Causes of Part Length Variation on Screw Machine Parts

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.