Using G41/2 on 5-Axis Path

[A_C_L_Barney]

Anyone know how to calculate the error that we might see if we use 3Axis compensation (G41/2) on a 5Axis tool path?

We are machining at a maximum angle of 6.2 degrees from vertical so it will be very small over a cutter comp of 0.5mm.

My first thoughts were [Error=Cutter offset * Sine(Angle from vertical)]


Anyone had experience of this before?

Just for ref. we're not talking precision engineering here (+/-1mm) and the surface is probed to get the finished size right so it will work even if we ignore the error.

[Chrliev]

I have never heard of 3D, 3-Axis or 5-Axis tool compensation using G41/G42...

Going back to the early 80's Fanuc 3 and 5, Cincinatti Acramatic and GE550 and 1050 series controllers, every machine that I have ever worked on had 2 axis toolpath compensation, though some were very complicated to use.

How would 3D tool comp work if I was using something like a 1" (25mm) bullnose cutter, with a .125" (3mm) radius, cutting accross a series of 3D surfaces. I am not sure how the controller would know if the corner radius or the flutes of the cutter were contacting the part surface. Even using a ballnose cutter it would be impossible to know where the ball was contacting up onto surfaces as the contact point would change constantly.

I can't even imagine how 5-Axis tool motion can be compensated. It would be nearly impossible to do 3D or 5-Axis comp, without being able to know what the entire surface looked like the way a programming system knows and calculates centerline files applied to the entire surface.

You didn't say what CNC machine or controller you are using, maybe I have missed something these last 30 years...?

[Superman]

The basic cutter comp only works in the plane ( G17/G18/G19 ) that is set before starting the pass ( G17 is X & Y ), the other axes do not have the comp applied.

Many controls do not allow plane changing whilst comp is active.

Some have an additional G-code for 3D comp, I have seen a G43 on Okuma controls. I think 3D comp is mainly used with a ball nose cutter, and run best when programmed to the centre of the ball. It may be an purchased option as well.

High end, 5 axis machines can have comp applied to toolpaths, but these may need special CADCAM posts to output the right code.
our Heidenhain ( MilPlus control ) could do it, but "vectors" are required with the XYZ co-ordinates.

You may be able to "fudge" the path, but remember that the other axes don't have comp on them