Mismatched z-axis helical coupleds

I'm doing @Ziggy's z-axis ribbing fixes (attached), and just noticed that I have two different z-axis helical couplers. The stepper motors also appear to be slightly different--the drive shaft is smooth on one, but the other has the 2 flats as described in Ziggy's doc.

Is this intentional from Robo 3D, or the result of a repair or assembly error? I know that my unit was "refurbished". For what, I don't know.

The coupler on the left is much springer than the other. It also uses different set screws and is about 2mm taller.

 

Hi Ziggy! First: thanks for the advice and taking the time to write up the dox. You've got a very methodical mind...something that this mess of a printer needs.

I determined that the motors are identical mechanically. The dimension in parenthesis indicates the length of the leads. I don't think that the different drive shafts will matter, especially if I make sure they're secured well to the couplers.

The helical couplers are definitely different, and after doing the ball bearing fix, the springier coupler is still springy. Did I mention that one of the set screws is stripped on the thread rod side? So yeah, I'm going to source new couplers for sure and M8 rods while I'm at it. After doing all the fixes, z-ribbing is lessened but still present.

I also want to replace the hex nuts with nylon nuts. The problem is finding them. Do you have a recommended source? M8 if possible because that will determine if I replace the rods. My search didn't turn up long nuts, though if I relocate the Z stop, that shouldn't be an issue.

 

JIC -- Im heading to these -- they will eliminate the couplers all together. Would think that would be a good thing... just need to find the necessary specs in order to get the right ones -- maybe someone will chime in with them....

http://www.robotdigg.com/product/8/Threaded-Rod-NEMA17,-280mm-Tr8*8mm-Acme-Leadscrew

 

That's what @donhuevo uses regal. He's in love with them

Though he bought his from http://www.omc-stepperonline.com/ i believe

 

@Mike Kelly you wouldn't happen to know the specs needed off hand would you? I know its a NEMA 17 but I haven't had time to measure the length of the rod + would it make any difference going to a 400 steps/rev over a 200 steps/rev? Obviously you'd have to make some firmware changes but would you be able to increase the vertical precisions?

 

The longer the better naturally. I think don bought 300mm because that was the longest they had.

The issue is that because the motors mount under the middle plate you lose some of that Z travel. I suggest mounting the motors on top of the middle plate, but that will take some reconfiguring of the bolts in the stepper.

As for 400/rev vs 200/rev it doesn't really matter. I think they have 2mm per rev, so break that up into 200 that's 10microns. You really don't need to print at that kind of vertical resolution, 10 steps per 100microns is a good point to be at.

If you REALLY want to do low layer heights, like sub 50 microns, then a 400steps/rev would be best, but a 200 is just fine.

I'll verify but I'm pretty sure he uses this: http://www.omc-stepperonline.com/th...per-motor-48mm-body-300mm-t635-x-2-p-225.html

 

Thanks for the reply Mike! Please confirm as I intend to at some point make the switch.

 

I confirmed with him those are what he uses

 

Awesome! Tx Mike!!

 

Admittedly, that seems like a great solution. It's just way beyond the scope of what I want to do.

Any ideas on the M8 rods + nylon nuts?

 

I am about to install a pair of these http://store.makerstoolworks.com/motion/z-axis-lead-screw-and-nut-single/ which are 10mm wide x 2mm pitch. I'll keep the stock steppers and use a proper pair of couplers. I choose these screws because they are 10mm in diameter and are very straight.

Note that these have a delrin lead nut which I think is the same as the integrated stepper/leadscrew that you are looking at. You might notice that the delrin has a bit of friction at first. Just run it through the leadscrew many times and it will form to the screw and move very smoothly. I used a drill to move it back and forth dozens of times. I using a nut adapter something like this http://www.thingiverse.com/thing:370914 and will add the autolevel switches.