Laser not cutting in absolute coords location

[Hendo206 (Mitch)]

Hello,

I have an Omtech Polar 510mm x 300mm work area and am trying to use Absolute Coords.

I draw a square with the corner starting at 200y axis, 200x axis on the LightBurn work area. When running the cut the laser makes the cut offset on the workpiece, It does not cut the square 200mm x 200mm it will be 20mm offset and not in the specified location.

Any suggestions?
Thanks

[berainlb (PY)]

How are you determining that the cut is offset? Are you basing this on the ruler markers on the bed? If so, from what I’ve seen those do not directly correlate to coordinate positions.

You can see this even after homing. Position after homing does not match 0,0 with respect to the ruler marks.

If not that, can you provide the following:

1. full screenshot of LightBurn with the design loaded and ready to burn
2. screenshot of Edit->Device Settings

@Hendo206

It does not cut the square 200mm x 200mm it will be 20mm offset and not in the specified location

Does this mean that the dimensions of the cut are not 200x200 mm? Or are you saying it’s just offset but the dimensions are correct?

Does the laser burn where the frame indicates?

[Hendo206 (Mitch)]

Thank you for the quick reply.

Just recently I have measured 50mm down and 50mm across with reference to the HoneyComb bed that comes with the device and then drew the square on the material. I then done the same on LightBurn exact same measurements.
The square that is drawn is the size specified, no problems there. It is just the location the square gets cut is offset.

I’ll post the screenshots shortly of device settings and the LightBurn design.

[thelmuth (Tim Helmuth)]

Put a piece of cardboard that completely covers your honeycomb bed then draw a rectangle the size of your work area in Lightburn. Burn this at a low power and you will see how the honeycomb aligns with the actual cut area.My guess is that the cut area is smaller than your honeycomb.

[berainlb (PY)]

@Hendo206

It is just the location the square gets cut is offset.

Based on what you’re saying I’m almost certain it’s just the difference between position in the controller and the markings on the bed. They’re simply not designed to correlate.

If this is important to you then you have a couple of options:

1. Somehow remark the bed so that the rule marks are correct
2. Adjust homing offset. This would likely only work if 0,0 on bed is farther away than home position, but not the reverse. You should be able to adjust home offset for X and Y in LightBurn Edit->Machine Settings->Vendor Settings
3. Not certain but you may be able to adjust homing sensor location to match the bed but this may be impractical on that machine.

[Hendo206 (Mitch)]

I will give #2 a go, moving the home position 5mm diagonal backwards towards the edge of the bed wont damage the device?

if not able to use the honeycomb bed as reference and line up a piece of material with absolute coords, how do you accurately centre a cut on the workpiece?

[berainlb (PY)]

@Hendo206

I will give #2 a go, moving the home position 5mm diagonal backwards towards the edge of the bed wont damage the device?

I don’t believe you can have a negative offset so this is not likely to work.

@Hendo206

how do you accurately centre a cut on the workpiece?

Some suggestions:

1. use the camera to provide a general sense of position
2. use framing to get a closer sense of position
3. I’d highly suggest adding a red light pointer to your system as this will make position for varying tasks much easier
4. create your own grid or placement markers
5. create a jig that can be properly indexed to the bed that provides a repeatable way of position material
6. burn temporary position markers that you can use as a reference point for placement

There are many other strategies that will be dependent on what you’re specifically trying to do.

[Hendo206 (Mitch)]

I’ve been trying to use the camera, I have calibrated and aligned the lens and its just not accurate…

[berainlb (PY)]

@Hendo206

its just not accurate

Can you quantify this? The camera on the Polar can be quite tricky but I’d expect you to be able to get within a couple of millimeters.

What types of tolerances are you dealing with in the work that you do?

[Hendo206 (Mitch)]

Apologies for being vague
I will draw a square on the material and then use the camera to trace the square in Lightburn. I then run the cut and it is also offset

[berainlb (PY)]

@Hendo206

cut and it is also offset

By how much is it offset?

And have you made any attempt to adjust for this?

[parsec (FerAS)]

Sorry to step in.
For the camera try the following video

Gweike Cloud Camera Calibration with Lightburn

.

For the offset and just guessing your laser lens isn´t center to the laser body, if that means something regarding distance to the home switches…