A new hope: Epoxy granite and steel.

[hardenum]

Hey,

Preface.

I've done a fair bit of research over the last few months and I decided to open a build thread. There's a bunch of things I haven't read about yet, hopefully I'll have a clearer picture of everything in the coming months.

Materials.
I'm gonna limit myself to 2 materials. Epoxy granite and toolsteel sheet up to 30mm thick.

Structural.
There are 2 options I'm considering:
A. Epoxy granite bed(Y-axis) and steel welded gantry(X-axis). Z-axis steel.
B. Epoxy granite bed(Y-axis) and epoxy granite gantry(X-axis). Z-axis steel. I'd prefer this option due to the free
form advantage of casting epoxy granite.

Motors.
Lichuan's A4ST 80's.

Linear Rails.
Hoping to snipe some mint Rexroth roller rails from ebay. I've seen a bunch of them come and go over the last few months so there seems to be a somewhat steady supply out there.
Size 35 for Y, 25 for X and Z

Belt driven ballscrews.
Hiwin 2510 on x_axis and y_axis(2x), Isel 2510 on z. For backlash 2x screw nuts on each ballscrew. 25mm Gates GT3 5M belt. 18 teeth on the motor and 36 teeth on the ballscrew,

Spindle.(max. 2x380V)
BT30 with a custom 'hydraulic' drawbar pushed be an axial pump driven by a 40/60 servo, mounted to the side.
driven by a servo size 130/140. RPM up to 5500.

alternative Teknomotor C60/67-D-DB-P-ER32. It's a 6000-9000RPM 3.3kW spindle for EUR 1000,00 https://www.damencnc.com/userdata/ar...24513-en-G.jpg


EDIT 2.

Some pics as promised.

Spindle

BT30 cartridge.

Thanks!

[jarjar]

Hi,
That sounds like a heavy build!
But you are missing some crucial informations: what would be the working area and what do you plan to make with it??

- There are also holes on the side of the carriages, is that so that I can move the lubrication port from the front to the sides?

Yes but you have to pierce a hole with a needle and tap the thread.

I'm thinking of a BT30 and a size 130 servo(180 might be too heavy for a moving gantry), something at the range 12-24Nm and able to get to 9000RPM. I got a google problem with this though, I'm not getting any matches for "spindle servo" or even "spindle cartridge", the results almost always show up regular router spindles.

Check out CTB servo in China. They make nice spindle servos, but they are quite bulky.

Alignment:
- aligning ballscrew with the rails, I know how to do rail-to-rail alignment, but how do I do it for the ballscrew ?, the old fashioned way of moving the carriage and then tightening the ballscrew mount? Is there a more foolproof way of doing it? How do I make sure there are no forces acting perpendicularily on the ballscrew?

https://www.youtube.com/watch?v=mLCHT2ywk5A

[JAZZCNC]

Motors.
Lichuan's A4ST 60's or 80's. Probably 60's due to lower inductance.

These are AC Servo's not DC steppers so inductance doesn't play such a large part in the performance as your using mains AC voltages so pushing volts/current through them isn't a problem, it's the rotor inertia you are more concerned with when it comes to Servo's.

[hardenum]

These are AC Servo's not DC steppers so inductance doesn't play such a large part in the performance as your using mains AC voltages so pushing volts/current through them isn't a problem, it's the rotor inertia you are more concerned with when it comes to Servo's.

Duly noted.

That sounds like a heavy build!
But you are missing some crucial informations: what would be the working area and what do you plan to make with it??

Target build volume 320(Y)640(X)180(Z). Primarily aluminium(AW-6060 / AW-6082 / AW-2007/ AW-1050A/ AW-5754/ AW-5083/ AW-7075), occasionally mild steel. Mostly sheet metal, sometimes a mold for silicone injection(low pressure).

Check out CTB servo in China. They make nice spindle servos, but they are quite bulky.

Thanks for the tip, I found one that I like. https://ctbservo.com/product/servo-s...75x175x360-mm/

I'm really not an EE guy, despite many attempts. What's the deal with Rated Speed and Max Speed.

Does this mean I can run any servo over it's Rated Speed or are "spindle motors" a different motor type that allows it?
ie. synchronous for positioning, asynchronous for spindle? Or can I take a eg. an oversized servo and use it to drive the spindle cartridge?

[JAZZCNC]

Does this mean I can run any servo over it's Rated Speed or are "spindle motors" a different motor type that allows it?
ie. synchronous for positioning, asynchronous for spindle?

Both types of motor can be run above their rated speed however the difference is how long for.? An Axis servo can typically be run 100-200% above rated speed and torque but only for a few seconds. A spindle Servo motor is nearly always running above its rated speed but with a loss in torque.

How does it work.?
Now, I'm no Motor expert so don't quote me, but I think it comes down to the Motor type and how it's constructed.

An axis servo motor type is (synchronous) and uses permanent magnets to drive the Rotor, this is why it can give constant torque through its speed range.

The Spindle Servo type is (Asynchronous) which has no permanent magnets and relies on the rotating field to produce a magnetic field. This means it can run at higher than rated speeds constantly but at the cost of lower torque than at rated speeds.

There are other differences in how they work regards the drive. An Axis servo is typically run using POSITION mode whereas a Servo Spindle is run in SPEED Mode. (There is also TORQUE mode but POSITION and SPEED are the most commonly used.)

This is why you can rotate the shaft of the Servo Spindle motor when powered up but you cannot spin the shaft of an Axis servo motor. The Axis servo drive is constantly monitoring the rotor position and applying corrections to keep it POSITION, if you turn it by hand too far it will fault the drive.
Now, if you ran the Axis servo in Torque mode then this is similar to POSITION but now the drive monitors the TORQUE and tries to maintain it and if the torque falls below a set range it will fault.

SPEED mode you can probably guess by now.! The rotor position isn't monitored at all and is free to spin without any faults in the drive but the Speed is monitored and the drive will try to maintain this speed and again if it falls below a preset threshold the drive will go into a fault.

Now Servo spindles can position the rotor shaft for things like tool changing, they do this by switching into POSITION mode, and using the encoder they can rotate the shaft to an angular position.

So in Recap, Axis Servo can run above rated speed/torque for limited time periods without loss of torque. Spindle Servo, mostly, constantly run above rated but with some loss in torque as speed increases. This due to motor construction, (synchronous) and (Asynchronous)

Hope this helps.

[m_c]

There generally isn't that much difference between an axis servo motor, and a spindle servo motor. The main difference is in how they're utilised.

A servo motor rated speed/torque is what it should be able to happily produce 100% off the time without any overheating problems.
In terms of an axis, you're never likely to sustain using 100% of that continually, so you can intermittently drive the servo harder, which is where the instantaneous torque figures come in.

The rated speed is where the laws of physics really kicks in.
Regardless of being AC or DC, motor torque is directly proportional to current. More current = more torque.
In the case of DC, motor speed is proportional to voltage. More voltage = more speed.
In the case of AC, motor speed is proportional to frequency. Higher frequency = more speed.

As a motors speed increases, the back emf (electromotive force) increases. Think of emf as if the motor was acting like a dynamo/alternator being spun, in that it produces power, aka emf. The faster the motor spins, the more emf it produces. Now this emf fights 'back' against the voltage being applied to the motor, so the faster you spin the motor, the more voltage you need to maintain a given current through the motor. This applies to both DC and AC motors.
At a motors rated speed, this is the point the rated supply voltage can still overcome the back emf to provide the rated current.

Above this point, with an AC servo, as speed is not reliant on voltage, you can continue to increase the frequency, but you then start to lose torque, as you don't have the voltage to force enough current through the motor.
The motor essentially goes from being a constant torque source, with power proportionally increasing as motor speed increases to the rated speed, to a constant power source, with torque proportionally dropping as speed increases.

This applies to pretty much all electric motors.

In terms of a standard servo, and a spindle servo. The main difference is likely to be the spindle servo is derated, with better cooling to reduce the risk of overheating. There is nothing stopping you from using a standard servo, and running it above it's rated speed, to drive a spindle. Most servo manufacturers will list a rated speed, but they'll also produce speed/torque graphs that show motors performance above the rated speed, up to the speed they deem possible to run the servo.


In terms of drives.
Torque mode is the most basic, and gives the most responsive control over the servo. The big downside is torque mode is inherently unstable. Anytime the load on the servo changes, the servo speed also changes, so the controller has to be very responsive and tuned very well to maintain position.

Speed mode gives almost as much control over the servo, but due to the additional filtering involved, it's not quite as responsive. Speed mode was the mode any old school DC servo with a tacho fitted used, as at the time, controllers just weren't responsive enough to use torque mode. The tacho and servo drive (well technically amplifier) essentially acted as a damper to reduce the responsiveness needed from the controller to maintain position.

Position mode sits on top of speed and torque modes. It's basically a closed loop controller within the servo drive.

How any servo and drive responds, is entirely down to settings.
I'll just correct Jazz on torque mode. If you set a servo to torque mode, and command it to produce say 50% torque. With no load it'll spin up to it's rated speed. Stall it, it'll sit and produce 50% torque against that stall. Load it so it spins the opposite way, and it'll still happily sit producing that 50% torque against how it's being spun.
The servo drive doesn't care how the motor is turning/being turned, as long as it can produce the request torque without triggering a fault, it'll continue to do so.

Servo tuning does vary between axis and spindle though.
In an axis you want positional accuracy, so they get tuned to hold that position as best as possible. The downside is you end up working the motor harder, as it continually changes output trying to hold position, and you'll often find what works well at low speed/stationary, doesn't work so well at high speed, so you need to compromise to minimise following error under all conditions.
With a spindle, you're not as concerned about position, so you can tune them to be far more sluggish to respond to changes. A spindle being a few turns from position at 3000rpm isn't a major issue, as long as the speed remains constant. The last thing you want is a spindle that surges when it encounters a sudden load change, so you'll generally tune them to be more sluggish to respond.
As somebody asked me when tuning the servo spindle on my little mill, why do you need a spindle that only has a 20 count position error?
Even when rigid tapping, all you need is a stable spindle that you can reliably stop, it doesn't have to be on position to achieve that. It's up to the Z axis is ensure the thread is where it should be.

Although I still love playing with the servo spindle on my lathe, but it highlights how sluggish it's tuned. Put it in C-axis mode, and you can rock the chuck, before the drive just sluggishly pulls it back to where it should be. It could probably be tuned to respond faster, but it wouldn't make any difference to the parts it's makes.
You have to consider the loads the spindle actually sees. My lathe has a 5.5KW 3000rpm spindle servo, so it only produces 17Nm of continuous torque at the chuck. Given it's got a 8" chuck fitted, that means it only takes 170N pull at the edge of the chuck to overcome the spindle. Doesn't sound a lot, but when you're drilling/milling within the capacity of the lathe, it's more than enough to keep things where they need to be.

[hardenum]

Again many thanks to JAZZCNC and m_c!

A dedicated direct drive spindle is too long for my build, the shortest I found is 385mm (https://sc02.alicdn.com/kf/HTB1l9RHX...XXaC.jpg_.webp) with a motor that puts me at almost 700mm Z axis and that's just too long, so unless I design my own spindle I don't see how I can fit in max 500mm length. I guess that's off the table then.

[hardenum]

gone.

[jarjar]

Can't see the picture :(

[hardenum]

Is the "Attachment 29166" not clickable?