litho question-after roughing path rezero?

[drrobin]

I just started my first litho and have finished the roughing toolpath and ready for the finishing. I had to change my ballnose...I'm sure I need to rezero...do I zero the finishing toolpath off the top of the product? What happens if you use the entire product (I didn't and maybe you can't but wanted to ask...). Also on the roughing I used a 1/8 tapered bn and it made a 'screeching' sound. Is that normal? Thanks!! Excited that my roughing pass looks like it's supposed to:-) Robin

[dhellew2]

If you set z-zero on top of the lithophane you must re-zero on top of the lithophane for the finish unless you have and are using offsets.
Two suggestions,
1. set z-zero on your leveled table, lithophanes are about what's left and since Corian, Avonite, etc. are not uniform in thickness you run the risk of cutting through the material.
2. since lithophanes typically are cut at 135 degrees the first cut is a hole and as long as your bit can cut to the bottom of the deepest cut, roughing is seldom necessary because every other cut is just the step-over. Most of my cuts are with a 3/64" 3-flute spiral bit.

Maybe this will help (there is a downloadable lithophane instruction .pdf)
http://forum.vectric.com/viewtopic.php? ... ns#p161101

Dale

[Xxray]

You always have to rezero when changing tools, zero on top of the material, and a roughing pass with lithos is not necessary.

[dhellew2]

What xxray said is always true unless you have a touch-off plate and are using offsets or have an automatic tool changer. Dale

[tonydude919]

I don't use a roughing pass for lithos only finish pass. Your not carving very deep when doing lithos, I carve down about .125 deep anyways.

Tony

[drrobin]

Thanks everyone. Since my roughing path zeroed off the top, can I now do the finishing path zeroing off the bottom? Do u see any problems with that? If not, would I change any of my other parameters on cutting depth, etc etc? Thanks! Robin

[drrobin]

I looked at the instructions and they were using Aspire. Mine was created in photo vcarve...it does give me the option of zeroing off the table so that may be the best. Thanks! Robin

[Xxray]

Just be careful you don't blow through the material zeroing off the bottom, I never do it but I guess you'd set a gap above in a precise amount to avoid that.
I know some guys do it regularly, I've never felt the need.

[dhellew2]

When using the CNC table for lithophane setup; on the material setup screen I set the gap below model to 0.03"
Dale

[drrobin]

My 1/16 bit only had a 3/16 inch cutting depth. ugh...such a novice. So, I ended up using my 1/8 inch ballnose ZO off the top of the block and set my cutting depth to max depth of .2 with 1 pass. It 'worked' but my pic looks a little blurry. Is that because of the detail lost using the 1/8 inch ballnose? Just wondering before I do my next one-ordered the 30 degree vbit and going to try that as it looks like some have had great luck with that. I'm just excited it worked though:-) With the .2 depth I was a little nervous of cutting through but it worked good. Thanks for help! Robin