# US 2015/0336190 A1 · Method of machining a rotor with variable-lead screw > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2015/0336190 A1 - Document ID: US20150336190A1 - Status: Published application - Kind: A1 - Application number: 14/651,872 - Filed: 2013-12-12 - Published: 2015-11-26 - Earliest claimed: 2012-12-12 - Assignees: Precision Technologies Group (PTG) Limited - Applicants: Precision Technologies Group (Ptg) Limited - Inventors: Daniel William Davey - Web page: https://patentgrep.com/patent/US20150336190A1 ## CPC - B23F 15/08: Making intermeshing rotors, e.g. of pumps - B24B 19/022: {for helicoidal grooves (B24B19/04 takes precedence)} - F04C 2/08: of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing - F04C 2/084: {Toothed wheels} - F04C 2/16: with helical teeth, e.g. chevron-shaped, screw type {(for non-parallel axes of movement F04C3/00)} - F04C 18/08: of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing - F04C 18/084: {Toothed wheels} - F04C 18/16: with helical teeth, e.g. chevron-shaped, screw type {(for non-parallel axes of movement F04C18/48)} - F04C 2230/10: by removing material - F04C 2240/20: Rotors - Y10T 409/107473: Making a noncircular gear, worm, rotor, or a planar-faced gear - B23F: MAKING GEARS OR TOOTHED RACKS (by stamping B21D; by rolling B21H; by forging or pressing B21K; by casting B22; arrangements for copying or controlling B23Q; machines or devices for grinding or polishing, in general B24B) - B24B: MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING (grinding of gear teeth B23F, of screw-threads B23G1/36; by electro-erosion B23H; abrasive or related blasting B24C; tools for grinding, buffing or sharpening B24D; polishing compositions C09G1/00; abrasives C09K3/14; electrolytic etching or polishing C25F3/00; grinding arrangements for use on assembled railway tracks E01B31/17); DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS - F04C: ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS (engines F03C); ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract A method of machining, with a formed tool, a first rotor and a second rotor with mutually complementary meshing threads involves rotating a first workpiece about a longitudinal axis of the workpiece. The tool makes one or more passes along the longitudinal axis of the workpiece as the workpiece rotates so as to remove material, thereby forming the flanks of each helix of the first rotor's thread. The value of at least one of the parameters that collectively define the relative position and relative movement of the workpiece and formed tool is varied during each pass so as to vary the lead of the thread. The above steps are repeated for a second workpiece, thereby forming the second rotor. Adjustments are made to at least one of said parameters during one or more of the passes in order to maintain mutually complementary shapes of the threads of the rotors. ## Claims ### Claim 1 A method of machining, with a formed tool, a first rotor and a second rotor with mutually complementary meshing threads, the method comprising: rotating a first workpiece about a longitudinal axis of the workpiece; making one or more passes of the formed tool along the longitudinal axis of the workpiece as the workpiece rotates so as to remove material, thereby forming the flanks of each helix of the first rotor's thread, the value of at least one of the parameters that collectively define the relative position and relative movement of the workpiece and formed tool being varied during each pass so as to vary the lead of the thread; and repeating the above steps for a second workpiece, thereby forming the second rotor, wherein adjustments are made to at least one of said parameters during one or more of the passes in order to maintain mutually complementary shapes of the threads of the rotors. ### Claim 2 (depends on 1) The method according to claim 1 wherein said adjustments include one or more adjustments to the speed of rotation of the workpiece. ### Claim at position 3 (depends on 1) 3 The method according to claim 1 wherein said adjustments include one or more adjustments to the spindle angle of the formed tool. ### Claim 4 (depends on 1) The method according to claim 1 wherein said adjustments include one or more adjustments to the centre distance between the workpiece and the formed tool. ### Claim 5 (depends on 1) The method according to claim 1 wherein said adjustments include one or more adjustments to the approach angle of the formed tool. ### Claim 6 (depends on 1) The method according to claim 1 wherein said adjustments include one or more adjustments to the axial position of the formed tool in a direction along its rotational axis. ### Claim 7 (depends on 1) The method according to claim 1 wherein the adjustments made during each pass are made according to a global adjustment distribution, each global adjustment distribution being determined in advance by: theoretically calculating the clearance distribution that would be produced by counter-rotating a hypothetical pair of meshed first and second rotors of the shape that would be produced by machining them using the method of claim 1 but without any adjustments being made, at a plurality of locations along the longitudinal axes of the meshed rotors; deriving a location-specific adjustment set for each of said locations, each location-specific adjustment set comprising one or more parameter adjustments which would cause the clearance distribution at that location to be maintained within a predetermined range of values; and collating the adjustments to each parameter according to the location-specific adjustment sets. ### Claim 8 (depends on 7) The method according to claim 7 wherein the collated adjustments include adjustments interpolated at points between said locations. ### Claim 9 (depends on 7) The method according to claim 7 wherein each location-specific adjustment set is derived by: determining the effect that an arbitrary adjustment of each parameter individually would have on the clearance distribution at that location; and determining a combination of adjustments, and the necessary magnitudes of those adjustments, which would maintain the clearance distribution within a predetermined range of values. ### Claim 10 (depends on 7) The method according to claim 7 wherein said locations are distributed at substantially regular intervals along the portions of the rotors that mesh with each other. ### Claim 11 (depends on 1, 7) The method according to claim 7 wherein the global adjustment distribution is calculated using a computerised model of the hypothetical rotors of the shape that would be produced by machining them using the method of claim 1 but without any adjustments being made. ### Claim 12 (depends on 11) The method according to claim 11 wherein the location-specific adjustment sets are calculated by manipulating said computerised model. ### Claim 13 A method of producing a rotor with variable-lead screw by machining a workpiece using a formed tool, the method comprising: rotating the workpiece about a longitudinal axis of the workpiece; and making at least one pass of the formed tool along the longitudinal axis of the workpiece as the workpiece rotates so as to remove material, each pass forming at least one flank of at least one helix of the rotor's thread, the value of at least one of the parameters that collectively define the relative position and relative movement of the workpiece and formed tool being varied during each pass so as to vary the lead of the thread produced by the at least one pass. ### Claim 14 (depends on 13) The method according to claim 13 wherein the formed tool is a grinding wheel. ### Claim 15 (depends on 1) A computer program comprising computer readable instructions configured to cause a machining apparatus to carry out a method according to claim 1. ### Claim 16 (depends on 15) A computer readable medium carrying a computer program according to claim 15. ### Claim 17 (depends on 1) A computer-controlled apparatus for producing a rotor with variable-lead screw by machining a workpiece using a formed tool, the apparatus comprising: a memory storing processor readable instructions; and a processor arranged to read and execute instructions stored in said memory, wherein said processor readable instructions comprise instructions arranged to control the apparatus to carry out a method according to claim 1.