# Gearbest T8 CNC DIY Engraver: Engraving inaccuracies



## Turtle_510 (Jul 31, 2019)

Hi all, 

I'm very new to the CNC engraver world and this is my very first project. I have everything setup and I'm running some rectangle tests cuts using Inkscape and Grbl Controller 3.6.1. However, there's a consistent mistake on the left edge of the rectangle where the bit does not go back perfectly to it's starting point. This causes there to be an offset to that edge, but the odd part is that the other edges seem to be correct. Beforehand, while engraving a more complex piece (turtle), you can also see the x-axis moving away significantly (both back and forth) from it's initial cut. 

I've checked the g-code, leveled the bed, tested the hardware, and have not found a solution yet. 

I'd like to ask the CNC community for some guidance on what might cause this silly issue :crying:.


----------



## ger21 (Feb 10, 2019)

Looks like a mechanical issue, like a slipping coupler or pulley.


----------



## difalkner (Jan 3, 2012)

Welcome to the forum, Amy! I agree with Gerry, seems like it has to be mechanical. Can you post some photos of your setup?

David


----------



## stevenrf (Jul 30, 2010)

Check fo backlash


----------



## MEBCWD (Jan 14, 2012)

Welcome to the Router Forums Amy.

I agree that it looks like a mechanical issue Post some pictures of your CNC machine so we can see how it is built.


----------



## Turtle_510 (Jul 31, 2019)

Hi all, 

Thank you all so much for your response! This community is so friendly. 

I went back and realigned all the rods and tightened all the screws. When doing some square test cuts (.2 depth step and 1mm deep total), they came out perfectly. Then I went on to cutting out something more complicated, the mushroom. The first two rounds were perfect, but during the third round, I hear a sort of click (I don't know where), and this caused the engraving to stray, again on the x-axis.


----------



## MEBCWD (Jan 14, 2012)

It doesn't look like you have a vary big working (cutting) area. You might have hit the limit of travel and lost some steps.

To visually show where your cutting area is you can run the table all the way to the left and put a piece of tape across the bed front to back at the point where your bit is, run the table all the way to the right and put a piece of tape across the bed from front to back at the point where your bit is. Do the same thing running the table all the way to the front and back, repeat with the tape. That way you can see if your design will fit in the working area.

With small CNC machines it is common that the user will hit the upper limit of the Z axis and lose the Z zero. Doing this makes the Z height reading higher and cuts will be deeper. Just watch out for this in the design file and setup for safe Z height.

What software are you using for design and output of your toolpaths? (Edit) Remembered you were using Inkscape!


----------



## difalkner (Jan 3, 2012)

Amy, does the spindle shaft have any wobble to it? With it off, can you move it in any direction except rotating? I just wonder what the runout is on that motor and shaft. I assume the bit is tight in the collet, but have you checked that? The square looks good so I'm not sure this is a problem but it's probably good to eliminate it as an issue.

David


----------



## Turtle_510 (Jul 31, 2019)

Great news! While checking all your solutions, I believe I found the problem. The spindle motor wires seemed to be affecting the axis stepper motors, so when separating these two components (and again, making sure all the screws are tightened), these two engraving came out perfectly. 

Thank your all for your help~


----------



## difalkner (Jan 3, 2012)

Ah, yes, electrical interference. The wires must not be properly shielded. If separating them worked then I guess you can either make sure they stay separated or replace with properly shielded cabling.

That looks much better, btw.

David


----------



## MEBCWD (Jan 14, 2012)

Well Amy you are well on your way to good carvings. Those look really good now. I like the turtle!


----------



## RainMan 2.0 (May 6, 2014)

Turtle_510 said:


> Great news! While checking all your solutions, I believe I found the problem. The spindle motor wires seemed to be affecting the axis stepper motors, so when separating these two components (and again, making sure all the screws are tightened), these two engraving came out perfectly.
> 
> Thank your all for your help~


Maybe Avid CNC has a good idea by keeping their VFD in a separate enclosure? Although it has been mentioned that they do it more because their main enclosure is to small.

Glad to hear you got this resolved,great find


----------



## BalloonEngineer (Mar 27, 2009)

RainMan 2.0 said:


> Maybe Avid CNC has a good idea by keeping their VFD in a separate enclosure? Although it has been mentioned that they do it more because their main enclosure is to small.


The main issue is running spindle wires parallel to others (like in cable chains). Shielded cables and proper shield termination helps.


----------

