# Centre finder problem

Hello, the centre finder does not work for me or a friend on a different machine. i drew a circle 160mm diameter and checked 3 points on the circle at coordinates (229.12 x, 223.66 y), (274.11 x, 85.71 y) and (146.13 x, 114.93 y). The calculated centre was 215 x, 176.2 y which the machine jogged to but it is way off the centre of the circle. The actual centre is at 220.88 x, 146.99 y

To rule out my machine being the issue, I then plotted the above points on the Lightburn screen with centre finder and it still calculated the same centre which is way off.
Any ideas?

Thanks

The way you’re describing this makes me think you’re doing something other than what’s intended for center finder.

Center finder is meant to find the center of an existing piece of material. So imagine you have a circular piece of wood that you’re trying to engrave to. Center finder would allow you to locate the center of that piece of wood so that you can properly align your shapes to the located center.

How you’re describing it makes me think you’re approaching this the other way around where you’re trying to take a circle you have in LightBurn to somehow be applied to the laser.

I may be misunderstanding so please clarify if I’ve misinterpreted.

Hello, the centre finder was used as you suggest to try and find the centre of a round piece of wood. Thankfully, it was so far out it was obviously wrong and no damage was done. The test on a circle was to prove if it works or not. I have done many tests prior to the circle test as described and every one of them failed to find the centre.
Thanks

After going through the Center Finder wizard there is an option on the last page to add guide circle to project.

If you add that it should be placed on your workspace at the absolute coordinates of the circle. If you select that circle and do a rubberband frame it should follow the perimeter of the material perfectly. You will need “Cut selected graphics” and Absolute Coords configured to do that properly.

Additionally, pushing “Jog to circle center” should in fact move to the geometric center of the circle.

Is this not how it’s behaving? If so, where is it deviating?

If not can you confirm the following:

1. You are homing your machine prior to use
2. You are not ever moving the laser head by hand after homing, using jogging controls exclusively.

Hello, Thanks for your reply. i did see the option to add a guide circle to the workpiece but I didnt understand that, I will try again tomorrow and let you know.
I can confirm that the machine was homed prior to using it and the laser was not moved by hand at any time. as far as i can see, the feature is to find the physical centre of a workpiece on the bed? The item was placed on the bed and the laser was jogged to 3 different points at approx 1/3 of the circumference. After this, the “jog to centre” button was pressed and the laser did indeed jog to the calculated centre but this was not the centre of the workpiece. I will check out the guide circle tomorrow but don’t understand why the calculated centre is not the physical centre of the circle from which the 3 points were taken from? Thanks.

Interesting. This should have worked so is telling.

Can you confirm the following:

1. What version of LightBurn are you running?
2. What OS
3. What laser?

I haven’t tried the Center Finder in 1.4.00 but will try to retest today.

Interesting indeed!
Lightburn version 1.3.01
Windows 11
Self built diode laser
Cheers

Hello, just tried it again. I made sure absolute coordinates were on this time as i normally use Current Position. It made no difference and the laser jog-to position was as far out as before. Its 32mm more Y and 10mm less X than it should be. The guide circle was placed on the screen and a rubber band frame went around where the circle should have been but not where it actually was.
I looked at the home position and found something odd. Home is in the front left corner and the switches are all tight and consistant in their switching position. The homeing pull off is 2mm and dust marks on the frame show that both axis have a wiped section 2mm long after homing. The “Get Position” button returns an X value of 2 as expected but a Y value of -18.

I feel sure this has something to do with it but i cannot understand why the system does not take the limit switch actuation point as zero and back off 2mm, like i said, the Y dust wiped mark is 2mm. Calibration has been checked and is fine. Even it the cal was out, why would it show Y as -18mm after homing?
Hope you can help!
Thanks

Can you run these commands in Console and return output?

``````\$H
\$I
\$\$
\$#
?
``````

Hello, this is what I got.
\$H

ok

\$I

[VER:1.1h.20190825:]

[OPT:V,15,128]

Target buffer size found

ok

\$\$

\$0=10

\$1=25

\$2=0

\$3=1

\$4=0

\$5=0

\$6=0

\$10=0

\$11=0.010

\$12=0.002

\$13=0

\$20=0

\$21=1

\$22=1

\$23=3

\$24=50.000

\$25=1000.000

\$26=250

\$27=2.000

\$30=1000

\$31=0

\$32=1

\$100=80.055

\$101=80.135

\$102=800.000

\$110=6000.000

\$111=6000.000

\$112=500.000

\$120=80.000

\$121=80.000

\$122=10.000

\$130=420.000

\$131=370.000

\$132=200.000

ok

\$#

[G54:-420.000,-350.000,-2.000]

[G55:0.000,0.000,0.000]

[G56:0.000,0.000,0.000]

[G57:0.000,0.000,0.000]

[G58:0.000,0.000,0.000]

[G59:0.000,0.000,0.000]

[G28:0.000,0.000,0.000]

[G30:0.000,0.000,0.000]

[G92:0.000,0.000,0.000]

[TLO:0.000]

[PRB:0.000,0.000,0.000:0]

ok

There is something odd as the bed size is X 700 and Y350. will take a look

Thanks

Found \$130 X travel to be 420 and \$131 Y travel to be 420 and 370. LB deice settings are X 700 and Y350.
Changed \$130 to 700 and \$131 to 350.
Home now gives a final position of X -277 and Y 2.0 so now Y seems right.

Changed \$130 back to 420 and now after homing, I get X2, Y2
Very odd that the X max travel has to be set wrong to make the home position right?

Checked Centre Finder again but no change, the offset is the same as it was.

Thanks

So Sorry, that first bit was wrong. Should read:
Found \$130 X travel to be 420 and \$131 Y travel to be 370. LB deice settings are X 700 and Y350.
Rest is right

Output of `?` isn’t listed.

Set \$130 to 700 and \$131 to 350.

You have a work offset configured. Is this intentional?

``````G10 L2 P1 X-700 Y-350
?
``````

You can enable soft-limits once \$130 and \$131 are correct if you like.

However, based on your last test I’m not sure this will make a difference for the center finding. I thought it might be possible when you had the negative home position.

Hello Again,

Thanks very much for the information. initially my 0,0 was back right and to get it to front left i had to put in the offset. at that time my bed size was X420, Y350.
I later changed the frame size to X 700, Y350 and although i changed the numbers in the LB device settings screen and the machine settings, i didn’t do a new G10 command!!
thanks very much to you, i now have the correct size in both places and the position is perfect.

it didn’t help with the centre finder though. I did find that the redlight laser offset is the thing that is causing the centre finder issue. if i turn OFF the pointer offset and run the centre finder again, it does indeed jog to the correct place. so the LB software does not take into account the pointer offset when calculating the centre. I can live with this by turning off the pointer offset, finding the centre of the circle an then turning back on the pointer offset. if you can think of a way around this to make it automatic that would be great. Thanks again for your help.

Ah. I didn’t realize you had a pointer offset configured but it makes sense that it could cause the issue.

This may just be an unaccounted scenario but it seems like pointer offset should be accounted for when using center finder.

@Rick @Colin Could you please review this? I don’t believe I’ve seen this particular scenario brought up before but seems to me that not accounting for pointer offset might be a miss.

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