[kNucklBustr]

Trying find what stepper motor, for the least amount of money, that will run the X axis.

This Older 80s Grizzly mill/drill is massive. The book says 1700lbs.
I have a 48v-12.5A PS, Gecko 540 3.5A driver.
Im going toward the NEMA34 motors because of shaft size.

I ran the mill w/ a 1/4"bit, .200 DOC while turning the X handle w/ a ft/lb torque wrench.
It wouldnt go up to 1 ft/lb, the lowest reading. So Im assuming the torque to turn the X is lower than 192oz/in.

Using Keling motors as an example, they have a KL34H295-43-8B (906 oz/in) that can be wired Series at 3.05A.
or the KL34H260-35-4B (465 oz/in) Parallel at 3.5A.

What would be the advantages/disadvantages between both motors ?

TIA

[P.Passuello]

Hi TIA,

The choice between the 2 motors you have listed is very easy.
The KL34H260-35-4B (465 oz/in) motor is the only one of the two that your G540 will drive in a half decent manor.
You are bound by the limitations of the G540. A lot of people see the large holding torque and low current and think that it is the way to go but in reality you will find that as soon as the motor starts to move it will have a large drop off in power. The only time that motor will have 900 ozin power is when it is not turning. It is the curse of the stepper motor.

Now to muddy the waters a bit.
The best option is to get motors that match the G540. That way you will get the best from the drive and maximum speed and power for your machine.
The Keling NEMA 23 Stepper Motor: KL23H2100-35-4B 381 ozin motor is a good match for the driver. You then gear it down 3:1 with a belt drive you will get more torque and higher speed than you will ever get with the bigger motor. Larger motors have larger internal losses to overcome causing more power loss.
The 425 ozin motor can only supply maximum amount of power when it is fully supplied with correct voltage and current. The required voltage is higher than the G540 can supply so it will loose torque a lot quicker than if it is correctly driven. The 381 ozin motor will have a lower starting torque but will be able to sustain it longer giving more speed. Gearing will give you any extra power if you need it.

Another way to look at it is that it is the power of the motor that will move the gantry.
The G540 is limited to 3.5 amp x 48 volts = 168 watts and that is all the power there is no matter what you do.
No matter how big a motor you put on it you cannot get more power from your driver to your motor and this will decrease as soon as it starts to move.
The only way you can get the maximum power from any driver is use motors that match best.

Sorry for the long winded rambling but hopefully it will help you decide.

Cheers
Peter

[kNucklBustr]

Thanks, youve explained it perfectly clear for me. Though Ive spent hrs reading about motors, I have a difficult time grasping the concept.
As a matter of fact, I do have a KL23H2100-30-4B 382 oz-in motor. Actually 2. One is mounted on an Ellis Divider. Used in the horizontal position.
Along w/ Mach3, touch screen, etc.
Originally purchased for a 10x26 lathe conversion.
I didnt think the NEMA23 382oz would be capable for direct drive. The easier route for mounting.
Going 3:1 w/ this motor will be a financial relief .

Cheers

[whateg01]

...

You then gear it down 3:1 with a belt drive you will get more torque and higher speed than you will ever get with the bigger motor.

...

Gearing will give you any extra power if you need it.
...

Cheers
Peter

Can you what appears to be a contradiction? I just want to make sure I understand what you are saying.

When I hear gear down, I think in terms of speed, so a 3:1 means if the motor turns at 300 RPM, the driven device will be turning at 100 RPM. This would make sense on a normal motor for getting more torque out of it, though it will come at a loss of upper speed. Using steppers, that means that you are forcing the motor into a range of RPMs that steppers naturally don't like. So, you get more torque at low RPM, but lower top speed, in the end.

Since we are talking about steppers, wouldn't the user want to gear it up so that for each turn of the motor, the leadscrew turns faster? This results in a reduction of low end, or holding torque, but it keeps the motor in a RPM range that it can deal with longer, so the machine has a wider range of travel speed.

Dave

[P.Passuello]

kNucklBustr

The 382 oz motor is a very poor match to the G540 as its inductance is far too high and doesn't take advantage of the current the G540 can supply. Having said that you could connect it to the leadscrew for a test and see how it behaves. You measured less than 200ozin in your test so it sounds like it is worth a try to direct drive and if it works, will give you a bit more confidence in a smaller motor.
I like your idea of using a torque wrench to measure turning force required.

If you have a look at the Gecko website they have excellent info on steppers as well as calculations on how to choose the best stepper for your application.

Can you what appears to be a contradiction? I just want to make sure I understand what you are saying.

When I hear gear down, I think in terms of speed, so a 3:1 means if the motor turns at 300 RPM, the driven device will be turning at 100 RPM. This would make sense on a normal motor for getting more torque out of it, though it will come at a loss of upper speed. Using steppers, that means that you are forcing the motor into a range of RPMs that steppers naturally don't like. So, you get more torque at low RPM, but lower top speed, in the end.

Since we are talking about steppers, wouldn't the user want to gear it up so that for each turn of the motor, the leadscrew turns faster? This results in a reduction of low end, or holding torque, but it keeps the motor in a RPM range that it can deal with longer, so the machine has a wider range of travel speed.

Dave

Good point Dave,
I badly worded it there. What I was trying to say in my own inept style, is that if you gear the 381 ozin motor to a ratio 2.4:1 which matches the same torque as the 900 ozin motor the top end speed of the smaller will ultimately be higher, as the drop off in torque from the 900 will be much greater. Especially as it is grossly underpowered by the G540. Other considerations are that the larger motor has more mass to get turning and larger internal losses to overcome.

Gearing up is an interesting idea but there will be a reduction of resolution. This will be counteracted by driving a leadscrew admittedly so probably not a consideration. I imagine that people don't do this because if they want a lower power motor they prefer to pay less money buying a small efficient well matched motor than to buy for a more expensive motor, under power it and gear it up.

I should also mention that I base my comments on the fact that a G540 is the specified drive for the motors as opposed to using a correctly matched driver for the 900 ozin motor. That would be a different story.

Hope I am making sense (It happens occasionally)

Cheers
Peter

[whateg01]

Peter, I apparently did a poor job of proof-reading my post as well. That first sentence is ugly! I think I understand what you are getting at. Ultimately, the OP needs to make sure that the drive and the motor will play well together.

Dave

[kNucklBustr]

I knew what Peter meant.
This is what I ordered from SPI/SI.

Pitch: .200"
Speed Ratio: 2.50
Center Distance: 3.8925

Timing Belt:
No. of Grooves: 64
Width: .375

Type: Metal Pulley
No. of Grooves: 14
Pitch Diameter: 0.8913"
Teeth in Mesh: 6
2 Flanges/With Hub .25 hub

Type: Metal Pulley Plastic Pulley
No. of Grooves: 35
Pitch Diameter: 2.2282"
Teeth in Mesh: 19
2 Flanges/With Hub Aluminum Insert .500 hub