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What data do I need to calculate a profile for a ZK worm?

Question asked by Richard Watt in #Mechanical on Mar 17, 2021
Richard Watt
Richard Watt · Mar 17, 2021
Rank E2 - BEGINNER

In my current job, I am responsible for maintaining an existing software application that generates a dressing program for a CNC external thread grinding machine that uses a grinding wheel and which includes the ability to grind worms (ZI, ZA, ZN, ZK forms). 

The program is generated as a set of relative moves between (X, Y) points and the application starts with creating the worm profile as a set of (X, Y) points based on a set of parameters entered by the user (mostly from a drawing, but can be saved to and recalled from a data file).

What I'd like to find out is what parameters are required to calculate the ZK worm profile because the process that was built into the software is as follows:

  1. Create the flank (X,Y) coordinates for the ZK generating tool
  2. Create the flank (X,Y) coordinates for the ZK worm
  3. Rotate the ZK worm profile 90 degrees clockwise
  4. Determine the (X,Y) coordinates for points at the outer diameter (OD), root and pitch circle radii
  5. Rotate the ZK worm profile 90 degrees counterclockwise/anticlockwise into the upright position
  6. Adjust the ZK worm profile width based on the measurement method used (3-wire or caliper methods supported)
  7. Add OD and root diameter points to the ZK worm profile
  8. Convert the ZK worm profile back to the (X,Y) coordinates for the ZK generating tool profile
  9. Add tip fillet radii to the ZK generating tool profile
  10. Add root fillet radii to the ZK generating tool profile
  11. Convert the ZK generating tool profile back to the ZK worm profile
  12. Add tip runout and clearance points to the ZK worm profile if required


The software was written to accept the following parameters for the ZK generating tool:

  • Tool tip diameter
  • Tool tip width
  • Tool left hand flank angle
  • Tool right hand flank angle
  • Tool tip fillet radii
  • Tool root fillet radii
  • Tool spindle setting angle


This is where the confusion arises because we use a Wenzel GearTec measuring system for performing QA inspections of parts ground in-house and the software for that only asks for the following information regarding the grinding wheel:

  • Diameter of the grinding wheel
  • Grinding wheel thickness (at the pitch circle)


This is why I am trying to find out what the actual parameters required for calculating the (X,Y) coordinate points on a ZK worm actually are: is anyone able to help me find more details on this?

Posted in: #Mechanical

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