Why a Tombstone Beats Four Angle Plates
A tombstone turns a horizontal machining center into a multi part machine: four faces carry four sets of parts, the table indexes ninety degrees, and the spindle cuts one face while the operator loads the next. The gain is spindle hours per part, because the machine no longer waits for a part change.
Four angle plates bolted to a cube look cheaper until the errors accumulate at every joint. A machined tombstone holds squareness across all faces from a single setup, so a single program runs on every face and the operator stops re-indicating between jobs.
One Datum, Four Faces
- All faces machined in one 5-axis setup, so squareness comes from the machine rather than a chain of re-chucks.
- Squareness between adjacent faces 0.02 mm over 300 mm, parallelism between opposite faces 0.02 mm.
- Base flatness 0.01 mm, because any error at the table is multiplied up the height.
- Dowel hole pair bored and reamed to 0.01 mm true position, used by every fixture plate that bolts on.
- Faces numbered and serial marked, so the setup sheet and the physical fixture always agree.
Cast Iron or Billet Aluminum
| Option | Best for | Watch point |
|---|---|---|
| Cast iron | Heavy cutting, long runs | Must be normalized, sometimes twice |
| Billet 6061 or 7075 | Aluminum part families, robot loaded cells | Weight and cost per kilogram |
| Steel weldment | Very large or irregular fixtures | Normalize after welding before machining |
Weight is quoted with the design, because the tombstone plus fixtures must stay inside the pallet capacity of the machine, and lifting points are sized for the finished weight.
Repeatability Comes From the Fixture, Not the Machine
Indexing repeatability is a property of the machine. The fixture must not add to it, which is why no face is used as a datum for another and why the dowel holes are bored rather than drilled. A drilled hole will not repeat after a fixture is removed and refitted.
Commissioning and Handover
Handover is where a good fixture either becomes productive or sits on the floor. Every tombstone ships with a dimension sheet, a CMM report with actual squareness values per face, and a datum sheet written for the customer machine, so the first setup is a measurement exercise rather than a guessing exercise. Fixture plates ordered with the tombstone are machined in the same batch, which proves the dowel fit before the parts leave the plant. Remote or on site support is available for the first production run, and the datum sheet is updated if the machine offsets differ from the drawing assumption.
Our four face tombstone fixture page covers face count, height, clamping manifolds and the CMM report supplied with each unit.
