Problem- x2 accuracy issues

[neilw20]

CNC stuff is usually accurate but there are or can be a few gotchas with rounding.

Often internally, like calculating the actual center of a circle, precision is required, so that end points don't go wonky.

I have discovered a few simple rules that work for me.

When drawing use at least one more decimal place than the accuracy of the machine.
ie. Machine OK at 0.001", draw like in autocad, to 0.0001" you will soon see rounding errors you did not expect.

In metric, do similarly with an extra decimal place.
Although your task may not need the precision, you can't input garbage into the machine, like an vertical line that is not.
3.1 is not equal to 3.0009 as far as an internal calculation is concerned, just proves 3.1 is not equal to 3.1 and now the machine tries to faithfully do what it is told but does something skewed, where you wanted it vertical.

Graphically creating drawings all with a mouse (read: Random Input Device) does not help.

Always try to enter parameters with the keyboards. 3.1 can = 3.1 sometimes.
Careful work at the modeling stage pays dividends, even with budget software.
GARBAGE IN, GARBAGE OUT.
Until I persisted with using the extra decimal, I always had problems with arcs and circles. When you print a drawing so you can input data into a system for g-code, the precision in the drawing will probably drive the inspector nuts.
2 different print setups, for the end user seems to solve this. They have different needs.

Expensive CAD/CAM software can make these issues invisible to the end users but most of us don't have that luxury.
At least some of us are not asking the government for handouts to keep our luxury systems going!