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molotow wrote:
Sorry, I have been away.
This will happen if your A axis can't move fast enough to keep up with a change in direction. You will either need to write G-code where all corners are slow arcs, and there are no reversals of direction, or "short-circuit" the position feedback in the HAL file so that LinuxCNC doesn't realise that the A-axis can't keep up.
Tangentkins isn't really the ideal way to do the job, it is just an easy way. The correct way would be to have the trajectory planner output the current motion direction. However that would need significant changes to critical code, and almost nobody needs it.

Hi,

thanks for your reply.
We've decided to use another software for that, but it's not as cool as EMC.
So I am still interested in cutting with EMC.

However I've tried to "short-cicuit" the position feedback this way:

net apos-cmd axis.3.motor-pos-cmd => stepgen.3.position-cmd
net apos-cmd => axis.3.motor-pos-fb

I simply set axis.3.motor-pos-fb to the input of axis.3.motor-pos-cmd.
This did not work, i got FOLLOWING ERRORS for all other axes. So i tried to do this for all other axes as well.
This worked ok, but now i get a new error:
Exceeded soft limit

This error appears, when axis position is out of range.

Have you any better idea, how to do that?
I don't think so. Even Mach3 has a tangential controller.
And it couldn't be that hard to implement.

Thanks

molotow wrote:
Any idea how Mach does it?

I think that the best way to do it is in the G-code, with a pre-processor that inserts an A-axis move prior to each linear XY move. (and adds an A-move to all arcs too)

As you can probably tell, I have rather gone of "tangentkins" as a solution, for the reasons you have found.

Hi all,

I installed a 4th axis to make cuts with tangent knife (using a circular blade) and got very good results with Gcodetools. Nick, the principal developer, is very friendly and helpful. In the last stable version (1.7) you have to change the 4th axis scale from 1 to 180/pi to have it generate the angles in degrees. I already tested it and works very well.

If you need, I can elaborate better how I did it.

Regards,

Dimitrios

Hello Dimitrios,

thanks for your reply. Do you mean the inkscape extension gcodetools?
Sorry but this is no option for me. I want to be independent of any CAM software.

When I've time I'll try to write a preprocessor for that, this is probably the best solution.

Hi Molotow,

I understand what you want, I thought about doing it too, but my programming skills fall short for this task

I am still learning to use inkscape, but the more I use, more I like it, and the Gcodetools interface is very simple, once you go through the learning curve. for now and for me, it is a good fit in the workflow.

I'd rather use inkscape and gcodetools to load it to LinuxCNC than using any other controller.

I will try to use the tangentkins soon, keep us informed of your progress.

Regards,

Dimitrios