I’m trying to make sure not to screw this up - engraving on a friends stainless steel flask.
The width of the flask is 92mm. The height at the sides is 20mm, center 25mm.
I want to engrave 80mm wide, centered on the flask.
Do I need to do some cylinder correction? or should that be within the realm of normal?
John
Just got a galvo myself and have not attempted this, but I have watched the video on setting it up and using it… Maybe that will help you…
Might want to state your focal length… How much depth of field you have is relative to the focal length… Longer lens, lager dot size, but greater depth of field.
Good luck… post some photos of the finished flask
Good point. It’s the F420 lens, with a 11x11" engrave area.
I have the same animal F420 and a F100 and F160. Probably the same machine. 
Let us know how it works out…
I have calculated the mirror height, but have no idea how to calculate the diameter with the information I have available. I was barely a C student in math :). Were it not for an A in geometry (theorums) in 8th grade, well, …
PS - cloudray 60w jpt mopa. I have an F100 lens too, and thankfully cloudray sent the COR files for lenses to me…
I would think you’d have to compute the size of the circle based on the curvature of the flask.
I haven’t used it, so I don’t have the issue… yet…
You might have to do some measurements to get a workable value… I drew this up real quick as an example of how it might fit into a circle…
Without the math, I think my lens has about a 5mm or so focal depth… I saw it somewhere specified and it was between 5 and 8mm at least somewhere in that area.
If you can determine how to mark some tape, you could run it taped at low enough power to not mark the surface… That may help…
They did set the focus to 1/2 the depth of the curve, so it’s in the middle of the focus area.
I tried it on a cheap black flask I picked up just for this purpose, and it seems there is some distortion. But still this is beyond me. Arrgh. Math is evil.
Math is nature and nature is math…
What is the shape of the flask…?
Can you measure from where the curve starts to where it ends?
Found this calculator… maybe that will help…
Is this over your head?
measurements - width of the curved space ~85mm
height at start/end of curve (measured laying it on a flat surface) 20mm
height at peak of curve - 25mm
That calculator says this - Online calculator: Circular segment
Did it work?
I’d like to see a photo …
The “correction” algorithm in lightburn asks for diameter - but diameter is not provided by that calculator? or am I just stupid and not seeing it?
also distance from mirror - is that ‘to the material’ or to the lens?
The mirror distance, just add the separation of the lens to the center of the galvo feed tube. Lightburn needs to know the distance from the object to the actual galvo mirrors.
It being a circle, they use the radius (R), so D is 2 times the radius (R)…
Or inversely, R is 1/2 of D…
So I get a D of 97.26. lens to center of feed ~60mm
Now if only I could find that flask I tested on!
John
Ok, when framing with those settings it didn’t look right, so I masked over the flask, and yeah, something isn’t right with what I’m trying to do. argh
I guess I’ll do it without ‘correction’ because my friend liked how the test looked. It was only me that thought the line “cigar bar” on the right side looked off by a degree or so…
Nope…
I question your numbers… can we do them again?
I’ll look at your calculator with the numbers … maybe it’s computational error… know how you like math so much…
Thanks , let me know what you come up with?
For the radius I got 183.13… What value did you come up with?
I used segment defined by chord and height. Which did you use?
what did I get? A computational error. I put in the full value for height (25) instead of the difference (25-20=5)… So, let me try this thing again…
Thanks for all your coaching! And math!
