[sabastion]

I've finally made up my mind on my mill to convert to CNC
it will be an LMS 3900

Motor...hmmm - stepper, digital steppers or servos?

any recommendations and why's? please advise
Richard

[sabastion]

hmmmm,ok...guess I will call manufacturers and be left at their mercy

[Al_The_Man]

Probably one of the reasons for not much response it is often a case of personal preference and/or cost.
It might pay to search here and other sites for explanations of the up and down side to each and make your decision based on those.
My personal preference has always been on the side of servo's which I use exclusively, but that does not mean that steppers would not also be just as capable.
There must be examples of users of this machine or similar out there that have used both.
Al.

[hoss2006]

One problem is you're asking about an SX2 in the X3 forum.
There are several threads in the benchtop foum about the lms 3900 sx2.
A g540 package with 381 oz/in steppers is more than adequate to run the mill.
Hoss

[sabastion]

One problem is you're asking about an SX2 in the X3 forum.
There are several threads in the benchtop foum about the lms 3900 sx2.
A g540 package with 381 oz/in steppers is more than adequate to run the mill.
Hoss

Thank you for your advice Hoss...I'm asking about motor types (specifically) because of my lack of knowledge/experience. I posted here because it seems that there are more X3 builds than X2 builds and want to benefit from you guys knowledge/experience. In all actuality the X3 thread should be in your aformentioned benchtop forum as it is a benchtop machine and that way all benchtop machines could be found in one place...but that's just my common sense 2 cents

I probably should have left out that I am getting an SX2. It wont remain an SX2...I will be making my own base, X and y axes and tables, vertical column and z axis...inspired by your Hossmachine_Cnc Conversion.

All I'm trying to find out is the difference between the motor types and what they're better for (speed, precision,control,dependability, noise, etc...)and why.

I will be converting to ball screws also increased x,y,z axes travel and larger tables with the possibility (large possibility) of larger t-slot bed
Richard

[hoss2006]

Thank you for your advice Hoss...I'm asking about motor types (specifically) because of my lack of knowledge/experience. I posted here because it seems that there are more X3 builds than X2 builds and want to benefit from you guys knowledge/experience. In all actuality the X3 thread should be in your aformentioned benchtop forum as it is a benchtop machine and that way all benchtop machines could be found in one place...but that's just my common sense 2 cents

I probably should have left out that I am getting an SX2. It wont remain an SX2...I will be making my own base, X and y axes and tables, vertical column and z axis...inspired by your Hossmachine_Cnc Conversion.

All I'm trying to find out is the difference between the motor types and what they're better for (speed, precision,control,dependability, noise, etc...)and why.

I will be converting to ball screws also increased x,y,z axes travel and larger tables with the possibility (large possibility) of larger t-slot bed
Richard

You may have noticed that this thread has been moved to the benchtop forum, why you've had more responses.
The X3 subforum is something new and does tend to add confusion when they do stuff like that, Taigs used to be part of the benchtop forum as well. volume of X2 conversions top the list btw.
Oh well, you're good to go.
The digital drivers are also something new to the forum. I've tested one and they are much smoother, faster and quieter
than their normal counterparts using the same stepper motor and I expect them to get much more popular.
The X2's really don't need the extra speed and the g540 has proven to be a good match for it.
You can use whatever you want, the trick is to get a motor that is a good match for the driver you choose.
G0704 Electronics
You'd want a bipolar parallel amperage equal to (or under) the drivers output (3.5 amps for the g540, 3.5 amps for the 381 oz/in stepper from keling)
and an inductance that gives a good match for max voltage.
take the square root of the motor inductance times 32.
keling 381 = 2.8mH which equals a voltage of 53.5, the g540 runs at 50 volts.
Hoss

[sabastion]

Again,ty Hoss

as always knowledgeable and informative

I still think cnczone should have everything that qualifies as a benchtop machine in one benchtop forum with with like-machine type subcategories for for easier locating...ecpecially for newbies like my self and good for regulars also.

example...
X1 types listed by manufactrurer subcategories
X2 types listed by manufactrurer subcategories
X3 types listed by manufactrurer subcategories
etc....makes finding exactly what you're looking for much easier than looking from forum to forum...again, just my common sense 2 cents worth

[yantra3d]

I just wanted to add my 2 cents here on the servos since I have been using them on my x3 for a while now. I also have steppers on my lathe and I like them as well. They are also very accurate and cheaper of course, but there are some advantages to servo's I think.

The first thing worth mentioning is that you don't HAVE to have a belt drive system if you are using decent-sized servos.

I am currently using a couple of Aerotech 1000D's without any belts and they are plenty powerful for the x3. I was originally using Keling servos and had to use some planetary gearheads at 3:1 in order to get the power needed for the x3. I wasn't happy with their performance though and so upgraded to the used Aerotech's I got for under $100ea off the bay. The funny thing is that the Keling's actually have a higher rating than the Aerotech's but the Aero's are clearly much more powerful.

I'm using these on the X and Y axis and for the z axis I have a much more beefy nema34 Cleveland servo that is also direct driven although it does use a belt (but at a 1:1 ratio) so no torque conversion was needed for this axis either.

Another bonus with servos is how quiet they are! I can just barely hear them running at all. What I hear are the ballscrews turning and the table gliding along the axis and that's about it. This is actually really nice for learning since you can clearly hear what is happening with relation to the cutter and the part (and the machine). This allows me to better diagnose what is happening during a cut so I can make effective adjustments on the fly. But, this is only the case if you dump the stock spindle motor setup because it is so crazy loud that it drowns out everything else!

Also, there have definitely been times on the mill when I was very thankful to have the closed-loop system to make up for lost steps (usually always user error) which saved me from having to scratch my part and start over from another piece of stock due to lost steps.

Here's some pics of the servos... if you want the specs on them then I can post them for you. Hope this helps!

[Al_The_Man]

Moved.
Al.

[rpovey]

Do you intend to use the stock screws or convert to ballscrews?

Either way on a mill that size I'd use steppers and I'd probably go with a G540 just because they are so easy to set up.
I just don't personally think the extra expense of servos is worthwhile at that size, properly setup with reasonably sized servos you shouldn't be missing steps.

[SCzEngrgGroup]

On a small machine like an SX2, there is absolutely no benefit to servos. Properly sized steppers will give you at least comparable performance, for significantly lower cost. Several of us here have X2-sized machines that will rapid at 250+ IPM, have enough power to break endmills if pushed too hard, and do not lose steps unless the operator does something stupid (like a rapid into the vise). What advantage would servos provide, other than bragging rights?

Regards,
Ray L.

[LUCKY13]

With the factory screws or ball screws steppers will do a good job here. I do tend to find myself going for better drivers than is called for though and the digital drivers are proving to be very good performers.


WIth that said, a G540 would give all the performance you could even think about needing. Plus it would save on money which will allow you to buy other needed tools/supplies. Plus it will be easier with steppers and a G540.



Spending money on ballscrews would be better than going with servo's. Also tools, cutters, work holding, software, measuring equipment will all cost more than the machine plus a CNC change over. It all ways takes more than most people realize so its good to save some funds when you can.


Jess

[sabastion]

On a small machine like an SX2, there is absolutely no benefit to servos. Properly sized steppers will give you at least comparable performance, for significantly lower cost. Several of us here have X2-sized machines that will rapid at 250+ IPM, have enough power to break endmills if pushed too hard, and do not lose steps unless the operator does something stupid (like a rapid into the vise). What advantage would servos provide, other than bragging rights?

Regards,
Ray L.

Yea...I don't care about high IPM speed's when milling...but when moving to home position and y axis to gain easier acces/inspection of parts, general axes movement to clear parts, work holders and to do ATC's. I would like some decent speed and precision for these movements...but not so much that it causes my mill to do cart wheels off of my work bench Lol
Richard

[rpovey]

The 1c version

Servos are a closed loop motion system, they have a feedback mechanism, so the system always knows where they are, if they can't make the commanded move, the controller can add power, or wait for them to make the move.

Steppers have no feedback they effectively get a move 1 step signal and they move one step, if they are overloaded they miss steps and the position the software thinks they are is no longer correct.

Steppers generally provide more torque at low RPM than Servos, so most Servo systems run with reduction belt drives.

Steppers and stepper drivers are a lot cheaper.

In practice with a mill the size of the X2, and with 300+oz-in steppers, you wont miss steps unless you run the mill into the endstop or provide enough force to break an endmill, so IMO at least the additional cost of servos isn't justified.

[sabastion]

The 1c version

Steppers generally provide more torque at low RPM than Servos, so most Servo systems run with reduction belt drives.

I definitely don't want to go with belts so I guess servos are out unless I use one on z axis to handle weight of mill head and accessories/attachments (would this offset the use of counter weight's, springs, air or hydraulic pistons cylinders?) Or can steppers and servers be used in conjunction with each other?

[sabastion]

Thanks for your help guys...your very helpful and informative. maybe someday I'll be in the position to help someone else out. :wee:

one thing hasn't been touched on as yet...digital steppers, or am I thinking about digital stepper driver? If there's no such thing as digital stepper motor I'm probably thinking about digital stepper drivers. If I want to run digital stepper drivers, does this have an impact on what kind of motor I use?

Thanks, Richard

[hoss2006]

That's the sound it makes using the MPG, you won't hear that under normal jogging or feeding.
Hoss

[sabastion]

That's the sound it makes using the MPG, you won't hear that under normal jogging or feeding.
Hoss

Oh, ok...cool! no more worries.

My uber newbness is really shining Lol
Richard

[yantra3d]

"Even without a fault, you'll be operating over only a small portion of the motors usable RPM range - kinda like buying a 500HP V12 Ferrari, and never driving it over 25MPH."

Because this is an x3 that we are talking about I would argue that the torque you are implying via a belt reduction system would be WAY more than you will EVER need for a mill this size - if you have some real servo motors. When I was using the keling servos they were way underpowered even with the 3:1 planetary gearheads! So perhaps the quality of the servo makes the difference here. In my case the the direct drive aerotech's have way more power than the keling's using the 3:1 reduction. If using real servos (as I mentioned in my last response) belt reduction then would truly be overkill for a mill this size and so, as I said, it's just not required.

"I have a stepper machine (X2), and a servo machine (knee mill), and I like the sound of both - neither is preferable, they're just different."

Hmmm, what kind of servos are you using on your mill? Mine are almost completely silent! They have nowhere near the noise that my lathe steppers have so I'm not so sure about that frankly.

"In any case, when cutting the sound of the tool will completely swamp the sound of the drive motors."

When I was using the stock X3 spindle motor setup I couldn't even hear the tool cutting the material! I have never had steppers on the mill so I can't say that they would actually drown out the cutting sound but, I do know that with the servos I hear nothing but the cutting sound from the tool which is why I said that it was a nice bonus.

"2. I have seen in some pictures that it looks like servos require the use of brushes (more noise and wear)...is this true? I haven't noticed this with stepper motors"

The brushes do not create any extra noise to be concerned about.

"Steppers have no brushes and are extremely durable when crashed. No damage will happen to the stepper itself."

No damage would ever be sustained by the brushes in the event of a crash.

Like Ray said, brushes are not an issue worth considering. If/when they do wear out you can replace them in a minute or so with new ones for next-to-nothing.

[SCzEngrgGroup]

"Even without a fault, you'll be operating over only a small portion of the motors usable RPM range - kinda like buying a 500HP V12 Ferrari, and never driving it over 25MPH."

Because this is an x3 that we are talking about I would argue that the torque you are implying via a belt reduction system would be WAY more than you will EVER need for a mill this size - if you have some real servo motors. When I was using the keling servos they were way underpowered even with the 3:1 planetary gearheads! So perhaps the quality of the servo makes the difference here. In my case the the direct drive aerotech's have way more power than the keling's using the 3:1 reduction. If using real servos (as I mentioned in my last response) belt reduction then would truly be overkill for a mill this size and so, as I said, it's just not required.

What that says is the your current servos are significantly over-sized for the machine, while your previous ones were significantly under-sized for the machine. That's fine if you're able to come across the servos at a bargain price, as you apparently did. But, if designing on a level playing field cost-wise, your solution would yield a more expensive system than right-sized servos with belt reducers that would give you exactly the same performance.

"I have a stepper machine (X2), and a servo machine (knee mill), and I like the sound of both - neither is preferable, they're just different."

Hmmm, what kind of servos are you using on your mill? Mine are almost completely silent! They have nowhere near the noise that my lathe steppers have so I'm not so sure about that frankly.

850 oz-in NEMA34 DC servos, exactly like the ones Keling sells. Mine are also almost completely silent. There is a slight whine at speed (you're probably not ever getting yours going fast enough to hear that). There is also a periodic (about once/second or two) quiet "chirp" from the servos dithering when stopped. If yours are tuned to be truly silent when stopped, you likely have not tuned them for best performance.

"In any case, when cutting the sound of the tool will completely swamp the sound of the drive motors."

When I was using the stock X3 spindle motor setup I couldn't even hear the tool cutting the material! I have never had steppers on the mill so I can't say that they would actually drown out the cutting sound but, I do know that with the servos I hear nothing but the cutting sound from the tool which is why I said that it was a nice bonus.

Same with the X2, as I indicated - The spindle motor is so bloody loud, I had to wear ear protection whenever it was running, even with a belt drive. That's one of the great things about the knee mill - it's relatively quiet, even when removing 8 cu. in./minute. The universal motors on the low-end mills are just painful.
"2. I have seen in some pictures that it looks like servos require the use of brushes (more noise and wear)...is this true? I haven't noticed this with stepper motors"

The brushes do not create any extra noise to be concerned about.

"Steppers have no brushes and are extremely durable when crashed. No damage will happen to the stepper itself."

No damage would ever be sustained by the brushes in the event of a crash.

Like Ray said, brushes are not an issue worth considering. If/when they do wear out you can replace them in a minute or so with new ones for next-to-nothing.

Regards,
Ray L.