# 4th axis



## kvom (May 11, 2015)

I decided to upgrade my CNC mill by adding a 4th axis.  They're very useful for gear cutting, and potentially other jobs.  Unit is basically your Chinese 8" rotary table with the manual handle replaced by a stepper motor. My mill's controller already had the electronics to drive it, so it was pretty much plug and play.  Novakon provided me with a Mach3 profile that had the basics for controlling it, and I just needed a few configuration mods to get it moving.

First job is to mount a chuck to the table.  With the table mounted horizontally I centered it under the spindle.







That turned out to be a waste of time since I found that I didn't have enough Z space to use the same center finder with a rod held in the chuck.  So went to plan B using a DI to center the chuck, which I just moved from my old manual rotab.






Managed to get it aligned to less than .001" all around, so quite happy with that.  Then set it vertical.






As can be seen, the motor extends out a long ways.  I might need to turn it the other direction because the tailstock wants to point from the left:






I suspect that once the aligned the tailstock can be operated OK with its back to me.


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## petertha (May 12, 2015)

kvom said:


> IThat turned out to be a waste of time since I found that I didn't have enough Z space to use the same center finder with a rod held in the chuck. So went to plan B using a DI to center the chuck...
> Managed to get it aligned to less than .001" all around.


 
I can relate to the 'wedding cake' stack (RT + mount plate + chuck + test pin) & then trying to use the longish co-ax. One thing I discovered that might help is I found an accurate ground arbor with matching MT shank to RT socket, but the straight segment protrudes high enough that it contacts the chuck jaws. I'm not even sure what the arbor was originally intended for, but they are available relatively inexpensive.

So after the RT is centered to spindle, place chuck/plate loosely in position, set the arbor in RT socket, lightly clamp the 3-jaw to arbor, then secure the chuck plate to RT slots. Whenever I measured mine it seemed to be as accurate as RT centering but saved the 2nd indicator setup & bumping the chuck around.


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## kvom (May 12, 2015)

When I made the chuck plate I neglected to make a through hole in the center.  That limits the length of stock that I can hold inside the chuck, but also means that if I drop something to the bottom of the jaws I can get it out.


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## Swifty (May 12, 2015)

I made my own morse taper to straight shank bar to help align the chuck, it gets it pretty close, just a few taps has it right. My rotary table has only 3 T slots, and it's a pain when you tap it around, seems to go in the direction it wants. I have also dropped parts when the chuck was opened, they go straight down to the bottom, it the parts are steel a long magnet is handy, but non magnetic parts are a pain to retrieve.

Paul.


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