Causes of Part Length Variation on Screw Machine Parts

There are many different ways part length can vary when using a cut-off tool on multi-spindle automatic screw machines.

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Photo Credit: "Acme Gridley Multiple Spindle Bar Machine Manual," First Edition 1961 page C11.

There are many different ways part length can vary when using a cut-off tool on multi- spindle automatic screw machines. Here are some of the major ones grouped into a rough classification by where the cause exists.

The cut-off tool itself:

  • Tool is dull
  • Tool is improperly ground (point angle too large)
  • Tool loose/improperly inserted into holder
  • Tool blade is too thin
  • Cut-off tool is hitting while in high speed
  • Cut-off tool being hit by die head or chasers

Cut-off toolholder:

  • Toolholder itself is loose
  • Toolholder is hitting work spindle
  • Toolholder is hitting tool post
  • Toolholder is warped or bent
  • Toolholder is worn

The work spindle:

  • Spindle has end play
  • Spindle has worn bearings
  • Spindle carrier has end play
  • Index lock pin spring is broken
  • Finger holder not adjusted properly
  • Broken pins or fingers in finger holder
  • Feed tubes bent or beat up
  • Wrong stock feed cam—overfeeding stock will cause bounceback from stock stop resulting in short part
  • Incorrect collet tension

The cross slide:

  • Cross-slide play
  • Cross-slide loose
  • Cam is loose
  • Cut-off cam is too large and causes too much feed
  • Cam drum is loose

Other tools:

  • Stock pushed back into collet by drill (dull drill pushing stock rather than cutting chip)
  • Stock pushed back into collet by reamer
  • Face-off tool is loose
  • Face-off tool is dull
  • Face-off toolholder is loose
  • Die head pulling stock out of collet, making part long

Part length can occasionally go awry when using cut-off tools on automatic screw machines.

This post lists more than 30 reasons that I can think of. What did I miss?

 

Originally posted on PMPAspeakingofprecision.com blog.