Engraving inside a bowl

My next project will be to engrave at the bottom of a two inch deep round tray. Once the laser is on and has finished homing I will jog the head to X200,Y200 and place it over the tray. From this point on I cannot press home, but I also need to make sure that nothing else tries to send it there either, such as at the end of a framing cycle. My plan was to use “Start From: User Origin” and a Job Origin at position 5 (the center most circle of the nine) so that it starts in the center of the image, and have a “Return to Finish Position” set at X200,Y200. In theory I believe this should keep the laser head from hitting the side of the tray, I just want to make sure something like framing doesn’t trip me up. Can anyone else think of something I might have missed, or have a better way of approaching this project?

My suggestions:

  1. Disable “Return to Finish Position” entirely. Just let it sit where it lasts burns. This will ensure no extraneous movement.
  2. Stick with Absolute Coords. This will ensure your laser only moves to where portions of the design exist in your workspace. This is of course achievable with user origin but that adds a variable.
  3. Before placing the tray under the laser, run a framing operation a number of times to make sure the laser never strays outside the boundary of the tray. Using rubberband frame might make this easier.
  4. If you can afford to, consider making a duplicate of the design on a different layer with frame level power or lower and run the job with just that layer. You could speed it up as well. This will ensure that everything works as expected without risk.
  5. Only run the actual job once you’re satisfied that your alignment is correct and job well setup.

I normally stick a piece of cardboard or other junk material in, run a test run / outline of whatever the engraving will be, that way I know exactly where it is going to end up and place the tray/item accordingly. seems to be the quickest & safest route I have come up with.
for your situation I would consider taping 2-inch pieces of cardboard on the outsides of the flat piece (roughly same dimensions as the bowl) just to make sure it isn’t going to hit the actual bowl. if the laser head ends up hitting the cardboard - no big deal, make adjustments if needed.

Thank you for your well thought out suggestions. The only one I’m having an issue with is number two. When I run the job in preview, with Start From in Absolute Coords, the red crosshair starts at 0,0 and ends up there when the preview is finished. In User Origin I start it in the center, and it ends at the tip of the letter “W”, which is just as good a place as any to stop. Unless I’m missing something, in Absolute Coords both the Job and Machine Origin are 0,0 at the start of the job which would not work for me. It needs to begin and end inside the circle once I press start. Is there something I’m not understanding about Absolute Coords? I’ve mostly used that and Current Position but have not messed around with User Origin much.

My expectation is that if you’ve framed the design that the laser is positioned at the lower-left most part of the design. If you start a job from that position it should not start from 0,0 position but rather the current position of the laser head. It should move directly to start point of the job from the last resting position. Are you getting different behavior?

This should be fine as long as you never re-home after the initial homing.

I could see this having some drawbacks compared to a solid user origin model as well. But that has its own drawbacks.

Success!! Thank you both for your suggestions as they were very helpful. After letting it home I prepositioned the laser head at X200, Y200 and carefully maneuvered the tray underneath without bumping the laser. It took a lot of finagling to get it in the right location (I must have run the rubber-band framing about a dozen times to make sure of my alignment). The orange plastic shield came within a quarter of an inch of the sides at some points but did not make contact. I had a stomachache the whole hour and twenty minutes it took to finish. The tray is made of Rubberwood (which stinks when lasered) and I ran it at 2000mm/m with 67% pwr with floodfill on.

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