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Author Topic: A axis not matching actual angle.  (Read 6007 times)

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Offline Hood

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Re: A axis not matching actual angle.
« Reply #10 on: March 18, 2011, 06:05:33 PM »
Yes thats correct.
Hood
Re: A axis not matching actual angle.
« Reply #11 on: March 18, 2011, 10:43:01 PM »
Excellent, it now reads what looks like the correct angle on the DRO. At least in MM. If I choose inches then it is still off by a lot. Ideas?

You all have been so helpful, Hope I can return the favor sometime. Any questions on watch repair or goldsmithing gladly answered.

Online Tweakie.CNC

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Re: A axis not matching actual angle.
« Reply #12 on: March 19, 2011, 03:33:49 AM »
Odd one this but you still seem to be confusing units.
The unit that a rotary axis uses is degrees, inches and millimetres are irrelevant to its angular position or rotational movement.  ;)

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline RICH

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Re: A axis not matching actual angle.
« Reply #13 on: March 19, 2011, 07:04:21 AM »
You can set up a rotary table to index, which is rotary / the Steps per unit is steps per degree, or linear where the rotary motion is expressed as distance traveled
relative to some diameter. You desire to index so you do the following:
1.In motor tuning for the A axis you input the steps per degree (  160 in your case case ) and additionaly input a value for velocity and acceleration. The velocity
and acceleration values require you to experiment to find where the stepper will not skip.
2. In config> General config check the box "A axis is angular" for  angular properties
    - also you have a 3 choices for what is displayed in the DRO's in the Rotational box. Information on those  settings can be found in the manual.
3. G0 Ax - rotates the axis  x degrees but note that the rotation can be incremental or absolute depending on Distance Mode settings

RICH
    
« Last Edit: March 19, 2011, 07:06:15 AM by RICH »

Online Tweakie.CNC

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Re: A axis not matching actual angle.
« Reply #14 on: March 19, 2011, 08:29:36 AM »
I think it only confuses the issue we are talking about here but to elaborate on what Rich has said, I wrote this some time back.

Some notes on setting up a rotary axis for use with Mach.
 
For such purposes as cutting spur gears, machining splines or flats on round stock etc etc the position of the rotary axis is usually expressed in degrees. A GCode command such as G0 A10 will rotate the axis 10 degrees and so on. To set up the axis within Mach it is necessary to specify the ‘Steps Per’ (degree) and this is achieved by taking the steps of the stepper motor and multiplying by the micro stepping setting (if any) and then multiplying by the gear ratio then dividing the result by 360. In my case this is 200 (steps) x 8 (micro steps) x 60 (reduction ratio 60:1) / 360 (degrees) = 266.6666 steps per. Unimportant really but had I thought about this a bit more at the time I was cutting the worm gear for my rotary axis I would have made the reduction ratio 63:1, then I could have had a nice round figure for the steps per degree.
 
Angular mode is the most common and also the most useful way in which a rotary axis is used but there are alternatives….
 
When engraving on the surface of a cylinder, for example, it is convenient to have the rotary axis set for movement in mm but as this will vary, depending on the diameter of the work, there is a trick to getting it just right. One method for finding the ‘Steps Per’ is to calculate how many steps are necessary for the axis to complete one revolution and divide this figure by pi. In my case this is 200 (steps) x 8 (micro steps) x 60 (reduction ratio 60:1) / 3.142 (pi) = 30553.787 steps per to enter in Mach. Now this figure represents a linear movement of 1mm around the circumference of a 1mm diameter cylinder. In order that this can be used for any diameter of cylinder another calculation has to be performed and that is 1 divided by the diameter of the work (1/diameter). The result of this calculation is then entered into the rotary axis scale DRO within Mach. My version of Mach did not have an A axis scale DRO (like the X,Y &Z axis have) so this had to be added using Screen4 (which can be downloaded, free of charge, from the Artsoft website – For reference the A axis scale DRO is OEM Code 62 and it’s associated LED is OEM Code 44).
As an example, to engrave on the surface of an 80mm diameter cylinder it is 1 / 80 = 0.0125 so 0.0125 is entered in the A axis scale DRO now a GCode command of G0 A10 will rotate the axis so that the surface of the 80mm diameter work rotates 10mm. Using this method means that simple, conventional, engraving programs and existing GCode programs can be used for engraving onto curved surfaces such as tumblers, cups etc.
Although perhaps not quite as accurate as when the axis has been set up for angular movement in the first place - entering pi / 360 or 0.00873 into the A axis scale DRO will allow the axis to then operate in degrees ie. G0 A10 will rotate the axis 10 degrees.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: A axis not matching actual angle.
« Reply #15 on: March 19, 2011, 10:26:13 AM »
Excellent, it now reads what looks like the correct angle on the DRO. At least in MM. If I choose inches then it is still off by a lot. Ideas?

You all have been so helpful, Hope I can return the favor sometime. Any questions on watch repair or goldsmithing gladly answered.

I see this here in sim as well. Not sure, but it appears the A dro is not Locked to Units as the others are. (Mach coords aren't either)
I would assume that even yhough the the value in A changes by the standard 25.4 conversion factor when toggling between G20/21, the angular movement would actually be accurate in degrees. (cannoit verify in sim tho)

Quote
from RICH:  - also you have a 3 choices for what is displayed in the DRO's in the Rotational box. Information on those  settings can be found in the manual.

Hi Rich, can you direct me to this please ?
Thanks

Russ
Re: A axis not matching actual angle.
« Reply #16 on: March 19, 2011, 02:19:22 PM »

I see this here in sim as well. Not sure, but it appears the A dro is not Locked to Units as the others are. (Mach coords aren't either)
I would assume that even yhough the the value in A changes by the standard 25.4 conversion factor when toggling between G20/21, the angular movement would actually be accurate in degrees. (cannoit verify in sim tho)

I'll give it a try tonight to see if it remains accurate in both. It is easy enough to zero the axis if it does.

Thanks again to everyone.

Offline RICH

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Re: A axis not matching actual angle.
« Reply #17 on: March 19, 2011, 07:48:10 PM »
Quote
can you direct me to this please ?
Russ,
Sorry, bad wording on my reply#13,  was thinking about the three check boxes in config and what they do are  defined in "Mach3 CNC Controller Software Installation and Configuration" manual page 5-37. Didn't look at the other manuals.
RICH