I’m fascinated by the mill-turn machines. They combine the best elements of a lathe and a milling machine to turn out complex parts quickly that would be much less productive if done as multiple ops across different machines. Here’s a great video of a Haas CNC lathe turning out such a part:
The secret behind these machines is two-fold:
First, they have the ability to treat the spindle as another axis, called the C-Axis. This allows positioning the part with great position to any angle.
Second, they have live tooling. Instead of an ordinary lathe tool in a turret position, there’s a miniature motorized spindle that can hold endmills, twist drills, saws, or whatever else is needed.
How does one convert a spindle into a C-Axis indexer?
One obvious answer, used in many machines, is to use a servo as the spindle motor. Think of it as the brute force approach.
Another approach is to use a secondary servo that may be engaged or disengaged. Here is such a setup on an Emco lathe:
Lathe C-Axis Mechanicals…
We can see a number of interesting functions from the photo:
– There is a collet pulling mechanism to open or close the collet or chuck.
– There is a toothed gear and hydraulic spindle lock. Considerable side force can be applied during C-Axis operations and it is often important to be able to lock the axis while that happens.
– The spindle is driven by a couple of large multi-groove belts.
– There is an auxilliary spindle indexing servo. It’s not visible in the photo, but it’s encoder (or possibly a transmission to engage/disengage it) as well as the cog belt system it uses to drive the main spindle are there.
Construction is pretty straightforward. Here’s another lathe with a sub-servo for the C-axis:
Lathe C-Axis uses a gear-driven sub-servo. Note the disc brake for locking the axis…
The gear-driven C-axis makes me wonder how the avoid backlash? Here’s one more that is cog belt driven:
Some sort of clutching mechanism would be used to decouple the C-Axis position servo when the main spindle drive is in operation.
Live Tooling: When a toolholder becomes a milling spindle
Most live tools include a coupler that allows the turret to drive the live tool spindle:
A Live Tool Angle Head: Power coupler is on the right, collet for tool on the left…
A simpler approach adaptable for lightweight work and gang tooling is to use an air-driven spindle:
Air-driven spindle on a gang lathe…
Even a small router motor could be pressed into service as this gang-tooling rig on a mill shows:
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Bob is responsible for the development and implementation of the popular G-Wizard CNC Software. Bob is also the founder of CNCCookbook, the largest CNC-related blog on the Internet.
I’m blown away with these machines. Are these manufactured turn centers or private builds? If private builds are there links to them? I’m wanting to do almost exactly this to my lathe. Currently I am building an ac servo driven turret using a 21 spline shaft and taper bearing collar to engage tooling with live tooling at one side and a small 40mm ac Servo enclosed at the other end for rotation with pneumatic unlock. I want to add a c axis with a brake and like the idea of a disengaging gear driven setup but I have been breaking my brain thinking about ways to go about it. I have the room to fix a large 120/150t module gear at the end of my spindle and with internal threading can make it removable so I can service if needed. Also it can maintain a through shaft up to 1” doing this not that I really use the feature much. This way I can leave the existing motor and vfd as is taking advantage of the gear box for various needs. I’ve contemplated just building an entirely new machine as well but this one is already prime to modify and won’t take much for me to do besides already having ball screws and parts here to build it. The plan is to remove the back splash plate and extend it another 8-10” back and machine a block of cast for a new upper dovetail carriage block giving me another 6” of travel and wider platform with 1/2” more height to utilize a larger, longer ballscrew. This will allow me to implement live tooling and maintain the tailstock for those 15% jobs I still need it. Deciding whether to setup live tooling off to the side or integrate into my turret is up in the air a couple more weeks before the remaining parts arrive. Both have clear advantages and disadvantages. Ultimately tailstock usage (interference) will be the deciding factor. I may have to get craft with a top mounted spindle and gear driven spindles to supplement powering an axial and radial turret powered mill cutter. Off carriage mounting means I may have to choose one or the other or formulate a manual adjustment for axial/radial cutting. The upside it could be easily removed if I wanted at any given time. I’ve explored a third option in adding a 70 degree bed off to the side with linear ways to drive a sub spindle. That seems like a lot of programming nightmares to me. We will see.
Can’t wait to get started