How do you drive large steppers?

[Jackal66]

I saw in the post at the top about "Stepper FAQ's"

In there, is this statement:

Method 2: You have a Bridgeport CNC conversion you are doing. The machine has a 5 TPI screw and you need a work feed rate of 120 IPM. 120 IPM on a 5TPI screw 5 * 120 or 600 RPM. How about force? Not a clue? Use your machinist's experience on a manual machine. The hand crank is about 6" inches in diameter. How much force would you place on the hand crank before you figure you're not doing something right? I hear about 10 Lbs. 10 Lbs is 160 oz, 160 oz on the end of a 3" moment-arm (6" diameter, remember?) is 480 in-oz (3 times 160) of torque on the leadscrew. The equation for rotary power is: Watts = in-oz * RPM / 1351 For this example, Watts = 480 in-oz * 600 RPM / 1351 or 213 Watts. 213 Watts is servo territory. You have to use a servo motor to get that, about a NEMA-34 one.

So then, how do people drive those 1200 oz./in. to 2380oz./in rated steppers????

Is there something missing in the rating of the steppers? Are they misrepresented & the evaluation in an RPM range the motor never really sees?

Could the motors be tested on a scale that shows higher level because their competitors don't use the same category?

I am just wondering if there is a standard, for power and the high numbers are in another class, that other manufacturers never use?

My thinking is 25-30 lbs torque on a Bridgeport wouldn't be uncommon.

Is this much torque irrational, for a machine this size?

Thanks in advance and let me know,


JAckal66

[Jackal66]

No answers yet?

JAckal66

[olf20]

I converted my bridge port clone to cnc about two years ago.
I did not know nothing about anything. I contacted Rick at homeshopcnc.com.
He was very helpful.

That being said I used the 1200 oz in steppers with gecko 201 drives.
Ball screws would improve the speed but, does the job for us.
Used 1:1 on the X & Y, 2:1 on the Z.
Power supply 72 volts.

Hope this answers your question.

olf20 / Bob

[Jackal66]

Thanks Bob,

So then, the Gecko drives will work on the large steppers. I figured you had to have some special or custom made drivers for the large steppers.

That clears up a lot.

Can anyone else that is running large steppers, list the motor size and drivers?



Thanks,
JAckal