# Tom Lipton’s Oxtools YouTube helical milling



## Tim9 (Feb 17, 2021)

Okay, I was checking out Tom Lipton’s YouTube video in which he set up a helical milling set up. Now just to be clear, I have no project in the works or even a need for helical grinding. But, I’m intrigued with the design and idea of this. My problem is that I have a huge learning curve to master ( or even hack ) most of the stepper motors, servo motors and digital encoders.





 
   My question is I was trying to find out more about the set up. Which parts used and where could I find out some more info about digital servos and encoders. I’m at a total loss about the digital encoder he has on the crank handle. I do have a little knowledge about stepper motors. In fact I even built a “ stepper indexer” which was designed by D. Liming and featured in Digital Machinist Magazine.
but... I copied his code and really didn’t go through the trouble of learning arduino code. Anyway I at least want to read something more about the theory. Mostly a curiosity thing. Here’s a link to the Liming website.


Http:/www.liming.org/millindex

like I say....not looking for a course in it yet. But looking for a little more than the wiki article I found on servos. I think they are different than stepper motors???

thanks, tim


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## ttabbal (Feb 17, 2021)

There are loads of maker forums and youtube channels that cover this stuff. You know what a stepper is, a servo is a motor with an encoder so you know for sure how far it moved. No need to worry about unknown missed steps. The motor could be a stepper, but "normal" motors do get used as well. 

The encoder is a lot simpler than it seems. It just sends pulses every x amount of movement. How much movement depends on the encoder type. Rotary types are usually specified in number of pulses per rotation. Much like stepper controllers. The pulses are usually quadrature encoded which gives you direction as well as distance. How to decode those is all over the net, and likely better presented than I could do. Some microcontrollers even have built-in decoders for those. Of particular interest to us, these encoders are the same type of signal most DRO scales use. 

Sparkfun and Adafruit are good places to start with basic articles about motors, sensors, coding etc..


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## Tim9 (Feb 17, 2021)

Thanks. I think what confused me most is that servos can be stepper motors or “regular” motors. 
In fact, when I first watched this video, that’s what caught my eye. It’s a stepper motor.


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## RJSakowski (Feb 17, 2021)

Back in 1980, Sears had a device called a router crafter that functioned in a similar manner.  The work was mounted on centers and turned with a crank.  Cables wound around a pulley pilled a router along guide rails to cut spirals.


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## rabler (Mar 24, 2021)

Having seen Tom Lipton's video when it came out, I have a K&T rotary table and plan to implement this on the table.  Both spiral milling, and simple turn through angle kind of features.  It'll probably be next year before I get around to it.


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## kb58 (Mar 24, 2021)

Just to confuse things a bit more, there are now "hybrid servos" that are stepper motors with an encoder, and the driver box handles any positional errors that may occur "behind the scenes." So for all intents, the unit acts like a servo motor, but at lower cost.


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## macardoso (Mar 24, 2021)

kb58 said:


> Just to confuse things a bit more, there are now "hybrid servos" that are stepper motors with an encoder, and the driver box handles any positional errors that may occur "behind the scenes." So for all intents, the unit acts like a servo motor, but at lower cost.


Sort of. They definitely have encoder and perform error corrections, but the physics of a stepper motor is a bit different than an AC or DC servo. They provide near max current at standstill, so there is not much the motor can do to correct for errors like a normal servo which can provide a high overload capacity. The real benefit is knowledge of stall (generates a positioning alarm) and smoother torque ripple during motion.

In summary, they are better than normal steppers, but don't quite fill the shoes of an AC servo.


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## kb58 (Mar 24, 2021)

I agree that I over-simplified the comparison regarding torque.


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## rabler (Mar 24, 2021)

Not to take away from the conversation on variations of servos and steppers, but Lipton's implementation used an encoder on the mill x axis, and a stepper or similar on the rotary head, so that the rotary head could be lock-stepped to some degree of rotation per inch of x axis travel.  So a coupled motor-encoder solution, while not irrelevant, doesn't replace the separate encoder on the x axis feed.


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