Gee Four One: Cutter Nose Radius Left
Before we look at how to use Cutter Comp it’s useful to understand “why” rather than “How” first.
So, setting up a tool using the tool probe or by making test cuts (if you managed to smack the probe off of the machine) what you are doing in effect is finding the furthest “forward” plane of the tool and the furthest “left” or “right” plane of the tool. This gives the machine a calculated position where those two lines cross. Except there is a problem, the tool in 99.9% of cases does not have an “Intersection point”, it has a tip radius that varies from cutter to cutter. Have a look at a quick pic of a generic CNMG tip with no tip radius.
Sharp corners with no radius.
From an overhead view below.
The dot shows where the furthest left and furthest forward intersection point would be , except it isn’t.
In the pic below you can see the edge on a CNMG120408 cutter tip (very common)
Here you can see that the tip “comes to and end” before any part of it reaches that intersection point due to the radius. That’s all good if you are cutting straight lines only in X or Z but if you are cutting a Radius or Chamfer that’s going to affect the sizes. This is why on the “Tool Geometry” page of the control you have a column that says “Cutter Rad” or “Tip Rad” or similar. This is so the machine knows how much to allow for the end of the tip in any movements due to the radiused end. There are two versions of this “compensation” on a lathe, Comp Left and Comp Right (G41 & G42)
Implementation.
On a slant bed CNC, Chuck to your left, tool the other side of the workpiece, turret to your right. Picture yourself sat on the tool as you are turning a part, facing the direction the tool is travelling, if the tool moves left you need G41, if it moves right you need G42.
Syntax:
G41
G41 Is A Modal Command
Additional Info:
If you do struggle with “Spatial awareness” (you find it hard to visualize movements in free space) a good idea is a PC type chair, that way you can sit at your desk and spin round while waving your arms like some geriatric version of John Travolta having a seizure to help picture what is going on.