CNC Maintenance & Calibration

The "keep it cutting accurately" page. Hobby CNC machines drift: dust packs into bearings, V-wheels loosen, lead-screws backlash. Lubrication and periodic recalibration are the difference between a 0.05mm machine and a 0.5mm one. Ties to Workholding (squareness), Touch Probes (calibration via probing), and Spindles & VFDs (VFD parameter tuning).

Way / linear-motion lubrication

• ★ Mobil Vactra No. 2 way oil — paid; the canonical mill way oil; ISO VG 68 with tackifiers that cling to vertical surfaces. Standard on Bridgeports, PM-25/30, G0704. Apply with an oil can or one-shot Bijur system.
• Vactra No. 4 — heavier viscosity; for bigger machines.
• Mobilgear 600 XP / Shell Omala — paid; gear-lube grade for ball-screws and reducers.
• Mobil Polyrex EM grease — paid; the standard for ball-bearing pre-pack and motor bearings.
• Way-oil pumps (Bijur Delimon, Lube-USA) — paid; one-shot meter that pulses oil to multiple zones.

Ball-screws

• ★ Ball-screw greasing — typical hobby ball-screws (1605, 1610, 2010) want grease, not oil. NSK NS7 / THK AFB-LF preloaded grease, or generic NLGI #2 with EP additive. Grease at every nut every 50–100 hours.
• Ball-screw vs. lead-screw: lead-screws (ACME, trapezoidal) are cheaper and self-locking but have backlash and slip; ball-screws are precise (sub-0.01mm preloaded) and efficient but can back-drive. Most hobby benchtop conversions move from ACME to ball-screw as a primary upgrade.
• Anti-backlash nuts — for ACME lead-screws; double-nut + spring; reduces but doesn't eliminate backlash.
• Ball-screw alignment — misalignment kills ball-screws fast. DTI-and-mandrel alignment procedure during install; pinned bearing blocks.

V-wheel routers (Shapeoko, OpenBuilds, X-Carve)

• ★ Eccentric nut adjustment — V-wheels ride on aluminum extrusion; eccentric nuts on one side adjust preload. Loose = play; tight = early bearing wear. Should rotate freely under finger pressure but not have visible movement.
• V-wheel cleaning — wipe extrusions weekly; chips embed in the wheel rubber. Carbide 3D / OpenBuilds sell replacement wheels (~$3 each).
• Belt tension (belt-drive routers) — should "twang" at finger pluck; over-tension wears teeth, under-tension causes lost steps. Vendors publish target tension (Shapeoko: ~12 lb on the X belt).

Backlash compensation

• Measure backlash — DTI on the spindle, jog +1mm, mark, jog -1mm, read; the difference is backlash. Repeat per axis.
• GRBL / FluidNC: no native backlash compensation; users insert it via macros or accept it.
• grblHAL: optional backlash plugin.
• LinuxCNC: native backlash via BACKLASH = X.XXX in INI.
• Mach3 / Mach4: native backlash compensation in motor tuning.
• Centroid CNC12 / PathPilot: native.
• The right answer: compensate ≤0.05mm; replace the leadscrew if more.

Squareness / geometry calibration

• ★ 3-4-5 triangle / diagonal check — cut a square, measure diagonals, adjust frame. The hobby standard squareness check.
• Tramming the spindle — using a tramming bar / Edge Technology Pro Tram; ensures spindle perpendicular to the bed. Critical on benchtop mills with movable heads (PM-25/30).
• Surfacing the spoilboard — re-surface MDF spoilboard yearly; restores the bed flatness reference.
• Nut-block adjustment — ball-screw nuts often have shims for fine alignment.

Stepper / motor calibration

• Steps per mm calibration — command 100mm, measure actual; adjust $100/$101/$102 (GRBL) or equivalent. Critical after lead-screw / pulley swaps.
• Motor current tuning — too low = lost steps under load; too high = overheating. Set to ~70–80% of motor rated current; verify motor body stays under 70°C in service.
• Microstepping — most drivers default 16 or 32 microsteps; higher microstepping is smoother but reduces effective torque. 8–16 is the hobby sweet spot.
• VFD parameter setup — Huanyang / Hitachi require setting motor pole-pair, rated current, max RPM, accel/decel. Vendor-specific docs; community guides fill the gaps.

Home / soft-limits configuration

• Home offset — distance from limit switch to machine zero; calibrate per machine.
• Soft limits — controller-side travel limits; prevent crashing into limit switches under jog. Always enable.
• Work coordinate systems (G54–G59) — machine zero (homing) is fixed; work zero (G54+) moves per-job. Hobby workflow: home machine, probe stock, set G54 to stock corner.

Spindle / runout checks

• Spindle runout — DTI on a precision pin in the collet; <0.01mm is acceptable hobby; <0.005mm is good; <0.002mm requires premium spindle. Trim routers (Makita) typically run 0.02–0.05mm runout. Chinese 2.2kW water-cooled often hit <0.01mm with quality ER20 collets.
• Collet cleanliness — chips behind a collet kill accuracy faster than worn bearings.
• Bearing replacement — water-cooled spindles want bearing replacement every 1000–2000 hours; Makitas die first at the brushes (~500 hours of moderate use).

Coolant / chip management upkeep

• Coolant concentration — semi-synthetic coolants want 5–10% concentration; check with a refractometer. Sour coolant smells; replace yearly.
• Chip clearing — daily on mill (chips trap moisture against ways).
• See Dust & Coolant.

Documentation / log-keeping

• Maintenance log — printed checklist + Sharpie on the machine; tracks lubrication date, belt tension check, spindle hours. Plain text in a notebook beats no log.
• Tormach PathPilot maintenance reminders — built-in; tracks spindle hours and prompts you.
• Centroid CNC12 alarms — periodic maintenance reminders.

Pick this if…

• Stock Shapeoko / Sienci / OneFinity, want to keep it accurate: weekly: clean V-wheels and rails, check belt tension. Monthly: tram the spindle, check eccentric nuts. Yearly: surface the spoilboard.
• Benchtop mill (PM-25, G0704, Tormach 440): Vactra No. 2 on ways daily, ball-screw grease quarterly, backlash check yearly, tram the head whenever something feels off.
• Bridgeport retrofit: Bijur one-shot every cycle, full ball-screw service yearly, full backlash + squareness check yearly.
• Started losing steps: raise driver current 10%, check belt tension, tighten couplers, ferrites on motor leads. See Wiring & Electrical.
• Cuts going out of square: 3-4-5 diagonal check, retram, resurface the spoilboard.