How do I Get a smooth finished lithophane

[Scotcat2]

I am trying to get a super smooth finish with no raster.
My finishing pass I use a 1/32” ball nose with a 12 spacing, I also increase depth .025 between rough, semi , and finishing pass.
I’m wondering if you can use a sanding cloth or something after the image is carved to get a really smooth result or is there a way in the carving of the image? Any suggestions would be appreciated.
Baffled

[Brady Watson]

You should be in the 8 to 12% stepover range. So a 1/32" ball should leave no raster lines with a stepover value of .0025 to .00375 inches.

Start with a 12% and run about 1/2" of the file. How does it look? If you still see lines, pull the stepover down to .0025" and try running it again, right over the original. See if there is a difference in quality between the two. You may find a happy medium at 10%, which is the default recommended stepover for most 3D things. Keep in mind that a 8% stepover means the tool will need to do 400 passes to go 1" and a 12% will only need 267 passes to go the same 1"...so doing a quality check is worth it if it's a big litho or you're doing a bunch of them.

If using Vectric software, crank up the 3D toolpath preview resolution all the way up (Toolpaths-Preview Simulation Quality-Maximum) and preview each toolpath at the desired stepover and look closely to see if you see raster lines in the finish. The previewer is very good and can save you a lot of time trying things out at the machine. Just hammer on that previewer until things look to your satisfaction. Lower simulation resolutions tend to get washed out and too cartoony to see the raster marks...so crank it up and have a look.

If you still have lines after making adjustments, you may have a mechanical issue like backlash in your incremental axis (if rastering in X, the Y) or the Z if you're getting "hammer marks".

Some improvement in quality can be had by making some adjustments to the VR settings of the machine. If you haven't already, read my article on it. Watch your cutting speed, and adjust your Slow Corner Speed to soften the ends of each raster pass. I'd be inclined to say 40-45 as a value. See what works best for you.

If you have a gantry (PRT/PRS) or BT machine, realize you are starting to come up on the limitations of the machine - so you have to make sure the machine is mechanically tight, and that you make some accommodations for that big gantry or table moving back and forth. Make sure the pinion gears are fully meshed into the rack gear and power up, then wiggle every axis of the machine to make sure there is no slop that can be adjusted out.

Let me know how you make out.