How to Cut Left Hand Threads on a Lathe

In the industrial world that we are all a part of, when it comes to threads on such things as nuts, bolts, screws and turned-in attachments, almost all of the threads are right hand threads. Only specialized applications where a nut would loosen due to shaft or spindle rotation, would there be a need for left-hand threads. Essentially, both procedures for cutting a left hand thread and a right hand thread are identical except for the positioning of the left-hand thread cutting tool.

You can cut left hand threads in the same way as right.
  1. Center the piece of material to be cut into the spindle and tighten it down firmly. Move the tailstock into position to support the other end of the material.
  2. Insert a left-hand cutting bit into the tool holder. These are obtained at hardware stores, online or any shop that specializes in lathe equipment. The tool holder is mounted onto the compound rest.
  3. Set the compound to an angle of 29 degrees. Use the guide on the lathe or use a protractor to achieve this angle.
  4. Reverse the leadscrew direction so that the compound and therefore the threading pass moves from left to right when the lathe is turned on.
  5. Turn the lathe on and position the cutting tool at the end of the piece of material to be cut. If the application warrants it, begin the cut with a taper. It may require several passes to cut the threads, depending on how deep you need them to be.

Things You Will Need

  • Protractor (optional)

About the Author

Dale Yalanovsky has been writing professionally since 1978. He has been published in "Woman's Day," "New Home Journal" and on many do-it-yourself websites. He specializes in do-it-yourself projects, household and auto maintenance and property management. Yalanovsky also writes a bimonthly column that provides home improvement advice.

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