effector rod design questions

Hi. I have a Kossel Mini that I bought in kit form. It has turned out to be inferior in many aspects and I am selectively upgrading.
I am looking at new effector-rods because mine have noticeable play and especially because my delta is setup for 3mm filament and that puts a lot of torquing stress on the effector. (ie lateral tilting)

My rods came pre-assembled and are probably cheap imports. Do those usually just crimp the ball in? Mine looked crimped.
However, I was told they can be tightened inside with a set-screw.

So I’m an trying to determine if I can usefully upgrade mine:
-Is the set screw in all (decent) hollow-ball designs?
-Is the set screw used to actually tighten up the play or for some other reason?
-Is it a given that once they are epoxied to the rods that any subsequent wear that causes play is permanent? Like ball-bearings, I can imagine that getting the play out without increasing the wearing on the joint is a narrow adjustment.
-Also, I wonder if because of the extra forces the 3mm filament causes that I should consider the moving to a heavy-grade graphite rod. I know that will add some weight but the trade-off might be worth it.
-The joints look like aluminum and these must take quite a beating. Are there chrome-plated or otherwise harder-surface options around? Plastic? Anodized? Seems like anodizing would really help the wearing issue.

Because of the extra stress on the effector from the 3mm filament, I am avoiding the magnetic-joint approach. (maybe later)
Thanks for your input.


TriDPrinting sells the Traxxas #5347 rod-ends. I notice many versions of rod-ends elsewhere. Is there a reason for choosing the 5347s ?

Maybe you would be better off switching to a 1.75mm filament hot end?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

A smaller filament would lessen the stresses 3mm causes but I'm still stuck with poor sloppy parts. Although smaller filaments have their own issues, the thought has occurred to me to step down to 1.75mm, except I've already invested enough in this path. (like $100 to replace the junk hot-end I received with a good one from e3d; $70 to print a newly designed effector base to replace the junky one I received, sigh) This kit I bought is one of the worse purchasing decisions I have ever made.

Sorry to hear of your woes with your kit. If it makes you feel any better, I built a Rostock not in kit form, and wound up spending pretty much twice what I thought I would, because I had to replace the rods since I made the first ones poorly, ordered some of the wrong parts, broke a couple of things, spent about a month trying to print a geared extruder so my underpowered extruder could actually extrude well enough... and the list goes on. I'm now onto making a custom Kossel, which will be much better built, and it has so far cost me about half of what the Rostock cost. But that's how it goes I guess...

So, regarding ball end joints. The Traxxas joints are chosen (I guess) because they're fairly cheap, and they're reasonably well made. They're just a press fit into the housing, so there's no set screw or anything keeping them there. To remove any play, I use rubber bands to join each pair of parallel rods. You could use springs or whatever, but rubber bands do the trick and I had them lying around. I've heard that over tightening the grub screw in the rod end will also eliminate play. I've had a few months and many, many hours of printing on them and they're holding up well. I was careful about how I epoxied them, and I can actually just unscrew the rod end from the grub screw. Having said that, replacing them and ensuring their lengths are actually equal would be a bit of pain in the ass. I've just accepted that I might have to remake the rods at some point.

I've not had any experience with 3mm filament, so I can't comment on that...

I'm honestly really pleased with the Traxxas joints. I'm building my Kossel with them, so maybe that says something. I used the original printed Rostock rod ends at first, and these are a heck of a lot better. Never used magnetic joints, but they sound like they can be a bit finicky.

And on a final note, If you need anything printed (just pay weight in filament, plus shipping costs) feel free to message me. I feel your pain. Not having a printer when you need to print crap is a major downer, especially when it costs an arm and a leg to have things printed by a service.

Edited 1 time(s). Last edit at 01/28/2015 10:32PM by iira.

@iira, thanks for the reply. I want to build some 'perfect' rods with precise length and no play. Despite the new effector platform I just installed, it is STILL visibly tilted. So now I am seriously thinking the rods are also a problem.
I also added rubber bands to my rods, just to keep them from vibrating like crazy. I suppose they might help the play some but I imagine under momentary stress they just give way. I also imagine that stronger springs would be better, but add more wear.
And thanks for the printing offer, I will keep in mind if I run out of arms and legs! I stalled as long as I could trying to print my own parts but my calibration is still too bad to print an important robot part. Chicken and egg!

In some ways I wish I had started from scratch; the initial cost would have been half of what I paid for the kit ($800!) and I could rely on my engineering skills (my profession) instead of trying to understand and anticipate somebody else's design process. I thought a kit would be faster but in fact was more frustrating because I'm trusting the kit instead of using my own brain from scratch. The plus side though is that both of us gained from our pain, although I'm sure I will keep paining for some time
I'm really frustrated with the wonky cold extrusion side and am mentally redesigning to use big rubber treads. No chew marks and no slipping at all, and no melt-through of thin filament, which I was told can be a problem on high-power print runs.
I'm still wrestling with fundamental performance on all the key aspects. (feeding and heating and calibration)
I also finally got tired of trying to ask questions about the firmware and started digging in myself, which is another 'project' step I did not anticipate. I thought I would be printing parts, not becoming a 3D printer designer! LOL
(on the plus side I can answer some auto-leveling questions about Marlin with some confidence)

Oh yeah me too, I thought that I'd be up and running in a month printing awesome things, not spending three months calibrating the damn thing, only to end up building another printer lol! Went much further down the rabbit hole than expected. But like you said, there is a great upside to all of this.

Anyhow, I found that discrepancies as small as 0.5mm in diagonal rod length can cause problems with print accuracy, and if you have uneven rods on a tower it'll cause visible twisting of the effector. I would advise testing each rod one by one on a jig, as I found that the screws I used on my jig (3mm screws in a piece of open beam) weren't dead straight so I had to measure on the same part of the screw. It helps to use the jig almost as a feeler gauge, too, since measuring rods without good calipers is mostly impossible. You'll quickly feel whether one rod is a slightly different size. If you happen to notice that you have pairs of uneven rods, you can actually pair them up to a tower and compensate for that in the firmware, but if you're gonna remake them then that's not really relevant.

Thanks for the accuracy details! I just ordered a rod kit (OMG, did I just say 'kit' ) and I plan on using drill-bit rod blanks to align the rod-ends to make them spot-on.