The 4th and 5th axis head unit was made from some surplus satelite positioning units of approx 4" diameter. There's some close-up pictures in the photo section here;
http://groups.yahoo.com/group/CNC_Toolkit/
The units are made by Globe Motors and the motor code is 409A582 rated at 12V. A quick Google search will bring up some links.
I removed the brake and tach sensor and replaced them with a US Digital encoder disc and pickup and drive them with Gecko 340 servo controllers. I had to make up some differential transmitter /
receiver circuits for the encoders as they were picking up noise over the cable run. (see
http://www.geckodrive.com and
http://www.usdigital.com )
The units have a flange that I machined off and I mounted them at 90 degrees to each other using some 8mm aluminium angle (this bracket should probably be beefed up)
There is an amount of backlash in these units, some more than others, but then they are very cheap. The motor / encoder assembly is quite long and sticks out beyond the unit a bit too much. You also need quite a bit extra clearance to allow the tool to rotate and your work area will be smaller than for an equivalent size 3-axis machine.
If I could find a low weight / low backlash / reasonable cost, etc.
alternative then I `d use that. I used a Sherline CNC-ready rotary unit for the 5th axis on my Taig
mill, but these are too heavy for the router. An alternative set-up
with timing belts and pullies could be constructed. I'm also looking at some parallel kinematics design ideas for tilting the tool angle as an alternative to rotary units.
I can quickly change out the Z-axis on my router from the 4/5 axis
unit to just a simple, but larger router if I'm doing a job that only
requires 3-axes, or indeed a vinyl cutting knife.
Regards,
Rab