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ball-cap rod-end concept pros and cons

Posted by shadowphile 
ball-cap rod-end concept pros and cons
September 08, 2017 09:44PM
Hello, after custom machining my effector and carriages I am now frequently getting .01 mm auto-levels on a machine with a 300mm print space, which I am pretty happy with.
However, the Traxxis rod-ends are definitely the weak link (no pun intended!) and I'm looking at alternatives.
The magnetic ball approach seems popular and easy to make accurate but I just don't trust magnets and shudder when I imagine my untended printer smashing itself to pieces.
Instead I recently learned about the ball-cap approach: the balls are mounted axially on the effector and the rod-ends are shaped to cap laterally on the ball, with a spring pulling the rod ends together.

My thought is that making the ball-cap end precisely centered on the ball itself is important, otherwise the effective rod-lengths will change with angle.
So far I have only encountered this design at Trick Laser
The parts are injected-molded Delrin so the accuracy is probably really good and likely to stay that way, IF you can find 3/8" ball studs. Most ball-studs I can find are 10mm, which differs from the Trick Laser parts by about 5%. Damn Americans using imperials units! (I am a damn American btw). A short ball-stud would directly replace the traxxis ball without any redesign (assuming the same M3 stud).

So far I have not found much hands-on or theoretical discussion of this idea so I am starting one now.
thanks
Re: ball-cap rod-end concept pros and cons
September 08, 2017 11:23PM
In another thread I read about IGUS-filament. If you have a working printer, you can try to print your own ball caps. Maybe make them fit with heat?
BTW: Many Deltas run on original IGUS ball ends, but they are expensive.
Re: ball-cap rod-end concept pros and cons
September 09, 2017 12:45AM
I recommend the magnetic rods and ball studs by Haydn Huntley. They have never come apart on me except when I applied force to the effector manually.

I've never used ball-end axles and caps, but user saffi on the Duet3D forum has used both the SeeMeCnc and the Tricklaser ones I believe and may be able to offer some advice. Here is one of saffi's posts: [www.duet3d.com].

Edited 1 time(s). Last edit at 09/09/2017 12:46AM by dc42.

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Re: ball-cap rod-end concept pros and cons
September 09, 2017 04:51AM
Haydn also sells 3/8 Ball studs separately Haydn's Ball studs
Re: ball-cap rod-end concept pros and cons
September 10, 2017 01:05PM
Would not be too hard to machine something that works like the Trick Laser-cups, I think. A countersinked hole in some slippery, reasenably hard material should do it. The trick is attaching the spring so the joints will self-center. A pure print might work too

Edited 1 time(s). Last edit at 09/10/2017 01:06PM by SlowFoot.
Re: ball-cap rod-end concept pros and cons
September 11, 2017 01:56AM
or machine it with a 3/8 ball mill
Re: ball-cap rod-end concept pros and cons
September 11, 2017 10:36AM
Go with Haydn's rods. You can order them on ultibots, they're fairly priced and outstanding.
Re: ball-cap rod-end concept pros and cons
September 12, 2017 06:03AM
+1 for Haydns magnets they won't disconnect unless you have a catastrophic impact with something and then you probably want them to.

They have zero backlash and are light.

My only suggestion would be thicker carbon rods/tubes for longer lengths I. E. 360mm plus as I can slightly bend my 360mm arms if I try, not that it seems to cause any practical issues, it just seems to make sense as length increases to increase stiffness.

Edited 1 time(s). Last edit at 09/12/2017 06:04AM by DjDemonD.

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Re: ball-cap rod-end concept pros and cons
September 15, 2017 04:49PM
thanks for the input. I still have a conceptual problem with the magnets. They get weaker as you pull away vs springs that get stronger as they stretch. The later sounds more shock resistant.
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