Craftsman's Cribsheet: 30 Potential Causes of Part Length Variation on Screw Machine Parts
There are many different ways that part length can vary when using a cut-off tool on multiple-spindle automatic screw machines.
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Here are some of the major reasons grouped into a rough classification by where the cause exists.
The Cut-Off Tool Itself
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• Tool is dull
• Tool is improperly ground (point angle too large)
• Tool is loose/improperly inserted into holder
• Tool blade is too thin
• Cut-off tool is hitting while in high speed
• Cut-off tool is being hit by die head or chasers
The 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 is not adjusted properly
• Broken pins or fi ngers are in the fi nger holder
• Feed tubes are 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 has play
• Cross slide is 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 is pulling stock out of collet, making the part long
— Precision Machined Products Association
