Newbie- G41 Offset Issues

[sail2steam]

Hello, all. I've lurked in this forum for quite some time and this is my first post. I've been experimenting with offsets lately by using a pencil in a drill chuck in my Sherline mill. I planned out a simple rectangle of 2" x .5" with a non-offset run. The second half of the code runs the exact same rectangle, only with a .125" radius offset. The machine is controlled through Mach3. My problems and questions are these:

1. Why does Mach change the offset path with a radius in the 90 degree turns? Why isn't it a straight, non-curved 90 degree path like in the non-offset run? If this is normal, how do I achieve a straight turn? Please see the picture below to see what I'm talking about.

2. The last line of code, G1 y0, WILL NOT transfer into the screen in Mach. It runs just fine on the non-offset path, but NOT in the offset? You can see the missing left side of the offset rectangle in the photo. What am I missing and how do I correct it? The obvious fix is to program in an extended run to compensate for the radius of the tool, but isn't this what G41/G42 is for? My code is below.

Thanks in advance!

g40 g1 x0 y0
g1 z0
g1 x2 f3
g1 y-.50
g1 x0
g1 y0

g0 z1
g41 d1 g1 x-.250 y-.250
g1 x0 y0
g1 z0
g1 x2 f3
g1 y-.50
g1 x0
g1 y0

[christinandavid]

Hi,

The radii in the corners show the path of the centreline of the cutter. The cutter is in continuous contact with the corner of the contour you have programmed - it will result in a sharp cornered part as long as you use the cutter you have defined in your offsets.

You will need to end your contour with a G40 to cancel cutter radius compensation. This may be possible in your Z move off the job - but most likely you will need to move the cutter clear of the contour in X and put the G40 in on that line. It should then complete the last Y move.

DP

[ger21]

Does the last line display in Mach3's g-code window? If not, hit enter after it and save. If it does, then add the G40 after it. You really shoud retract before the G40, and it's good practice to have a lead out move after the G40.

[sail2steam]

The last line WOULD NOT show up in the Mach3 control window. However, you guys were spot-on. The line successfully showed up and executed when I introduced G40 and a lead-out line of code. This makes sense now that you guys have pointed it out. If you have to use a lead in, it is logical to assume that you need a lead-out. Thanks so much for your help!!

Martin