Tombstone
Is a tombstone only for horizontal machining centers?
No; while strongly associated with HMCs, tombstones are also built for vertical machining centers and 4th/5th-axis workflows, offering the same multi-side and high-density benefits.
Why use a tombstone instead of single-part setup?
To increase spindle uptime, machine multiple parts or multiple sides in one load, and maintain consistent datums across all operations, reducing re-fixturing and cycle time.
What matters most in tombstone specification?
Face squareness, flatness, parallelism, hole location accuracy, and overall stiffness are critical because they directly control part location and machining repeatability across all stations.
A tombstone is a rigid CNC workholding fixture—typically a vertical column mounted on a machine table or pallet—that enables multi-side machining in one setup. By mounting parts, vises, or subplates on multiple faces, it reduces re-indicating, speeds changeovers, and improves spindle utilization on horizontal and vertical machining centers.
On the shop floor, a tombstone is bolted to the CNC table or pallet and precision-machined to a known datum, making each face a repeatable setup plane for vises, soft jaws, nests, or direct part clamping. The primary production advantage is density: one tombstone carries multiple part stations, allowing the machine to cut on one face while another face is being loaded or indexed, which raises throughput. In programming, each face is treated as a controlled work offset or face-specific coordinate system; CAM workflows use tombstone setup data to output correct toolpaths and B-axis rotations. Typically made from cast iron or steel for stiffness and damping, the tombstone is often drilled and tapped on the machine to create the hole pattern for modular workholding. The real shop-floor value is better repeatability because the part stays referenced to a rigid fixture instead of being torn down and re-indicated between operations.
Fixture geometry drift: Unchecked flatness or perpendicularity errors on the tombstone face cascade into cumulative part position defects across all stations, leading to out-of-tolerance features and scrap.
Insufficient rigidity: A tombstone that is too light, tall, or asymmetrically loaded chatters under interrupted cuts, degrading finish, wandering true position, and shortening tool life.
Bad offset management: A wrong face call or stale work offset sends the tool to the wrong side or causes a collision, as tombstone machining requires strict coordination between face numbering, CAM setup, and machine coordinates.