PhotoVCarve lithophane issue: rough cut tool marks visible after finish cut

[kfitz]

PhotoVCarve lithophane issue: rough cut tool marks visible after finish cut. It is not uniform, i.e. it is worse in some others than others.
ShopBot Desktop with vacuum hold down
Material- 1/4" cast white acrylic
Parameters-
Rough: 1/8" ball nose, pass depth .125, carving max depth .1, line angle 45, line spacing 20%, feed 1.5 ips, 12000 rpm
Finish: 1/32" ball nose, pass depth .0313, carving max depth .1, line angle 45, line spacing 20%, feed 1 ips, 16500 rpm

Any ideas?

[kfitz]

Change the rough carving max depth to .08?

http://www.talkshopbot.com/forum/attachment.php?attachmentid=25274&stc=1

[jerry_stanek]

normally I don't use a roughing pass as I do the 45% cutting option and once it plunges the first time there is very little material being removed on each pas after that.

[Xray]

I wouldn't use a roughing pass, also acrylic is not the ideal medium for lithos, you'd be lucky to get decent results in any scenario.

I like to push it to the limit, if I am doing a litho with .25 corian I set max depth to around .21, of course this demands very accurate Z setting and perfectly flat table. I also go more in the 10% line spacing, adds some time but the detail is worth it.

[kfitz]

What size cutters are you both using? The Vectric tutorial video I watched said max depth should always be between .08 and .1. I wonder where they came up with that? For practice purposes, acrylic is much cheaper and easier to get than Corian. My latest attempt was much better.

http://www.talkshopbot.com/forum/attachment.php?attachmentid=25277&stc=1

[Xray]

I use the same as you, 1/32 tapered ballnose.

The whole concept of lithos is to let as much light as possible pass through the lightest areas, that is why you want it as deep as you dare. Don't go deep enough and the light parts won't look very white, dark parts will pass no light at all. Cut too deep, well, then the project is ruined. You can use a belt sander to grind away material off the back if you don't go deep enough, but this can be tedious & messy if there is a good amount of material left. But I have saved otherwise useless projects doing that in the past.
I stopped looking at acrylic as a corian alternative a long time ago, suggest you do the same. Results are far and away much better and more predictable with corian. If anything, probably less stressful on the bit as well, and never any melting/gumming issues.
For that matter, "Corian" is simply a name brand of solid surface material, the original and most well known - Same as when we call any tissue we blow our noses on a "kleenex" when it can be any brand. [Perhaps you already know this]. Anyhow there are cheaper alternatives often more readily available, Wilsonart & Gibraltar 2 of the better known competitors.
This guy http://candlestonegifts.com/candlestone-material-for-lithophanes/ sells material that may be superior to all, and fairly cheap too. If you are serious about lithos, and for sure if you are going to sell them, the plexi will have to go. My opinion anyhow, I wish white plexi was a good alternative, my experience is it isn't.

[kfitz]

I use the same as you, 1/32 tapered ballnose.

The whole concept of lithos is to let as much light as possible pass through the lightest areas, that is why you want it as deep as you dare. Don't go deep enough and the light parts won't look very white, dark parts will pass no light at all. Cut too deep, well, then the project is ruined. You can use a belt sander to grind away material off the back if you don't go deep enough, but this can be tedious & messy if there is a good amount of material left. But I have saved otherwise useless projects doing that in the past.
I stopped looking at acrylic as a corian alternative a long time ago, suggest you do the same. Results are far and away much better and more predictable with corian. If anything, probably less stressful on the bit as well, and never any melting/gumming issues.
For that matter, "Corian" is simply a name brand of solid surface material, the original and most well known - Same as when we call any tissue we blow our noses on a "kleenex" when it can be any brand. [Perhaps you already know this]. Anyhow there are cheaper alternatives often more readily available, Wilsonart & Gibraltar 2 of the better known competitors.
This guy http://candlestonegifts.com/candlestone-material-for-lithophanes/ sells material that may be superior to all, and fairly cheap too. If you are serious about lithos, and for sure if you are going to sell them, the plexi will have to go. My opinion anyhow, I wish white plexi was a good alternative, my experience is it isn't.

Thank you for the great info and advice. I'll give the candlestone a try and experiment with cutting deeper in one pass. My ball nose is not a taper bit, but I'd prefer to use one for increased strength. Where did you get yours? Thanks again.

[Xray]

I wish I knew where I got the one I use the most, must have got it on ebay, maybe amazon. It performs like a champ, I have cut dozens of 3d and litho projects with it in corian, plexiglas and wood probably over 100, it is nearing the end of its life.

This is a good source http://www.precisebits.com/products/carbidebits/taperedcarve250b4f.asp, many others to chose from, none cheap. Tell the candlestone guy Xray from Cam sent ya, may or may not get a little discount. Best to order at least 5 or even 10, as many as will fit in a flat rate box. $8 for an 8x10 is as cheap as you'll find, and the material is excellent, probably better than corian or at least equal. I routinely sell 8x10 lithos [with box and lights of course] for $100+ so they can be profitable if you find the buyers. They practically sell themselves given the right exposure.