Is it always in the same spot on the part/program? If it is, singleblock when you get there and watch it happen.

I haven’t seen an error line this, but it might be serious. Could be a bad encoder.

As you say mach3 it’s a hobby machine and it can be a simple solution that some axis is not sunning smooth. And is you only have stepper motors it’s quite easy to have it skip a few steps and then you will have a part that isn’t ok.

The learning curve for operating a CNC Router is steep.  There is much more to learn than what is listed below (tool bits: mills and V-Bits, fixtures for holding your wood down on the spoil-board, feeds and speeds, etc.). Don’t get discouraged! Remember, all the so called “experts” you see online (i.e., YouTube) stood in your shoes at one time.

CNC Routers require that you use a certain step-by-step process in order to generate a “G-code” file (example file, GEAR.gcode). The G-code program file (i.e., “Toolpath”) tells the CNC router how to move the X, Y, and Z Axes (motors) in order to cut-out your wood design.

Here are the three software programs (CAD/CAM/CNC) and the procedure you need to follow in order to generate a G-Code program:

CAD ———>CAM——–>CNC

Drawing —->Toolpath—->Control Software (runs the G-code program to move X, Y, and Z-Axis)

STEP-BY-STEP PROCEDURE TO CREATE A G-CODE PROGRAM FILE (i.e.,”TOOLPATH”):

You need to create your design in a CAD program like Fusion 360, Vectric’s ‘Cut 2D Desktop’, or some free CAD program online. Some CAD programs like Vectric’s Cut 2D combine the CAD and CAM functions into one software package.

Next, you ‘Export’ or ‘Save’ your finished CAD drawing as a ‘.dxf’ file. This ‘.dxf’ file is the file you import into a CAM program in order to generate a “G-CODE” program file (i.e., “Toolpath” file). A G-code program is just a list of instructions that tells your CNC Control Software how to move the X, Y, and Z axes in order to cut-out your design. [Note: Just make sure you select (in the CAM software settings) the correct “Post Processor” for your particular CNC router. In other words, the CAM software needs to know what CNC router (Model) you are using in order to generate the correct G-code file (i.e.,‘Toolpath’) for your machine].

Next, you load the G-code file (GEAR.gcode) into your CNC Control software (for example, Mach ³⁄₄, UGS, etc.).

Next, setup and clamp down your material (wood) onto your spoilboard (waste board– sits on your table).

Next, using a “Z- Setter Probe” or the “Paper Method”, you lower the Z-Axis (tool bit) to the lower left-hand corner or the center location of the workpiece (wood) as your “Part Zero” location. In other words, you lower the tip (i.e., center) of your tool bit to the corner of your workpiece and then individually zero-out the X, Y, Z buttons on your DRO (Digital Read Out display). Do NOT zero out the “Home” button at this time. Also, make sure you select the ‘Top’ surface of your workpiece in your CAD/CAM software as the starting point of the cut.

Next, you return the spindle/router to the “Home” position (Machine Zero)–that’s where the spindle goes to when you first turn on the machine. Also make sure you check that your ‘Work Offset’ setting (see CNC Control Software menu) is still set to G54–this is usually the default setting on most machines.

Finally, load the GEAR.gcode program into your CNC control program (MACH ³⁄₄ for example) and hit ‘Run’. Your router will move from the Home position (Machine Zero) to the Part Zero position on your workpiece (corner or center of the wood). The Z-Axis will lower the tool bit to the surface of your workpiece and begin to cut out your design. Done!

Here’s an old article I wrote just for beginners - (NOTE: This article is a little dated, but it will teach you the basics of using a CNC router):

https://www.servomagazine.com/magazine/article/beginners-guide-to-cnc-routers

Because the toolpath preview inside Mach3 itself is shifting and ~300 is popping into the A-axis DRO, something is corrupting Mach3’s work offset registers mid-run rather than the steppers mechanically losing steps. On an RNR EcoMotion 2.0 USB board, static shocks from a plastic wood-dust vacuum hose or spindle VFD interference over an unshielded USB cable will scramble packets into RnRMotion.dll and dump garbage into G54 and the A DRO, and if A-Rotations Enabled is checked inside Config -> ToolPath, any random number in the A DRO rotates the toolpath display diagonally on screen. Ground your dust hose, uncheck A-Rotations Enabled in Config -> ToolPath, and if it still happens, temporarily move Mach1Lic.dat out of C:\Mach3 to test in Demo mode in case the machine shipped with a blacklisted license file.