CNC Retrofitting

Bringing an old manual or earlier-generation CNC machine onto modern controls. The two dominant FOSS paths are LinuxCNC + Mesa FPGA cards (for serious iron — Bridgeports, retrofit knee mills, Hardinge lathes) and GRBL/FluidNC (for benchtop conversions — PM-25, G0704, Sieg X2/X3). Paid options dominate on the prosumer side: Centroid Acorn for benchtop retrofits, PathPilot if you bought a Tormach, Mach3/4 if you're on the Windows track. See Controllers & Firmware for the firmware story and Spindles & VFDs for motor electronics.

Retrofit targets (the iron)

• ★ Bridgeport Series I / II knee mills — the iconic retrofit candidate. Boss-series old CNCs are usually scrapped for control; the iron underneath is excellent. Standard recipe: strip the original control, fit ball-screw conversions (front and side), drop in Yaskawa servos + Mesa 7i77 + LinuxCNC.
• ★ PM-25 MV / PM-30 MV / Grizzly G0704 / Sieg X2/X3 — Chinese-import benchtop mill family; the most-converted hobby mill. Ball-screw kits available from CNC4PC, ArizonaCNC. Common control: Centroid Acorn or Mach4 with closed-loop steppers; LinuxCNC less common but works.
• Tormach 1100 (older) / 770 (older) — Tormach-original conversions to LinuxCNC + Mesa for users who want full control. Modern Tormachs ship with PathPilot which is already LinuxCNC under the hood.
• Hardinge HLV-H / HC — manual toolroom lathes; LinuxCNC retrofits common.
• Hurco / Fadal / Matsuura / Cincinnati VMCs — older industrial VMCs scrapped for control; Mesa + LinuxCNC retrofits documented but not for the faint of heart. Centroid Hickory is the paid path.
• Sherline / Taig — micro-mill / lathe; LinuxCNC stepper retrofits trivial; many ship "CNC-ready."

Motion-control hardware

• ★ Mesa Electronics 7i96s / 7i76e / 7i92 — paid (~$200–350); the FOSS retrofit standard. FPGA-based step/dir + I/O cards talking to LinuxCNC over Ethernet or PCI. The 7i96s is the modern entry point.
• ★ Mesa 7i77 / 7i48 — paid; analog ±10V cards for closed-loop AC/DC servo retrofits. Pair with Yaskawa, Delta, Mitsubishi servo drives.
• Mesa 5i25 / 7i85S — paid; older PCI-bus options; still supported.
• Pico Systems USC / PPMC / PWM Servo — paid; older parallel-port-derivative; mostly legacy.
• Galil DMC-21x3 / DMC-30x10 — paid; commercial industrial controllers; LinuxCNC has Galil drivers, but Galil's own software is the typical path.
• PMDX-126 / PMDX-411 — paid; parallel-port breakout boards; legacy.

Retrofit kits (turnkey)

• ★ Centroid Acorn retrofit kit — paid (~$300 board + ~$300 software + accessories); the prosumer Mach3-killer for benchtop conversions. Strong support for PM-25/30, G0704, Grizzly G0759, Bridgeport (small). Windows-based; CNC12 is their software. Excellent docs.
• Centroid Oak / Hickory — paid; bigger retrofits (Bridgeport, knee mills, VMCs). Hickory is the modern flagship.
• Mach Motion / Ajax CNC — paid; turnkey Mach3/4 + servo + breakout retrofit kits; midwest US suppliers.
• DDCSV / Newker — paid, cheap; standalone retrofit controllers; common on Chinese 6040/6090 conversions.
• MASSO G3 — paid (~$1100); standalone touchscreen controller; turnkey on benchtop and small VMC retrofits. See Controllers.

Servo / closed-loop retrofit electronics

• ★ Yaskawa Sigma-7 — paid; the gold-standard AC servo for retrofits. Documentation, used market, parts availability all excellent.
• Delta ASD-A2 / B2 — paid; mid-range AC servo; popular on prosumer benchtop.
• Mitsubishi MR-J4 / J5 — paid; industrial; common on machine-tool retrofits.
• AMC / Glentek / Centroid DC drives — paid; for older DC-servo machines.
• Teknic ClearPath — paid; USA-made integrated servo; the "drop-in step/dir replacement for steppers" path on benchtop. See Spindles & VFDs.
• See Spindles & VFDs for stepper-side electronics.

Conversion mechanics

• Ball-screw conversion kits — paid (~$500–2000); replace ACME lead screws with double-nut ball screws; major rigidity / backlash improvement. Vendors: Linear Motion Bearing Industries (LMBI), CNC4PC, ArizonaCNC, CNC Fusion (kit-form).
• Linear rail upgrades — for older box-way mills; HiWin / PMI / NSK profile rails.
• Spindle upgrades — VFD swap on existing AC motor, or full ATC spindle (rare for hobby).
• Spindle encoders — required for rigid tapping in LinuxCNC; US Digital E5 / E6 encoders.

Documentation / community resources

• CNCZone "Open Source CNC Design Center" / "LinuxCNC" subforums — the canonical retrofit knowledge base.
• Practical Machinist "CNC" forums — for serious iron retrofits.
• LinuxCNC Forum (forum.linuxcnc.org) — the official community.
• Tormach community — for owner-driven Tormach upgrades.
• John Saunders / NYC CNC retrofit videos — popular reference content for PM-class conversions.
• Machsupport.com — Mach3/4 retrofit forums.

Software stack on the retrofitted machine

• LinuxCNC + QtPyVCP / probe-basic / GMOCCAPY — open source; the modern UIs. See Controllers & Firmware.
• Centroid CNC12 — closed source, paid; ships with Acorn / Oak / Hickory.
• Mach3 / Mach4 — closed source, paid; for the Windows retrofit path.
• PathPilot — closed source, free for Tormach owners; LinuxCNC underneath.

Pick this if…

• Bridgeport Series I retrofit, no closed-control needed: LinuxCNC + Mesa 7i96s + closed-loop steppers (or Yaskawa servos with 7i77).
• PM-25 / G0704 conversion, want supported software: Centroid Acorn.
• PM-25 / G0704 conversion, want FOSS: LinuxCNC + Mesa + JMC closed-loop steppers.
• Tormach owner, stick with PathPilot unless you actually need a custom UI.
• Old industrial VMC with working servos / drives: LinuxCNC + Mesa 7i77 — keep the existing servos.
• Just want a touchscreen and a working machine: MASSO G3 — non-FOSS but very low fuss.