Question on using FP numbers in python 2

[Steven D'Aprano]

On Sat, 15 Feb 2014 00:07:49 -0500, Gene Heskett wrote:

>> Can you extract the float calculations and show us, together with some
>> sample data, expected result, and actual result?
> 
> Not extract, but let you get & look at the code, its the top entry on
> this page:
> 
> <http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Simple_LinuxCNC_G-
> Code_Generators#Counterbore_Software>

Here is the direct link to the Python code:

http://wiki.linuxcnc.org/uploads/counterbore.py


> Assume no bolt size is clicked on, but a wanted diameter is entered in
> the lower left pair of boxes, and its to carve .700" deep in the other
> box. The cutting tool is .250 in diameter, its to do a stepover of 25%
> of the tool diameter, while carving an additional .015" out of the .850"
> hole with the tool bit turning 2000 rpm as it spirals down.

If I've understood the purpose of this program correctly, it generates 
code in some language called "G-code", presumably to control some sort of 
actual physical cutting machine. So the first thing you ought to do is 
have a G-code expert look at the generated code and tell you it does what 
it is supposed to do. Or perhaps your cutting machine is buggy.

> But the hole it will cut will only be .650" in diameter,  And the
> backplot, shown in the axis interface, shows no spiral, its doing what
> it thinks is full diameter in one circular plunge cut.


Scroll to the GeneratePath method, and read the comments at the top of 
the method. They tell you that the *intention* is:

* If the tool diameter equals the hole diameter, then just Plunge 
  down to the hole depth.
 
* If the tool diameter is less than 80% of the hole diameter, 
  then Plunge to each Level and Spiral out.

* If the tool diameter is greater than 80% of the hole diameter,
  then Spiral to each Level and Spiral out.

But a little later, we see this code:

    # Figure out what kind of entry into the hole
    if (self.ToolDiameter * 1.25 <= self.HoleDiameter):
        self.CutType = 'Spiral Down to Depth of each Pass and Spiral Out'
    else:
        if (self.ToolDiameter < self.HoleDiameter):
            self.CutType = 'Plunge Down to Depth of each Pass and Spiral 
Out'
        else:
            self.CutType = 'Plunge Down to Hole Depth'


Assuming that the comments are correct, the CutType is wrong. It looks 
like a simple logic error, and should be something like this:

    # Figure out what kind of entry into the hole
    if (self.ToolDiameter * 1.25 <= self.HoleDiameter):
        self.CutType = 'Plunge down and spiral out'
    elif (self.ToolDiameter * 1.25 > self.HoleDiameter):
        self.CutType = 'Spiral down and spiral out'
    else:
        self.CutType = 'Plunge down'

CutType is, I believe, merely a comment, but it leads me to believe that 
there are probably similar logic errors in the rest of the GeneratePath 
method. In fact, the description states:

"At this time there is a bug if you have a path that does not require a 
spiral... working on it"



-- 
Steven