tool nose offset 1

[grinderguy]

I need to draw in autocad the same radius offset that is created by g41 and 42 in cnc gcode. As you do a g2 and g3 raduis the actual tool position is not actually offset by the amount of radius. How do you draw the g2,g3 with raduis comp in AutoCad?

Robert Setree

http://www.advanced-grinding.com

 

[thalon]

Would not simply offset the tool path radius by the tool offset?

 

[grinderguy]

When traveling in z direction the left quadrant of the radius is the leading edge and the lower quadrant is trailing by the raduis amount. As you go thru a larger radius the machine actually moves in the part raduis- the tool raduis. The start and stop points are changed by the tool tip radius. Most machine tool computers have this built into the controllers. These controllers require specific start and stop points in order for the radius comp to work. I don't have the space, ususlly 2 time the radius , to turn these on and off.

Robert Setree

http://www.advanced-grinding.com

 

[thalon]

I'm not sure I understand what you getting at.
What kind of machine? 3axis milling?
What kind of tool? Flat nose end mill?
If xy defines the surface of the table. Is the arc you want in the xz plane?

if so...
Exaple of a 90° arc. xy plane for simplification
(arc1) draw an arc rad 12" from 0° to 90°
(line1) draw a line from the 0° end of the arc 0.5" long in the x direction. This represents the cutter (0.5" flat end mill) at the beginnign of the arc.
(line2) draw a line from the 90° end of the arc 0.5" long in the x direction. This represents the cutter (0.5" flat end mill) at the end of the arc.
(line3) draw a line from the mid point of line2 12" in the negative y direction (radius of arc1)
(ellipse1) draw an ellipse centered on the lower end of line3 with the two remaining point the midpoint of line1 and line2

ellipse1 from 0° to 90° will then define the travel path of the tool to create arc 1.

Is this what you were looking for?

 

[grinderguy]

I am using xz on a 2 axis lathe. I am trying I am using a tool with a .031 nose radius to generate a .125 radius. The machine moves .125-.031=.094r to make the part .125 radius. The start and stop points of the radius are what I need to generate.

Robert Setree

http://www.advanced-grinding.com

 

[thalon]

Tool is round?
Where on the tool is the defined point? where does trhe machine think the corner of the tool is?

Assume: (please forgive the poor artistry)

+ --
/ \
/ \
| |
| |

is the + the defined point of the tool?

 

[BobM3]

For an arc the offset command will work. Use the endpoints of the offset lines or the offset radius for the start and stop points of your tool. Chamfers are a bit more involved - you have to offset and then extend and trim the lines to get the start points.

 

[grinderguy]

BobM3 is making a little sense to me. This is a link to an example.

http://www.cnczone.com/forums/showthread.php?t=961&page=2&pp=15

. Notice the g2 line has 2 "z" s which means it will not work. I may understand this by decerning the difference between the drawing certerline of the raduis and centerline that must be used by the gcode. Thanks for everyones help so far. I am thinking there is probable a dxf to gcode converter that does this math internally.
Bob

Robert Setree

http://www.advanced-grinding.com

 

[thalon]

I wrote a VBA program for autocad to convert gcode into an autocad script. This allowed me to text the gcode I wrote. I only used it on 2d machines, a whitney GE1050 punch-plasma machine and an MPC2000 flat bed plasma cutter (like a laser cutter).

 

[grinderguy]

This link is to a drawing showing the tool geometry

http://www.cnczone.com/forums/attachment.php?attachmentid=392

Bob

Robert Setree

http://www.advanced-grinding.com