Stepper motor selection

[MetalMagus]

Hi,
This is my 1st post. I'm looking at retrofitting a bench top milling machine such as a Sieg X3 or similar to use stepper motors. I have found some stepper motors with the following specifications and wonder if they would be up to the job. Could I ask for some help in determining the best motor for the job.

Motor details:

Frame Size: 1.65"
Maximum Holding Torque: 36 oz-in
Rotor Inertia: 0.3 oz-in
Rated Current: 1.2 A/phase
Voltage: 4.00
Resistance: 3.3 ohms/phase
Basic Step Angle@ 1.8
Inductance: 3.2 mH/phase

Regards

Sean

[doorknob]

Maximum Holding Torque: 36 oz-in

Typical mini-mill CNC conversions that have been described on this site have used motors with a rated holding torque of perhaps eight or ten times (greater than) that. For example, commonly-seen motors used in such conversions typically have holding torques such as 270 oz-in or 381 oz-in or more.

[MetalMagus]

Typical mini-mill CNC conversions that have been described on this site have used motors with a rated holding torque of perhaps eight or ten times (greater than) that. For example, commonly-seen motors used in such conversions typically have holding torques such as 270 oz-in or 381 oz-in or more.

Doorknob,

Thanks for the info. I suspected the holding torque was too low but wasn't 100% sure. Back to the drawing board in my search for suitable motors.

Cheers

Sean

[MetalMagus]

Why not upgrade from stepper to servo, the performance is much better.

CNCmakers001.

This is an amateur build on a low budget. So steppers meet my requirements.

Thanks for the "link" to your site though.

Sean

[James Newton]

doorknob is right, people generally use much larger motors, but it really depends on how fast you want the mill to move. If you can accept slower motion, you may be able to get by with a smaller motor. The best way to proceed is to first figure out how heavy the load is (or how much torque it actually takes to turn the lead screws) and then decide how fast you want the mill to move. This gives you the total power you need for that axis and then you can find a driver and motors that match that spec. See: techref.massmind.org/techref/io/steppers.htm#Estimating for details.

[MetalMagus]

doorknob is right, people generally use much larger motors, but it really depends on how fast you want the mill to move. If you can accept slower motion, you may be able to get by with a smaller motor. The best way to proceed is to first figure out how heavy the load is (or how much torque it actually takes to turn the lead screws) and then decide how fast you want the mill to move. This gives you the total power you need for that axis and then you can find a driver and motors that match that spec. See: techref.massmind.org/techref/io/steppers.htm#Estimating for details.

Thanks for the info James. Thinking about it your approach is the most sensible. I can always get the motors after the mill. This will give me a chance to evaluate the required torque. I suppose I fell into the trap that appears to be fairly common. "I've bought these motors. Now will they work."
Regards

Sean

[James Newton]

Thanks for the info James. Thinking about it your approach is the most sensible. I can always get the motors after the mill. This will give me a chance to evaluate the required torque. I suppose I fell into the trap that appears to be fairly common. "I've bought these motors. Now will they work."
Regards

Sean

Exactly right! It's my "mission in life" to correct all the examples of that out there and get people switched around to getting the load worked out first, /then/ buying the driver and motors. I wonder why so many people ('cause it isn't just you, trust me) go for the motors first? I guess there are a lot of people trying to sell motors and drivers who don't ask about the load... they just want to sell the motors and drivers! LOL...