I think there may be a couple of different concepts being interchanged. The short answer is you can’t always trust what you see in the browser, but you can always trust a placement jig.
Focal height, set focus - the laser beam is an hourglass shape with the narrowest point being where the most power is concentrated. For engraves, how far above or below the surface of the material the focal point is set has a detrimental or beneficial effect depending on personal taste and some other technical factors. For cuts, it’s more about how wide the kerf will be and how much charring there will be. Changing the focal height, using set focus, also adjusts the dewarping of the lid camera and makes the view displayed in your browser change. It does not affect where the laser head travels.
Alignment - all about placement of your file on your material. Some machines are better than others, but the lid camera is probably never going to provide pixel perfect placement unless it’s coincidence. For that you need to jig. Using set focus or an accurate manual height entry will help, but perfect is unlikely.
For something you cutout you can always make a placement jig. If you have cut something out and then notice you forgot to engrave/score/cut something place a piece of cardboard in your machine. Cut the object from the cardboard. DON’T do any interior cutting/scoring/engraving - it’s a waste of time and cardboard is too flammable for a bunch of lasing. Remove the cutout piece of cardboard, without moving the larger piece of cardboard. Place the piece you forgot to do something on into the hole in the cardboard. Set focus on the piece and then do what you forgot to do. The image in your browser will show that the alignment is off - ignore it and use the force Luke. I have pretty good alignment on my machine for the initial file placement. After that, all subsequent placements are shifted a bit to the right. The placement on the material, however, is always perfect.
If you do not find this to be true one of three things is happening:
- I have not properly communicated how to do a placement jig.
- The artboard in your file is not 12"x20" (not sure if this still matters, but it did a couple years ago and it’s just habit for me.)
- There is something wrong with your machine.