The HDD Bore Path Calculator draws one path beneath level ground in five phases. Measurements and specifications remain your inputs. A passing arithmetic constraint does not establish that a real bore can be drilled.
1. Start from a measured datum
Entry is horizontal station zero and depth zero. Depth increases downward; entry and exit ground are level. Supply exit station X, center depth D, entry and exit angle magnitudes, requested circle radius R, actual in-ground rod advance L, straight entry lead and envelope diameter. Rod or adapter outside the ground is not counted by this schedule. There is no rating database or automatic design optimum.
2. Separate grade, angle and rod advance
Percent grade equals 100 tan(angle). Twenty percent is about 11.31 degrees, not twenty degrees. Output locator-style pitch is negative entering, zero on the level part and positive exiting. Rod endpoints follow distance along the path, not horizontal steps. A rod can traverse multiple phases, so one endpoint pitch is not a constant pitch for that entire rod.
3. Read the circular geometry
PPI MAB-07, printed pages 55 and 70, distinguishes circle radius from quadrant distance and supplies circular-exit geometry. A hypothetical 157 ft quadrant divided by its rounded 1.57 factor gives 100 ft radius; a 10 ft advance at that radius turns through about 5.72958 degrees. Neither figure is a rating preset. For angle a, the exact entry setback is D cot(a) + R tan(a/2). Entry lead requires D at least lead sin(a) + 2R sin²(a/2). The mirrored exit uses its own angle. Exit station minus both setbacks is the level run; a negative run refuses.
4. Compare both entered criteria
The conservative distributed pitch derivation is 100 L sec²(max angle) / P, then eight upward binary steps for its comparison bound. It is a sufficient mathematical bound, not a maker rating conversion. Both mode selects the largest of requested radius, entered minimum and pitch bound. It keeps all other inputs fixed, states which entered criterion governs and shows hypothetical single-limit alternatives. A larger requested radius can exceed both criteria without changing the governing label. Radius-only and pitch-only modes refuse an undersized request.
For the specific JT20 PowerPipe HD illustration, 107 ft minimum radius, 10 ft advance and 9.4 points per rod at 18% grade yield about 109.830 ft for the pitch criterion. At 107 ft, the distributed full-rod bound is about 9.649 points. These entered specifications are tied to the checked manual, not every Ditch Witch rod. Vermeer distinguishes rod from installed-product bend limits. Premier lists an overall rod length including joints, which does not establish in-ground advance.
5. The JT20 chart is a one-row illustration
With 8 ft 8 in along-path lead and 107 ft radius, the model at 18% grade gives 3.227710 ft minimum depth and 27.484960 ft setback. At nearest-inch rounding these agree with the manual chart depth of 3 ft 3 in and setback of 27 ft 6 in. The entire chart and begin-steering labels do not agree with this exact along-path model. Model minus chart differences below are in inches; they must not be represented as a reproduced full chart.
| Grade magnitude | Depth difference (in) | Setback difference (in) | Begin-steering difference (in) |
|---|---|---|---|
| 18% | -0.27 | -0.18 | -0.58 |
| 20% | -0.67 | -0.21 | -0.60 |
| 22% | -0.67 | -0.55 | -0.65 |
| 24% | -0.27 | -0.22 | -0.73 |
| 26% | -0.51 | -0.25 | -0.83 |
Other depth differences are consistent with the chart using horizontal lead times grade. The calculator retains along-path lead. Its full-plan fixture adds hypothetical exit, span and envelope inputs; those are not published chart dimensions.
6. Read the entered gap
Each measured crossing interval must fall entirely between the two level-segment breakpoints. Computed gap is D minus half the envelope diameter minus obstacle bottom depth. Margin is gap minus your required gap. Exact zero requirement is permitted; none is assumed. This arithmetic does not resolve locating uncertainty or clearance on the curves. 811 Before You Dig describes contacting the state center before digging; timing and required responses depend on location.
7. Keep the complete schedule and revision
Row zero is the entry datum. Each later row records start and end path distance, actual advance, x/depth, signed angle and pitch, pitch change, proportional allowance, slack and traversed phases. The final partial advance is labeled. Five separate breakpoint rows identify every phase end. Letter or A4 exports include all rows, units, date, identifier, revision, source basis and exclusions. The fitted schematic has different x and depth axis scales and is not a 1:1 drilling drawing. Unit switches preserve canonical measurements; invalid edits remove the report.
8. Understand the scope beside a paid planner
Vermeer publicly describes BorePlan Premium setback and exit calculations, reporting, actual-path capture and CAD-compatible or state-report-compatible exports. Its free app already advertises rod planning and overbend checks. This ToolGrit release supplies explicit one-bore paper geometry and free branded PDF/CSV; it has no as-built logs, crew projects, equipment database or proprietary export. The comparison is based on public advertised features, not a paid session, field trial or accuracy benchmark. Vermeer product description.
9. Source basis and limitations
Sources checked 2026-09-30: PPI MAB-07 geometry, Ditch Witch JT20/JT20 XP manual ID0318836_09_SVC Prepare 65-70, Vermeer BorePlan manual page 24, Premier manufacturer datasheet and NIST exact international-foot factor. The remaining five-phase, distributed-rate, clearance and numerical rules are explicitly derived model choices. No source certifies this app, rod/product suitability, utility position, steering behavior or actual field performance.