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Author Topic: how to set A-axis to move continuously,not in steps?  (Read 6270 times)

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Offline xaco

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how to set A-axis to move continuously,not in steps?
« on: September 16, 2010, 06:11:31 AM »
hello,i have stepper motor on my 4th axis(2 deg/per step,written on it)and its always moving in steps,can it be set to move continuously?
                                                                                                                                                                               Motor is directly connected to  chuck,no transmission.
..Also,it makes 4 steps to make 1 degree,is this  minimal movement for this motor or it can be set to make smaller steps for better detail?

Offline RICH

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Re: how to set A-axis to move continuously,not in steps?
« Reply #1 on: September 16, 2010, 06:53:43 AM »
Usually for indexing the steps per is in steps per degree. If you are using like a linear axis then the steps are step per inch or mm.
In indexing you can just command a large number of degrees and it will run continously until  it achieves the rotational move.
Similar for linear move.
Now you can use the stepper for the spindle / constant turing of the lathe spindle. The steps per unit would be steps / rev. You will need set
spindle pulleys in Mach and some other configuration.

Irrelevant of the above, I suggest you don't use a stepper for turning the spindle since the torque goes way down and the rpm will not be linear.
 
BTW, if used directly as described, then if indexing, you may not get  exact degree displayed in the DRO because of resolution.

RICH

Offline xaco

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Re: how to set A-axis to move continuously,not in steps?
« Reply #2 on: September 16, 2010, 07:59:06 AM »
thanks RICH,i want to make a ring on my 4th axis,lets say i want to engrave letters using v-bit carving so where letter is thicker v-bit will go deeper. Currently  i can do this but as my chuck is heavy and steps r big(1/4 of degree) i get bad result...i also want to make rings with 3D relieves using toolpath thats not along x(my 4th axis is along x).                                                                                                i now tried  to set my 4th axis as a spindle but i didnt know how...
Quote
This is from the mach3 yahoo group,

Config> ports and Pins> motor output> enable the spindle and enter the pin
numbers for the indexer step and direction pins.
Don't forget to click on apply.
Next, click on Config> ports and Pins> Spindle set up> put a check mark in"Use
Spindle Motor output" and another check mark in step and direction.

Last go to
> config> pulley set up
and provide the necessary info.

Then in your G code you will need the M3 command and the S value.
Such as S 200 for 200 RPM ...........................................................i didnt get if i set spindle pins do i leave my a axis pins same?and what pulley is right,and do i have to set ports for spindle.what should i set to be able to make a ring ?and can my motor be set to make more than 4 steps per degree?
« Last Edit: September 16, 2010, 08:05:22 AM by xaco »

Offline stirling

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Re: how to set A-axis to move continuously,not in steps?
« Reply #3 on: September 16, 2010, 10:36:55 AM »
Just wondering but when you ask "how to set A-axis to move continuously,not in steps?" do you really mean "continously" or do you mean you want more resolution. I think maybe there's a misunderstanding going on here - at least that's what I get when I read your second post.

Offline xaco

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Re: how to set A-axis to move continuously,not in steps?
« Reply #4 on: September 16, 2010, 10:57:42 AM »
Just wondering but when you ask "how to set A-axis to move continuously,not in steps?" do you really mean "continously" or do you mean you want more resolution. I think maybe there's a misunderstanding going on here - at least that's what I get when I read your second post.
  You are right,i realized that now too,well,I would like to have better resolution,smaller steps when i do toolpath along x as i do now, I also want to be able to execute toolpaths with 4th axis that are perpendicular to x axis.For that i need 4th axis to move smooth and not in steps.I gues smooth is right word ,not continuous like lathe.I did set my 4th axis as spindle but than i cant use it as A axis,so now i changed Steps Per in motor tuning for A axis from 4 to 2000 and now i have smooth movement but now degrees  dont match in DRO as RICH said.So,is it possible to calibrate degrees from DRO with actual degrees?

Offline stirling

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Re: how to set A-axis to move continuously,not in steps?
« Reply #5 on: September 16, 2010, 02:44:22 PM »
xaco

The only ways I know of to increase a stepper's resolution is by gearing or by microstepping and microstepping for this purpose is not ideal. From what you've said in your OP it looks like you're already using 8 microsteps. 10 is the accepted maximum so it would appear you're left only with gearing.

Ian

Offline xaco

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Re: how to set A-axis to move continuously,not in steps?
« Reply #6 on: September 16, 2010, 03:04:40 PM »
Ian,how can i set those microsteps? i have steper motor(2degress/step),its not microsteper motor.The only way i managed  to get  a full circle  in practice and i DRO is if i put "4" in motor tuning "steps per" box for my 4th axis...So,can i put 2000 in "steps per" box and calibrate it to get full 360circle  in DRO and in real, or thats imposible? and how can i set my motor to do more than 4 steps per degree without adding gearing?

Offline stirling

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Re: how to set A-axis to move continuously,not in steps?
« Reply #7 on: September 16, 2010, 04:28:06 PM »
how many revolutions does your motor turn if you command G0 A360

Offline RICH

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Re: how to set A-axis to move continuously,not in steps?
« Reply #8 on: September 16, 2010, 05:33:28 PM »
- a Stepper ( 1.8 DEG ) REQUIRES 200 STEPS or pulses  to turn one rev
                  ( .9  DEG  )   "               400              "

- So if you have no gearing, or like you describe, attached directly to the the spindle and are micro stepping
 then 200 steps/rev x 4 us = 800 steps / rev for indexing. No more and no less........

- lets say you want to rotate 90 deg, then 800 steps / rev  x 90/360 = 200 steps and you would see the dro indicate 45.00 deg
                       "                       30       "         800 x 30/360 = 66.6666 steps so you will see the dro display 29.*********xx deg and not a
  even number for the degrees. That's becuase you can't  move a fraction of a step like .66 steps.In fact it may be something different than the
  calculated depending on the stepper used.

- The best you will do in movement accuracy, if all was ideal would be 1/800=.00125 of a rev = 0.45 degrees, thus your something less or more
  than a degree. Now if you increase the resolution via gearing then the resolution will improve such that you will get a display which would show 30 deg
  for a commanded G0 A 30. So if you use gearing with a ratio of 10.8 then you will get even steps and the dro will show even deg.

-Now if you use gearing, then the stepper will need to run faster for a given feedrate, and as you increase rpm of the stepper motor, the stepper
  will loose torque and thus you start to limit the max speed you can index at. Because the spindle has drag and that drag increases with velocity then
  the velocity will not linear. Just like a typical stepper curve shows.

So as Gerry (oops...Ian) said, you need gearing to get an true increase in resolution. ie: more pulses to the stepper to move the same axis travel,

RICH
              
« Last Edit: September 16, 2010, 05:40:31 PM by RICH »

Offline xaco

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Re: how to set A-axis to move continuously,not in steps?
« Reply #9 on: September 16, 2010, 05:36:42 PM »
how many revolutions does your motor turn if you command G0 A360
   if i put "4" in Steps Per it makes 1 turn (4 steps for 1 degree,so it makes 1440 steps).  ..if i put 8 in steps per-it makes 2 turns,if i put 2000 in Steps Per it will make....500 turns. ...problem is that when i set it on "4 steps per" the movement is in steps,not smooth,and i have heavy chuck and its shaking after every step,..but when i set it on "2000 steps per" the movement is fast and smooth but it dosnt match the degrees  in DRO...