Cutting Tool Engineering
February 2012 / Volume 64 / Issue 2

Stirring runout to zero

By Alan Richter, Editor

A 3µm (0.0001 ") runout for a hydraulic toolholder is usually accurate enough to enable users to achieve tight tolerances for shape, position and surface quality. But when tolerance specifications require a holder with better concentricity or when a spindle is not true, Schunk Inc. offers the TENDOzero hydraulic expansion toolholder, which users can adjust to achieve a runout accuracy of 0µm (0.0000 "). “They’re tweaking out that last little bit of runout until it’s essentially zero,” said Jeff Keith, product manager, tooling for Schunk. “The guys in the industry say ‘stirring’ or ‘tramming’ it in.”

A Torx-plus key is used to adjust four radially located setscrews integrated into the holder’s nose area to correct the angular position of the clamped cutting tool. That can be done in a presetter or in a machine using a dial indicator when a shop needs to compensate for spindle runout errors. Keith noted that total possible compensation travel is about 20µm (0.0008 "). “If you have a really old machine in which the spindle is all beat up, chances are you’re going to need more than 3µm (0.0001 ") of adjustment.”

Courtesy of Schunk

Schunk’s TENDOzero hydraulic expansion toolholder enables users to adjust runout accuracy to 0.000mm.

TENDOzero holders are offered in “sleeveable” clamping bores of 12mm, 20mm and 32mm, which are capable of holding smaller tools shanks using intermediate sleeves to reduce the clamping diameter down to 3mm (0.118 "). Even with a sleeve, adjustment to “zero” runout is possible, Keith added.

By machining with the least runout possible, cutting tools last up to 50 percent longer, the company reports.

Schunk initially introduced the toolholder in Europe with HSK-A 63 and 100, SK 40 and 50, BT 40 and 50, and Capto C4, C5 and C6 tapers. It recently introduced CAT-taper versions for the North American market (3⁄4 " bore, which is also sleeveable).

For more information about Schunk Inc., Morrisville, N.C., visit or call (919) 572-2705. CTE

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