GRBL: inaccurate on X axis by ~4mm on 40cm

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This is GRBL-related. I have a laser-engraver type machine, Chinese, ~55 cm X axis, aluminium extrusions, 2mm-pitch T belt, Nema 17H3430 motors, one mechanical homing switch for X, Arduino-based.The X-axis accuracy is not up to par. When I make a mark on the X axis and jog to that mark (after homing), depending on the day, the position varies within ~4mm or so from G00 X-418 to G00 X-422. I checked the belt tension, it is seems OK, not too tight, not too lose. Is there something else I should check? Another idea I have: put a homing switch on the other end of the X-axis, then home both ends of the X axis, measuring the difference in machine position, then modify the steps/mm value for each session to force to command that puts me on the mark to be constant (e.g. G00 X-420). Any other ideas? Thanks.

Last Edited: Mon. Oct 21, 2019 - 01:58 PM
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Have you contacted the machine manufacturer and/or supplier for support?

 

Do they have any test / calibration utilities?

 

Have you googled the make & model to see if this is a common complaint?

 

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awneil wrote:
Have you contacted the machine manufacturer and/or supplier for support?

It's a cheap, no-name Chinese kit, no manual, no brand name, I can't really contact anyone. The included software was Benbox, I don't use it. The issue isn't really one-time calibration but repeatability. With a ruler, I can measure the distance from home 0 to the mark on the X axis and set the steps/mm correctly so that e.g. G0 X-420 arrives at the mark. However, the next day, the same command may be off by 2mm either way, i.e. the next day the required command (after homing) could be G0 X-418 etc. I'm trying to either 1) improve mechanical accuracy, 2) come up with some automated homing procedure that ensures accuracy

Last Edited: Mon. Oct 21, 2019 - 02:10 PM
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element333 wrote:
It's a cheap, no-name Chinese kit

So has it ever performed any better?

 

element333 wrote:
The X-axis accuracy is not up to par. 

How are you defining, "par" ?

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  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
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Do you have control over the speed at which it seeks to a new position, if so what happens if you cut your speed in half?

 

Jim

 

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I’d be checking the motor, driver, power supply and the mechanics (does it slide easily?). 10% error is way too much, so it seems you’re missing steps. The longer you run it, the greater the error.
Check the torque output from the motor by using your fingers. Compare this to the y motor at the same speed. Not a precise methos, but should give an idea if the x torque is significantly less than the y.

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Its 1%, not 10%. 4mm out of 40cm.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

Last Edited: Mon. Oct 21, 2019 - 09:28 PM
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Oops! Must’ve sneezed when i put the decimal point in!

Generally, with these cheap chinese machines, you need to tweek them to make them work properly. Ie check alignment of the guide rails, some lube etc. all the things that take time on the production line that don’t get done properly. If it’s a common machine, there should be a website where people post their ‘fixes’.

Last Edited: Mon. Oct 21, 2019 - 10:33 PM
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element333 wrote:
This is GRBL-related

Is it?

 

Or, as Kartman suggests, is it down to the cheap mechanics ?

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...