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### Author Topic: DRO Doesnt Match Real World  (Read 3368 times)

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#### innsoft

• 6
##### DRO Doesnt Match Real World
« on: April 02, 2009, 01:09:53 PM »
I recently purchased a Taig Mill that I have been experimenting with it in my spare time the last couple of months.  One problem that I have in trying to get started is that the readings in the DROs is way off.  All that I have learned to do so far is to use the jog feature and when I try to move the head of the unit manually in any axis then the readings are way off.  If I move 4 inches it will tell me about 30.********* inches - anyone that could help I would appreciate it.

#### Hood

• 25,838
• Carnoustie, Scotland
##### Re: DRO Doesnt Match Real World
« Reply #1 on: April 02, 2009, 01:37:56 PM »
you need to set the steps per unit correctly. If you are using imperial (Inch) then this is what you need to work out.
If its steppers are they 200 step per rev or 400, they will most likely be 200.
What stepping or microstepping are your drives? this could be full, half or 8 or 10 or?
Do you have any reduction between motor and screw?
What is the pitch/tpi of the screw?
When you know that you can work it out, I will give an example  of 200 step motor 10 microstepping drive, 2:1 gearing and 10 tpi screw.
200 x 10 =2000 ( pulses for one motor rev)
2000x 2 =4000 (2 motor revs for one rev of screw)
4000 x 10 = 40,000 (10 turns of the screw to move 1 inch)
So your steps per inch would be  40,000

Hood

#### innsoft

• 6
##### Re: DRO Doesnt Match Real World
« Reply #2 on: April 02, 2009, 06:24:32 PM »
Thank you for your help!  The question next is: how can I find out if there is gearing (I dont think that there is) and what the tpi is of the lead screws?
the steppers are PowerMax II - BiPolar - 200 steps per rev - (1.8 steps)
The Lead Screw is 5/8 inch dia.

#### Hood

• 25,838
• Carnoustie, Scotland
##### Re: DRO Doesnt Match Real World
« Reply #3 on: April 02, 2009, 06:33:40 PM »
I am not familiar with the Taig mills but I am sure a few here have them.
If the motors are connected direct to the screws then there is no gearing, if they are connected via a belt then the pulleys will determine whether they are geared or not, ie if the motor pulley is half the size of the scew pulley it will take 2 revs of the motor to turn the screw one turn.
To find out the TPI its just a matter of counting the teeeth in one inch of screw.
Hood

#### budman68

• 2,354
##### Re: DRO Doesnt Match Real World
« Reply #4 on: April 02, 2009, 07:14:03 PM »
innsoft, the Taig originally has 1/2"-20 leadscrews on all axis and the steps per inch should be 8000 for those motors-

Dave
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Just because I'm a Global Moderator, don't assume that I know anything !

Dave->

#### innsoft

• 6
##### Re: DRO Doesnt Match Real World
« Reply #5 on: April 02, 2009, 09:31:04 PM »
The Threads are 20 per inch

#### budman68

• 2,354
##### Re: DRO Doesnt Match Real World
« Reply #6 on: April 03, 2009, 04:55:56 AM »
As mentioned in the post just above yours -

Dave
----------------------------------------------------------------------
Just because I'm a Global Moderator, don't assume that I know anything !

Dave->

#### innsoft

• 6
##### Re: DRO Doesnt Match Real World
« Reply #7 on: April 05, 2009, 11:19:33 PM »
Thank you for your help I am getting much closer DRO readings now compared to before