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Scaling Problem - Help Needed
« on: October 13, 2009, 08:37:10 AM »
Hi all

I need help with scaling :

I have set up my milling machine using Mach 3 software but i've come across a scaling problem between the X and Y coordinates on the screen and the X and Y coordinates on my milling table.

For example : a movement of 200mm on the table relates to 0.9mm on the DRO's

How do i set the correct scale on both X and Y axis so that 100mm on the DRO's equal 100mm on the table.

I've comfigured the software in mm's and i've set the milling table size in the Homing/Limits page.

Kind Regards

Rick

Offline Fastest1

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Re: Scaling Problem - Help Needed
« Reply #1 on: October 13, 2009, 08:40:02 AM »
It sounds like your steps per unit is incorrect. What pitch is your leadscrew? how many steps on your steppers? and what microstep did you select? These are what will affect the differences in travel from what I understand.
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)
Re: Scaling Problem - Help Needed
« Reply #2 on: October 13, 2009, 09:27:58 AM »
It sounds like your steps per unit is incorrect. What pitch is your leadscrew? how many steps on your steppers? and what microstep did you select? These are what will affect the differences in travel from what I understand.

Thanks for the quick reply

The stepper motors are 1.8 degrees full step but i'm running them at 1/2 step.

I'm not using a lead screw on the X and Y drivers. My milling machine has a toothed wheel and belt system, each belt pitch is 2.03mm and the toothed wheel outer diameter is 12.93mm and the pitch is 2.03mm with 20 teeth.

The size of my working table area is 435mm x 275mm

see here for more info :
Pully - http://www.mcmaster.com/#1375K39
Belt - http://www.mcmaster.com/#7959K21

Kind regards

Rick

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Re: Scaling Problem - Help Needed
« Reply #3 on: October 13, 2009, 09:46:42 AM »
Sorry I wont know the equation for the belt system but your steppers are at 400 steps now not including the travel part of the equation. But with some crude and probably incorrect figuring, I come up with about a 6 to 1 ratio on your pulleys (I could be wrong here). This is only a guess 200 steps x 2 (1/2 steps) x 6 (reduction gear) I would plug in 2400 steps per unit and test the movement. Just change 1 axis and check it. You can always go back.
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

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Re: Scaling Problem - Help Needed
« Reply #4 on: October 13, 2009, 10:01:42 AM »
That figure I provided sounds low. I run 8000 steps per unit. Can you measure travel of the table only using 1 revolution of the pulley on the stepper (even manually)? While not under power?
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)
Re: Scaling Problem - Help Needed
« Reply #5 on: October 13, 2009, 12:09:45 PM »
Hi

I've been reading the manual and i've now set the steps to 1/16 and i'm using for the time being 800 steps per unit. this figure seems to be as close as i'm going to get it until i can work out the proper equation!!

regards

Rick
 

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Re: Scaling Problem - Help Needed
« Reply #6 on: October 13, 2009, 12:11:58 PM »
Find Hood or Tweakie here on the forum. They seem to be quite experienced. Good Luck
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

Offline Hood

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Re: Scaling Problem - Help Needed
« Reply #7 on: October 13, 2009, 01:50:11 PM »
Not really sure how to calc with pulley and belt but heres what I think.

If you have 200 steps per rev of the motor and 16 micro steps that is 3,200 steps per rev of the motor.
You have a pitch of 2.032mm and one rev moves 20 teeth so thats 20 x 2.032 =40.64mm per rev
Steps per mm will be 3,200/40.6 = 78.74015748031496062992125984252 steps per mm.

Hood
Re: Scaling Problem - Help Needed
« Reply #8 on: October 14, 2009, 10:12:37 AM »
Hood

Thx for working out the steps per mm.

Quick question. I've tried using the Automatic Setting of Steps per Unit and is almost sync in the X, Y and Z axis.

Would using your calculation be more accurate than using the Automatic setting built into Mach3?

If it's better to use the Automatic settings is it better to measure over a longer or shorter distance?

The reason i ask regarding the distance to measure is because at the moment after using the Automatic settings over a short distance the movement is perfect but as the distance increases the accuracy reduces, this can be up to 1mm over a distance of 100mm.

Thanks for your help in advance

Rick


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Re: Scaling Problem - Help Needed
« Reply #9 on: October 14, 2009, 10:18:50 AM »
The automatic calculation will only ever be as accurate as you can measure, if you can measure accurately over a long distance then it will be more accurate than over a short distance.

Calculating will be the most accurate method as you are not relying on measuring but it will of course depend on the hardware such as belts and pulleys being accurate.

The thing that has me wondering if I have calculated correctly is your previous post said you had 800 steps per unit set and my calculation is ten times less.

Hood