Me and the BIL re-arranged the fiber setup yesterday, it's been sitting on not-the-flattest table in the world so we stuck a flatter piece of plywood under the thing. It's also been propped up on pieces of 2x4's and shims and stuff to level and steady it. We weren't being exactly dainty with it, but it IS a 'portable' unit so I figure it should handle some light abuse ...
anyway, got it set up, and for once I got the top of the scanhead and the top of the table dead to rights center-bubble. The distance from the worktable top to the lens housing is the same all around the lens and table...
So I had a 6x12" aluminum license plate to engrave an oval logo that worked out to 6.3" long x 4.08" tall. After the first pass, the bottom 1/3 of the oval-logo was barely engraved while the top 1/3 was bright white. I ended up raising the table quite a bit just to get the bottom to start engraving decent. This is across the 4" height, and I have a 6" lens--
SO I just just drew up some skinny ovals and stretched them along the X and Y axis's to determine the absolute max work area allowed by the mirrors: 159.1mm X, 167.2mm Y. Beyond this, the mirrors would clip the ends of the ovals. Doing this I also found that the X and Y dead centers are very close, X to the right less than a mm, Y to the top by about half a mm
So I ran a continuous 6" tall x about 1.5" wide oval at zero power over some black anodized, and kept shimming up the bottom of the table and re-adjusted the central focus until I got an evenly marked oval. I then measured the distance from the top of the oval to the lens, and the bottom, and it's a 5mm difference!
Drawn to scale in Corel it looks like this:
lensout.jpg
Otherwise, everything is fine!
So, I'm thinking this is must be just an optics thing, but I'm trying to figure out what's going on. We didn't just DROP the machine or anything, but it was jostled some. So if for example, when we moved the machine, the-- I have no idea what it's called, but the 'tube/housing' at the end of the fiber cable that's clamped down on top, if that housing moved and the incoming beam hitting the mirrors is now skewed a bit, could that account for the wacky focus, even though the beam seems to be centered up nicely in relation to the work area AND engraves okay?
--I've noticed with my Triumph 'dumpster' when using a hand-held laser pointer aimed at he mirror above the lens, that the final dot position moves very little in relation to where and how the beam hits the mirror, so I assume the lens is pretty forgiving as to where it centers the beam spot. And so I'll also assume (probably wrongly ) that these fiber lenses are a bit forgiving too, at least concerning position. But the nearly 1/4" difference in focus distance across 6" of Y axis space has me stumped. X focus is fine...
I haven't pulled the covers and looked inside yet, and I also haven't done a 'size-wanted v size engraved' test yet, which I'll do shortly, got other fish to fry at the moment
Any ideas?