Node edit (green square)

I have this cutout for a stereo cover. It is too large for my machine, so I’m cutting it symmetrically on the other axis.

4.55mm-plybox-stereo-top.lbrn2 (11.0 KB)

The issue is in the circle (reference), seen in the preview screen. The tool isn’t going where I want, makes a double pass before it continues on with the cut.

I was node editing this, but I don’t seem to have been able to key into what exactly the green square means. It did this on the bottom of the horizontal cut. I deleted the line, added a new line, now I have this behavior on the vertical cut.


Well that’s pretty weird.
I can see the problem you’re describing but don’t see any way to fix it.
The other oddity noticed is that I can’t change or even see the start point.
Curious if Oz & co have any input on that one.

Oh, and I see you have some kerf offset enabled, and of course that isn’t going to work since your shape is open. But that’s not related to the other weirdness…

Need the kerf and it can’t be closed since the part is too big… :frowning:
I need to cut the end, then flip the material top to bottom and run it again to get the symmetry correct. I hope :slight_smile:

I see the problem also, do you know what the green square indicates? Couldn’t find that either …

Thanks for looking… :slight_smile:

I have no idea what the green square is about. But I’ll be watching this thread closely 'cuz I may be about to learn something. :slight_smile:
Hoping that the Great and Powerful Oz will make an appearance to edumacate us.

The kerf offset is gonna be tough. No matter what number you enter LB isn’t going to apply it to a open shape so you’re out of luck there.
If you can’t close the shape then I think the only other choice is to design the piece with the offset built in. Or just use enough glue & paint that it doesn’t matter :smiley:

I understand the problem, from a programming point of view. In this case, the other two ends are closed shapes and I can apply a kerf to that and fix the issue. But if that wasn’t the case…

For example this part is 18x13 inches. Too large to fit in the machine, but I can get it in as a 13x18 with the ‘extension’ slots open. I can cut one end of the parts ‘fingers’. I have to remove the part, flip it over and run the same cut on the other side for a complete part.

I understand the issue, without a closed object, it’s tough to tell inside from outside. The start and end, in this case, would be easy, where the laser start to where it ends on that line. The only other information that is needed to to identify ‘outside’ or ‘inside’. I’m sure it’s not that simple, but it’s a problem for projects that are larger than you can cut in one peice.

So how do I connect two shapes?
How did you know the green square is the start of a shape?

This dxf file was the origin. From a python box generator, I believe.

Somewhere along the trail of experience with LB I discovered that the green square node (GSN) was the head or start of the line. I too have had occasional challenges related to the GSN as it concerns open shapes and start of cut, and thus trying to move the GSN such that it was an end of the open shape rather than stuck somewhere in between the ends. The GSN is usually the default start of the cut, although some Optimization parameters can influence otherwise, and there is the “Set Shape Start Point” tool also to affect this; although the latter doesn’t work when the GSN is not an end node on an open shape. There in lies a problem, not your problem, but it’s related.

These things are important to me because I use LB for plasma cutting process, in which its very desirable to control the starting points (as well as direction) of cuts. Open shapes are common in plasma cutting process since the kerf is so large that simply just the kerf can suffice as one dimension of the “shape” in a design with small details, so literally cutting out a closed shape is not always necessary nor desired.

Anyway, I had learned some time ago that the GSN on an open shape can be manipulated by deleting it and thus having it move to the adjacent node in the cut direction, or by closing the shape and then welding or union it with another shape. That suggests to me that LB does some shape node cleanup whenever it has to perform more than single node computations on a shape edit. I have also learned it is much better (more predicable) to close a shape by dragging one end point to the other, rather than by adding a new line and snapping the end points, the latter does not always yield a closed shape that will Fill.

So here’s a tip that I just discovered to move the GSN of an open shape to an end node… First close the shape by inserting (keyboard I while hovering over the insert point on the line) a node near an end, then drag the end to the other end snapping the shape closed, then delete the line you just established in the drag to close the shape but do it with keyboard D command while hovering over the line segment. LB will magically force the GSN to both ends of the renewed open shape !

JW - As an aside, you mentioned that you “added a new line” in the circle area, but even though I can’t seem to separate it from the longer open shape, there appear to be two lines overlapping (based on cut behavior) that are causing the double cut in the vertical segment. The method I describe above solves the problem, but another way to solve it is to use the Optimization param “Remove overlapping lines”.


Thanks for the procedure. As you can tell I had the same issue where I needed the kerf cut on one end of a symmetrical cut that wasn’t a closed object. I will try your method. Makes all the holes in the machine for feeding material though next to useless since you can’t control the kerf if you can’t have a closed object.

Again, thanks :slight_smile:

Also consider that you have the LB tool “Print and Cut”, which is intended to be used to index, for the purpose of making multiple cuts, a work piece through the laser machine when the laser work area (bed) is not large enough to cut for the full shape or design in one run or lay. Look it up, there is good tutorial on it also.

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