A Weldon shank is a cylindrical end-mill shank with a ground flat for a side-lock toolholder screw. The flat’s depth and position affect how the screw contacts the tool. A holder and cutter must use compatible dimensions; the word “Weldon” alone does not specify every shank length, flat location, or tolerance.
Selected inch-series shank dimensions
The selected table lists nominal shank diameter and length, flat depth X, and flat length. X is measured from the bottom of the flat to the opposite side of the shank in the referenced drawing. Flat length is a separate axial dimension. Do not confuse either value with cutting diameter or overall tool length.
[gs_table id=”11163″]
Use the flat with a matching holder
A side-lock screw bears on the flat to resist rotation and retain the tool. If the flat is too shallow, too deep, or positioned incorrectly, the screw may contact the shank’s round surface, bottom out, or interfere with the toolholder. Confirm the tool’s drawing and the holder’s screw position rather than relying only on the nominal shank diameter.
The flat does not make a tool interchangeable with every collet, shrink-fit holder, hydraulic holder, or milling chuck. Those systems have their own clamping requirements. Use the toolholder manufacturer’s torque and insertion-depth instructions, keep the shank and bore clean, and inspect the screw point for wear. Do not grind or deepen a flat by eye; removing material can weaken the shank or create an unsafe fit.
For a physical check, measure the cylindrical shank away from the flat with a suitable micrometer, then measure the flat depth from the opposite surface using the datum shown on the drawing. Measure flat length parallel to the shank axis and confirm where the flat begins relative to the shank end. A caliper reading taken across the flat is not automatically the specified X dimension.
ASME lists B94.19-1997 as the current stabilized-maintenance edition, reaffirmed in 2024. The older handbook page identifies its selected Weldon dimensions with B94.19-1997 (R2019). Manufacturer guidance also notes that flat dimensions and position are standard-specific. Newer solid-carbide and metric tools may use different geometry or a maker’s own specification, so these selected high-speed-steel reference values should not be assumed to apply to every end mill.
Tool drawings may specify tolerances, minimum shank engagement, neck relief, or a flat position that differs from this selected table. Use the revision and product series associated with the cutter in hand. If the maker identifies a proprietary flat, obtain its drawing instead of assuming that a familiar inch diameter guarantees the standard profile. A side-lock screw should contact the flat in the intended region without protruding into a flute or neck.
After tightening the holder, check the tool’s runout and make sure the screw has not distorted or shifted the cutter. A clean, undamaged shank and correctly seated tool are part of the setup; the flat dimensions alone do not guarantee concentricity. Follow the machine builder’s precautions before adjusting or measuring a tool in the spindle.
When a tool will be used at high speed, verify the holder’s maximum rated speed, balance condition, and retention instructions as well as its size. The selected dimensional values do not address balance, tool projection, cutting load, or machine guarding. Those setup limits remain necessary even when the shank and flat appear to fit.
Before ordering a replacement, compare shank diameter, flat depth, axial flat location, and insertion depth with the cutter and holder drawings. A tool can have the right cutting diameter but the wrong shank. For other tooling references, see our taper-shank reamer fit guide, drill chuck mounting sizes, and straight-shank reamer dimensions. These cover different tools and do not define Weldon-flat fit.
References
- ASME B94.19 identifies the current edition and standard scope.
- IMCO’s Weldon-flat note explains the standard-based flat dimensions it uses.
