Partially Solved z-axis rods vibrating and making a noise at top interface

I have run about 2 kg of filament thru my printer. At first, the noise was just on tall slender builds on long x-y transits and then became pretty much a constant noise. I determined it was due to play between the z-axis rods and the top housing. It went away when I attached a miniature bungee to pull both rods against the inside of their bores in the housing. I searched the forum, didn't see anything posted, curious if someone has developed a more elegant solution?

I am a little concerned that the side preloading may increase z-axis friction too much on tall builds.

It would also seem that the play at the top would cause z-axis banding. After I added the bungee, layer to layer mis registration in x-y decreased.

Thanks in advance!

 

Make sure they are lubricated! ******* Added later I meant the rod bearings)
This will kill the vibration. Loosen the top cover enough to fill the rod mount holes with
Permatex Ultra Copper Gasket Maker. Then replace the top with the rods embedded.
This will kill any vibration.

 

So you mean to have the ends coated with oil or a mold release agent so that RTV doesn't stick? That would make future disassembly easier.

I would also point out that you would want the z-axis positioned near the top of travel while the RTV is curing.

 

I meant lubricate the rod bearings, but your assumption sounds good.
The gasket maker dries like flexible rubber. That is why it will kill vibration.
Carriage near top sounds good too.

 

Print these caps to put on your rod to secure them in place:

https://www.dropbox.com/s/p2qplbikfsjs1vm/rodcap.STL?dl=0

 

I think I like the RTV silicone approach better as there are tolerances between the base and top housing which a spacer housing would potentially over constrain or misregister the z-axis rods with respect to the lower base. Where as the RTV silicone allows them to be in the state which allows the least amount of parasitic side loading, yet still significantly stiffening the entire structure. However I am surprised that the z-axis didn't seem to stick with the bungees pulling the tops of the rods together. For instance the gentleman that made the rigid couplings on the z-axis threaded rods is probably making a mistake, the root cause of his issues are that the z-axis guide rods aren't being held in place.

A hybrid approach of using spacers will more clearance and silicone RTV would still allow the rods to be in their most favorable position, while minimizing the RTV gap, creating a stiffer connection which would improve x-y registration.