Anyone know of software to engrave on a bat  without a 4th axis

What fixture and anaesthetic are you using?

But seriously, it will depend on the shape of the bat, you can only go so far around a cylinder with any cutter form, I use an engraving spindle of the type used on pantograph engraving machines which has an adjustable collar to set the engraving depth, it's belt driven and on it's own spring loaded slide, for most work on cylindrical surfaces I can just use a flat engraving program with depth set deep enough to follow far enough around the cylinder,

 - Nick

I use artcam to do i think what would work for you or I use rhino and madcam.
might want to look at some of my signage to see my curved signature style.
but its all about layers with artcam rhino its about projections and wraps

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