The Setup Sheet Is Where Tombstones Fail
A four face tombstone with good squareness can still produce scrap if the setup sheet sends the operator to the wrong datum. The fixture is only half the system; the paperwork that tells the machine where the faces are is the other half.
One Datum, Then Offsets
- Pick the base dowel pair as the primary datum. Every face offset is derived from it, so moving the tombstone to another pallet does not invalidate the work.
- Record the four face offsets as values, not as "probe each face". Probing is fine, but a recorded value lets the operator detect a collision or a chip under the fixture.
- Number faces physically and in the program. A mismatch between the laser marked face number and the program offset is the most common cause of a mirrored part.
- Keep the reference face and dowel drawing in the setup sheet, not in a folder on a server nobody opens at 2 am.
The First Part Check
The first part on each face should be checked for position relative to the datum, not just for size. Size tells you the tool is right; position tells you the offset is right. Check one bore position and one face height per face, and record the values on the sheet so trends appear before scrap does.
| Check | Frequency | Catches |
|---|---|---|
| Bore position vs datum | First part per face | Wrong offset, mirrored program |
| Face height | First part per face | Chip under fixture, wrong tool length |
| Squareness across faces | First part per pallet change | Fixture moved, dowel damage |
| Bolt hole pattern | First part per job | Program revision applied to one face only |
Why Squareness Must Be Measured Standing Up
A tombstone measured lying on a surface plate can read square and still be out when it stands on the machine. Measure it in the attitude it will run in, with the base clamped as it will be clamped. This is also why the fixture report should state how the part was supported during inspection, not only the values.
Handling the Pallet Change
Most tombstone scrap happens on the second pallet, not the first. Establish a repeatable load: same dowels, same clamp sequence, same torque, and a probe routine that confirms the base before the first cut. Ten minutes of probing is cheaper than a face of scrap.
Squareness, dowel position and the inspection report format for the four face tombstone fixture are listed on the product page, including values per face rather than a pass stamp.
