A few things to keep in mind.
When working with a model from 3D modelling software (I use Freecad) but the principles
are the same for all of them.
If you can roll back the timeline on your model to a point where the model has not had the chamfers
created yet, and export that.
If you don’t do this, then you lose the true Z position edge of the hole as when imported and
edge detected you get two polylines, the one on the top face is equal to the hole
diameter + 2 * the chamfer width, and the bottom polyline (which is the correct diameter) is
displaced in Z by the depth of the chamfer.
So you must select those polylines and raise them up to the surface Z height of the top polyline.
In the pic you can see the finished model and a rolled back model which is the one to export
as it will save you a ton of time and eliminate a lot of possible errors as you don’t have to adjust
the Z heights of the polylines.
Your 3D modelling software will have export settings for step files, If you step import doesn’t
work correctly, then in pic 2 are my settings used to export the step file.
Here for this model, I have un-checked “write out curves in parametric space of surface”
This simplifies the model and exports it as individual faces\lines.
For 3D printing I have this checked.
Another thing to keep in mind is that when the plugin starts up the default values give
a 1mm chamfer 1 mm up from the tip of the tool.
Starting to cut one mm up from the tip of the tool is the bare minimum and I use 2 mm, this
is so that I don’t break the tip off the tool and the further up the tools cutting face you
start cutting, gives a better finish, because the actual surface cutting speed will be higher.
The other thing is you can use all of the length of cutting edge, as the tool wears.
Dave