WS39 casing tooth
JM cutter tooth
B47K22 bullet toothAround 35–50 metres is a practical field-experience reference for a set of MH-3 roller bits working in granite at approximately 100–150 MPa. This range comes from DRILLNOVA’s past site feedback. Use it as a starting point for planning; the barrel arrangement, rock abrasivity, drilling practice and cutter condition affect the result.
01 / FIELD EXAMPLE
Zengcheng: 1,200 mm barrel, 10 MH-3 roller bits
At this Guangzhou site, the customer’s existing core barrel was rebuilt with 10 MH-3 roller bits—five inner and five outer—and four scrapers. It worked on a SANY 415R rig. The June–August 2022 follow-up reached approximately 57 m of cumulative drilling.
The first visit described monzogranite / granite-amphibolite and estimated strength at 100–200 MPa. Later notes recorded weathered mudstone through moderately and slightly weathered gneiss. These are site descriptions, rather than laboratory UCS results for one uniform rock interval.
The case therefore adds a real barrel configuration and drilling history to the 35–50 m experience reference above.
02 / RECORDED METRES
What did the site record?
| Inspection date | Cumulative advance |
|---|---|
| 26 August | ≈45.9 m |
| 30 August | ≈51 m |
| 31 August | ≈57 m |
The 45.9 m total combines 35.9 m in earlier records + approximately 4 m estimated for four unlogged piles + 6 m drilled on 24–25 August. The later totals are rounded site updates.
At about 45.9 m, the position-by-position inspection identified three roller bits needing replacement. The complete replacement timing is not recorded, so the 57 m total describes the barrel’s cumulative work, not a verified unchanged-set life.
03 / CONDITION IN SERVICE
Real wear at two inspection stages
The photographs show different positions at the two inspections; they do not track one identified roller bit over time. Condition differed by position: outer 2 and inner 2 had seized bearings; outer 3 had more insert breakage. The review identified these three for replacement while assessing the other positions individually. See all ten inspection positions in the complete case.
04 / OPERATING CONTEXT
The operating record behind the metres
On 1 July, the depth display moved from 22.67 m to 27.46 m: 4.79 m of advance between 12:59 and 18:24. That is the complete work window, including interruptions and handling, rather than continuous cutting time.
The same entry recorded 6–7 rpm on initial rock entry, then 8–10 rpm after stable contact. These are settings recorded on that rig and job, not universal operating instructions. The field review also addressed cuttings removal and fragments left after core recovery.
For your own project, start with the 35–50 m MH-3 reference for 100–150 MPa granite, then compare the barrel diameter, cutter count, rock condition and operating sequence. Record replacements by position so that cost per metre uses the actual cutters consumed and the corresponding drilled interval.
05 / COST PER METRE
How do you calculate roller-bit cost per metre?
Roller-bit cost per metre = cost of roller bits consumed in the recorded interval ÷ metres drilled in that same interval. Use actual replacement and drilling records. The 35–50 m experience range is a planning reference; it does not establish the cost achieved on your job.
| Record | What to include |
|---|---|
| Ground and advance | Pile or hole ID, depth from and to, rock description, actual metres, barrel diameter and rig. |
| Roller bits consumed | Model, numbered position, installation and removal points, quantity, unit cost and reason for replacement. Account consistently for cutters already partly used at the start or still usable at the end. |
| Other tool costs | Record removal, fitting or welding, and repair separately. If downtime is costed, state the time and rate used; keep this distinct from cutter-only cost. |
| Basis for comparison | Use the same currency, cost scope and drilling interval. Pair the record with wear photos and note changes in ground or operating method. |
A barrel’s cumulative advance does not show how far every individual roller bit has worked. The Zengcheng record does not contain a complete replacement-cost ledger, so it supports a field review rather than a verified cost-per-metre figure.