4th axis engraving ??

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Re: 4th axis engraving ??

Postby Gary Campbell » Fri Mar 16, 2018 1:04 am

Terry, et al...
I didn't intend to resurrect this older thread, but it may be relevant. With Terry's Wrapper aside, and assuming that I have a viable CAM application (Vectric) that will output rotary wrapped code. Assume the code originated as X to B or X wrapped around Y. X remains at 0, on the axial center of the rotary axis

There is a discussion ongoing where one user proposes G93 may be the only way to accomplish the following, but my position is that most controllers can accomplish it via G94

Assume machine position is X0 Y0 Z1 B0
If given the line: G1 Y10 Z1 B720 F120 There appears to be 2 scenarios:
1) Where B is rotated at 120*/min and line execution time is 6 minutes
2) Where Y and Z move at 120 ipm, rotary is synced and line execution time is 5 seconds.

The difference seems to be in the ability to "sync" or "slave" a rotary axis to the linear.

Can someone in the know inform me which of the above would be true using UCCNC, or provide an example of a scenario that would be true?
Thanks in advance, Gary
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Re: 4th axis engraving ??

Postby Vmax549 » Fri Mar 16, 2018 1:52 am

Hi Gary, UCCNC at this point does not really support rotary axis. It does but only in a rudimentry way. All axis are interpolated at feedrate. So you are limited by the slowest axis which normal is teh rotary because it is setup in deg/min.

So to answer your question method[1] is what you got.

G94 cannot do it because it runs all axis at the commanded feedrate and teh rotary is by far teh slowest so it goes SLOOOOW.

To do rotary engraving where you can get done in this century(;-) you would need either G93 mode or radius based velocity correction for the rotary based on the Diameter of the part you are engraving. Then your rotary would have to support high speeds to keep up.

That is why the 4th axis engraving Wizard came about ;) Haas does it as a Gcode G107 I believe. I can also do it as a Programmable macro rather than a Wizard.

M93{xxxxxxxxxxxxxxx } Setup for 4th corrections
M94 return to G94 mode

(;-) TP
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Re: 4th axis engraving ??

Postby Gary Campbell » Fri Mar 16, 2018 2:13 am

Terry...
That's what I had assumed because I had heard of "no current support for rotary axes", but wanted to make sure. Thanks for the clarification.

That definitely places UCCNC in the minority of todays popular (router) controllers, regardless of price.
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Re: 4th axis engraving ??

Postby cncdrive » Fri Mar 16, 2018 2:15 am

Terry is right, that there is no specific "rotary" axis in the UCCNC.
All axis are handled as linear axis which does not mean that you can't do rotary work, you can: https://www.youtube.com/watch?v=Ox4SrYt-qEY

And non of your points 1. or 2. is the case.
When you code G1 Y10 Z1 B720 F120, then all axes will move syncronised and all axes will reach the target point the same time and the feedrate F120 is on the vectorial sum of all axes which is a virtual space of YZB axes in this case, but it could be upto a 6 dimensions space of XYZABC in case you code all axis in once.
It's hard to visualise this, because the space in this world has 3 dimensions only, but if you think into it I'm sure you will understand.

To do so called specific "rotary axes" support a software could have 2 options (The UCCNC does not support any of these at the moment):

1.) To support rotary axis in a way when it is defined how to compensate the movement distance on that radial axis. So, that the feedrate will be calculated on the surface of the cylinder around the rotary axis.
E.g. to define that the A axis is rotary and it's center line is at Z=0 and so the software will then know the geometry, the circumference of the axis, because it then knows that the radius is defined by the Z axis.

2.) To support kinematics and so the user let the software know the properties of the machine, around what lines are the rotary axes are bending around in the workspace and also how the axes are connecting to eachother. A good example is a rotary BC table where the table can bend to one direction and there is a table on the top of it which can rotate around.
So, then the software knows the kinematics of the machine and so it could make the required matrix transformations to execute different motions, e.g. linear interpolation and orientation commanded moves.
Another example is a robotic arm where the joints connect to eachother and so doing a linear interpolation with set feedrate which requires matrix transformations on the geometry to calculate how the joints have to be rotated to do the commanded linear or other movements with the set feedrate.

Ofcourse the first point is much simpler to achive than the second. I know, because I've studied robotic arms a long time ago when I was in college, we even had to do exam in which calculations like that had to be done on paper. It's not easy math I can tell you, especially when you have to do it on paper. :)
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Re: 4th axis engraving ??

Postby Vmax549 » Fri Mar 16, 2018 3:54 am

AH but that is not engraving or carving a surface with interpolated axis's . THAT is indexed milling a 3d surface ;)

(;-) TP
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Re: 4th axis engraving ??

Postby ger21 » Fri Mar 16, 2018 10:49 am

To do so called specific "rotary axes" support a software could have 2 options


Don't forget about G93 mode.
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Re: 4th axis engraving ??

Postby cncdrive » Fri Mar 16, 2018 12:45 pm

Gerry, yes, I know, I just always considered G93 as a special and infrequently used code.
One reason for that is that I have not seen any CAM programs so far which have used it, second it wastes lots of data space with the requirement of codeing the F feedrate on every single motion code line which might be OK with some hand coded short files, but will quickly qrow the file size when the code is from lots of line segments when a drawing is wrapped around a cylinder with enough arc resolution and the code looks not so nice when there is an Fxxxx on every lines.
And the third reason is that even some CNC controller manuals mentioning it as a rarely used code.
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Re: 4th axis engraving ??

Postby Vmax549 » Fri Mar 16, 2018 2:36 pm

Aside from a 4th axis wrapper you only have a couple of options for 4th axis engraving.

G93 mode and even there you are limited by how FAST your 4th will move. And yes G93 is still used today.

4th axis vel corrections based on part diam which is really just an internal approach to G93.

I cannot see where Kinematics would help much as you would still need to sync teh rotary based on part diam.

You also have to consider that not everyone does machining teh same way. Some used center of axis as teh reference point(Z0.000) . Others use teh surface of teh part as the point of reference. AND a few others use Zhome as teh point of reference (Z0.000).

Not saying you have to cover all of these methods but some retraining will be necessary by the user.

AND yes [1] does apply here for UCCNC. You have no choice as that is the only way that UCCNC can do it.

UNLESS I have missed something, :?:

(;-) TP
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Re: 4th axis engraving ??

Postby cncdrive » Fri Mar 16, 2018 3:02 pm

Hi Terry,

I was talking general about this type of application.
I've tried to concretize as few as possible.

I'm not saying that everybody using the Z=0 as the center line for a rotary axis. I'm just saying it as an example for usage. And I said it only to let see that the controller must have somekind of information about what the actual cylinder diameter is. In other words the controller must have some information about the machine kinematics. Even if it is only that the Z=0 is the center line and the Z distance is the cylinder diameter, but that is still information. Without any informations the controller can't have an idea about what the actual diameter is and so then how could it do a feedrate on the cylinder of that axis...
OK, there could be other ways (like inverse time feed G93), but this was mentioned as one way...

And no, point 1. does not apply to the UCCNC nor to any other controllers which doing linear interpolation. That would apply only for G1 B720 F120, but not when other axes are also moved in the same line, because the feedrate is calculated on the movement vector in the N dimensions space, where N is the number of axis moved and the vector lenght and direction is the summary of all vectors on all moved axis. So, mathematically point 1. does not covers it.
To understand it just think in e.g. 2 dimensions and let they be X and Y. And let's make a move from X=0 Y=0 to X1 Y1 with a feedrate of 1.
So, the feedrate on the movement vector will be 1 units per minute and in the mentioned point 1. it is assumed that this movement will finish in 1 minute, but it is not.
It will finish in 1.414 minutes, because the length of the movement vector is 1.414 units, because by the Pythagoras equation the length is c = sqrt(a^2 + b^2) = 1.414 units which will be finished in 1.414 minutes with the 1 units per minute feedrate.

The same way in point 1. when B=0 and then B720 and F120 will not finish in 6 minutes when other axes are also moved together, because the summary length of the movement vector is not 720 units for the same reason as I above described...
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Re: 4th axis engraving ??

Postby Vmax549 » Fri Mar 16, 2018 5:50 pm

HUM, ok if you use teh example starting at Y0 B0 Z0 and move to G1 Y10 Z1 B720 F120 Will not all teh axis arrive at there end point at the same time based on feedrate ? IF so then all axis are restricted to teh slowest axis motion which in this case it is B @ 120deg per minute so it would take 3minute to move 360 deg and and 6 minutes to move 720 degrees.

Or am I still missing something ?

(;-) TP
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