Eliminating Hadron z wobble

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Eliminating Hadron z wobble

Postby robotdad » Mon Nov 26, 2012 3:19 pm

I beleive I'm getting some z wobble on my prints, here is an example.

https://skydrive.live.com/?cid=3DA4361D ... 95C%211067

I see references in the forum to rebuilding the z axis to fix this. Is that it? What specifically am I looking to change? They seem to run smooth now, and wherever this ripple is coming from it isn't something visible to me in the machine running. I don't like the idea of blindly reassembling the z axis and hoping that fixes things.
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Re: Eliminating Hadron z wobble

Postby mikegrundvig » Mon Nov 26, 2012 4:27 pm

Is it being caused by bed shake as the machine changes direction? That could be hard to visibly see while still causing noticeable problems.
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Re: Eliminating Hadron z wobble

Postby orcinus » Mon Nov 26, 2012 4:31 pm

Two key questions for debugging striated prints:

1) does the striation frequency coincide with the threads on the threaded rods?
2) are striations symmetrical (i.e. caused by variations in layer height) or assymetrical (i.e. causes by X-Y offset)?
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Re: Eliminating Hadron z wobble

Postby robotdad » Tue Nov 27, 2012 2:20 am

To my eye they look like they line up fairly well with the z threads and yes, they are symmetrical.
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Re: Eliminating Hadron z wobble

Postby orcinus » Tue Nov 27, 2012 4:14 pm

Then yes, Z-wobble it is.
Make sure your frame is square and the rods are parallel to the Z makerslides.

Easy way to do it:
- level your printer (the printer on the table, not the bed)
- remove one rod from its coupler
- unscrew it a bit until it's hanging loosely from the delrin nut block above the coupler
- unscrew the stepper plate and move the stepper until the hole in the coupler is right beneath the free-hanging rod
- tighten the plate
- reconnect and re-tighten the rod inside the coupler
- repeat for the other side

What kind of couplers are you using?
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Re: Eliminating Hadron z wobble

Postby robotdad » Wed Nov 28, 2012 5:08 am

Uhg. Doing the best I can here but...

The couplers are what came with the kit. I have maybe the second batch of Hadrons.

The motors are larger than the feet, so to keep them suspended and balance the machine on the actual feet I've got it sitting on a piece of ply that doesn't go under the motors.

The motor mount pieces flex, eve with no weight on them. So lining the z rods up with them is difficult as the motors tilt. They stop tilting when they get attached to the z rods.

However, after trying to recalibrate here one of the motors has decided to have it's entire mount move back and forth when the z axis is moved. It didn't do that before, before both motor mounts simply flexed when in use.And no I can't tighten the plate anymore, the screws can't go down further. You can get it to play easily by hand as well though. Not sure what's going on here.

And hanging the z rods, well there they don't hang straight. They have a significant amount of play while hanging, so it's difficult to get them centered over the motors without holding them to maintain square with the z maker slide.

Gonna play at this a little more before throwing in the towel for the evening.
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Re: Eliminating Hadron z wobble

Postby robotdad » Wed Nov 28, 2012 5:59 am

Gave it another go. Found that one of the Z makerslides was off a bit, fixed it to square. Readjusted that sides motor and rod. From the previous post the main effect that had was that motor mount stopped moving back and forth. While I didn't amke careful note of this the z rods seem to have less visible play in them than before at the tops. I think I always ignored that before thinking the makerslide would remove any play introduced from the rods.

So with that, a test print of the last single wall before I began adjusting.

No impact. It's the same.

Shit.
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Re: Eliminating Hadron z wobble

Postby fma » Wed Nov 28, 2012 6:18 am

Are all v-bearings of the gantry correctly engaged on the Makerslide? Because of the plastic spacers, the 6 v-bearings can't be all in the same plan, and so, there still have play on the Z axis.

I also have very visible wobble, and I think rpelacing the plastic spacers by metal ones will do the trick.
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Re: Eliminating Hadron z wobble

Postby brnrd » Wed Dec 19, 2012 9:44 pm

I just uploaded a thing to eliminate z wobble due to bent threaded rods. I'm still in the process of building a Hadron so I haven't tested it yet, but I expect it to work.

Image
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Re: Eliminating Hadron z wobble

Postby fma » Wed Dec 19, 2012 9:57 pm

Very interesting! As soon as I receive my hot-end, I print a set...
Frédéric
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