Five readings came back off the real hardware. Two internal cross-checks passed, one reading was revised, and the result overturns what the field-test document said was wrong with the gripper — the crossing fingers were never a hole-position problem.
Two bolt positions were read independently — R_in at (27, 2.5) and
R_out at (36.7, 5.0), both relative to the fixed jaw's inner bolt with the fixed
jaw's bolt line as the x-axis. The distance between them computes to 10.017 mm against
a known bolt spacing of 10.0 mm — 0.017 mm out. Nothing about the points, the
frame or the caliper is wrong.
Drawn to scale, and the outline is lifted straight out of Blade_v4_final.stl —
not a sketch. The blade stands 89.4 mm from the bottom of its mounting foot to the tip.
| Reading | Measured | Predicted | Status |
|---|---|---|---|
| R_in — right jaw inner bolt | (27, 2.5) | — | baseline |
| R_out — right jaw outer bolt | (36.7, 5.0) | (36.8, 4.4) | ✓ matched |
| Right pair spacing (derived) | 10.017 | 10.000 | ✓ self-check |
| θ — angle between bolt lines | 14.45° | 10.79° | ! 3.66° out |
| Official blade: outer bolt → protrusion face | 22–23 mm | 23.52 | ✓ matched |
| Official blade: bolt centre → bottom face | 2.5 mm | — | new |
| Official pair, fully closed | just touching | — | the spec |
| Previous printed pair, fully closed | crossing | — | the defect |
The outer-bolt-to-face distance first came back as 19 mm and was then revised to
22–23 mm. The first value produced a confident conclusion of
HOLE_DX = −3.163 mm — retracted. Nothing was changed in the repo on the
strength of it.
The operator also caught an error in the prediction that accompanied it: the outer bolt is on the far side from the protrusion face, so its distance to that face must be larger than the hole-pair centre's, not smaller. The predicted 13.52 mm should have been 23.52 mm. With the sign fixed, the prediction and the revised measurement agree.
| Blade | Outer bolt → protrusion face | Behaviour when closed |
|---|---|---|
| Previous version — printed, field-tested | 26.27 mm | crosses |
| v4 — never printed | 21.77 mm | unknown |
| Official | 22–23 mm | just touching |
Both versions carry their bolts at the same x positions — −0.857 and 9.143, 10 mm apart. The holes never moved. What differs is the depth of the blade body: the previous version reaches 3–4 mm further toward the other jaw than the official one, and that is what makes the fingers cross.
v4 already changed this. At 21.77 mm it sits at the edge of the official 22–23 mm band — between 0.2 and 1.2 mm short. So requirement 2B's instruction to shift the hole pattern inward was written against a blade whose real problem was elsewhere, and applying it to v4 would likely push it the wrong way.
The remaining discrepancy is 0.2–1.2 mm, which is inside the precision of a "22 to 23"
reading, and TPU is compliant enough to absorb a few tenths. Changing it in the wrong
direction costs more than leaving it. If a reading to 0.5 mm comes back — a single number,
not a range — then HOLE_DX = reading − 21.768 settles it in one step.
| Blade | Bolt centre → bottom face | Hole edge → bottom face |
|---|---|---|
| Previous version | 3.500 mm | 2.100 mm |
| v4 | 2.250 mm | 0.850 mm |
| Official | 2.500 mm | 1.100 mm |
The operator's note on why this matters: without it the holes will not line up with the bolt
openings on the mounting bracket. Raising HOLE_Z by 0.25 mm matches the
official part and improves the material left below the hole from 0.850 to 1.100 mm — the
source comments call 0.865 mm the practical floor for TPU, so v4 is currently just under it.
This one is a clear improvement in both directions and has no downside.
| Item | What it needs |
|---|---|
| θ disagreeing with the URDF by 3.66° | Most likely the bolt line is not perpendicular to the jaw's long axis, in which case the URDF figure simply cannot be used to predict bolt geometry. The measurement wins either way — but the closure page's prediction needs qualifying. |
FLATTEN sign — mating face angle | Needs A (foot outer corners) and T (tips). Decides whether the mating face should be flattened to the blade axis or left following the rail. |
HOLE_DX to 0.1 mm | A single-number reading of the official blade's outer bolt → protrusion face, to 0.5 mm. |
| Sleeve jaw opening | The sleeve costs 18.68 mm of opening. Whether a 90 mm cup still fits has never been checked, and it runs the gripper motor so it needs the operator present. |