Hello Tweakie,
Thank you for you rapid response and helpful attachment.
I like your comment regarding pressing on in spite of endless setbacks. It gives me some encouragement
Mind you, we Australians regard Winston's (mis-) handling of Gallipoli as no great eventual triumph, just a disaster dressed as a victory. But back to the topic...
I have tried your suggestion regarding 'Save Files of Type' by running my Tinkercad .stl file through Meshmagic and then their Spin 3D mesh converter.
I pasted the file, in various file type suffixes, into the Load GCode window and all I find in the display window (appropriately a really gloomy black place) and all I have ever been able to find, is a group of lines with no resemblance to the model.
I don't see any lines if GCode in the window, either.
When I run the Road Runner .tap file I can (just) see the dark blue lines on the black background and the tool path trace in green when I run it. It seems to work only for .tap files.
I just don't get it. Why would a CAM program be so hostile to loading a simple mesh model. I 3D print stuff all the time and my Anycubic machine with Repetier + Slic3r, etc. and it works seamlessly and reliably. It's even intuitive!
I will try remove and reload the Mach3 program and start again from the proverbial 'square 1' , just in case there's a dud file lurking somewhere.
I have trawled through Wikipedia, etc., to try to discover the attributes of .tap files but the silence is deafening. This is amazing, considering the number of Mach3 users who (presumably) know all about it and don't need to sort out this file compatibility problem. Am I the only person with this gap in my knowledge?
All comments gratefully received, as always.
Scintilla.