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Homing my lathe, please help
« on: August 23, 2009, 09:31:57 PM »
 I am a beginner with all this so sorry for basic questions. I just finished hooking up my stepper motors to my lathe along with installing mach 3. The kit i bought with the steppers showed me how to set up the pins and ports on mach 3 with my setup. My question is how do i home my machine out? I have no limit switchs so i would imagine i need like a soft limit or something but i really dont know where to even start. Another question would be how do i jog using mach 3, i dont have and controllers.

Thanks
Mike

Offline RICH

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Re: Homing my lathe, please help
« Reply #1 on: August 23, 2009, 10:25:02 PM »
Mike,
I assume you are using the Mach3Turns lathe screen set.

To Jog Just hit the TAB key on the keyboard and you will get the fly out for jogging. TAB again to close it.

How do you home your lathe?
Well if you don't have any limit switches  , go to the Members Docs, and there is a little write up on how to home a lathe without limit switches. ( Frankly, without limit switches, it's a PITA for me, so i don't use it ) . here is the link      http://www.machsupport.com/forum/index.php?action=dlattach;topic=11502.0;attach=15178

If you go to the Manual Screen, click the Zero World X & Z as that will cancel  all / any offsets and resets home to z=0, x=0.

Click the Home X & Z and that will set your current location to home.

The problem with all this is that you have a number of things going on and it can get confusing.
Machine coordinates - where the controlled point  ( the tip of the cutter that actually does the citting ) is at any time.
Work / Part coordinates - this is the location of the part away from home
Part Zero - where zero is on the part.

Some other confusing stuff:
Machine coordinates always read absolute and the X is Radius.
Program and part coordinates also read absolute but the X  is in Diameter or radius depending on the mode you are in.

Home can be any where you want it to be ie; at soft limits, at some part coordinate, part zero.
In fact Machine, part and home can all be at Z=0 and X=0.

Hope this helps and suggest you read the Lathe manual and play around jogging to see all this in action.
All depends on how you want to work.
RICH
« Last Edit: August 23, 2009, 10:27:16 PM by RICH »
Re: Homing my lathe, please help
« Reply #2 on: August 24, 2009, 06:22:31 PM »
Rich i cant thank you enough. I was pulling my hair out trying to find a way to home it and to jog. Thank you very much. Is it possible to jog with the nuimber pad on the keyboard? (like 4 and 6 is +z -z and 8 and 2 is +x -x)

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Re: Homing my lathe, please help
« Reply #3 on: August 24, 2009, 08:52:13 PM »
Yep,
Just go to config>system hotkeys pick the keyboard key you want to use for each of the axis.
They are on the left side fo the screen, just click the axis and it will activate a fly out asking you to press a key.
RICH
Re: Homing my lathe, please help
« Reply #4 on: September 07, 2009, 10:58:19 PM »
Here is my new problem. I watched the link you gave me on homing my machine, i jog both x and z , zero x and zero z in parts corr. I then click on machine corr and click set x home and set z home. For some reason my x starts moving and won't stop. It won't let me home it out. Anyone have this problem?

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Re: Homing my lathe, please help
« Reply #5 on: September 08, 2009, 02:46:19 PM »
Mikey,
Are you still trying to set up a lathe which dosn't have swithes to go back to a home position?

RICH
Re: Homing my lathe, please help
« Reply #6 on: September 08, 2009, 03:49:29 PM »
correct, I am trying to home it without having switches. I saw in that link on how to use the soft limits and such but as soon as i hit set x home it desides to start moving and wont stop.

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Re: Homing my lathe, please help
« Reply #7 on: September 08, 2009, 07:37:01 PM »
Mike,
Lets see if i can be of help.

1. Open Mach Turn, click the AUTO button, in Auto screen and located under the axis position DRO's there is a button "Soft Limits ON and OFF".  CLick that button so the box next to it is black and not green. This turns off
any soft limits you may have set up.

2.Click the Quit Load button in the lower right corner of the screen.
   You will be taken back to the screen that Mach Turn opens with.
 
   Now click on the Manual button ( takes you to the manual screen ).

- Just jog the carriage to some safe spot like the middle of Z & X travel  of the axis.

3A. In the Manual mode screen

    Click the Zero World X button and also click the Zero World Z button.     
    This cancels any fixture offsets that may exist ( like g54, g55 ).
    Notice that the DRO's are now zero.

3B. Click the Set Home X and also the Set Home Z. The axis should not go anywhere.
     You have just defined to Mach that this is "HOME".
 
     CLick the HOME X  and then the HOME Z buttons and also the HOME ALL button.
     Nothing happens because you are home!

4. Now jog both axis away from home some distance , say  1" approx.
   Note that how far you moved is shown in the DRO's.

5. Now click the HOME All button.The X axis moves to home and then the Z axis will move to home.
     Notice that the DRO's are back to 0,0.

So, you can set home anywhere you want it to be. Mach keeps track of the movements / offsets from home
and if you were to type  G28 ( return home command ) in the MDI box the axis will always go back to home.

ANALOGY:
Captain Kirk tells Scotty that he's tired of having his crew get lost when they beam down to the planet Earth from the Enterprise.
Scotty say's that will not be a problem any more becuase he has programmed everyones trackiing device such that no matter where they are , all they have to do is hit the G28 key or the home all key and they will be beamed right
back up to the spaceship.

So try # 1 to #5 above and let me know how it went. Then we will continue on with the story.!  ;)
RICH
Re: Homing my lathe, please help
« Reply #8 on: September 08, 2009, 08:23:50 PM »
Thank you rich, it sounds like it should work although i wont be able to find out till thursday, tomorrow im taking a day trip to atlantic city  ;D . I have another question maybe you can answer and i understand it has nothing to do with homing my machine but you seem to know everything i throw at you so ill ask you this also. I have my nema 23 motors hooked up to my fet/3 dynamic driver from stepperworld.  (note im still in the process of setting everything up) I hooked up a dial indicator and used a command line to move the x axis like .020 . the dial indicator shows it moved like .003 . Now i know i need to tune the motors to my specs and i need to change that "steps per" number according to my calculations for the lead screw and whatnot. My problem is the math. I feel like the number needs to be between like 8000 and like 12000 but im not really sure if that seems right. I looked at all the formulas on the manual and i keep messing up the answer for it. Perhaps you can help? or is that uncharted territory? Let me know cause i can write back with the numbers but if its too much trouble dont worry about it

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Re: Homing my lathe, please help
« Reply #9 on: September 08, 2009, 09:58:20 PM »
Mikey,
It takes 200 steps to turn the stepper motor 1 compete revolution. ( this is for a 1.8 degree stepper which you probably have, there are .9 degree steppers and they would need 400 pulses to turn one rev )

Most drives provide for micro stepping, ( 2,4,8,10,16, 32 ? look at your drive info ), mine uses 10.

Then you have the screw lead. If the screw has 20 threads per inch, then you would need 20 revolutions
of the screw to go one inch.

Thus for a unit of 1 inch: ie;
200 steps / rev x 10 u steps x 20 rev/ inch= 40000 steps / unit for my lathe.

The resolution is equal to 1/ steps unit.
so  1/40000=.000025" ( the smallest unit of axis movement is dependant on just how good the system components are).
For example; I have an engraving machine that uses 254000 steps / unit. So the resolution is 0.000003".
I can split a thou into 10 parts  and measured the movement with a microscope, the point is, practicaly speaking, is that the theoretical resoltion is very small so you can move the axis in small increments. Big whoop! The engraving points have more than .002" of run out.


For a new retrofit i am currenty doing, i will provide  a reduction of 2:1 but the screw is 5mm ( .197" pitch, so 1/ .197=5.076 revolutions required for 1 inch of axis movement)

Thus: 200 x 10 x 2 x 5.076 = 20304 steps / unit  
Resolution is 1 /20304= .00005" hopeful i will have the ability to move in less than .001" movements, accurately......we will see)

Hope the examples help,
RICH