Post Processor Circular Interpolation Settings

[testyourdesign]

@breezy, @cncnutz

The Fusion360 post-processor appears to use K words for arc motion programs. Could this K-Word command in our G-Code be playing havoc on the Arc and Interpolation motions?

Fusion360 post processor appears to be missing the option to use Radius Words instead of the I, J words like they have in the Mach3 post-processor. Should we add the R-Word option in our Masso Mill Post Processor for Fusion360?

Cheers, Stephen Brown

 

[breezy]

@testyourdesign, @cncnutz

Stephen,

Found time to compare MASSO.cps and MACH3.cps.

The K word is only used when the Z plane is involved so I don't think that is the cause of the problem.

Yes the useRadius property has been removed from the masso post, I can only think that it was removed because MASSO couldn't handle an arc based on radius and maybe that is the cause of John Harvey's arc / helix problem, but then MASSO-SUPPORT said that bug only affects G3 units.

So I'm going to add it back in on my copy of MASSO.cps and test it next week and report back after testing.

Regards,

Arie.

 

[cncnutz]

@testyourdesign, @breezy

As Arie said the K is a component of the Z axis and not usually used. I'm not sure why you would want to use 2 different types of arcs in a gcode file and I,J,K seems to be the best option

I've been reading up about R and I,J,K this tonight and it is interesting reading.

https://www.cnccookbook.com/cnc-g-code-arc-circle-g02-g03/

Seems that arcs greater than 90 degrees can sometimes cause confusion calculating centers when using radius where I,J,K specifies the center coordinate.

Cheers

Peter

 

[testyourdesign]

@cncnutz

The thing that caught my attention was that the K component is missing from the documentation section for G2 and G3. I am curious to know if @masso-support had implemented the K component into a helical move or if it was not implemented yet. By the description in the documentation and the example they gave it looks like K is not used/needed. It's probably just an omission in the documentation but I thought it better to ask. Users that are expecting an interpolated Z motion with a K component might get a different result than they expected. I also did not know what effect a K component would have if the code includes it as Fusion360 does.

I find that the only advantage to R values is that they are easier to code manually. The only reason I asked is that I wanted to test them out using Fusion360 but noticed it was missing. I agree that its sort of obsolete when you use a proper CAM program to generate the code. It's probably better to leave well enough alone here but I figured Arie might find it interesting.

Cheers, Stephen Brown

 

[cncnutz]

Hi @testyourdesign

I think you will find the Helical tool paths don't use the K component as a helical spiral is linear in the z axis not curved. The addition of a Z value to the G2 or G3 creates a spiral.

Sample Helical spiral Gcode

G3 X-243.000 Y0.000 Z14.375 I0.000 J-243.000
G3 X0.000 Y-243.000 Z13.750 I243.000 J0.000
G3 X243.000 Y0.000 Z13.125 I0.000 J243.000
G3 X0.000 Y243.000 Z12.500 I-243.000 J0.000

I confess that I,J arc's give me a headache at the best of times and I can't find a lot of real information on how the K value is normally used. I don't have CAM software that generates anything with a K value for testing.

Cheers

Peter

 

[testyourdesign]

@cncnutz

Actually the Masso post for Fusion360 publishes a K value so it's being tested every day. Hopefully it's simply ignored if Masso doesn't support it.

Cheers, Stephen Brown

 

[cncnutz]

Thanks Stephen, Sounds like it is supported and is just an omission otherwise it would probably have been reported as not working by now.

Now I think about it, I'm sure it is used in lathe work for arcs which is X and Z axis only using I & K, working in G18 mode.

Cheers

Peter