question about couplings

[15mgtar]

Hi all I have 12Nm nema34 stepper motor that needs couplings but I don't know which kind of couplings are suitable for my motor, can you guys help me out? Is it ok to use rigid coupling?

[finishlinewrx]

I used LoveJoy brand "spider type" on mine. when i asked i got a couple different options.

I didnt use soild ones due to not allowing much if any misalignment. Just my preferance though.

http://www.cnczone.com/forums/showthread.php?t=78976
Here is what they told me ^^

[rlwoodjr]

I like the helical couplers. I also have had good luck with the rubber inserted ones. I would agree that solid is not the way to go due to alignment.

[garagefela]

Oldham couplings seem to be the way to go and I will be using one on my X axis but they are not cheap.

Zero backlash is what I am after.

For 12 Nm the chart says that a unit at 41 mm has a rated torque of 14.8 Nm.
The next size down is 33mm but only has a rated torque of 8 Nm when using an Acetal center disc.

http://docs-asia.electrocomponents.c...6b80020553.pdf

I also wanted to use solid couplings but was convinced away from doing that by very cluey people here.

That being said some have run their machine for years with solid but have also heard that some have snapped the motor shaft clean off after running slightly out of alignment.

Cheers M

[FandZ]

I'm useing spider couplings now but on my next build I think I'm going to try out these nifty K-couplings. http://www.beemerprecision.com/kcoupling.asp Searching around there are different verities between $10 to $30 depending on the size. Reading up on them, they allow for some miss alignment and have good vibration dampening. Zero backlash. They just look slick.

[garagefela]

Yeah they do look good but zero backlash?? They just don't look like they are rigid enough to provide that function.

Hmmmm.



Cheers M

[15mgtar]

a friend of mine said that using a rigid coupling may damage the motor bearing due to vibration is that true? I'm very concern about damaging the motor shaft bearing since you can't open it and replace it yourself.

[rlwoodjr]

Originally Posted by 15mgtar a friend of mine said that using a rigid coupling may damage the motor bearing due to vibration is that true? I'm very concern about damaging the motor shaft bearing since you can't open it and replace it yourself.

Yes, if you have a rigid mount and you stepper is not aligned the bearings will wear out. If you are a lot out of line they will wear quickly, if you are close to true alignment they will last longer.

When I say aligned, I mean both radially and along the axis. It is my opinion that this would be hard to get correct on a DIY machine.

You could use a rigid mount and soft mount the stepper motor.