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Edge Finder Basics
Guide · Updated October 27, 2026
An edge finder locates a part edge relative to the spindle so you can set your zero. The common mechanical type has a spring-loaded offset tip. It runs off-center until it touches the edge, then centers, then kicks sideways.
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Step by step
- Mount it: Hold the edge finder in a collet or drill chuck.
- Set the RPM: Run about 600 to 1,000 RPM. Too fast and the tip flings off-center.
- Offset the tip: Push the tip sideways so it wobbles.
- Approach the edge: Feed slowly toward the part. The tip will run true, then suddenly kick sideways.
- Apply the offset: At the kick, the spindle center is half the tip diameter from the edge (0.100 in for a 0.200 in tip). Move by that amount and zero the axis.
- Repeat: Back off and approach again to confirm the position.
Tips
- Approach from the same direction each time to remove backlash.
- Clean the edge of burrs first.
- Don't use a mechanical edge finder on a running CNC at high RPM.
Checking accuracy
- Touch both sides of a gage block of known width. The difference should match the block size plus one tip diameter.
- Build the reference width with the free Gage Block Calculator.
Related: milling speeds and feeds, checking a test indicator.
Worked example: picking up the left edge of a part
A plate is clamped in the vise and you need X zero on its left edge. Chuck a 0.200 in edge finder, run about 800 RPM, and nudge the tip off-center. Jog X toward the edge in coarse steps until the tip starts to run true, then switch to 0.0001 in steps. At the moment the tip kicks sideways, stop. The spindle center is now 0.100 in to the left of the edge, so move X +0.100 in and zero it. Back off, raise Z, and repeat the approach: the kick should happen at -0.100 in on the readout. If it doesn't, clean the edge of burrs and try again.
FAQ
What RPM should an edge finder run at?
Typically 600 to 1,000 RPM for mechanical edge finders. Check the maker's guidance.
How accurate is an edge finder?
About ±0.0002 in to ±0.0005 in with good technique and a clean edge.
What offset do I use?
Half the tip diameter: 0.100 in for a 0.200 in tip, or 5 mm for a 10 mm tip.
Can I check an edge finder with gage blocks?
Yes. Pick up both sides of a known block and compare the travel to the block width plus the tip diameter.
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General shop information only — follow your gage manufacturer's instructions and your quality system.