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.
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.