steppers, digital steppers or servos??

[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

[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]

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

[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]

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

[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?