X and Y Axis Travel Calibration

Hey Guys,
This has probably already been asked before, but after hours of reading I cannot find any answers.

I have a harbor freight x3 mill, with a cncfusion double ball nut kit on install it. I installed the kit years ago and then the machine sat for a couple of years. I tore the machine apart because one of the ball nuts came loose on the x axis. I cleaned everything up and put the machine back together.

So after putting it back together I configured my axis's in mach and put a dial gauge on the x axis to see if I got the steps calculated right.

Here is my math
Stepper motor 200 turns per revolution
Ball screw 5mm pitch
1" = 25.4mm
Stepper Driver 10usteps
200 * 10 = 2000 steps per revolution
25.4 / 5 = 5.08 revolutions per inch for the ball screw

2000 * 5.08 = 10160 steps per inch
I think the math is right on that.

So I attached the magnetic base that holds the dial indicator to the table. Ran the point of the dial indicator into the head of the machine and zeroed out the dial indicator. I zeroed out the x axis in mach and ran the table 1 inch. The reading on the dial indicator read 1.012. So I ran the table back and forth numerous times and the reading was always the same and when I ran the table to zero the indicator showed zero.

I was thinking that if the problem was step counts per inch then if I ran the table from 0 to .5 inches then the reading should be .506 inches but it actually read .496. So I am not sure what to think. Years ago when I set the machine up it would run perfect over an inch distance. Perfect to me that is always within .001 of and inch of the desired movement.

I'm not sure what the problem is, if it was backlash the indicator would not go back to zero. Or is that an incorrect thought?
Would over tightening the 2nd ball nut cause this?

Does the dial indicator have to be perfectly perpendicular to the head and parallel to the x axis for the reading to come out right?

Thanks
Nick

My guess is that your screws are 5 turns per inch, not 5mm pitch, though they come out very similar in actual effect. That means that instead of 5.08 in your calcs you should use 5.00. This will give you 10,000 steps per inch. That said, you should be able to input a measured distance versus a commanded distance and the software will calibrate that accordingly. I’m not sure what control software you are using, if it’s Mach 3, there is a steps per unit option that is used for calibration.

CL_MotoTech,
You are right about the turns per inch, I just went back to the cncfusion site. The deluxe ballscrew kit is 5mm pitch, the standard kit I got is 5tpi. I will try that tonight. I am using mach right now, once I get the machine setup I might play with linuxcnc.

Thank You