Eliminating Hadron z wobble

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Re: Eliminating Hadron z wobble

Postby gyrogearloose » Sun Dec 23, 2012 7:34 am

That's where it's most visible. It's also very subtly noticeable in other parts of the image. Don't get me wrong, it's a good print! I was just stating the obvious (to me), that the wobble has been greatly reduced but not eliminated.[/quote]

You are right, well spotted. I looked at it again under a magnifier glass and yes, there are still slight periodic aberrations. Not to worry though: Hmmmm, perfection attain we must, Luke. There is no other way and am sure I am on the right track. As you can see, made a change to the coupler to ensure concentricity even more. The coupling is tapped M8 on one end as before, but cut with the hacksaw lengthwise along the center line. This allows the coupling to be compressed around the 8mm rod with a SS hose clip. I have also replaced the SS rod with a brass one. Brass with stainless has a better friction coefficient than stainless on stainless. It is generally not recommended to use the same material for a lead screw and nut anyway. Brass is also easier to straighten if necessary. I will report once i have printed a test piece.
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Re: Eliminating Hadron z wobble

Postby gyrogearloose » Sun Dec 23, 2012 8:48 am

Ok, here it is. You be the judge(s).
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SANY1072.JPG
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Re: Eliminating Hadron z wobble

Postby gyrogearloose » Sun Dec 23, 2012 9:21 am

The finished piece (30x30 cube)
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SANY1076.JPG
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Re: Eliminating Hadron z wobble

Postby fma » Sun Dec 23, 2012 10:43 am

Nice print. I found that white ABS/PLA shows more defaults, because of more visible shadows...

To answer cvoinescu, yes, they are grouped, so it is not good.
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Re: Eliminating Hadron z wobble

Postby cvoinescu » Sun Dec 23, 2012 2:44 pm

gyrogearloose wrote:The finished piece (30x30 cube)


The wobble is now negligible. I wouldn't see it if I didn't know what to look for, so I guess that's it: you've cracked it.
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Re: Eliminating Hadron z wobble

Postby brnrd » Wed Jan 09, 2013 1:32 am

I finally got the Hardron printing so I had a chance to test the wobble suppressor that I proposed in this forum post and in this thing. Here's a photo showing a comparison of a 20mm square x 100 mm tall single wall print with (left) and without (right) the wobble suppressor.

The parts were lighted along the z axis to highlight the walls. Note that the I stopped the print without the wobble suppressor when the z motors started skipping steps due to misalignment between the z nut and the threaded rod. There was significant wobble in the z threaded rods of up to 4 mm due to the threaded rods not being concentric with the motor shafts. A better rigid coupler even with slightly bent threaded rods should virtually eliminate z wobble.
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IMG_3330.JPG
Comparison of a 20mm square x 100 mm single-wall print from a Hadron with the rigid metal z coupler with (left) and without (right) the wobble suppressor.
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Re: Eliminating Hadron z wobble

Postby robotdad » Wed Jan 09, 2013 11:21 pm

brnrd that looks great! I've got those parts printed out and waiting to be installed, hopefully tonight but probably not.

How tight is the fitting of the post between the two parts? Of the bed mine slide together but their pretty snug. Wondering if I should sand them down so their really smooth, or further more so they barely touch.
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Re: Eliminating Hadron z wobble

Postby brnrd » Thu Jan 10, 2013 12:38 am

I've been trying to improve it since yesterday. I tried using Nophead's z coupler with some improvement but I can still see signs of z wobble. The single wall print seems to show this effect easily since the transparency of the filament is very sensitive to the extrusion width which changes with z wobble. I realized that on one side, that's the nut holder was a bit snug on the post and I could feel the z motor move up and down with my finger as I step the z at about 200 mm/s. I sanded it down so it slides easily and I just started printing another test piece. So far, after printing about 20 mm tall, there's no sign of z wobble.

Here's the picture of the single-wall print with no sign of z wobble whatsoever. In summary, the nut holders need to slide freely on the posts. This is probably due to the z motor mounts which flexes easily. I ended up changing to Nophead's z couple but it might have also worked with the rigid metal couple that came with the Hadron kit. I also added an 8mm washer between the two parts with the smooth side facing the nut holder.
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IMG_3351.JPG
Z-wobble free print using wobble suppressor that allows the z nut to move laterally.
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Re: Eliminating Hadron z wobble

Postby roberlin » Thu Jan 10, 2013 4:01 am

Are the threads taken off of your rod at the end?

For me, nophead's coupler worked great (no wobble that was visible to my eyes, although I didn't try single wall transparent like you're suggesting) with the rods I bought from precisiontech, which were turned down at the end.

But a previous attempt with the nophead coupler on some acme from mcmaster-carr that still had threads on the end didn't go very well (it seemed worse than my good rigid couplers from dumpstercnc).
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Re: Eliminating Hadron z wobble

Postby brnrd » Thu Jan 10, 2013 11:42 am

No. The rods had threads at the ends as supplied by ATI. I changed the scad file for Nophead's coupler so that the ID of the lower hole is 5 mm so it fits snugly over the motor shaft. It did take a lot of playing around to get the rods straight on the shaft because of the threads. I got lucky and got both rods to be fairly straight and there was very little wobble of less than 1-2 mm on both rods. I think the wobble suppressor works well under that condition. After that I replaced one of the couplers (which was incomplete due to an extruder jam) with a complete one and I couldn't get the rod straight. So I switched to the metal couplers from ATI and I was able to easily get it fairly straight. I did this by raising the carriage to its highest point, lining the rod so that it's centered in the hole on the carriage and then tightening the setscrews. It's slightly off center at the coupler but there's little wobble at the top. I'll do a print test with the metal coupler later today.
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