Discovered setting my tool offsets while the spindle is stopped was costing me parts

Been running CNC lathes for 12 years and always zeroed my tools with the spindle off because that's how my first supervisor taught me. Last week I tried touching off with the spindle running at 500 RPM and my first part came out within 0.0005 inch of the print. Any other old-timers run offsets this way or is it just me?

3 comments

3 Comments

webb.hannah17h ago

Has anyone thought about how this affects your actual tool life data? When you touch off at 500 rpm, you're setting the tool where it actually cuts under load. That means your wear compensation numbers are more real too. I've been tracking tool life for a small production run and the numbers are way more consistent now. The stopped spindle offsets would drift over time because the insert wasn't seating exactly the same each time you touched it off. Now my tool change predictions are actually matching reality instead of guessing.

white.keith19h ago

Running it live at 500 is the only way I do it now for tight work. Touching off with the spindle stopped lets that tiny runout in the holder or insert pocket throw everything off by a thou without you knowing. Had a job last month where I was chasing a size issue for three parts, finally tried a live touch off and it locked right in. Plus you catch the actual tool pressure right at the start instead of guessing what it's gonna do when the cut begins.

keith16418h ago

The part about chasing size for three parts really hit home. I had a similar nightmare with some stainless steel parts last year, kept getting off by about half a thou and couldn't figure out why. Just like you said, soon as I started doing live touch offs at 500 rpm it fixed everything and I haven't gone back. Its crazy how much those tiny vibrations or runout can mess with your reference point when the spindle is stopped. Plus that bit about tool pressure is spot on, you can feel if the tool is gonna deflect or chatter before you even make a real cut.