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tangential control problems...
« on: March 13, 2007, 06:16:40 AM »
Hi there...

I tried to cut contours with a cutter and wanted to use the tangential control for it.
Here are the problems i have:

I had to configure my a-axis in steps/rotation instead of steps/degree as usual when using this axis as rotation-axis.
Why is that so ? Why can't it be configured in steps/degree like all other rotation-axes? ???

Therefore the maximun speed of that axis is 60 units/min (=> 60rpm).

If I now cut a contour with activated tangential-control this maximum speed is ignored and my tangential axis is forced to rotate with the same speed I defined for the x- and y-axis. So if I want to cut with 1000 mm/min the t-axis tries to rotate with 1000 rpm. No chance to do that... The only way was to reduce the speed down to 60 so I had to cut with 60 mm/min. Much to slow...

Why is the maximum speed ignored when tangential control is activated?

Is there any scaling factor for the different speed settings per axis?

There is only one speed you can define in g-code ( feedrate F) for all axes. Different axes are configured differently in motortuning:
mm/min, degree/min, rotation/min ( and if you like: inch/min). A scaling factor imo is absolutely necessary to compensate that.
Also if you are milling with 4 axes and different workpiece diameters. The feedrate for the a-axis is defined by F (degree/min), but it's a big difference if you are working with 40mm diameter or with 300mm diameter.

What about this radius-correction? How do I use it? (->only setting the diameter in settings-menu?)
Could that solve the problem with the tangential-control, too?

I hope you can help here...
« Last Edit: March 13, 2007, 06:19:00 AM by rubens »
Re: tangential control problems...
« Reply #1 on: March 13, 2007, 11:27:42 PM »
I never use it :( This is not as simple as you may think... I will see about testing it here
Fixing problems one post at a time ;)

Re: tangential control problems...
« Reply #2 on: March 14, 2007, 08:53:33 AM »
Could you please post your XML as well
Fixing problems one post at a time ;)

Re: tangential control problems...
« Reply #3 on: March 15, 2007, 06:00:53 AM »
Hi Brian,

sorry that it took so long...

The problem occurs when you are using metric units. An example (like attached as tangential.xml):

The resolution of my x and y axis is 400 steps/mm. The resulting maximum feedrate is 1500 mm/min.
The resolution of my a axis is 14.4 steps/degree (in normal mode). The maximum feedrate is 8000 degree/min (even more, to be honest...).
The resolution of this axis in tangential mode is 5184 steps/rotation. The maximum feedrate is 60 rotations/min.

Now my problem in tangential mode:

When I try to cut with a feedrate of 1000 mm/min and the defined maximum feedrate of my rotation axis is ignored (in tangential mode) Mach3 tries to rotate this rotation axis with 1000 U/min. Doesn't work of course...
The only chance was to manually reduce the feedrate down to 60 (my defined maximum speed for this axis).
That also means the x and y axis also move only with 60 mm/min which is much too slow.

Art wrote that defining the tangential axis in steps/rotation is for technical reasons.
But ignoring the defined maximum feedrate results in a big problem here.
It must not be ignored for the tangential control to work imo.

Now switch to imperial units (like attached as inch.xml):
The resolution for x and y now is 10160 steps/inch. The resulting maximum feedrate now is 60 inch/min!!!
The setting for the tangential axis remains the same: maximum feedrate is 60 rotations/min.

When I try now to cut with a feedrate of 40 inch/min everything works fine!!!

The problem is that you have to use the same feedrate for axes that are configured differently (mm/min, degree/min, rotations/min).
If you are using imperial units (and I suppose you do  ;)) the maximum feedrate settings are almost identical.
But not if you are using metric units!

And I didn't like to switch to imperial units, because we are living in a metric world here in Germany ;).

A feedrate scaling factor that compensates the differences of the different used units for linear and rotation axes would be very helpful.

A similar problem occurs when milling different workpiece diameters with a "normal" rotation axis. As far as I understand this can be compensated with the radius correction feature which appears right to DRO of a rotation axis.

Kindest regards

Norbert ( aka rubens...)

Re: tangential control problems...
« Reply #4 on: March 15, 2007, 06:02:17 AM »

also the tangential.xml...
Re: tangential control problems...
« Reply #5 on: March 15, 2007, 08:37:32 AM »
Okay I think I see what the problem is and how to fix it... The people running the tangential control are in the states and that would explane why this is the first time i have heard this. I am thinking that I need to look at the Vel of the X,Y and Z and see if I can fit the A axis move in. This is in a section of code that is hard so please let me finish some of the other stuff that I am working on and I will get back to it.

Fixing problems one post at a time ;)

Re: tangential control problems...
« Reply #6 on: March 15, 2007, 01:29:16 PM »
No problem, meanwhile I can use imperial units.

Good to see that this problem is recognized and might be fixed in the future :D

Thank you very much