Article · Aluminum
An End Mill Designed to Control Chatter
RobbJack's Mirror Edge™ geometry keeps a flute in contact with the work until the next one engages — synchronizing vibration to kill chatter and unlock a fivefold jump in metal removal.
Originally published in Modern Machine Shop, 2017
5×
metal removal vs. a traditional end mill
42 in³/min
removed in aluminum
0.005" × 3"
wall thickness × height achievable
Chatter is two things vibrating out of sync — the tool and the workpiece knocking against each other until the cut tears and the edge chips. RobbJack's answer wasn't more rigidity or less speed; it was a geometry that keeps the cut continuous. The Mirror Edge™ end mill is built so that a flute stays in contact with the work until the next flute engages, so the system never gets the chance to fall out of sync.
What the Mirror Edge actually is
The Mirror Edge is a special edge preparation that adds a narrow surface — 0.001 to 0.002 inch wide, highly polished and shiny — along the trailing side of each tightly spiraled flute. On the three-flute aluminum tools it's paired with, that land keeps the flute riding the workpiece until the next flute takes over the cut.
Why continuous contact kills chatter
Vibration doesn't stop — but the destructive knocking does. By maintaining constant contact, the tool and workpiece can't vibrate out of phase and slam together, which is what produces chatter marks and chips edges. Because the polished land minimizes frictional rubbing, it generates virtually no heat while it's doing it.
What it buys you on the machine
- A fivefold increase in metal removal rate compared with traditional end mills.
- As much as 42 cubic inches of aluminum removed per minute.
- Thin walls down to 0.005 inch and as tall as 3 inches, machined without chatter.
- Standard on the A1-303 and FM aluminum series; custom versions available for steel and titanium.
Don't fight chatter with caution — engineer it out. Keeping the cut continuous let RobbJack run aluminum five times faster on the same machine.
Tools in this story
Have a job like this?
Tell us your material and operation — our application engineers will recommend the tool and the speeds & feeds to run it.