Are nema 23 motor shafts reliable?

[mauribastidas]

I need to know what happens if I put some motors bigger than necesary in my machine, I saw a similar machine to my own with nema 23, 430 oz/ inch motors , but I think than the shaft of this motors is not reliable, is it right?, so I've decided to buy some nema 34 600 oz/inch motors, help me

[RomanLini]

The shafts of the size 23 motors should be very reliable, unless you are abusing them with great forces outside their spec. The motor datasheets usually list their spec for axial and radial shaft loads.

If a shaft has broken off it is most likely due to extreme bending force from a motor that is not aligned properly to a leadscrew and has a solid coupling.

[JD_Mortal]

You also have to remember, or know, that there is nothing in the name "Nema 23"...

Anyone can make a "Nema" motor, and does... Nema is just a standard for size. That is like asking if 2" conduit pipe adequate for a suspension bridge. Depends, is it 2" cold-rolled steel, hot-rolled steel, aircraft aluminum, copper, recycled aluminum... does it have 1/16 inch thick walls, 1/8", 1/4"...

Nema standards only depict the length, and width, but not exactly the height, and the mounting pattern. To be a true "Nema", with a label, certain expectations, within a wide range, have to be met... (However, there is no real legal enforcement of the use for the name "Nema"... If Nema does not have the info on that motor, it is just a nema-style motor.)

However, those ranges are wide... So you can have a motor strong enough to mill metal slow, or one that can only cut foam-board fast. One may be 10watts, another may be 100watts. One may operate at 1vDC another may operate at 100vAC. One may use cold-rolled stainless steel axles on similar bearings, another may use hot-rolled non-stainless chromed steel on similar bearings.

NEMA - National Electrical Manufacturers Association

You have to know your motor, by the specs. That may be impossible if you can not find the EXACT model # data-sheet. Never assume that an unlisted model-number, that may be close, is the same... Those "custom" motors have been modified, and similar model numbers usually have nothing to do with the item you may have. (They use "unused" model numbers, so that there is no accidental confusion, of you thinking it is the same specs as another model # that it is not. Eg, calling it a 340b does not make it between a 330 and a 350, and does not make it a 340 if one exists. The "b" is not a sub-variation relevant to another listed model. It can be a custom modification or it can be a completely different motor.)

So... To answer the question, we need to know more than, "Nema 23"...

If it is a true "Nema", that is not "custom", it will have exact model numbers and other information listed, as per the "Nema" standards website. However, if it is a custom motor or a generic motor that is just "nema 23" size, you will have to determine the ratings yourself, or contact a manufacture who had the motors custom made for "xxx" device that it was made for.

[cyclestart]

I've given a Pacific Scientific 425 oz*in a pretty good torture test.

In the attached photo the motor (only the top is visible) is supporting a 7 lb beam and the beam is in no way balanced. After many hours of operation the motor developed a lot of end play but otherwise was completely functional.

Later that same motor was used to test the X axis on my router. The motor was connected to the ball screw by aluminum helical coupler. The motor itself was sitting on a block of wood but not bolted to the machine in any way. Eventually the coupler snapped, the motor survived.

Other threads tell stories of these motors snapping lead screws. This was probably caused by turning a shoulder to a sharp internal corner (my guess)

[mauribastidas]

Great answers, you taught me a lot, , I'll get the specs and study the issue, thank you so much. And Cyclestart your experiment is really nice, you motor is a survivor I hope mine too.

[cmnewcomer]

I wouldn't say reliable as much as more sensative. I have a CNC mill I made and used 23's for the Z axis using the 1/4 inch shaft. They are belt driven so I didn't think I could overtighten the belts but apparently I did as the shaft broke after many hours of use. Clearly my fault but as a hobbyist it's sometime hard to get the proper tensions. While I'm still using 23's for the Z axis, they are 3/8th shafts and not the 1/4 shaft. I'm also a little more careful on the belt tension.

Best Regards.

Carl

[packrat]

Originally Posted by cmnewcomer I wouldn't say reliable as much as more sensative. I have a CNC mill I made and used 23's for the Z axis using the 1/4 inch shaft. They are belt driven so I didn't think I could overtighten the belts but apparently I did as the shaft broke after many hours of use. Clearly my fault but as a hobbyist it's sometime hard to get the proper tensions. While I'm still using 23's for the Z axis, they are 3/8th shafts and not the 1/4 shaft. I'm also a little more careful on the belt tension. Best Regards. Carl

Your 3/8 shaft motor is a NEMA 34 not a 23. See this for the NEMA standards;

NEMA Motor Dimensions

cary

[ger21]

Originally Posted by packrat Your 3/8 shaft motor is a NEMA 34 not a 23. See this for the NEMA standards; NEMA Motor Dimensions cary

Actually, it's neither. It's sometimes called a 60mm motor, due to the 60mm mounting flange and body, compared to the Nema23's 56.4mm.
It has the same mounting dimensions, and can have either a 1/4" or 3/8" shaft. See the first two motors here.
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[Fastest1]

Originally Posted by mauribastidas I need to know what happens if I put some motors bigger than necesary in my machine, I saw a similar machine to my own with nema 23, 430 oz/ inch motors , but I think than the shaft of this motors is not reliable, is it right?, so I've decided to buy some nema 34 600 oz/inch motors, help me

What are you trying to acheive? Do you want faster rapids? Are you running your controller and steppers on the maximum voltages allowed? Or are you just scared of the shaft diameter being 1/4" and suspicious of its breakage?