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Offline 1hxo

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inaccurately Jogging
« on: April 18, 2013, 08:58:16 PM »
Hello
I have build an cnc machine with the pokeys 56U.It works all fine on the first look.
Now i have a Problem when i jog my axes with keyboard or joystick the continue jog are work fine but when i reach the edge of whatever i must use the step jogging.
And there is my problem.When i zero my axes and then step jogging with cycle jog step 0,0100 the first move are go to 0,0094 the second goes to 0,0219 and so on.
At the fifth push im at 0,0500.
When i use cycle jog step 0,0010 then there move with 0,0031 steps.
When i use cycle jog step 0,0001 then mach3 do nothing.mach3 should go one up but he does nothing.
This phenomenon its on my cnc computer with aktiv machine and the same its on my home pc without machine.
I have different mach3 version testet all the same.And different Hardware and windows too
At this point where i gave my settings for my driver and motors in mach3 this problem beginns.
I tested whether it is on Pokeys plugin.without success.
Now on a fresh mach3 install without nothing only the settings in motortunnig for my motors the same problem.
is it possible with mach3 of positioning accurately with joystick or keyboard?
When i use cycle step 0,0100 why does mach3 0,0094?
Did i missing some setup?Have i oversee a adjustment?

Offline Chaoticone

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Re: inaccurately Jogging
« Reply #1 on: April 18, 2013, 09:13:24 PM »
What are your steps per unit in motor tuning? If you are trying to jog .001 and the resolution will not allow it mach can only get as close as possible.  to move .0001 accurately you need your steps per to be 100,000 even.  if the steps per are 96,000 for example, no way to make a .0001 move accurately.

Brett 
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Offline 1hxo

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Re: inaccurately Jogging
« Reply #2 on: April 19, 2013, 03:22:02 AM »
Hi
Thanks you for the info.now it seems clear to me
I have my steps per unit at 320.
it´s 1/8 mode at 5mm spindle pitch it makes 0,003125 mm per step
to be more accurately i must use a higher stepdriver mode or use a spindle with 3 mm pitch.

Offline Hood

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Re: inaccurately Jogging
« Reply #3 on: April 19, 2013, 03:45:39 AM »
Personally I wouldnt bother, 0.001mm is a very small amount and unless your machine is of very high quality and rigidity you are not going to be able to achieve that and certainly not with  steppers unless you gear so that the motors are at least a factor of 10 greater than the accuracy you want. Microstepping in itself is not accurate so increasing the microstepping will not necessarily get you better accuracy, it may make the numbers in the DROs look better but is unikely to make any real life difference.

To put this into perspective, even a C5 ground ballscrew has an acceptable deviation of 18um over 300mm, a C7 is 50um over 300mm.
 
Hood

Offline 1hxo

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Re: inaccurately Jogging
« Reply #4 on: April 19, 2013, 04:51:52 AM »
You're right, I think I can live with it.The only Think was that the dro looks a bit crazy.
I have made the Parts for my machine on a cnc machining center with a precision of 0.0001.and now I wanted to emulate this machine but its not possible with low cost parts.
It only took me a little confused.
And now where im thing about this its clear.
I have a C7 ballscrew.

Thank you

Offline stirling

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Re: inaccurately Jogging
« Reply #5 on: April 19, 2013, 05:33:35 AM »
With regards to ACCURACY (as Hood has said) you should not factor in your microstepping because their accuracy is LESS than the *usual* 5% of the full step accuracy of stepper motors. If you want the cosy numbers AND a more realistic expression of your machine's ACTUAL accuracy you could go into a screen designer and reduce the decimal places of your DROs from 4 to 2.

Ian