CNC Engraving Rotational Rotary Axis

Hi folks,

I want to do some engraving on some aluminum and brass tubing. I have the Hobby Lathe and my 3 axis cnc. I thought it may be simple just to add say

http://www.ebay.co.uk/itm/CNC-Engraving-Rotational-Rotary-Axis-50mm-chuck-3-jaw-4th-A-Axis-Tailstock-/251889999308?pt=LH_DefaultDomain_3&hash=item3aa5d0 5dcc

http://www.mycncuk.com/attachment.ph...id=15723&stc=1

to the bed of the cnc and it looks like it plugs into the 5th axis plug on my controller, if it doesn't have a 5 axis board I'll use a redundant axis.

Has anyone had any experience with them.. any advice ?

Ive heard ones with a harmonic drive are the way to go as they have far less backlash. Im thinking about building one that can take a 125mm 4 jaw chuck that i also use on my lathe.

I have one exactly like this one, but I have no idea how to do cam for it. I dont think the backlash is the biggest problem with this one, its the lack of holding power. But yeah, for sure harmonic drives are definitely a much better option.

Thanks guys, or the info, I'm not doing stress cuts with the cnc its basically engraving. Harmonics look good must look further into them. Sure backlash wont be a problem though.

I have a similar Chinese 4th, slightly bigger but the same principle.
Engraving will be fine, you can easily add a belt tensioner to eliminate backlash for low torque operation.
For milling operations the backplate and stepper shaft rigidity both come into play but there are cheap and smple solutions,
Regards,
Nick