Best flexible couplings according to redditors

Look into z rod couplers for 3d printers. The most common size is for an 8mm threaded rod.
There should be a lot of different options.

Here is an example of what I was thinking of:
uxcell 8mm to 8mm Stainless Steel Shaft Coupling Flexible Coupler Motor Connector Joint L30xD25 Silver https://www.amazon.com/dp/B07G6Q1GHN/ref=cm_sw_r_cp_apa_i_kCjhDbQB6CMGQ

As others have stated it looks like Z wobble

Do you use Flexible Coupling's? (eg:https://www.amazon.com/uxcell-5mmx8mm-Helical-Coupler-Coupling/dp/B00KHTVOEU/ref=pd_lpo_328_lp_img_4?_encoding=UTF8&psc=1&refRID=C2PXGYBEHJNE7GHTR8RY)
To connect your Z motors to the rod/lead screw?

If so, I would swap this to a solid connector (And upgrade to lead screws if you haven't already)

Even these work better than the Flexible Connectors
http://www.thingiverse.com/thing:602481

I've got a Jr where I've got some intermittent wobble issues. Tried unscrewing my lower stepper motor with some success but I'm fairly certain this should help a lot. I got this guy http://www.amazon.com/gp/product/B004HW7190/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1

No problem. I believe most people use something like this to connect the screw to the Z stepper.

X and Y look awesome, but you are experiencing LOTS of Z banding/wobble. Look into some Z axis stabilizers or some flexible Z axis couplings like these. Also it looks like you have some underextrusion on the top. Try either increasing the number of top layers or run an E-step calibration for your extruder

I made the mod to my Simple Metal and while it's sort of functional, it's making noises that obviously indicate some issues. I'm hoping someone here has some suggestions on what's wrong.

I used this leadscrew: http://amzn.com/B015PS2Z4K and this coupler: http://amzn.com/B00KHTVOEU that I'd picked up a few months ago. I'm using the Machine Control Panel of Simplify3D for my testing.

There's a small "thunk" every time I start moving the Z axis. Aside from that, moving the extruder assembly up is smooth. But moving the extruder assembly down is very herky-jerky. Something must be binding and catching but it's not obvious to me what.

If I remove the set screws attaching the lead screw to the adapter I can manually lift and lower the extruder assembly fairly smoothly. The lead screw can be pushed up and will drop down smoothly under gravity. The stepper spins smoothly both directions. Is it an issue with the coupler I'm using? I tried pushing the lead screw down as far as I could before tightening and leaving it up a bit before tightening it down to no difference. I'm thinking the "springy" coupler design was a bad choice?

Or is my problem elsewhere?

I ended up getting a double loop coupler this one so far it had reduced most if not all of the wobbling issue I was having it allows the shafts to be a good 2 or 3mm off and still spin as if they were perfectly aligned. I didn't think it would be very good because it looks like it wouldn't, but it actually seems decent so far. just waiting to see what the life of the thing is. hopefully it doesn't rip apart after 10 hours or something.

The first photo shows the orientation on the bed. If you look, you can see lines at the bottom of the print, but they aren't too bad, if at all as the print goes up.

This is on a Tevo Tarantula on which I have relocated the z-axis motor to the bottom and I am using this coupler - https://www.amazon.com/Befenybay-Aluminium-Flexible-Coupling-Connector/dp/B07RMZCLZ3. I am running this oldham coupler - https://www.thingiverse.com/thing:2568712. I am wondering if the coupler is causing more wobble at the bottom than the oldham can compensate for but as it goes up, the oldham is better able to compensate?

Any help will be appreciated.

I have a similar weekend! Adding an aluminum extruder and this coupler for the lead screw:
https://www.amazon.com/dp/B07RMZCLZ3/ref=cm_sw_r_sms_apa_i_dTu2DbW7VEA45