making my machine distance work accuratly

What didn't work about the config?

If your mechanics are inch, set up your config in inches and just use G21 for metric.

John

Yes, just add G21 at the very top of the G-code and all distance will be interpreted as mm but moved in inches.

(ie G0X25.4 would move exactly one inch).

As for getting the scaling right, I find stepconf a little confusing.
The final number you want to see in the INI file is the number of steps per inch or steps per mm.

One complication may be that the rack is likely to be an imperial DP rack. That means that a 20-tooth pinion will have a pitch-circle diameter of 1", so the movement is 3.14159….. inches per rev.

I am not entirely clear what the gearing is between the motor and the pinion on the rack.
If you have a 64-tooth pulley on the motor and a 20-tooth pulley on the rack pinion, and a 20-tooth rack pinion then:
One rev of the motor is 64/20 turns of the pinion, which is 10.0531 inches. (which sounds much too big, by the way)
Assuming no microstepping that is 200/10.0531 steps per inch = 19.8943.
So, the number you want to see in the INI file is 19.8943. If all my assumptions are correct. But you probably do have microstepping, and I am not sure that the 64:20 ratio on the drive to the pinion is right either.

revo wrote:

the setup is Y and X
64 teeth on the motor pulley
20 teeth on the rack pulley
so i was thinking on the stepconf to do 3 to 1 but the step conf ask on how many teeth so do i put 64 to 20?

Well, 64:20 is not 3:1, if you put 3:1 then it will be inaccurate.
Stepconf tries to help out by doing the maths for you. But, as you have found, it isn't always helpful.

for Z, the screw move 0.5'' per revolution.

So that's either 2tpi in the Imperial setup, or 12.7mm pitch in a metric setup.
If there is no pulley involved, then just use 1 for both sizes.

i am confuse on the X and Y i dont have leadscrew. what do write there.
on the Z i dont have pulley teeth so what do i write there?

The leadscrew pitch is how far the machine moves for one turn of the screw. In the case of a rack system that means how far the machine travels for one turn of the rack pinion.
How many teeth are on the rack pinion, and what size are the teeth? This may be given in DP, mod, or possibly circular pitch.
Do you have a link to the rack and pinion specifications?

the driver microstepping, what is it exactly? some forum post say you write 1, 2, 10 or 16? this really confuse me.

It is a setting on the drives. You need to make this number match what the drives are set to.
Normally a stepper motor has 200 steps per rev, but you don't have to step in full steps. Most drives allow you to move half, a quarter, a 16th or sometimes even smaller divisions of a step.

revo wrote:

the rack is 20 pitch and 20degres pressure as it say on the cnc router parts site.

Unfortunately there are three ways to define gear pitch.
1) Module. The pitch-circle diameter divided by the number of teeth. Normally used for metric gears, bigger numbers = bigger teeth.
2) Diametric Pitch. The number of teeth divided by the pitch-circle diameter. Normally used for Imperial gears. Smaller numbers = bigger teeth.
3) Circular Pitch. The pitch-circle circumference divided by the number of teeth.

I think we can be sure that your rack isn't 20 mod, as that would mean teeth 60mm wide.
Assuming 20 DP the distance-per-rev is (pi * number-of-teeth) / 20
If it is 20 circular pitch, leave out the pi.

You can tell by measuring how far you need to move the gantry for one rotation of the pinion.