOND SENSE COMING ULTIMATELY FROM LATIN TURRIS, "TOWER". (TOUR REVOLVER, TOUR TOURELLE, AND TOUR TOURELLE REVOLVER ARE VARIOUS WAYS TO SAY "TURRET LATHE" IN FRENCH.)

FLAT-TURRET LATHE

A SUBTYPE OF HORIZONTAL TURRET LATHE IS THE FLAT-TURRET LATHE (MORE COMMONLY STYLED FLAT TURRET LATHE BY CAREFREE HYPHENATORS). ITS TURRET IS FLAT (AND ANALOGOUS TO A ROTARY TABLE), ALLOWING THE TURRET TO PASS BENEATH THE PART. PATENTED BY JAMES HARTNESS OF JONES & LAMSON, AND FIRST DISSEMINATED IN THE 1890S, IT WAS DEVELOPED TO PROVIDE MORE RIGIDITY VIA REQUIRING LESS OVERHANG IN THE TOOL SETUP, ESPECIALLY WHEN THE PART IS RELATIVELY LONG.

HOLLOW-HEXAGON TURRET LATHE

HOLLOW-HEXAGON TURRET LATHES COMPETED WITH FLAT-TURRET LATHES BY TAKING THE CONVENTIONAL HEXAGON TURRET AND MAKING IT HOLLOW, ALLOWING THE PART TO PASS INTO IT DURING THE CUT, ANALOGOUSLY TO HOW THE PART WOULD PASS OVER THE FLAT TURRET. IN BOTH CASES, THE MAIN IDEA IS TO INCREASE RIGIDITY BY ALLOWING A RELATIVELY LONG PART TO BE TURNED WITHOUT THE TOOL OVERHANG THAT WOULD BE NEEDED WITH A CONVENTIONAL TURRET (ONE NOT FLAT OR HOLLOW).

MONITOR LATHE

THE TERM MONITOR LATHE FORMERLY (1860S-1940S) REFERRED TO THE CLASS OF SMALL- TO MEDIUM-SIZED MANUAL TURRET LATHES USED ON RELATIVELY SMALL WORK. THE NAME WAS INSPIRED BY THE MONITOR-CLASS WARSHIPS, WHICH THE MONITOR LATHE'S TURRET RESEMBLED. TODAY LATHES OF SUCH APPEARANCE (FOR EXAMPLE, THE HARDINGE DSM-59 AND ITS MANY CLONES) ARE STILL COMMON, BUT THE NAME MONITOR LATHE IS NO LONGER CURRENT IN THE INDUSTRY.

TOOL POST TURRETS AND TAILSTOCK TURRETS

TURRETS CAN BE ADDED TO NON-TURRET LATHES (BENCH LATHES, ENGINE LATHES, TOOL ROOM LATHES, ETC.) BY MOUNTING THEM ON THE TOOL POST, TAILSTOCK, OR BOTH. OFTEN THESE TURRETS ARE NOT AS LARGE AS A TURRET LATHE'S, AND THEY USUALLY DON'T OFFER THE SLIDING AND STOPPING THAT A TURRET LATHE'S TURRET DOES; BUT THEY DO OFFER THE ABILITY TO INDEX THROUGH SUCCESSIVE TOOL SETTINGS.

 GEAR PRODUCTION METHOD

BECAUSE OF THEIR CAPABILITY FOR TRANSMITTING MOTION AND POWER, GEARS ARE AMONG THE MOST IMPORTANT OF ALL MACHINE ELEMENTS. SPECIAL ATTENTION IS PAID TO GEAR MANUFACTURING BECAUSE OF THE SPECIFIC REQUIREMENTS TO THE GEARS. THE GEAR TOOTH FLANKS HAVE A COMPLEX AND PRECISE SHAPE WITH HIGH REQUIREMENTS TO THE SURFACE FINISH.

GEARS CAN BE MANUFACTURED BY MOST OF MANUFACTURING PROCESSES DISCUSSED SO FAR (CASTING, FORGING, EXTRUSION, POWDER METALLURGY, BLANKING). BUT AS A RULE, MACHINING IS APPLIED TO ACHIEVE THE FINAL DIMENSIONS, SHAPE AND SURFACE FINISH IN THE GEAR. THE INITIAL OPERATIONS THAT PRODUCE A SEMI FINISHING PART READY FOR GEAR MACHINING AS REFERRED TO AS BLANKING OPERATIONS; THE STARTING PRODUCT IN GEAR MACHINING IS CALLED A GEAR BLANK.

GEAR MANUFACTURE CAN BE DIVIDED INTO TWO CATEGORIES, FORMING AND MACHINING. FORMING CONSISTS OF DIRECT CASTING, MOLDING, DRAWING, OR EXTRUSION OF TOOTH FORMS IN MOLTEN, POWDERED, OR HEAT SOFTENED MATERIALS. MACHINING INVOLVES ROUGHING AND FINISHING OPERATIONS.

TWO PRINCIPAL METHODS OF GEAR MANUFACTURING INCLUDE

·         GEAR FORMING

·         GEAR GENERATION.

EACH METHOD INCLUDES A NUMBER OF MACHINING PROCESSES, THE MAJOR OF THEM INCLUDED IN THIS SECTION.

FORMING GEAR TEETH:

CHARACTERISTICS: IN ALL TOOTH-FORMING OPERATIONS, THE TEETH ON THE GEAR ARE FORMED ALL AT ONCE FROM A MOLD OR DIE INTO WHICH THE TOOTH SHAPES HAVE BEEN MACHINED. THE ACCURACY OF THE TEETH ARE ENTIRELY DEPENDENT ON THE QUALITY OF THE DIE OR MOLD AND IN GENERAL ARE MUCH LESS THAN THAT CAN BE OBTAINED FROM ROUGHING OR FINISHING METHODS. MOST OF THESE METHODS HAVE HIGH TOOLING COSTS, MAKING THEM SUITABLE ONLY FOR HIGH PRODUCTION QUANTITIES.

GEAR HOBBING

GEAR HOBBING IS CONSIDERED TO BE THE MOST PRODUCTIVE AND VIABLE OF ALL A GENERATING PROCESS. WITH GEAR HOBBING PROCESS TOOTHED WHEELS OF GEARS ARE MANUFACTURED WITH HIGH QUALITY AND GIVES EXCELLENT PERFORMANCE.
HOWEVER, HOBBING IS ONLY USED TO PRODUCE SPUR AND WORN GEARS. INTERNAL GEARS OR SHOULDER GEAR CANNOT BE WORKED UP IN HOBBING PROCESS.

THE HOBBING PROCESS WORKS LIKE THIS. THE HOB IS APPLIED FOR GENERATING THE INVOLUTE TEETH. THE HOB IS ESSENTIALLY A CYLINDRICAL TOOL WHICH IS POSITIONED STRAIGHT. IN HOBBING PROCESS THE HOB AS WELL AS THE WORK PIECE ROTATES CONTINUOUSLY DISPLAYING A ROTATIONAL RELATIONSHIP. A THREAD HAVING THE SIMILAR CROSS SECTION AS THAT OF RACK TOOTH IS HELICALLY WOUND AROUND THE HOB. THE HOB IS THEN SUBSEQUENTLY ROTATED. THE GEAR BLANK IS FED ONTO THE HOB BASED ON THE DEPTH OF CUT. THE HELIX PATTERN OF A ROTATING HOB IS IDENTICAL TO THAT OF A MOVING RACK.

FOLLOWING POINTS CAN PROVE TO BE USEFUL WHILE GOING FOR A GEAR HOBBING PROCESS:

·         ALWAYS CHOOSE THE PREMIUM QUALITY TOOLS.

·         REMEMBER TO REGRIND TOOLS CORRECTLY.

·         ENSURE THE AVAILABILITY OF CORRECT EQUIPMENT IN A GOOD CONDITION.

·         APPLY CORRECT HOB SHIFT STRATEGY.

·         USE A CORRECT, PROPER CUTTING DATA AND APPLY LUBRICANTS (UNLESS DRY MACHINING).

A HOBBING MACHINE IS A SPECIAL FORM OF MILLING MACHINE THAT CUTS GEARS. IT IS THE MAJOR INDUSTRIAL PROCESS FOR CUTTING (AS OPPOSED TO GRINDING) SPUR GEARS OF INVOLUTE FORM.

THE MACHINE FORMS THE GEAR VIA A GENERATING PROCESS BY ROTATING THE GEAR BLANK AND THE CUTTER (CALLED A HOB) AT THE SAME TIME WITH A FIXED GEARING RATIO BETWEEN HOB AND BLANK. THE HOB HAS A PROFILE GIVEN IN CROSS-SECTION BY THE FUNDAMENTAL RACK FOR THE GEAR TOOTH PROFILE AND IS IN THE FORM OF A HELIX SO THAT THE SIDES OF THE TEETH ON THE HOB GENERATE THE CURVE ON THE GEAR. THE HELIX HAS A NUMBER OF CUTS PARALLEL TO THE AXIS TO FORM THE CUTTING TEETH AND THE PROFILE IS SUITABLY RELIEVED TO PROVIDE CUTTING CLEARANCE.

FOR A TOOTH PROFILE WHICH IS A THEORETICAL INVOLUTE, THE FUNDAMENTAL RACK IS STRAIGHT-SIDED, WITH SIDES INCLINED AT THE PRESSURE ANGLE OF THE TOOTH FORM, WITH FLAT TOP AND BOTTOM. THE NECESSARY ADDENDUM CORRECTION TO ALLOW THE USE OF SMALL-NUMBERED PINIONS CAN EITHER BE OBTAINED BY SUITABLE MODIFICATION OF THIS RACK TO A CYCLOIDAL FORM AT THE TIPS, OR BY HOBBING AT OTHER THAN THE THEORETICAL PITCH CIRCLE DIAMETER. SINCE THE GEAR RATIO BETWEEN HOB AND BLANK IS FIXED, THE RESULTING GEAR WILL HAVE THE CORRECT PITCH ON THE PITCH CIRCLE, BUT THE TOOTH THICKNESS WILL NOT BE EQUAL TO THE SPACE WIDTH.

HOBBING IS INVARIABLY USED TO PRODUCE THROATED WORM WHEELS, BUT IT IS NOT POSSIBLE TO CUT ALL USEFUL TOOTH PROFILES IN THIS WAY; IF ANY PORTION OF THE HOB PROFILE IS PERPENDICULAR TO THE AXIS THEN IT WILL HAVE NO CUTTING CLEARANCE GENERATED BY THE USUAL BACKING OFF PROCESS, AND IT WILL NOT CUT WELL. THE NHS SWISS TOOTH STANDARDS GIVE RISE TO SUCH PROBLEMS. SUCH SMALL GEARS NORMALLY MUST BE MILLED INSTEAD.

GEAR SHAPING

A GEAR SHAPER IS A MACHINE TOOL FOR CUTTING THE TEETH OF INTERNAL OR EXTERNAL GEARS. THE NAME SHAPER RELATES TO THE FACT THAT THE CUTTER ENGAGES THE PART ON THE FORWARD STROKE AND PULLS AWAY FROM THE PART ON THE RETURN STROKE, JUST LIKE THE CLAPPER BOX ON A PLANER SHAPER. TO CUT EXTERNAL TEETH, A DIFFERENT MACHINE CALLED A HOBBING MACHINE CAN BE USED.

THE CUTTING TOOL IS ALSO GEAR SHAPED HAVING THE SAME PITCH AS THE GEAR TO BE CUT. HOWEVER NUMBER OF CUTTING TEETH MUST BE LESS THAN THAT OF THE GEAR TO BE CUT FOR INTERNAL GEARS. FOR EXTERNAL GEARS THE NUMBER OF TEETH ON THE CUTTER IS LIMITED ONLY BY THE SIZE OF THE SHAPING MACHINE

GEAR FINISHING METHOD

GEAR SHAVING

GEAR SHAVING IS BASICALLY A FINISHING OPERATION. THIS TAKES PLACE AFTER THE OPERATIONS OF ROUGHING WITH A HOB OR CUTTING WITH A SHAPER CUTTER IS OVER. THE SHAVING PROCESS CONSISTS OF THE REMOVAL OF TINY PARTICLES OF METAL FROM A GEAR TEETH'S WORKING SURFACE. GEAR SHAVING PRODUCES FINE HAIR LIKE CHIPS. THE CUTTER COMES IN THE FORM OF HELICAL GEAR. IT HAS SPECIAL SERRATIONS IN THE FLANK AREA OF GEAR TEETH. THESE SERRATIONS ACT AS THE CUTTING EDGES.

ADVANTAGES
GEAR SHAVING GIVES THE GEAR THE FOLLOWING ADVANTAGES:

·         IMPROVES TOOTH SURFACE FINISH.

·         ELIMINATES, THE PROBLEM OF TOOTH END LOAD CONCENTRATIONS.

·         EFFECTIVE REDUCTION IN THE NOISE OF GEARS WITH MODIFICATION IN THE TOOTH PROFILE.

·         INCREASE THE GEAR’S LOAD CAPACITY IMPROVED SAFETY AND SERVICE LIFE.

TYPES OF SHAVING CUTTERS

THERE IS A WIDE RANGE OF AVAILABLE SHAVING CUTTER TYPES:

·         TRANSVERSE SHAVING CUTTERS

THE GEAR THAT IS SHAVED RECIPROCATES IN THE DIRECTION OF ITS OWN AXIS. THE TOOL AND THE GEAR ARE IN MESH. WITH EACH STEP OF RECIPROCATION, THERE IS AN OCCURRENCE OF SMALL QUANTITY OF RADIAL FEEDING OF THE SHAVING CUTTER. FOR A CLEAN SHAVING OF THE EDGES IT WOULD BE USEFUL TO CALCULATE ONE EXTRA STROKE PER MODULE. HOWEVER, THIS METHOD IS NOT SUITED TO SHAVING SHOULDER GEARS.

1. DIAGONAL SHAVING CUTTERS

HERE THE GEAR SELECTED FOR SHAVING RECIPROCATES OBLIQUELY IN DIRECTION TO ITS OWN AXIS. THE GEAR AND THE TOOL ARE MADE TO STAY IN A MESH. THE DIAGONAL ANGLE CAN BE GOT BY POSITIONING OF THE WORK PIECE TABLE IN AN OBLIQUE MANNER OR BY THE PROCESS OF INTERPOLATING OF THE TWO MACHINE AXES. AS WITH EACH RECIPROCATION, THERE IS A RADIAL FEEDING OF THE SHAVING CUTTER. THIS IS DESCRIBED IN THE DIAGRAM:

2. PLUNGE SHAVING CUTTERS

IN THIS METHOD THERE IS NO WORKTABLE TRANSLATION. INSTEAD THERE TAKES PLACE A RADIAL FEED OF THE WORKPIECE AGAINST THE TOOL THAT IS USED AS SHAVING CUTTER. PLUNGE SHAVING IS PARTICULARLY GOOD FOR SHAVING OF SHOULDER GEAR.

3. UNDERPASS SHAVING CUTTERS

UNDERPASS SHAVING IS PRIMARILY IDENTICAL TO DIAGONAL SHAVING WITH A SMALL VARIATION IN THE FORM OF A DIAGONAL ANGLE OF 90 DEGREES. IN UNDERPASS SHAVING NO AXIAL TABLE RECIPROCATION TAKES PLACE. IN ITS PLACE, THE WORKPIECE RECIPROCATES AT RIGHT ANGLES TO ITS OWN AXIS.

GEAR BURNISING

A GEAR BURNISHING SYSTEM HAS A PRE-CHECKING STATION FOR DETERMINING AN AMOUNT OF BURNISHING PROCESSING NEEDED BY THE GEAR TO BE BURNISHED, AND A GEAR BURNISHING STATION FOR PERFORMING THE BURNISHING OPERATION ON THE GEAR ACCORDING TO PARAMETERS SET BY THE PRE-CHECKING STATION. IN A PREFERRED EMBODIMENT, THE PRE-CHECKING STATION DETERMINES THE CONDITION OF THE GEAR WITHIN ONE OF A PLURALITY OF PRE-SET RANGES FOR THE BURNISHING OPERATION. IN THIS MANNER, APPROPRIATE GEAR BURNISHING PARAMETERS CAN BE APPLIED DEPENDING ON THE ACTUAL CONDITION OF THE GEAR.

GEAR GRINDING

1. INTRODUCTION

GEAR GRINDING CAN GENERALLY BE DIVIDED INTO TWO TYPES; GENERATING AND FORM GRINDING. GENERATING GRINDING USES SIMILAR PRINCIPLES TO GEAR HOBBING BUT UTILIZES A THREADED WORM GRINDING WHEEL TO REALIZE HIGH PRECISION AND EFFICIENCY FOR THE MASS PRODUCTION USER. BECAUSE THE DOMESTIC MARKET FOR GENERATING GRINDING MACHINES HAS, IN THE MOST PART, BEEN MONOPOLIZED BY EUROPEAN SUPPLIERS, AN URGENT CALL FOR A COMPETITIVE DOMESTIC GEAR- GEAR GRINDING IS THE PROCESS OF FINISH GRINDING GEAR TEETH, OFTEN HARDENED TO GIVE A FINE FINISH AND HIGH ACCURACY. THE GEAR IS TYPICALLY MACHINED WITH A GRINDING ALLOWANCE BEFORE BEING HEAT TREATED (USUALLY CASE HARDENED). AFTER HEAT TREATMENT THE GEAR TEETH ARE PRECISION GROUND TO THE FINAL DIMENSIONS, IMPARTING A FINE SURFACE FINISH AND PRECISION SIZING.

PRECISION GEAR GRINDING IS CARRIED OUT USING SPECIALIZED GEAR GRINDING EQUIPMENT. THE PROCESS IS USUALLY CARRIED OUT USING A CNC GEAR GRINDER. GROUND GEARS CAN BE ALMOST ANY SIZE FROM SMALL MICRO-GEARS RIGHT UP TO LARGE, HEAVY POWER TRANSMISSION GEARS FOR THE MINING OR POWER GENERATION INDUSTRIES

GEAR LAPPING, GEAR FINISHING

GEAR LAPPING IS THE PROCESS OF IMPARTING A VERY FINE FINISH AND HIGH DEGREE OF ACCURACY TO GEAR TEETH. LAPPING TYPICALLY IMPROVES THE WEAR PROPERTIES OF GEAR TEETH.

TO ENSURE SMOOTH AND QUIET RUNNING, THE GEARS AND PINIONS ARE LAPPED AFTER HARDENING. LAPPING IS ACCOMPLISHED BY RUNNING MATING PAIRS TOGETHER IN A GEAR LAPPING MACHINE AND FEEDING A LIQUID ABRASIVE COMPOUND UNDER PRESSURE INTO THE GEAR PAIR. THE COMPOUND REMOVES SMALL AMOUNTS OF METAL AS THE GEARS ROTATE, THUS REFINING THE TOOTH SURFACE AND ACHIEVE DESIRED CONTACT PATTERN.

GEAR HONING

GEAR HONING IS A HARD FINISHING METHOD TO ELIMINATE THE GEAR ERRORS AFTER HARDENING AND SMOOTH THE SURFACE OF THE GEAR TEETH. HONING IS ALSO CALLED “SHAVE GRINDING”. THE MACHINING KINEMATICS AND THE TOOL GEOMETRY IS SIMILAR TO GEAR SHAVING, THE TOOL MATERIAL AND CUTTING SPEEDS ARE SIMILAR TO THE GRINDING.

CONVENTIONAL GEAR GRINDING REMOVES MATERIAL FROM THE GEAR FLANKS LEAVING MACHINING MARKS NOT IN THE DIRECTION OF THE GEAR CONTACT IN THE MESH, BUT PERPENDICULAR TO IT. THE HONING PROCESS SIMULATES THE TRUE KINEMATICS IN THE GEAR MESH. FURTHERMORE HONING PROVIDES A BETTER SURFACE FINISH THAN GRINDING. A COMMON MISCONCEPTION IS THAT HONING DOES NOT IMPROVE THE PROFILE ERROR, LEAD ERROR ETC. FROM THE PREVIOUS MACHINING (HOBBLING) AND THE DISTORTIONS FROM THE HARDENING. THIS IS HOWEVER NOT CORRECT, MODERN SPECIALIZED GEAR HONING (SHAVE GIRDING) MACHINES CAN REMOVE A SUBSTANTIAL AMOUNT OF MATERIAL TO CORRECT THE GEAR ERRORS, ESPECIALLY IN GEARS WHICH ARE PREVIOUSLY PRECISION HOBBED AND CASE HARDENED UNDER CONSTANTLY CONTROLLED PROCESS WHICH MEANS THE GEAR ERRORS ARE MINIMIZED ALREADY BEFORE THE HONING. GEAR HONING REQUIRES DEDICATED SPECIALIZED TOOLS AND ALSO SPECIAL VERY STIFF DEDICATED MACHINES. CURRENTLY ONLY NEUGART IS APPLYING GEAR HONING AS A HARD FINISHING METHOD FOR INDUSTRIAL SERVO GEARS.

ADVANTAGES:

·         REDUCED NOISE GENERATION

·           HIGHER INPUT SPEEDS

·           INCREASED SURFACE DURABILITY AND LOAD ABILITY

·           NO “WEAR IN” NO LUBRICANT CONTAMINATION WITH WEAR PARTICLES

·           VIRTUALLY NO INCREASE OF BACKLASH

·           IMPROVED GEAR EFFICIENCY

·           HIGH GEAR QUALITY (AGMA 12 OR HIGHER)