Craftsman's Cribsheet: 30 Potential Causes of Part Length Variation on Screw Machine Parts

Here are some of the major reasons 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 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