[jcposada]

My searches are not leading to any definitive answer.

Has anyone attempted to swap out the spindle motor for a servo?

[kirk_wallace]

My guess is that you won't find information on using a servo motor on a mill or lathe spindle because there is not much call for it. I have heard of using a brushless servo motor on a spindle, but in this case it was used as a simple three phase motor and not a servo. Using a servo on a spindle might allow one to use the spindle as a rotary axis, but rotary axes are usually not fast enough for normal operations. If the servo configuration catered to a higher speed it would not be usable as a rotary axis were positional accuracy and rigidity are important. My guess is that some fancy machines have two systems, one with a motor, pulleys and belt for spindle mode, then a servo and gearing (maybe worm) for rotary axis mode. A means is needed to engage one or the other, plus a means to index the axis mode when it gets engaged.

I happened to find these links:
Projects 5
Duality Lathe 4th Axis | Tormach Inc. providers of personal small CNC machines, CNC tooling, and many more CNC items.
Why Y-Axis For Turn/Mill Machines? : Modern Machine Shop (see "C-Axis Makes Four" half way down)

Another one:
C-Axis Turning and Live Tooling: Turning and Milling on One Machine - CNCCookbook CNCCookbook

[underthetire]

Sure, just got a retrofit in that uses a servo for spindle motor on a large lathe. Pretty nice setup. That motor alone with 10 million count encoder probably cost as much as the whole Tormach. Small size, lots of torque, exact RPM, and can use it for a C axis.

[SCzEngrgGroup]

A servo motor and drive in an appropriate size (1.5kW on a PCNC1100) will not be cheap, and really offers few advantages, other than the ability to do rigid tapping, which Mach3 does not easily support. The Novakon Pulsar has a servo spindle, and it require special electronics to make it do rigid tapping, due to limitations in Mach3. It is otherwise really no different, and no better, than the much cheaper 3-phase AC motor and VFD that is standard on the Tormach and most other machines in this class. You can just as easily do "semi-rigid" tapping using a tension/compression tap holder, albeit at a small time-penalty.

Why do you believe this would be a worthwhile thing to do?

Regards,
Ray L.

[jcposada]

No preconceived notions, really. Just trying to learn. Novakon makes it one of their big selling points so it made me wonder...

Thanks for the education!

[SCzEngrgGroup]

No preconceived notions, really. Just trying to learn. Novakon makes it one of their big selling points so it made me wonder...

Thanks for the education!

If you do a lot of tapping, rigid tapping is nice, and can save some time. But for most operations, I see no really compelling advantage. I do have both a Novakon Torus Pro, with VFD spindle, and a Novakon Pulsar with servo spindle. The servo spindle is nice, but not something I'd pay extra for unless I had to do a whole lot more tapping than I do now. Higher RPM would be of FAR more value, and you won't get that for a reasonable price, without sacrificing power. I do 99% of my work on the Pro, and use a tapping head or thread-milling for threading.

Regards,
Ray L.

[CNC-Dude]

Hi Group,

I just have to ask. What is the advantage of rigid tapping? Just saw this concept show up all of a sudden and I am curious as to where is this technology such an imminent need. Is the idea here that rigid tapping is the only way to thread really hard materials?

I am also wondering why would you need a servo on the spindle. I can see a lathe spindle benefitting from a position control methodology as now you can make threads super easily. On the same fashion, I can imagine the mill could have the screw mounted on the spindle and the blade fixed on the table, and in this case it could also benefit from the servo. But that is pretty much all I can think of!

With that being said, machining is just a hobby for me (read complete illiterate on these matters), so I am curious as to what other operations does a Servo comes to serve the day. I don't know, it seems to me that you could just build a servo based system to do those operations. Servos are not even that hard to make nowadays. Heck! I bet there are people coding servo systems with Arduinos!

[mountaindew]

A servo motor and drive in an appropriate size (1.5kW on a PCNC1100) will not be cheap, and really offers few advantages, other than the ability to do rigid tapping, which Mach3 does not easily support. The Novakon Pulsar has a servo spindle, and it require special electronics to make it do rigid tapping, due to limitations in Mach3. It is otherwise really no different, and no better, than the much cheaper 3-phase AC motor and VFD that is standard on the Tormach and most other machines in this class. You can just as easily do "semi-rigid" tapping using a tension/compression tap holder, albeit at a small time-penalty.

Why do you believe this would be a worthwhile thing to do?

Regards,
Ray L.

As noted and speculated in another thread, tormach is moving away from or offering a controller system not using mach XX .
Looks like this would no longer be a product cycle problem and one reason I seen their slant bed lathe product was slow to market.
Again this is observations from a new user and I have little long term knowledge or bias.
md

[underthetire]

Hi Group,

I just have to ask. What is the advantage of rigid tapping? Just saw this concept show up all of a sudden and I am curious as to where is this technology such an imminent need. Is the idea here that rigid tapping is the only way to thread really hard materials?

I am also wondering why would you need a servo on the spindle. I can see a lathe spindle benefitting from a position control methodology as now you can make threads super easily. On the same fashion, I can imagine the mill could have the screw mounted on the spindle and the blade fixed on the table, and in this case it could also benefit from the servo. But that is pretty much all I can think of!

With that being said, machining is just a hobby for me (read complete illiterate on these matters), so I am curious as to what other operations does a Servo comes to serve the day. I don't know, it seems to me that you could just build a servo based system to do those operations. Servos are not even that hard to make nowadays. Heck! I bet there are people coding servo systems with Arduinos!

Rigid tap is really nice for blind holes, nothing to do with material. Been around since the early 80s. In all reality, the big machine mfg have been using a form of a servo motor for years on spindles. May be able to build one, but its tough to make one that has torque, and high rpm. Most high end mills today use the spindle as the armature and a set of double windings around that, with an induction type non contact encoder for position. Pretty fun watching a large mill rigid tapping at 6000 rpm.

[Al_The_Man]

I am also wondering why would you need a servo on the spindle.

I set up a Fanuc AC servo motor on a my Lathe retro-fit, mainly for constant surface speed, and the C axis.
Al.

[kirk_wallace]

Just to keep things straight...

Servo spindles and rigid tapping have nothing to do with each other. Rigid tapping can be done with nearly any spindle motor type. On common CNC machines, the main feature is in keying the Z feed to the spindle angular position. The spindle needs a position encoder do do this. When the spindle turns, the Z axis is feed a distance that matches the spindle angular distance based on a ratio that matches the tap pitch. Z distance = spindle angular distance * pitch ratio. While tapping normal g-codes are used to get the tap to the hole, then a code invokes tapping mode. The Z feed is held until the spindle encoder index is triggered, at this point the Z axis is locked to the spindle rotation. The g-code command also has a feature that keeps track of how far the Z axis has traveled and automatically reverses the spindle at the set Z depth.

The _only_ spindle motor issues with respect to rigid tapping are how much control one has with stopping and reversing the spindle and this _only_ affects how far the tapping continues after the spindle reverse triggers. For through holes this usually isn't a problem. For blind holes, my 770 VFD usually reverses within a revolution so I tend to leave two pitch lengths space at the bottom. A much bigger issue is ejecting the chips or leaving enough room for chips at the bottom of the hole. Since the Z axis is slaved to the spindle motion and not the other way around, tight spindle angle control is _not_ needed.

My guess as to why Novakon has a servo spindle is that the motor they use is a DC brushless DC motor. A feature of DC motors is that they have good low end torque, so that means fewer belt changes to get to the needed torque range. This DC motor just happens to be brushless, so an encoder is needed to electronically replace the brushes. Since the motor has an encoder, it can be considered a servo for marketing, but it is only there for commutation and not angular position control. I think it is better to market the spindle as being a DC spindle. If the spindle were a true servo, it would be a C axis and could be commanded with a C command in g-code.

That's just how I see it.

Wikipedia has a good link:
Servomotor - Wikipedia, the free encyclopedia

and:
G Codes

[SCzEngrgGroup]

My guess as to why Novakon has a servo spindle is that the motor they use is a DC brushless DC motor. A feature of DC motors is that they have good low end torque, so that means fewer belt changes to get to the needed torque range. This DC motor just happens to be brushless, so an encoder is needed to electronically replace the brushes. Since the motor has an encoder, it can be considered a servo for marketing, but it is only there for commutation and not angular position control. I think it is better to market the spindle as being a DC spindle. If the spindle were a true servo, it would be a C axis and could be commanded with a C command in g-code.

Your guess would be wrong. The Novakon spindle that supports rigid tapping uses an AC servo, just like the other three axes.

Regards,
Ray L.

[kirk_wallace]

Brushless AC and DC motors are very similar. The basic difference is in the shape of the constant torque signal. AC brushless motors are designed to be driven with AC sine waves. DC brushless motors are designed for a trapezoidal signal.
http://www.compumotor.com/catalog/catalogA/A17-A19.pdf

They are both permanent motors with good low end torque.

The axis and spindle motors being the same makes sense, but I suspect the spindle driver is a speed controller with a velocity input and the axes being step/dir (position input) servo drivers, but I'm guessing again and I could be wrong.

[SCzEngrgGroup]

Why do you keep making guesses, when you've been TOLD what the actually hardware is? It IS an AC servo motor. Is is driven by an AC servo drive, NOT a "speed controller". The exact, same make and model AC servo drive used to drive the X, Y, and Z axes. I do not have to guess. I OWN the actual machine, and I am quite familiar with the hardware and electronics.

Regards,
Ray L.

[daniellyall]

kirk guessing just gets your arise dragged over the coals

Wikipedia is a don't ref to sight it can be very wrong over hear if you put Wikipedia in a uni paper it gets crossed out

[kirk_wallace]

I don't mind a good natured debate and I try to frame my comments as guesses to politely leave the option open that I may be wrong or I may lack some information, rather that impolitely saying "I am right because well... I'm just always right and I'll bite your head off if you test me". My reference links may not be perfect, Of all the information resources, Wikipedia has got to be the biggest target for peer review and I tend to trust it. I also tend to cross check any information I get from the Internet before I put it into practice. I welcome any references that contradict anything I have said. I have absolutely no way of knowing what Ray has installed in his machine. Simply posting the model numbers of the spindle and axis driver would clear this up without ambiguity and with very little stress. Ray could easily prove me wrong on another point, that being that the spindle angle can be set with a g-code, proving that it is actually a servo. I would hope that Ray could say "I don't agree with such and such and here is why and here is what it's based on".

I don't mind being wrong, if I am wrong, then I learn something new, but I feel I need to speak up when I don't agree with the prevailing "wisdom" when my research and practice have so far indicated otherwise. If I'm right or wrong doesn't matter if each person reading this thread is prompted to learn for themselves what they can, and not take _anything_ on the Internet at face value.

I'm going to sign off for a while to help prevent anyone and myself getting bounced.

[daniellyall]

you wont get bounced unless you are very rude and abusive but ray does make stuff for Novakon he makes there fancy things so if hes says that's how it that is how it is so he does not need to prove a thing at all if you wont to know whats on novakon machine look at the manual its all in there.

Wikipedia is a online add to by anyone thing so stuff can be very wrong or out of date it was in the rules for my diploma to not use Wikipedia as reference material unless you can find where that info came from.

also the best reference material you can find for cnc is here there are neck jumpers on here that will kick your arise if you say something that is completely wrong or complete BS. after a year or two you get to know who to listen to and who to block

so point is don't guess fact only or your head will get ripped off.

[LeeWay]

I tap a lot of holes and this is why rigid tapping has become important to me. It wasn't important to me when I didn't realize it existed. I build my own mill and use a DC motor and controller with timing belt drive on it. It is possible to put a brake on it to get the spindle to stop fairly quickly, but it has rather low torque at slow speeds. That compared to a servo motor. I have a Pulsar as well. It does have Servo spindle and is driven by a servo drive. When rigid tapping, it turns into A axis and syncs with the Z axis. It is a 1.2 KW AC Servo as Ray mentioned. Here is a link to the drive manual.
http://novakon.net/static/servo/driv.../ep1manual.pdf

So for years we tapped hundreds of holes each week by hand. Smaller ones done with a cordless drill. Larger ones in a manual tapping fixture. I much prefer rigid taping. That lets the mill come that much closer to producing finished parts. So far, my lathe is the only machine that actually produces finished parts.
Everything else requires more operations.

[underthetire]

If you have the funds and know how, why not use a servo, not only can they rigid tap, you can peck tap, that's a helpful one for hard materials. Its all in what specs you want your machine built to. Properly set up spindles we don't have to fudge a couple threads for slow down, simply program exactly how deep you want the tap to go.

[LeeWay]

That is one plus side and they are just like a normal tool if you do have an ATC. I don't but will when I win the lottery. Wait! Then I will just hire all the work out.

They are shorter than any of my drill tools. Fit nicely in an ATC caddy. Can't say that a tapping head would be easily accommodated by all ATC's.