i'm new to mach 3 but not cnc programming and my mill is not doing what i expect it to.  i think i have multiple problems going on and it may be just with how mach interprets what i enter in the code.

1. tool slot number too large?  i am calling up T1.
2. cutter comp moves 1" cutter to some random number?  do you need to call up D1.0 to let cutter comp know what diameter the cutter is or will it pick that up from T1?
3. what info needs to be enterred in the tool table.  (brand new 1" end mill so i know the wear offsets are zero and i have enterred tool height and diameter.  tool height is -15.76 and diameter is 1.0.)
4.i am moving off of 0,0 and trying to step into the part calling up cutter comp.  so i make a move to

T1
G1 x-1.0 y-1.0 F10
g41
g1 x0 y0 F10

now with code i expect the cutter to be at X-.5 and y-.5 am i mistaken?

any help is greatly appreciated.

G41 - uses the current tool
G41 D1 - uses tool #1
G41 P0.5 - uses a tool diameter of 1.0 (0.5 radius)

now with code i expect the cutter to be at X-.5 and y-.5 am i mistaken?

Depends on the next move. Mach can't determine where to go with comp if it only knows two points.

Also, wear offsets have no effect on comp. mach doesn't use them.

This thread might shed some light on using comp.
http://www.machsupport.com/forum/index.php/topic,9030.0.html