Servo equivalent to Stepper Help

[Cartierusm]

I'm planning a CNC router 4' x 8' build and loved the features of the DMM servos I used on my Mori Seiki Lathe Rebuild. So I was thinking a stepper in the 900-1200 oz in range would work for my design. What servo would I need that would compare to that?

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[ger21]

It's not that simple.
It depends on how fast you'd be spinning the stepper, and the servo.
A 1200 oz stepper probably has maybe 400oz of torque at 500rpm, and about 150oz at 1000rpm.
A 400w DMM servo has 170oz of torque at 3000 rpm. If you gear it 3:1, that's over 500oz of torque at 1000rpm, or about 3x that of the stepper. And the Servo has a peak torque about 3x higher, so for short bursts, like during acceleration, it can be nearly 10x more powerful than the stepper.

Depending on how much weight you are moving, and how fast, the 750wmay be a better choice.

[Cartierusm]

Ok thanks. Yeah I'll probably be doing a 3:1 ratio or more. Not sure how heavy the gantry would be; haven't gotten that far.

[mactec54]

I'm planning a CNC router 4' x 8' build and loved the features of the DMM servos I used on my Mori Seiki Lathe Rebuild. So I was thinking a stepper in the 900-1200 oz in range would work for my design. What servo would I need that would compare to that?

750w to 1Kw depending on your machine build

[Cartierusm]

Hmm if I go that big I'm getting into some cost. I don't mind using steppers; I have steppers on most my machines, but what I was aiming for with the servos was accurate homing.

With the DMM you can set a function to have the servos home to index zero on it's own encoders so I'm dead accurate right from the start. This is necessary on my lathe.

Are there any options for accurate homing with steppers? In the past I found that limit switches are just not that accurate. I guess one way would be to use a fixed block near home on the machine and on every start up use my Haimer 3D sensor to set zeros on my axis so any fixed jigs would be in the same position.

[Jim Dawson]

Why not use linear encoders on the axes? That way they will work with servos or steppers and homing is not dependant on limits. However, using proper limits, the positioning can be very accurate also.

[ger21]

Are there any options for accurate homing with steppers?

Mount an encoder to the shaft, and you can home to the index, just like a servo.

Or simply buy better home switches.

[Cartierusm]

What homing switches do you recommend?

[Jim Dawson]

Here are a few options
https://www.automationdirect.com/adc...Limit_Switches

[Cartierusm]

Thanks. I'm amazed that I haven't come across those before. I use automation direct a ton. I'll try that.