What moves, and why

“144-60” is the nominal sheet class, not the footprint. The 2023 specification sheet lists a 153 × 61 × 8 in (3.89 × 1.55 × 0.20 m) movement area and a 168 × 91 × 67 in (4.27 × 2.31 × 1.70 m) footprint; the May 2022 assembly guide still describes the conventional 6 in (152 mm) Z, with 12 in and 24 in tall-Z options.[1,2] These are catalogue reference dimensions, not usable clearance for a job. Before running a tall setup, have staff check that the stock, fixtures, tool length and retract height fit. Do not disable limits.

table

bolted steel legs and supports with aluminium T-slot side extrusions; not a welded one-piece frame. Base layer 3/4 in plywood on 3/8 in carriage bolts, replaceable 3/4 in MDF spoilboard on top.[1,2,3]

rails

hardened steel V-rails with V-roller bearings on X and Y; eccentric rollers set the preload on the YZ car. Z rides a captured rail on five bearings per side (three concentric, two eccentric).[1,13,18,19]

drive

rack and pinion on all three axes, including Z. Two X motors (one per side), one Y, one Z. Pinions: 30 teeth on X and Y, 25 on Z. Gearboxes 7.2:1 low-backlash tapered-hob.[1,2,27]

motors

This machine uses Oriental Motor ARM98AC-T7.2 alphaStep closed-loop steppers. Feedback is at the motor shaft — not at the rack, the bit or the workpiece.[2,23,27]

resolution

2482.8 steps/in on X and Y (0.0004 in ≈ 0.010 mm), 2979.4 steps/in on Z, resolution multiple 5.[1,27]

speed

positioning 1800 in/min (30 in/s, 762 mm/s) XY and 900 in/min Z; up to 720 in/min (12 in/s) XY and 360 in/min Z under full cutting force; about 150 lbf of cutting force at 60 in/min.[1]

control

Windows PC → USB → PRSalpha control box (control board, four drivers, contactors) → motors. Files are OpenSBP .sbp text. 8 inputs / 8 outputs at 5 V logic (~5 mA). This machine's control box: Alpha control Box Model# 10372, firmware 224; SB3 version 3.8.70.[1,2,10,11]

spindle

Spindle: HSD AT/MT 1073-140. Nameplate rating: 3 kW S6, 220 V three-phase, 300 Hz, 18,000 rpm, 13 A. S6 is an intermittent periodic duty rating, not an S1 continuous-power claim, and 18,000 rpm is the nameplate operating speed, not a confirmed maximum. Spindle controller: Yaskawa V1000, CIMR-VU2A0020GAA. ER25 collets with their matching nut. 24 V cooling fan. (ShopBot's packages: HSD 2.2 or 4 HP, or Colombo 5 HP.)[2,20,21,41]

sensors

input 1 Z-zero plate, input 2 X proximity, input 3 Y proximity, input 4 stop circuit, input 5 Z proximity; output 1 spindle, output 4 safety/spindle-enable.[2]

2 · How the mechanisms work

The gantry (X)

The bridge is an aluminium extrusion between two end plates. Each plate hangs four V-rollers on the hardened rail that runs along the top of the side plate; two ride above, two below, so the car cannot lift. A motor on each end plate sits on a hinged mount pulled by a spring (3.5 turns past contact on spring mounts; on bolted motor plates, hold the pinion into the rack with 15–20 lb while tightening the four plate screws) so its pinion stays pressed into the rack on the outside of the side plate.[2,13] Both X motors receive identical step trains. If one side stalls, its driver alarms and everything stops. If a pinion jumps teeth or slips on its shaft, the motor still turns the commanded amount: the bridge racks out of square silently.

The car (Y) and the Z plate

The YZ car repeats the same idea rotated 90°: rollers on a V-rail across the face of the beam, one motor on a pinion in the beam's rack. The Z plate rides one captured rail between two rows of five V-bearings (three fixed, two eccentric) per side and is lifted by a vertical rack — no leadscrew — so it moves at the same 7.2:1 ratio as the other axes. Because the gear train back-drives, Z can drop when unpowered; never push any axis by hand with the motors connected — position is lost and the drivers can be damaged.[2,18,27] Too tight on the Z eccentrics means binding and lost position; too loose means a lateral slop you will see as a bad fourth side on every pocket.[18]

Closed loop, but closed around the motor

An alphaStep motor runs open-loop until rotor position deviates by ±1.8° from command; at that point the driver switches to closed-loop correction. If correction cannot hold (an obstruction, a wrong feed, a damaged cable), the driver alarms, the control board stops everything, and the software says the location is no longer accurate.[1,22,23,30] Red LED blink codes on the AS driver: 1 overheat (~85 °C heatsink), 2 overload (>5 s above max torque), 3 overvoltage, 4 speed error, 5 overcurrent, 6 overspeed, 7 EEPROM, 8 sensor.[22] What the loop cannot see: a pinion slipping on its shaft, a bit creeping in the collet, or a sheet moving under the clamps.

Spindle and VFD

The VFD makes the spindle's three-phase supply; the control box only tells it on (output 1 through the key interlock and the pendant Start) and, on packages with the RPM controller, how fast (the TR window or TR,12000 in a file, SB3.5.5 or newer).[4,21,53] The lab's full sequence: the screen prompts “Press START on control before pressing OK” → pendant Start → check the spindle runs at the commanded speed → OK → cutting begins. There is no separate RUN step on the VFD.[4] Warm-up (C5, the lab's standard routine): 9000, 10 000 and 12 000 rpm for 3 min each at the start of the day or after more than 4 h idle.[4,13] Chipload = feed ÷ (rpm × flutes); the figure runs a 6 mm two-flute bit at 60 mm/s and 12 000 rpm, 0.15 mm per tooth.[11]

Zeroing and homing

C3 drives to the X and Y proximity switches and backs off to the configured home. C2 touches the Z-zero plate twice; input 1 must light when plate meets bit and clear when they separate. Zero can be the material top or the table surface — it has to match what the CAM post expects. If CAM assumed the stock top and you zeroed on the bed, every rapid and retract runs inside the material and every cut goes a sheet thickness into the spoilboard: crashes and broken bits. The reverse mismatch cuts air. Check &PWZorigin in the file header against the surface you touched.[4,6] In this lab the ground clip stays clamped on the aluminium carriage plate; the circuit runs through plate → spindle → collet → bit, and C2 is the only way students zero Z. Z2 sets a temporary job origin where the tool stands; SA/SR switch absolute/relative, and units are set in Values → Display (VD), not by any of those.[10,47]

Dust extraction and hold-down

The brush skirt under the spindle is clamped to the spindle collar; a 4 in flex hose runs to the collector. The dust collector is switched manually at the collector itself and is on whenever the spindle runs.[13] Hold-down is a separate matter and, in this lab, mechanical only: screws into the spoilboard through the waste, clamps and shims for bowed stock, and tabs or an onion skin of 0.25–0.75 mm for every part that will be freed from the sheet.[12]

“144-60” is the nominal sheet class, not the footprint. The 2023 specification sheet lists a 153 × 61 × 8 in (3.89 × 1.55 × 0.20 m) movement area and a 168 × 91 × 67 in (4.27 × 2.31 × 1.70 m) footprint; the May 2022 assembly guide still describes the conventional 6 in (152 mm) Z, with 12 in and 24 in tall-Z options.[1,2] These are catalogue reference dimensions, not usable clearance for a job. Before running a tall setup, have staff check that the stock, fixtures, tool length and retract height fit. Do not disable limits.

table

bolted steel legs and supports with aluminium T-slot side extrusions; not a welded one-piece frame. Base layer 3/4 in plywood on 3/8 in carriage bolts, replaceable 3/4 in MDF spoilboard on top.[1,2,3]

rails

hardened steel V-rails with V-roller bearings on X and Y; eccentric rollers set the preload on the YZ car. Z rides a captured rail on five bearings per side (three concentric, two eccentric).[1,13,18,19]

drive

rack and pinion on all three axes, including Z. Two X motors (one per side), one Y, one Z. Pinions: 30 teeth on X and Y, 25 on Z. Gearboxes 7.2:1 low-backlash tapered-hob.[1,2,27]

motors

This machine uses Oriental Motor ARM98AC-T7.2 alphaStep closed-loop steppers. Feedback is at the motor shaft — not at the rack, the bit or the workpiece.[2,23,27]

resolution

2482.8 steps/in on X and Y (0.0004 in ≈ 0.010 mm), 2979.4 steps/in on Z, resolution multiple 5.[1,27]

speed

positioning 1800 in/min (30 in/s, 762 mm/s) XY and 900 in/min Z; up to 720 in/min (12 in/s) XY and 360 in/min Z under full cutting force; about 150 lbf of cutting force at 60 in/min.[1]

control

Windows PC → USB → PRSalpha control box (control board, four drivers, contactors) → motors. Files are OpenSBP .sbp text. 8 inputs / 8 outputs at 5 V logic (~5 mA). This machine's control box: Alpha control Box Model# 10372, firmware 224; SB3 version 3.8.70.[1,2,10,11]

spindle

Spindle: HSD AT/MT 1073-140. Nameplate rating: 3 kW S6, 220 V three-phase, 300 Hz, 18,000 rpm, 13 A. S6 is an intermittent periodic duty rating, not an S1 continuous-power claim, and 18,000 rpm is the nameplate operating speed, not a confirmed maximum. Spindle controller: Yaskawa V1000, CIMR-VU2A0020GAA. ER25 collets with their matching nut. 24 V cooling fan. (ShopBot's packages: HSD 2.2 or 4 HP, or Colombo 5 HP.)[2,20,21,41]

sensors

input 1 Z-zero plate, input 2 X proximity, input 3 Y proximity, input 4 stop circuit, input 5 Z proximity; output 1 spindle, output 4 safety/spindle-enable.[2]