My CNC engraver has progressed to the point that it is ready to use. Before buying design software, I decided to try hand coding a G code program.
The task here will be to mill the complex perimeter profile of the rear end plate (or front end ring) of a raised pillar reel. The blank will be screwed to an aluminum tooling block that is clamped to the X-Y stage.
To align the block, I have made a brass pin that goes through the block and screws into a tapped hole in the stage. A test indicator mounted to the milling spindle show total runout.
I did not buy stepper motors with double shaft extension, which would allow manual cranks for axis zero adjustment. But I find it reasonably easy to turn the screws by gripping the acme shaft collars on the thrust assembly.
To create a G code program for the outer profile, I set up an Excel spreadsheet that calculates the end points of the 20 arcs that define the profile. The top section of the spreadsheet does the calculations, and the lower part organizes the X and Y coordinates into a table that can be read as G code.
And here is the profile milled into the blank. It is not perfect; there is a visible cusp at each point where the base circle meets a fillet at each side of a lag. I was able to trace this problem to an error in the Excel spreadsheet.
To turn the spreadsheet into a G code program, I export it as a “formatted text (space delimited)”, which has extension .prn . After editing out the calculations in the top part of the file and changing the extension to .txt, the file is ready for use by a G code interpreter.
Note 3 Jan 2020: The main intended use of the CNC machine was engraving. This post shows that the intricate outline of a raised pillar end plate could also be profiled, perhaps saving much time of manual mill operation. However, I have continued to do the profile manually. As you will see in an upcoming post, I had a lot of trouble with cutters working loose from the spindle chuck. This traumatic experience discouraged further work with “heavy” milling cuts.