Print and Cut Accuracy (limits with just two points)

Dear Oz,
in short, do you have any “tolerance” value for the Print&Cut function?
Let me explain more in detail the situation.
I’ve been using the Print&Cut (with scaling) function for a while on a Chinese laser with Trocen controller.
My red pointer is in the laser path (before 1st mirror) with a pretty good collimation with the laser, but I always fire the laser to make sure it is spot on, on the target.
We recently cut some big 1300x900mm plexy and we arrived at a point where some shapes would cut perfectly wrt the cut path and others were out by as much as 1.8mm, even if we set the targeting elements as far apart as possible and at the opposite corners to minimize the effect.
I wanted to buy a better machine and I asked the seller to run a similar test. The result was still a 0.8mm apart from the correct path on a A1 format, with other shapes perfectly cut.
For big shapes (signs etc) that is ok, and it’s always possible to extend the color (bleed) so that the laser doesn’t cut on white but it is not for small items like keychains where that difference becomes noticeable. Granted there are some tolerances also because of the printing process (we are talking about big machines with really high level of accuracy).

We know that Trotec with the JC Vision feature (the camera that read the dots) always uses 4 points to recognize the cut path.

Is there any theoretical way to calculate the offset based on the pointers offset? I.e. for every 0,1mm in one direction, the distortion will be X% and Y% or the degrees?

Is this a limit of the two targets system instead of more?

Any help would be pretty much appreciated!


Of course laser comes out of the center of the cone and the X&Y are calibrated over the biggest distance possible to minimize the error.

You are using cameras I assume to line up your stuff which is different than my experience, but I will tell you some of the things I have ran into.

We needed accuracy to .002" And we needed to hold ±.002 over the whole area. 700mm,x500mm

We machined setup plates with reamed holes at 1 inch increments x and y over the whole area. We CMM verified the hole positions.

I calibrated x and y travel using acylic. I would burn holes in the acrylic 24" apart, and use a optical comparator to get centerline of the holes and calibrate. I started having geometric inconsistencies… both lasers were not square. and the travels had a slight “bow” to them.

I had to slot the linear way mounts and make nuts from square stock to remount the slides and indicate then straight and square. This took about a week for two machines. Finally I got everything pretty good. I am probably at max out about .005" on each machine at its worst spot.

Now I have to fix the z axis orbit. there is no guide on the z axis so the table orbits some when you move up and down. This means you have to shift x and y to make features line up when you have different z levels. The orbit is about .01-.015 at max, but its messing with us.

I got done calibrating lasers, and installing our table fixtures and was in production. One laser started creeping… x and y started moving and I was getting out of center of mirrors every couple hours. I was pissed. Then it quit lasing… The cooling head on lense end of laser tube had fell off and some really interesting heat damage had occured.

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