FANUC Robodrill α-D21MiB Plus
Key Specifications
X Travel
Y Travel
Z Travel
Spindle Taper
Tool Capacity
Table Size
Overview
The FANUC Robodrill α-D21MiB Plus is the medium-bed variant with 500 x 400 mm X/Y travel, balancing work envelope and compactness in FANUC’s latest-generation RoboDrill α-DiB Plus lineup. The RoboDrill has been the industry benchmark for high-speed compact machining since the 1970s, and this Plus-generation model represents the most refined iteration of the platform to date.
Tool-to-tool changes happen in 0.9 seconds with chip-to-chip time of 1.5 seconds. The standard spindle runs at 10,000 RPM with a 24,000 RPM high-speed option available for aluminum-dominant work. Rapid traverse hits 54 m/min (2,125 ipm) across all axes, ensuring minimal positioning time between features. The 21-position servo-driven turret magazine provides rapid tool indexing that is fundamental to the RoboDrill’s cycle time advantage over conventional VMCs.
The FANUC 31i-B Plus control delivers reliable CNC operation with high-speed look-ahead, AI contour control, and nano interpolation for superior surface finish quality. While this model uses the 3-axis-optimized control, rotary table options are available for 4th-axis work.
The Plus designation marks the latest generation of the RoboDrill platform, incorporating updated servo drive technology, improved thermal stability, and enhanced control features over the previous iB generation. With over 500,000 RoboDrills installed worldwide, this platform has the deepest production track record of any compact machining center, and the Plus generation builds on that foundation with measurable improvements in acceleration, surface finish quality, and energy efficiency.
New pricing for the FANUC Robodrill α-D21MiB Plus typically ranges from $85,000 - $135,000 depending on spindle configuration, automation packages, and options. Methods Machine Tools is the primary North American distributor, providing sales, service, applications engineering, and turnkey automation cell integration. The RoboDrill competes directly with the Brother Speedio series and Haas DT/DM series, and remains the first choice for production shops where cycle time and uptime drive profitability.
Full Specifications
| Parameter | Value |
|---|---|
| X-Axis Travel | 500 mm (19.7 in) |
| Y-Axis Travel | 400 mm (15.7 in) |
| Z-Axis Travel | 330 mm (13.0 in) |
| Table Size | 650 x 400 mm (25.6 x 15.7 in) |
| Max Table Load | 200 kg (441 lb) |
| Spindle Speed | 10,000 RPM (24,000 RPM optional) |
| Spindle Motor Power | 14.2 kW (19 hp) peak; 26 kW (35 hp) peak @ 24K RPM option |
| Spindle Torque | 12 Nm continuous; 100 Nm max (high-torque option) |
| Spindle Taper | BT30 / BBT30 |
| Tool Capacity | 21-position turret |
| Tool Change Time | 0.9 sec (tool-to-tool), 1.5 sec (chip-to-chip) |
| Max Tool Length | 250 mm (9.8 in) |
| Max Tool Diameter | 80 mm (3.1 in) |
| Max Tool Weight | 3 kg (6.6 lb) |
| Rapid Traverse Rate | 54 m/min (2,125 ipm) all axes |
| Positioning Accuracy | ±0.003 mm (±0.00012 in) |
| Repeatability | ±0.002 mm (±0.00008 in) |
| CNC Control | FANUC 31i-B Plus |
| Machine Weight | 3,900 kg (8,598 lb) |
| Floor Space Required | 2,050 x 1,750 mm (80.7 x 68.9 in) |
| X Axis | 300 |
| Y Axis | 300+100 |
| Z Axis | 400 |
| Tool Storage Capacity | 28 tools |
| 14 Tools | α-D14SiBADVPlus |
| 21 Tools | α-D21SiBADVPlus |
| Spindle Spec | Max. speed |
| Standard | 10000 min-1 |
| High Torque | Heavy machining of steel parts (Max. 100N·m) |
| High Acceleration | High speed and high efficiency machining of aluminum parts |
| Tapping | 12000 min-1 |
| High Speed | 24000 min-1 |
Specifications sourced from fanuc.co.jp — verified 2026-03-28
Strengths & Limitations
Strengths
- 0.9-second tool-to-tool changes remain faster than virtually all conventional VMCs, delivering meaningful cycle time savings across production runs
- Lower entry price than ADV models while maintaining the same core RoboDrill speed and reliability platform
- 54 m/min rapid traverse on all axes minimizes non-cutting time, compounding with fast tool changes for industry-leading cycle times
- 21-position servo-driven turret provides ample tool capacity for most production parts without the complexity of a side-mount magazine
- 31i-B Plus control delivers proven reliability with AI contour control and nano interpolation for excellent surface finish quality
- 500 x 400 mm work envelope balances part size capability with compact footprint, fitting the widest range of small-to-medium production parts
Limitations
- BT30 taper limits rigidity for aggressive roughing in steel and hardened materials — this platform excels at speed, not heavy metal removal
- FANUC 31i control has a steeper learning curve than Haas NGC or Mazak SmoothG, requiring dedicated training for shops transitioning from those platforms
- 500 mm X-travel may be insufficient for longer parts that would fit on the L-body variant with 700 mm reach
- 200 kg table load can be limiting with heavy steel tombstones or multi-vise production fixtures
Best For
Frequently Asked Questions
01
The Plus generation brings updated servo drive technology for improved acceleration and deceleration, enhanced thermal stability management, and control software updates on the FANUC 31i platform. The mechanical platform is largely carried over, but the cumulative improvements in servo performance and control processing deliver measurably shorter cycle times on complex parts with many tool changes and positioning moves.
02
The RoboDrill’s key advantage is its servo-driven turret with sub-1-second tool changes, compared to 1.4 seconds on the Brother Speedio and 2.2 seconds on the Haas DT-2. Rapids are also faster at 54 m/min versus 50 m/min (Brother) and 30.5 m/min (Haas). The Haas wins on price (~$50K) and Z-travel (508 mm).
03
Yes, but with appropriate expectations. The BT30 taper limits cutting forces compared to 40-taper machines. Production shops regularly cut mild steel, 4140, stainless steel, and even titanium on RoboDrills using lighter depths of cut at higher speeds. For heavy stock removal in hardened steels, a 40-taper VMC is more appropriate.
04
Methods Machine Tools is the primary North American distributor for FANUC RoboDrills. They offer sales, service, applications engineering, and automation integration through locations across the US. FANUC also has direct service capabilities through their network. Used RoboDrills are widely available through machinery dealers, and the large installed base means independent service providers are common.
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