Tool Length Probe Error Analysis

Tool Length Probe Error Analysis

Automatic tool length probing avoids manual measurements and touch offs and helps verify lengths already in the tool table. Probing tool-length offsets is done into LinuxCNC with an automatic tool length sensor. The sensor has two electrical connections to a Mesa 7i76e board for detecting the tool and for protecting against over travel, and an air solenoid controls an air blast to clear chips between the probe and tool. Reproducibility on a CNC retrofitted mill is high but accuracy is so-so. A good amount of the video is the analysis of sources of error.

The analysis code (Python) and raw data are available. I don’t plan to clean them up or post them to GitHub, but will send them to anyone who asks.

Chapters
00:00 – Introduction

03:08 – Initial testing

04:27 – Backlash and homing error

07:07 – Spindle nose error

08:28 – Modeling tilt error

10:06 – Tramming

12:05 – Probe elevation

13:07 – Following-error

15:14 – Error modeling

18:21– Closing thoughts

GitHub repository of LinuxCNC config and routines.

Full project notes on Notion.

Parts from Amazon (affiliate links):
Automatic Tool Sensor
Air solenoid
Silicone Tubbing 2mm ID x 4mm OD

Parts from McMaster:
51835K232 D.O.T. Brass Compression Tube Fitting for Air, Straight Adapter, for 1/4″ Tube OD x 1/4 NPTF Male
62005K133 Air Flow Control Valve, Elbow, 1/4″ Push-Connect Female Inlet x 1/4 NPT Outlet
5097T41 D. O. T. Hard Nylon Plastic Tubing for Air Opaque Black, 11/64″ ID, 1/4″ OD, 25 ft.
4429K412 Low-Pressure Brass Threaded Pipe Fitting, Bushing Adapter with Hex Body, 3/8 Male x 1/4 Female NPT
4464K562 Low-Pressure 302 Stainless Steel Plug with Hex Drive, 1/4 NPTF
5975K12 Aluminum Right-Angle Flow Rectangular Manifold, Anodized, 4 Outlets on 1 Side, 3/8 NPT, 6-1/4″ Long
4450K3 Muffler, 3/8 NPT Male, Steel, 23 scfm @ 100 PSI Maximum Flow Rate
47865K22 Brass On/Off Valve with Lever Handle, 3/8 NPT Female
44615K463 Standard-Wall Steel Pipe Nipple, Threaded on Both Ends, 3/8 NPT, 4″ Long

Parts from Northern Tools:
Milton M-Style Safety Coupler — Push Button, 1/4in. MNPT, Model# S99706