question on cutting an arc with a mill

[ozmodiusnc]

Hi Folks!

Im a relative newbie to the forums. I am a machinist student and we have run across a problem with cutting an arc with a mill that we, including the teacher cannot trig out to get the right tool path. Ill try to explain the problem as completely as I can...

We are trying to write a program to cut a 6x6x1" alum. plate using a 1" end mill. On one corner we have an arc to cut that that is 2" in from the corner with a 4" radius, and .5" from each edge. We are cutting .5" into the edge of the part, so the center of the end mill is following the edge of the part. What we are trying to figure out is where would the start point on the cut would be from the tool path on the edge to make the 1" end mill start cutting in the right place to make the corner of the arc end up 2" from the edge. I know it is somewhere between 1.5" and 2" from the corner of the part, but I cant find the right trig formula to make it work. A sketch of the cut is attached. Any help would be appreciated from any of you programming gurus out there.

Thanks,

Mike

[orizaba]

I may be able to help. Do you want the gcode, or just the math?

[mactec54]

Hi ozmodiusnc

I will try & attach some Gcode this will do your job the part 0.0 is in the
left hand top corner that is X&Y 0.0 The Z. 0 is top of part

If you need it in a different place & can put it there
you did not have how deep you wanted to go so I went .5 It will do 5 0.100
passes & then 2 clean up passes of .005 to give you the finished size if you need this to be different I can change it. PM me your Email & I can send you
the file

The Z will ram down for each cut you can change the spindle speed & feeds
to suit

The centre point for the 4"rad is 2.0890 from the corner at 45deg through the centre

[ozmodiusnc]

Originally Posted by orizaba I may be able to help. Do you want the gcode, or just the math?

The math would be great. Will the formula work with any radius that is past the physical corner of the part?

thanks in advance.

Ozmo

[Kiwi]

Withdrawn
Misread the Question

[Kiwi]

This time
See attached picture1.
How to calculate.........
2.121 = Square(1.5^2 + 1.5^2)
0.143 = 4 - Square ( 4^2 - (2.121/2)^2)
1.768 = Square (1.25^2 + 1.25^2)
2.089 = 4 -1.768 - 0.143
1.477 = Square((2.089^2)/2)
Centre of Arc is 1.477 from outer edge in X and Y directions
Draw the actual profile and offset with G41/G42.

To calculate the tool centre at corner..
See Picture2
3.173 = Square((4 - 0.5)^2 - 1.477^2)
1.696 = 3.173 - 1.477

Hope I've got it right this time.

[ozmodiusnc]

Thanks to all who helped out with this probelm!! Ill get an A+ for this

Thanks again everyone!

Mike