Z Axis - precision and accuracy

Speed threaded rods can not move nearly fast enough

 

Using threaded rod and a nut to move things is really the opposite of what it was designed for. The very purpose of the thread and nut design is to create enough friction to tighten up the nut and have it stay there. Backlash is irrelevant.

Of course the intent on the printer is to have the nut move freely with little friction and minimal backlash.

On a printer lubing up the rod and nut is really, really important. I'm using white lithium grease (ie bicycle grease) but I am not convinced it's the best lube.

better suggestions re lubing up the rod very welcome!!!

 

White lithium is really all that is need no special heat spec required been using it since I got my printer in June without any issues

 

I have now

- Replaced the wobbly couplers ( Jerry from Robo Support sent me replacements - thanks)

- Installed the 8mm, coarse thread, stainless threaded rods and the trimmed 8mm stainless nuts

- Flashed the firmware with 2560 steps/mm on the Z Axis to match the 1.25mm pitch of the rods

- Tweaked the torque setting of the Z Axis steppers so they work smoothly with the new rods.

- Installed the adjustable Z Axis stabilizers.

Below is a before and after print. These are different models but both were done in PLA at 0.2mm and with exactly the same Slic3r settings. I am not sure which part of the upgrade has given the most improvement - maybe all have helped.

 

My Vote 90% wobbly couplers 10% Z axis stabilizers

 

No I am not I do not think that mod actually does that much to affect printsfrom what I have seen and experienced the thread size and it layout dhould not have that much of an effect. Remember the thread rods is mainly used as a lifting force gravity moves things down the nut raises them. The smooth rod is by far more critical. In this case the couplers being out of round was the major cause and then I fall back on what I have seen in the the stability of the smooth rods is critical as well. If a person gets a printer and the base smoothrod support is broken or cracked the printer can be unusable and what has been recommended is to find a way to just temporarily fix it in place long enough to print another one or two and replace them . After that is done the change is significant and accurate prints can be made.The other aspect of the smoothrod is the upper end and adding a piece to fix that in place has also been seen to increase quality because it does increase teh stability of the smoothrod.

The threaded rod as I said produces mainly a lifting affect and many people who have implemented that mod have not seen any significant change some have seen some improvements but the improvements usually came along with other modifications as well as in this case couplers, threaded rods, and upper supports and I simply feel the couplers and the smoothrods supports did the work and if nothing had been done to the threaded rods I think you would have still seen the same improvement.

Identify what physical aspects will be altered that affect the print when this mod is done
Actually I believe the same can be said about the change from .1, .2 or .3 in layer heights to the funky .1xxx, .2xxx and .3xxx. No one has been able to give me a logical reason why that does anything.

The process works by having a stepper motor make a set amount of steps to raise or lower the z axis a fixed amount period if a movement is required that is less than a full step there are micro steps that will adjust to get the distance as accurate as possible but how does setting a print height to any number over another affect a how this movement is calculated or done.

When people have issues sometime grasping at something that sounds like it could help actually makes people believe it helps when there is no real logic behind it.

I wish you luck if you do this mod but before doing any mod understand the working and know why it works if this can't be done then do not be disappointed if it doesnot change anything.

I am not against mods like this as all the information about them may not be available and if something new is known to happen I will embrace it but I need some solid facts about mods before I do them.

 

Putting aside any differences between the number of steps to raise a 5/16 versus 8mm rod and any possible rounding errors in the firmware.....

The main reason I changed to 8mm is that the couplers are designed for 8mm rod. If you use a 8mm coupler for a 5/16 threaded rod (OD 7.75mm) you either have to centre the rod accurately using some kind of packing or the 5/16 rod will be off centre and wobble. On the stock Robo, teflon tape was used in an effort to centre the 5/16 rods and avoid having to overtighten the coupler.

A metre length of 8mm stainless rod is < $7. I didn't see much point in sticking with 5/16.

 

I could see that it is a valid reason to make the couplers more secure and make it fit properly in the coupler

 

I am glad you got good prints your last line is amazingly accurate just because mod exists does not mean it is the absolute end or even if it in any way correct the biggest thing and I think you understand it now is at time and incorrect fix can be put in place along with something else and it can be mistakenly identified as being the correct answer I am glad you identified the real issue.