Can't cut accurate circles - Any Ideas what to try next?

I've been researching and trying stuff for around a week and need to figure this out. I will put this out there - I am new to the plasma side of things but been working with CNC mill for over 5 years so I am not a complete newb.

I made my machine and just got it fired up 2 weeks ago - it cuts well and everything works. The issue I am having is that smaller circles turn out more like a square with large radius corners. At first I was thinking it was my plasma settings and then I read a post from Jim Colt about adding a marker to the torch so I did that and low and behold it has nothing to do with the plasma side of things. It still looks the same.

Here is my machine specs:

X, Y and X-Slave is running clearpath servos SDSK 3421S-ELS. I am running gear rack 20 Degree pressure angle with a 20 tooth gear running 1:1 (Direct Drive) . Gantry (X-Axis) weight is 148LBS. I am running UCCNC software and AXBB-E control .

So far I have torn everything back down and checked for any slop or anything loose. Everything is good. I have checked all the step settings and fine tuned them. I have even put them back to what I calculate them to be. In UCCNC I adjusted the Linear Error Max setting like I saw in a post and that didn't do anything. I have been using sheetcam to generate the g-code and thought that maybe it was that so I went into fusion 360 and had that generate the code and it is still is not round.

I am at a loss as to what to try next. Hoping someone had some other ideas to try.

Attachment 471534 Attachment 471538

Hi TT - Are you using dxf to transfer geometry to UCCNC? If so look at the CAD export settings. Arcs could be being decomposed into straight lines due to its settings? Peter

I am using DXF - I will look into this.

I am using Coreldraw and checked the DXF settings but there is not any really to check. Is there a better file format to use?

Hi TT - UCCNC will only import dxf. If you can open the dxf file in coreldraw you well see if it the arcs have been turned into polylines. There will be some export settings for dxf somewhere. I suspect its the dxf export thats creating the issue.. Peter

I was mistaken - I actually created the test file in Fusion 360 after I noticed that a project that I did didn't have round holes. I searched fusion 360 and didn't really see any dxf settings that I can change. Thank you for the reply - I appreciate it!

Hi TT - when you do the export the menu may have settings there. Not a 360 user so can't help but in other systems that's where its at. Peter

Try writing some test programs to draw explicit circles, withOUT using any CAD.
That will tell you whether the problem is with your CAD or your CNC.

Cheers
Roger

Here is my Gcode for my test program. Its pretty basic 1/2" circle. Does anyone see anything wrong with the following code that I can't create a circle?

(1001)
G90

(2D Profile1)
M3
G54
G0 X0.4425 Y0.0984
M10 Q64
G1 X0.272 Y0. F40
G2 X0. Y-0.272 I-0.272 J0.
X-0.272 Y0. I0. J0.272
X0. Y0.272 I0.272 J0.
X0.272 Y0. I0. J-0.272
G1 X0.4425 Y-0.0984
M11
M5
M30

I loaded your program into Mach3 in simulator mode (on my desktop).
It created a very nice circle with entry and exit at the right.

Now, if this does not create a nice circle on your CNC, then you have either a problem with the interface between your PC and your hardware, or you have a problem with your hardware, or more remotely, you could have a problem in a Mach3 setting.

You wrote " that smaller circles turn out more like a square with large radius corners". I would rephrase that as saying that smaller circles had flats on the 4 sides. This could mean very bad backlash settings in Mach3, or (more likely) some serious backlash in the mechanics. The odds of a problem with the pulse engine are rather low.

Cheers
Roger

check the screw hold the ball screw/ ball thread sometime it loose.

This is rack and pinion setup - I have checked all the racks and pinions and I even ground a flat spot on the motor shafts for the set screw and used a retaining compound on the motor shaft/pinion. I have scribed a line on the pinion and shafts to make sure they are staying where they are supposed to. I have ran that file at different speeds to see if maybe something is deflecting under a load to see if the circle gets better or worse and it is the same no matter speed. I am leaning towards a hardware or software issue but not sure where to begin with that.

I am using an older laptop to run this with a dedicated ethernet port (not a USB adapter) - I may have to hook up something newer just to rule that out and go from there? if it isn't that maybe try Mach4 ?

to see if the circle gets better or worse and it is the same no matter speed.
So the PC and the electronics are sending out exactly the same instructions? Yup.

No use trying Mach4 imho. I think there is a hardware problem somewhere.

Hum: can you write a small test program to oscillate the X axis back and forth, by (say) 1 mm?
Does the X motor spin at all?
Does the X axis move at all?
Ditto Y axis.

Cheers
Roger

Have you actually cut circles ?
Or
Do you think you will have a problem ?

It may be as simple as a wonky pen attachment, flex etc.

a wonky pen attachment, flex, etc
I never thought of that! How very humbling.
But was there a problem before that?

Cheers
Roger

Quote:

---

Originally Posted by turbotoys

This is rack and pinion setup - I have checked all the racks and pinions and I even ground a flat spot on the motor shafts for the set screw and used a retaining compound on the motor shaft/pinion. I have scribed a line on the pinion and shafts to make sure they are staying where they are supposed to. I have ran that file at different speeds to see if maybe something is deflecting under a load to see if the circle gets better or worse and it is the same no matter speed. I am leaning towards a hardware or software issue but not sure where to begin with that.

I am using an older laptop to run this with a dedicated ethernet port (not a USB adapter) - I may have to hook up something newer just to rule that out and go from there? if it isn't that maybe try Mach4 ?

---

It is sound to me it is setting issues, baudrates and take a look at tolerance interpolation. Try baudrates at the highest setting see if it make a difference.

Before try to change anything i thing try to cut something simple first like 2x2 square and measure it then another one maybe 6x6 see if the machine go to the right location. If square is come out good then baudrates is next thing you want to look at, the software not sent out fast enough signal the machine is jerking.

Could be that the stepper drives and axis drive type doesn’t have sufficient resolution to navigate a circular path accurately. So it tends to look choppy. Squares will look ok.


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Hum: can you write a small test program to oscillate the X axis back and forth, by (say) 1 mm?
Does the X motor spin at all?
Does the X axis move at all?
Ditto Y axis.

Get to the root of the problem.

Cheers
Roger

No - I can tell you what it isn't... LOL

Today I tried a different computer on it - same issue. I checked all of the power supplies today under use to make sure I didn't have any weird voltage drops. I found a loose ground connection and fixed that but it still draws the same circle - On a positive note at least it is a consistent crappy circle.

Consistent is good.
Crappy is not.
Test.
Cheers
Roger