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can not calibrate axis
« on: September 04, 2008, 07:36:50 PM »
i am about to pull all my hair out. i have a knee mill i converted with 3 stepper motors  3 kl4030 driver cnc4pc breakout board and a 36 volt power supply i have tried everything to calibrate my axis i have used calibrate axis button if i calibrate axis for 4" then go to mdi line and type y 4 the axis moves exact 4 then y -4 it moves exact if i type y2 it lacks about .25"then is i type y 6 it over shoots by .1 if i calibrate for 6" then six is exact  or if i do 2" it is exact.  i took a dail indicator and put on the axis and turned motor by hand and counted revs and figured how many /inch and multiply by my micro step by 200 for 1.8 degree stepper this was not even close on movement can noise cause this or maybe its my computer i have spent about a week trying every thing i can it is driving me crazy

Offline Hood

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Re: can not calibrate axis
« Reply #1 on: September 05, 2008, 02:12:37 AM »
What is the pitch of your ballscrews, what is the microstepping? What is the gearing between motor and axis? Are your steppers definitely 1.8degree?
If you give us that info we can tell you what your steps per should be set to and if its not accurate at that then there are other problems. There have been a lot of reports recently about the CNC4PC breakouts having problems, is this a problem on ALL axis or just one?
 For your computer have you run the driveer test to see what the pulse looks like?
Hood

Offline jimpinder

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Re: can not calibrate axis
« Reply #2 on: September 05, 2008, 06:42:44 AM »
As Hood says - a bit short of details.

You do not calibrate for different distances, or over different distances. In Config/Motor Tuning bottom left hand - Steps per, the question being asked is - How many pulses must Mach3 put out to move 1 unit - inches or millimeters. We assume you are in inches.

This figure MUST be calculated - not measured. It is simple.

If yours are 1.8 degree motors - 200 steps. On your drivers you have the ability to use microstepping - try 1/8 step as a good compromise - 200 x 8 = 1600. Any gearing between the motor and the leadscrew - mine is 3 to 1 - 1600 x 3 = 4800 and finally the pitch of the leadscrew. Don't try measuring - unless you bought it from a car boot sale , the seller will know what pitch it is and tell you. If you are using the original leadscrews on the machine, then the dials will tell you - mine are 10 rev to 1 inch. If it is a metric leadscrew then set the machine up in metric it is easier ( and use G20 to move back to Imperial)

Therefore my steps per is 4800 x 10 = 48,000. Enter this in steps per. Set your velocity to something modest to set off with - say 4 and your acceleration to 0.5 or at the most 1.

The way to measure if this is accurate is  - make sure backlash compensation is OFF -  (starting at x0y0) enter in the MDI line g0x0y1. The table will move 1 inch. Do not try and measure this, it was only to take up any backlash. Set up your measuring device (I use digital calipers) and zero them. Type in g0x0y2 and the table will move another inch. Measure this and it should be accurate to within (+ - )1 or 2 thou. You cannot measure better than that unless you have some very expensive measuring equipment.

If your answer is 1 inch, you are calibrated. If it is seriously astray then something is wrong and come back.

If you then type in g0x0y1 the table will return -1 inch, although it wont be 1 inch becasue of backlash. If you measure the shortfall this is backlash and can be entered in the backlash table.

Repeat for the other axis. (including the calculation of steps per if the set up is different).

You are calibrated. Switch on backlash compensation, set it at 50% and you are ready to roll.

You can go back to the Motor Tuning and gradually increase the velocity until the motors start to miss steps - you will hear this as a loud whining sound - set the velocity back a couple of steps to ensure this does not happen when you are using the machine in anger. Do the same with the acceleration.

On the Motor Tuning page - after any alteration - click Save Axis Settings BEFORE you leave that page, otherwise the settings will revert to what was previously set.

Like the flag - has Independance been declared  ;D
« Last Edit: September 05, 2008, 06:44:25 AM by jimpinder »
Not me driving the engine - I'm better looking.

Offline Hood

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Re: can not calibrate axis
« Reply #3 on: September 05, 2008, 10:02:44 AM »

Like the flag - has Independance been declared  ;D

Hopefully that will be the case in two years time :)

Hood
Re: can not calibrate axis
« Reply #4 on: September 05, 2008, 12:29:23 PM »
Quote
Hopefully that will be the case in two years time Smiley

Yes and with a bit of luck the unelected twat currently running the country ::) will be back there with you Hood  ;D

Phil_H
The Good Thing About Mach3, Is It's very Configurable

The Bad Thing About Mach3, Is It's Too Configurable

Offline Hood

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Re: can not calibrate axis
« Reply #5 on: September 05, 2008, 12:33:17 PM »
Nope he is more of an Englishman than a Scotsman, you can keep him, after all it was middle England that voted his party into power.
 If however you insist on sending him North then I am sure we could get a good case against him and thus hang him for treason :)
Hood
Re: can not calibrate axis
« Reply #6 on: September 05, 2008, 12:44:55 PM »
Quote
Nope he is more of an Englishman than a Scotsman, you can keep him, after all it was middle England that voted his party into power.

That's where Jim is.

I seem to remember a story about some terrorist's that had been caught plotting to to kill him and Tony "Honest" Blair.

I now know its true that not all terrorists are bad. ;D

Phil_H
The Good Thing About Mach3, Is It's very Configurable

The Bad Thing About Mach3, Is It's Too Configurable

Offline Hood

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Re: can not calibrate axis
« Reply #7 on: September 05, 2008, 02:28:38 PM »
Now thats a good idea, send him to Jim, I am sure they will become best of buddies ;D
Hood

Offline jimpinder

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Re: can not calibrate axis
« Reply #8 on: September 06, 2008, 03:57:18 AM »
My mother was Scottish - I might come home :D


Have we lost the thread of this post ?
Not me driving the engine - I'm better looking.

Offline Hood

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Re: can not calibrate axis
« Reply #9 on: September 06, 2008, 04:10:56 AM »
My mother was Scottish - I might come home :D


Have we lost the thread of this post ?

we can only allow half of you in that case  ;D
Hood