is there any z wobble fix without changing the z rod? for a SD4?
thank you

Post a picture of a print that you think is exhibiting Z wobble.  Many people call any type of Z artifact "wobble" but there are many potential causes of problems.  Maybe it is actually banding, non-optimal layer heights, even over extrusion... who knows?  I suggest making a new thread to diagnose your specific problem, and someone will reference you back to this one if needed.

is there any z wobble fix without changing the z rod? for a SD4?
thank you

take the time to read through this thread - your question may be answered.

Thanks for the info on the half-nuts.

I will be posting something on a new thread I just figured out that creates an adjustable anti-backlash via 2 nuts with minimal parts!

The well nut is made of rubber with a wee brass thread in one end. You tighten it down so the rubber acts as the spring and creates the axial force, just as you show above. It's handy because they're widely available, very cheap, and a no-brainer to install.

Note that with a half-nut, or two laterally-offset nuts, the opposing force comes indirectly from the angle of the threads: as the outer thread is pushed radially against the inner, an axial force is created too - if the thread contact surface is perfectly lubricated, it can only react on the normal direction (which has both a radial and axial component). If you can push it in far enough to get both opposing thread surfaces to contact, then there will be no backlash - of course until the axial force is enough to push the nut back out, again using the thread angle:

Here you can see the backlash of a single nut. This backlash really only matters when reversing direction or the weight/momentum causes it to lose surface contact since that's when the threads change/lose load surfaces.

This is what an anti-backlash setup should look like except you need an opposing force like a spring to push them against the opposing load surfaces. Without an opposing force, they wouldn't be forced on opposing threads and you would essentially have the same backlash as before. You would also need to find the max force you need to apply to the carriage/bed to move it from the stopped position. I suggest adding ~10% and that would be the force you want to apply to the nuts. If you didn't have enough pressure, you would induce backlash. Too much pressure is going to create excessive friction which will wear out components faster and work your motor harder.

Note: I think the warped/bent 5/16-18 rod is a lost cause to try and remedy. Even with a perfect system that had angular and translational (the nut huger only has translational) flexibility, the misalignment is going to cause some height discrepancies anyhow. Also any more freedom you try and give it to fix this is just going to cause more free play which in turn is going to cause more height discrepancies.

I was thinking about it when I was planning my m8 zrod swap. You would need a force greater than the force it takes to move the bed up and down to remove the backlash. A spring would work but I'm probably going to build a spring type design out of nylon or something flexible.

How does your nut hugger design eliminate backlash?

The theory is the offset of the two nuts eats it up, much like a pair of half-nuts on an acme thread. I'm not convinced this translated into reality when I tried this mod though... Maybe just my impatience!

But the anti-slop (by it's freedom to slide around laterally) works a charm on banding, so worth it for this alone, even if you don't eliminate backlash at the same time.

Currently I run a version of this thing with a single nut in it (no harm in the two-nut version though), and a well nut on top to ensure minimum backlash in the thread. Definitely no longer my primary source of z hysteresis!

Fig. 1: well nut

Looks like m3 is the way to go? Has anyone who went this route compiled a list of parts needed and stl files? I'm trying to scour thru this thread but it appears that various changes have been made over time so I want to make sure I get the right stuff!

If your concerned about lubrication.....

Something I have found that works well.  Go to a motorcycle dealer and get chain lube.  It usually has a coagulant (some form of wax) that after spraying it on keeps the lube from whipping off at high speeds.  Granted our printers wont be going 96 kmh (60 mph for us heathens), yet the point is that the lube wont drip down if it is an excess.

As a newbie, I'm working my way thru this thread as I don't like the banding on my SD4.

However, I can contribute in the area of lube - us motorcyclists are pretty religious about keeping our chains in good shape, and the general consensus is that DuPont Chain Saver is the best stuff out there. As I have it around, I use it in a lot of other applications and it will be the first thing I reach for when my SD needs re-lubing..

What I did was print out the  5/16 version, put down the thin flat piece, then the block. I then threaded the nut down and as stated above, there is just a little play and that seems to be OK. I then put the cover on. You need 3m or m3 screws.  I used these.

http://www.ebay.com/itm/111068993459?_t … EBIDX%3AIT

and these

http://www.ebay.com/itm/111104351108?_t … EBIDX%3AIT

I hope this helps. Sorry it took so long but with my printer needing some work, I haven't been on the forums.

Could anyone offer help?