Tombstone fixtures

Haas lists 400 kg maximum pallet load for the cited EC-400 and 227 kg with its pallet pool. In the 227 kg example, a 100 kg column, four 14 kg vises and 12 kg of other hardware leave 59 kg for parts. The mass budget leaves center of gravity, rotary loading and swept clearance to check on the complete assembly. Haas EC-400 specifications.

Use Choosing workholding to compare location, support and restraint across fixture types.

Purpose and construction

An HMC pallet can carry an upright column and index its workholding faces toward the spindle. Jergens offers two-sided, four-sided, cross-shaped and vise columns. Jergens tooling-column range

Each face can hold several parts or a dedicated operation, subject to reach and loaded clearance.

Jergens's four-sided cast-iron columns use stress-relieved Class 40 cast iron and single-piece construction. Their bases and sides are specified milled flat, perpendicular and parallel within 0.001 inch per foot; mounting holes accommodate popular 400 and 500 mm pallets. This is a geometry specification for those columns, not a tolerance on a machined workpiece. Jergens four-sided cast-iron columns

A different construction appears in Jergens QLS tooling columns: two-piece 6061-T6512 aluminum, hardcoat-anodized upright faces and installed QLS bushings, intended to support Fixture-Pro or OK-Vise RM rails on HMCs. Material, section geometry and joint construction therefore belong to the particular column design; “aluminum” or “cast iron” alone does not specify stiffness or allowable cutting load. Jergens QLS columns

Mounting and location

There are at least two distinct interfaces: the column base to the machine pallet, and the fixture to the column face. A pallet's nominal size does not define either complete hole pattern or locating arrangement. In Jergens's Ball Lock system, shanks pass through liners and anchor in receiver bushings to locate and secure fixture plates on tables or tombstones. A removable plate is thus a separate component from the column itself. Jergens fixture-system components

Jergens specifies ±0.0005 inch (±0.013 mm) or better repeatability for its Ball Lock fixture plates, alongside a separate 0.001 inch parallelism specification. Repeatable plate relocation does not establish spindle-to-part accuracy: column geometry, pallet location, workpiece locators and machining effects remain in the chain. The cited product claim is not a universal tombstone repeatability. Jergens Ball Lock fixture plates

Mass and machine limits

The supported mass includes the column, fixture plates, clamps, workpieces and other carried hardware. Haas's tombstone guidance explicitly subtracts tombstone and vise weight from available pallet capacity. Its comparison uses a lighter cast-iron column to leave more workpiece capacity, illustrating that column construction can consume a substantial share of the load allowance. Haas tombstone mass guidance

Configuration matters. The cited Haas EC-400 product specifications distinguish 400 kg maximum pallet load from 227 kg with the pallet pool. These are limits of that documented machine configuration, not a rating for every EC-400 generation or every tombstone. Haas EC-400 specifications

Original mass example: using that 227 kg limit, assume a 100 kg column, four 14 kg vises and 12 kg of additional carried hardware. Remaining mass allowance is 227 − 100 − 4 × 14 − 12 = 59 kg for workpieces. This is only mass bookkeeping; it establishes neither acceptable center of gravity nor rotary acceleration, cutting moment or clamping capacity.

Swing envelope and tool access

The relevant envelope is the loaded assembly throughout rotation and pallet transfer, including clamps and overhanging stock. Haas's EC pallet-pool technical page specifies a maximum diameter of 559 mm and height of 889 mm for workholding plus workpiece, separately from its 400 mm-square pallet and load limit. Pallet width is therefore not the available swing diameter. Haas EC pallet-pool specifications

Original swing example: assume a centered 200 mm-square column with a loaded extremity at coordinates x = 150 mm, y = 100 mm relative to its rotary axis. That extremity sweeps radius √(150² + 100²) = 180.3 mm, or a 360.6 mm diameter. A 300 mm overall width alone would miss the corner's sweep. This ideal planar envelope excludes clearances, tools, machine structure and transfer motion; comparison with one diameter limit does not demonstrate collision-free operation.

Cutting access and structural loading are separate from swing clearance. A tall fixture may fit yet place the cutting load far above its base. For an original static example, a 1,500 N horizontal force acting 0.45 m above the base produces an overturning moment of 675 N·m about the corresponding horizontal base axis. This is not rotary drive torque about a vertical B axis or a permissible fixture load.

Coverage limits

The cited product pages provide no verified issue dates here. Their dimensions and ratings remain source-specific. Column face geometry, quick-change repeatability, pallet mass and swept clearance describe different properties; none alone establishes a finished-part tolerance, safe lifting capacity, cutting-load rating or usable production arrangement. Actual mounting, loading, tool reach and machine configuration determine applicability.