Connection between Zstepper & threaded rod? z wobble

I have a high precision 40tpi 6mm Haydon-Kerk LS and Anti-Backlash nut sitting right here.  There are 8mm left on Ebay, but they did not have the 40 tpi as this 6mm does.  As far as attachment goes...there are a couple of options: Shaft Replacement (ideal) or a coupling (hose or pro made).

http://goo.gl/TKqkp Left: after tightening sd2 plywood nutholder and reprinting Znuthugger -- Right: before 

The wobble is pretty much consistently across the whole print.

This weekend I took apart the solidoodle plywood nutholder and re-assembled it and tightened everything keeping a close eye on measuring the distance between the threaded rod and the smooth guide rods (with digital calipers) at various places along their lengths making sure it was the same along the whole length to within .1mm. This did seem to help a bit and I re-printed the Z-nuthugger ( http://www.thingiverse.com/thing:36177 ) at .95% its original size for a closer tighter fit.

While the plywood build platform stock nutholder was removed I did try moving the Z stepper to see the wobble with no support from the nut. You can clearly see the rod wobble from left to right, front to back within the hole in the build platform. I'd say its moving about 2 -3 mm.

Once back together I could see it visibly moving from side to side when it is about 4" down.

This begs the question I set out to answer in this thread, how does the stepper connect to the threaded rod? Has anyone replaced it? Do you have any photos? Experience, knowledge, know how, magic spells... etc.

Like I said it may be an alternative that I will look into for getting my printer as fine tuned as possible.

The bottom of the Z rod is drilled out so it slips over the motor shaft.  Earlier models used a couple made of ABS.  At least one person in the Google Group replaced theirs with a lead screw and used a steel coupling.

http://www.ebay.com/sch/i.html?_trksid= … ;_from=R40

like that?

the only thin that would concern me is:

Solidoodle switched to a drilled/press fitted z screw as the coupled z screw gave loads more wobble.
will a metal fitted Z screw coupler actually fix the problem or will it introduce more problems?
so far as changing to a proper lead screw goes,
I'm not convinced that this is the be-all-end all solution.

I don't think that a direct replacement (e.g. m6 for m6 replacement) would be enough.

after all the threaded rod started life straight. -thin rods are likely to bend!
If I were replacing the z-screw and going for a proper lead screw and nut I'd got for a larger diameter if only because that would be less likely to warp. (although if would also mean firmware changes as the step - moved distance will have changed).

basically, I think a similar gauge lead screw will sort out backlash problems, but I would think that the screw would be just as susceptible to bending during shipping as the threaded rod was as it was shipped to Solidoodle.

They sent me a new screw, I haven't had time to replace it, but they told me how.

using a metal tube larger than the screw, slide that down over the top.

Then using a nut thread that down against the tube until the leadscrew pops off from the motor.

Attach the new leadscrew using some sort of super glue.

"Get a shaft which is slightly larger than the Z-screw.  Then you'll need a nut which you can screw down against the shaft. What is going happen is that the shaft will eventually force the Z-screw off of the motor. "

"You said you're using a new brass screw.  We use a special metal glue.  It's a super-glue.  You can use any super glue.  We use threadlocker red.  Apply 2 drops to the opening in the screw.  Apply one drop to the top of he motor and hold the motor so you can push down onto a firm object holding the screw against the motor.  When you've set it.  Put it aside for about 4 or 5 hours to dry.  Then reinstall the z-screw onto the printer."

The only thing here the I question is the "brass" part I didn't think the new screw they sent me was brass, I'll try and find time this week to take a look and maybe even do this procedure.

so the coupler. (be it ABS, alu or steel) is likely not the answer.

(actually I feel that it *could* be the answer for some, the trouble with the coupler is that it's so easy to get the rod and stepper axle non-aligned/non concentric, so if you were really really careful you probably could get decent prints using this...)

The best fix is probably always going to be a precision drilled screw that is either exactly the same size, (and you'll heat the screw to expand it before press fitting onto the stepper) or driller slightly oversize, (and you'll glue it to the stepper).

The glued method would seem to allow more play in the fit and more opportunity for the z screw to set at an angle and give you problems.

Even then I'm still not convinced that the standard diameter z screw is going to hold up that well, if we seriously believe that the amount of people reporting wobble issues all have bent screws then why do we think that a similar diameter lead screw is less likely to bend, either in transit or in use?

but we still come back to the questions:
is everyone experiencing wobble? -is this a generic issue.
how are we identifying this wobble? -what do prints look like, heavy banding, but at what spacing?
is one persons wobble verified against another persons printer?
(so imagine that one gcode file has heavy banding on your printer, but no banding on mine. then we know that all settings flow etc are the same (and assuming that we both measure our filament width to be the same and nozzle temp is measured (with hardware not just what's reported) then we could say that a printer was *likely* to be at fault.

it would seem that is one person had issues on all prints then there are two likely candidates.
Z screw or slicing software settings.

There is a thread where one user is seeing near perfect prints from skeinforge and heavy banding from slic3r, in this case do we blame the machine or blame slic3r?

i have also wobble probleme on all print...

the probleme is even worst...

i have a S2 1st batch with a abs coupler.. i use the original skinforge of the pack.... no wooble or very little in .3mm print, but moderate wobble in .1mm print..

Solidoodle send me a new motor without the coupler.... not i have always wooble (in .3 or .1mm)..
less with skinforge... but a lot with Slic3r...

i made some test and it seems that the wooble are linked with the speed of the printing head...

speed increase.... worst wobble

Another variable appears! I'll be sure to give that a shot tonight Ian. Thanks!!

Although I gotta say, when printing the calibration .5mm hollow square it moves realllly really slow.. It took an hour to do it at .1mm

here are my prints  .1mm (repetier/slicer) , .2mm (pronterface/skeinforge) and .3mm (pronterface/skeinforge) http://goo.gl/8FIsa

Don't just make a brass version of what solidoodle uses if your going to replace everything: get a good name brand leadscrew. They have better thread profiles and generally come with anti-backlash nuts. Plus, the machine shop will have less work to do, as they just have to cut it to size and bore the hole on the end. You can get them for 40 dollars on ebay, with nut.

The stepper shaft itself looks to be about 5mm, so a drill in the neighborhood of 5mm or #9-#8 would be good. I would give them the motor and tell them what its for and let the machine shop decide. As to depth, boring it extra deep probably wont hurt anything, so have them bore it 3/4 inch (19mm).

I hear you. I just ordered a Hayden-Kerk leadscrew off of ebay, http://www.ebay.com/itm/130803264561?ss … 1423.l2649 to be exact, and it's going to take a bit of work to get it to fit properly, but it should be exactly what I'm looking for. It's too long, but thats easy to fix. The major issue is the mounting system requires a 3/4-20 threaded plate to mount it to the bed. I'm probably going to print a blank out and then thread it on a lathe, assuming I cant just print the threads themselves (though I seriously doubt it'll print nicely).
Hayden-Kerk standard leadscrews are accurate to within .0006 in per inch of travel, which means over the full travel of the printer, it will, at most, be off .1mm. With their nut, it has at most .0125mm of backlash.