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"S" Axis.... Hot end Rocking - SOLVED... I hope....

Posted by gregstah 
"S" Axis.... Hot end Rocking - SOLVED... I hope....
January 06, 2014 04:25AM
One of the huge problems I had was a "Rocking" Hot end, so much so that it would lift prints most, if not all of the time, it made calibration and printing impossible. It turns out that a bit of patience and some figuring out was all that was needed. See the attachment. :-)

Edited 1 time(s). Last edit at 01/06/2014 04:30AM by gregstah.
Attachments:
open | download - reprap x Rib.jpg (254 KB)
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 06, 2014 05:07AM
Sounds just like the x-plate and x-rib that I received with the kit. RRP has now made the slots bigger to stop this happening.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 06, 2014 06:00AM
Well done Greg. I'm trying to resolve my bent X rib, but mine is dead straight on the top, but has a curve along its bottom length. I'm sure I remember it slotted together very easily, so I'm not sure what is causing it?
At X20 and X180 my z readings are the same but at X100 it is at least 0.5mm higher, with a gentle slope off either way. At first I thought the glass was bowed up in the centre. As you say, this can't be calibrated out.

I think I may strip it down to see if the acrylic is straight with nothing attached to it.

On the pictures the ruler is touching the acrylic at each end, but is about 1mm away at rhe 18cm mark






RS Ormerod #472
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 06, 2014 01:55PM
FWIW I stuck my x-plate on a flat surface (side of a spirit level in my case) with double sided tape, then glued the x-rib to it with cyanoacrylate from B&Q. I roughened the mating surfaces with 400 or so wet and dry paper first and used masking tape to prevent the glue going where it shouldnt, (taking care to make sure there were even layers beween x-plate and flat surface so it remained flat.)

EDIT: Make sure the two arent a tight fit first.. should go together easy and make sure the tenons dont stick out the back
regards
Andy

Edited 1 time(s). Last edit at 01/06/2014 01:56PM by kwikius.


Ormerod #318
www.zoomworks.org - Free and Open Source Stuff smiling smiley
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 06, 2014 04:48PM
Thanks Andy, that's a good idea and should make it much more rigid. I might have a go at glueing it when I strip it down, but as the novelty has not worn off yet I spend all the free time I have printing stuff!

Edited 1 time(s). Last edit at 01/06/2014 04:48PM by tim_h.


RS Ormerod #472
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 07, 2014 02:42PM
Gutted, broken it!

Just stripped it down to check this and found the X axis rib was protruding as gregstah described above, so I wanted to file it down, but found it was very firmly fixed into the x axis plate and snapped as I was gently prying it apart. Got to say I was surprised how easily it broke though, I'm not usually that ham-fisted!

Looks like I will be using glue then!


RS Ormerod #472
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 04:24AM
Just received my replacement X axis and rib. I had hoped to get Mk 3 with the new Z nut trap, but it is one with the nut trap still in the rib.
Feels more substantial, and this was confirmed by measuring the thickness. The nominal 5mm is mostly in the region 4.9mm to 4.95mm, whereas the old 'S bend' version was down to 4.4mm in places.
New one is nice and straight.
Now for the wiring ....


Ormerod #17
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 04:57AM
My x-plate is only 4.65mm thick. If it's meant to be 5mm then this partially explains why a 9mm x-runner bearing is too small on my build. The original x-plate I received was only slightly thicker, 4.70mm.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 05:44AM
I've just noticed that there is a small gap between my x-rib and x-plate along part of its length:



Assuming the x-rib is straight, the x-plate must be bending slightly. I'm already using the new-design plate and rib from RRP. I tried to eliminate the bend by loosening the end-piece, adjusting and re-tightening, but to no avail. The gap is a little over 0.1mm, so it will cause the head sag to vary by about 0.15mm.

I think the problem is that there is nothing clamping the x-plate and x-rib together over most of its length, between the end piece and the z-runner. Perhaps another screw hole and nut trap should be added about half way between them?

EDIT: I think it's the x-belt tension that is applying the stress to the x-plate that causes it to bend. Maybe the x-plate should be made from 6mm acrylic rather than 5mm? That would also solve the problems I had with head sag due to the slot for the x-runner bearing not having enough range.

Edited 1 time(s). Last edit at 01/08/2014 05:53AM by dc42.



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

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

Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 06:34AM
Hmm, just thinking out loud, but it's strange that yours is convex along the back, mine was concave and gregstah's was S shaped?
This part of the design really needs improving otherwise the head will never stay at the same height along the x axis.

I agree that it the laser cut parts should be fixed together better, but not sure if extra screws or glueing are the best option, maybe both? It needs to be straight and remain straight when assembled.


RS Ormerod #472
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 09:20AM
When assembling these parts I was amazed at the fit and worried that the parts might snap, but with gentle pressure it all went together perfectly. I checked the gap between parts and there was nothing, not even a hairline of light.
It has now been used a few times but nothing very much and last night I checked with a steel rule edge as per the earlier pictures and it was bowed, but similar to DC42's pic with a similar gap. I pressed the parts together by hand last night and on just checking it has not moved, there is no gap. But doing the ruler edge test again I would say that overall it still bows outwards but there are two equally concave dips, guess this is a "W" shape, presumably a surface flatness issue.
How much this impacts on prints and how stable the assembly is time will tell, but I will be looking to upgrade.


Ormerod #007 (shaken but not stirred!)
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 09:47AM
I'm considering drilling a 2mm hole through the x-plate and into the x-rib, gluing a piece of 2mm thread into the end of it (prefer not to try and tap it, it might break), and then putting a nut on the end to hold it tight. Perhaps do this at 2 or 3 places along the length.

Alternatively (and probably easier), drill 2.5mm holes in the x-plate just above and below the x-rib, and use M2.5 screws to clamp the x-rib to the x-plate. I would need to find a way to stop the sensor board wires catching on it. If I do this in the right places, there would still be room to fit the other 2 extruders.

But first I'm going to measure how much the nozzle height varies along the x-travel. I already have some evidence that the z-height isn't quite right in the centre of the bed, and this could explain it.

Edited 2 time(s). Last edit at 01/08/2014 09:49AM by dc42.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 10:32AM
@dc42, I like your idea when I could ask my workshop to do things, but now it's just me, I tend to shy away from such mods! My plastic parts seem to chip on their own, without me helping!
As an alternative 'low(er) risk' change, what I was thinking of trying is some brass angle clamped each end of the X plate on the bearing edge could be good cure. The bearing is fully home, so moving it away will not be an issue. The angle was quite rigid about 5 or 6mm side and thought a piece of this could be easy to incorporate.
I just can't remember where I saw it (last summer), but think it was B&Q., but it's probably readily available.
(edit) just noticed limited clearance for angle under the between the X plate and the hot end slide, so may be a bit close!

Edited 1 time(s). Last edit at 01/08/2014 10:47AM by Treth.


Ormerod #007 (shaken but not stirred!)
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 10:50AM
Quote
dc42
My x-plate is only 4.65mm thick. If it's meant to be 5mm then this partially explains why a 9mm x-runner bearing is too small on my build. The original x-plate I received was only slightly thicker, 4.70mm.

Well I never measured mine until now and mine measured 4.77 mm thick with the protective film on both sides and 4.55 mm with no film, but yeah the 100mm bearing worked great,

Paul


RS Ormerod No 436
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 10:52AM
Another idea. I had considered using a single screw through the x-plate just above the x-rib, with some sort of one-sided clamp on the end (printed part with a nut trap?) to pull the x-rib against the plate. I shied away from this because a single screw would apply an unsymmetric force to the x-plate, which might bend it. But then it occurred to me that the weight of the extruder motor already applies such a force, in the opposite direction. So I think a single-sided clamp, mounted next to the extruder clip, would be OK.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 11:29AM
Quote
tim_h
Hmm, just thinking out loud, but it's strange that yours is convex along the back, mine was concave and gregstah's was S shaped?
This part of the design really needs improving otherwise the head will never stay at the same height along the x axis.

I agree that it the laser cut parts should be fixed together better, but not sure if extra screws or glueing are the best option, maybe both? It needs to be straight and remain straight when assembled.

Glue ! smiling smiley



regards
Andy


Ormerod #318
www.zoomworks.org - Free and Open Source Stuff smiling smiley
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 11:35AM
Andy, what sort of glue do you use? I've heard that the only really effective glue for acrylic is acrylic monomer,



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: "S" Axis.... Hot end Rocking - SOLVED... I hope....
January 08, 2014 11:43AM
Quote
dc42
Andy, what sort of glue do you use? I've heard that the only really effective glue for acrylic is acrylic monomer,

Superglue .. (Cyanoacrylate) I am pretty sure cyanoacrylate is an acrylic monomer Wikipedia- cyanoacrylate

Anyway own brand "Superglue" from B&Q sticks it like "stuff" to a shovel smiling smiley

regards
Andy


Ormerod #318
www.zoomworks.org - Free and Open Source Stuff smiling smiley
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