4th Axis for CNC Router

[Haik]

Here's a 4th axis I built from a 6 inch rotary table and a high-torque NEMA 34.  The rotary mount is fixed to and MDF bed and the tailstock slides to accommodate the workpiece.  The whole unit bolts down to the table of my CNC Router.  A Gecko G203V (Vampire) drive quick connects to the NEMA 34 and safely disconnects when not in use (don't try this with other drives... it'll burn them out!).  A Perske 24k rpm spindle (on a VFD) holds the tool.  I use either a laser or dial-indicator to true to gantry, that usually takes about 5 minutes.

This setup works great and I can cut using full numerical rotations or via indexing.

-Haik

[Glenn]

Hi Haik,
I noticed your build on this forum, and would like to build one like this; Would a rotary table like this be a good place to start, or how much backlash and slop is in one of these cheap tables?    http://cgi.ebay.com/4-ROTARY-TABLE-PRECISION-GROUND-FOR-MACHINIST-NEW_W0QQitemZ190335313338QQcmdZViewItemQQptZBI_Tool_Work_Holding?hash=item2c50de65ba&_trksid=p3286.c0.m14   

Thanks for any replies,
Glenn

[gfroe123]

I found a place on the web called the Little Machine Shop.  The rotary table boasts a 10 second backlash. I see this as .5 degree.  This is OK as long for some applications if you keep the rotation one way. If you are willing to spend a little more the Sherline is the way to go. Good luck

[Overloaded]

 

The rotary table boasts a 10 second backlash. I see this as .5 degree.

10 second = 0.002 777 777 777 8 degree
.5 degrees = 30 minutes or 1800 seconds
RC

[RICH]

Hmm.....
You never know until you try one. My Sherline rotary table has 5 minutes of backlash.
So at 1" from the center the backlash is equal  to 1/2 the thickness of a hair on your head.


Now it all depends a little on what your trying to do. Linear to angular conversion :
1 minute = .0003" per inch   or .0009" in 3"
1 arc sec= .000005" per inch

So 10 arc sec= .00005" backlash at 1" distance Or if you had a piece out at 3" that's .00015" at 3" distance.
I don't think your machine can machine to that.
So there is backlash and there is position. Now do you think for $99 you are going to get backlash equal to that?
Then you can also ask what is the positioning accuracy you are after?

Being practical about it all, the table may be perfectly fine for what you want to do.

Now i do have a positioning rotary table, that position wise, it's repeatable to 3 arc seconds. And if you bought it new it would be around $5000. That's not too much better than 10 arc seconds. Then of course, how would the average joe  measureing it to find out!
 
Just some things for you to think about,
RICH