# Weird kerf offset issue

So I followed a youtube video explaining how to determine the kerf offset.

We cut 5 squares and measured both the x and y axes on all 5. We tehn added it all up and found the average. we then subtracted that average from the original size of the square as it was drawn in light burn. We then cut that in half and this was supposed to be the kerf adjustment.

I started at .0215mm as my kerf, but after about an hour of sample cuts it is now looking pretty good at .086mm.

wtf?

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I literally came to the forum to search for thisâ€¦ And you posted it 3 minutes ago. Amazing! Followingâ€¦

For a 20W diode, .086 sounds about right.

I would need to see your math to really understand what went wrong there.

Also, donâ€™t confuse kerf offset with plain old-fashioned axis inaccuracy. If the axis doesnâ€™t accurately and precisely move the distance you command, no amount of kerf offset fiddling will make the parts right.

You did not say which machine. If you got this with a CO2 laser, you would be way ahead of the other guys. Be aware the kerf varies with the intensity of the laser beam. High power will burn a wider path. To get an accurate kerf (with of the cut), make 5-6 passes at lower power. And do not cut to both edges of the material.

You also did not indicate what instrument used to measure the kerf. Using digital calipers is iffy. Best id to lay a finely marked ruler across the kerf and use a magnifier (like a USB microscope) to get the most accurate value.

Yes, sorry, this was the Omtech CO2 machine. It actually worked GREAT at 0.90 om 2mm plyâ€¦when I used that offset on 5mm ply the joints were loose again
I used a digital caliper to measure in mm

That explains the difference between the different thicknesses of wood

This link is about measuring the kerf. @BillieRuben built a vernier scale kerf tool. Itâ€™s pretty slickâ€¦

If you follow the link to my tool youâ€™ll see that I measure about 0.164 for the kerf on 3mm basswood. Considering these were done with a 2" lens, which has a spot size of ~0.10mm. The proper kerf would be 1/2 the measured kerf 0.082mmâ€¦ You want half the kerf applied to each side of the cutâ€¦

Your beam size or kerf would have to be 1.8mm, something is wrong hereâ€¦

If you are making a dot that is smaller than 0.10mm youâ€™re doing good for a co2. Do you know what length of lens is in that polar?

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I believe itâ€™s a 2" lens

For reference, nice digital calipers are only accurate to around Â±0.03mm. Varies by measured size/range, and make/model. Without calibration docs and/or a nist standard to reference against, you really have no idea what you got. In our gage lab, we donâ€™t use calipers for anything requiring accuracy tighter than Â±0.005" or 0.1mm. The tool itself may be accurate to, say, 0.05mm, but user technique is a HUGE variable.

You can increase effective accuracy by averaging, but something to considerâ€¦

This is a Mitutoyo reference doc â€¦

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