# Problem



## Mike_indiana (May 16, 2018)

Hi guys. I am a new one here.
And I have a question.
I bought a Chinese 60/40 USB-CNC Router. When I give command Z-20 movement is 20mm down.When I give command Z20 movement is 12 mm up.
I mean I give the same command but the movement is different. I have problem with electronics or I miss something with settings? Please help.


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## woodknots (Mar 7, 2012)

Mike in Indiana - welcome to the forum - when you get a chance go into your profile and add your first name - when this post disappears from the front page, folks will have to guess at your name. Anyway, I'm not into CNC but there are a lot of experts here and I'm sure they'll be along soon enough to get you some answers.


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## difalkner (Jan 3, 2012)

Welcome to the forum, Mike! Ditto what Vince said on your profile. Otherwise you'll get called N/a at some point...

Just out of curiosity, type the full command and see what happens - G01 F25 Z-20.0 and G01 F25 Z20.0

Are you relying on the DRO for the 12mm distance or are you measuring it? Could be that your DRO is off but the machine is actually moving 20mm up.

It may not make any difference at all but more curious than anything else.

David


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## old55 (Aug 11, 2013)

Welcome to the forum Mike.


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## Mike_indiana (May 16, 2018)

Hi again guys.
I will add some info about my problem and I will fill up my profile later.
As I said I bought a Chinese USB-CNC.
This machine is connected with a computer through USB and and it use Chinese software. This software allows to give different numbers to X Y Z A axes to calibrate real movement of any of them.
I put 380 for X and Y and they work good.
There is a small window where I can type for example
X20/ enter and X axes moves right 20 mm
X-20/enter and X axes moves left 20 mm.
The same is for Y axes.
The shaft of Z axes is different and the machine needs different number.
It is easy to get the right number.
When I type 
Z-20/ enter Z axes goes down 20 mm and it is Ok. The problem is when I type
Z20/enter Z axes goes up not 20 mm. It goes up 12 mm. The motor turns 5 times when it goes down and it turns 3 times when it goes up. In fact the command is the same. Difference is direction only.
After first energizing of the machine in 5 minutes power supply was out of order.No power.No work. I texted the seller and he/she instead of power supply sent me a new board. It contents 3 drivers and a break out and another small one for A axes.I didn't want to wait time and I bought power a power supply and I installed it and I explained you the result.
I switched the boards but the result was awful. X was moving 20mm in positive direction and 30 in negative.
Y - 5mm and 35mm
Z - 20mm and 15mm.
My question is it possible to fix this using settings or I need a new electronics?
Thank you for your time.


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## BalloonEngineer (Mar 27, 2009)

What you get when you enter those commands depends on whether your machine is in g90 mode or g91 (absolute vs. incremental). See if your controller lists which modal commands are in effect, on Mach3 or Mach4 they show up on screen. 

Generally machines default to absolute mode. X20 means move to where x=20, not move 20 units. X-20 means move to where x=-20. Depending on where you started, these may not be the same distance. You are better off entering the commands in full, 
G0 X20. (make sure you enter G ZERO, NOT G OH)

Enter G0 X0 Y0 to see where “home” is, then enter those commands. You may find you need to calibrate your axes. 
Most people set up their machine home position (G53) in lower left corner, so all points are in positive quadrant, and no coordinates are negative. They may set a temporary work “home” at center of a workpiece (G54), if that’s how it was set up in their CAM. 

G0 and G1 are modal commands like G90 or G91, and stay in effect until cancelled. G0 moves at each axis max speed (may not be in straight line), G1 moves in a straight line, coordinating all axes at once. Most controllers allow switching the DROs between showing “machine” coordinates or “work” coordinates.


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## difalkner (Jan 3, 2012)

Are your stepper motors calibrated correctly?

David


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## reuelt (Dec 29, 2008)

*Trouble shooting*

You need to troubleshoot in correct order.

1. With power-off. Check mechanical coupling and freedom of movement.

A Crank like (or make one yourself) can helps
https://www.ebay.com/itm/CNC-Steppe...9632?_trksid=p2349526.m4383.l4275.c1#viTabs_0
Crank or turn the z axis stepper motor manually to check freedom and accuracy of z-axis movement.
Counting how many rev. you turn up and down and measure movement.
A loose coupling must be tightened.

2. Then check you z-axis wiring for proper continuity.
Many people replaced the signal cable with shielded cable with the shielding grounded.

3, Calibrate you z-axis stepper motor. The speed, accel of the z-axis is usually 1/2 of those set for x or y axis.
Slow down if you have missed pulse meaning the stepper did not reponse with all the pulses.

4. Check whether you are in absolute or relative mode in software and re-calibrate your z-axis.

Crank is useful even when no more troubles.


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