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3d - Printworx

Adjusting the nozzle home position

Started by nate80, Thursday,February 15, 2018, 10:37:56

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nate80

I got up early this morning to test print a little bracket to double check the size before ordering some acrylic that would fit inside it.  The Malyan M150's print nozzle was sat a couple mm's off the glass surface so I needed to lift it.  I was tired, and stupidly adjusted the Z height the wrong way  :banghead:  and the nozzle was forced down into the bed.  I immediately realised my mistake and wound the control knob the correct way and the nozzle lifted.  Unfortunately the home position has now changed, and it's so low I can't fit the glass on the bed as the springs are already at max compression.

It all happened so fast (plus I was super tired, so slower than usual) that I don't know exactly what happened.  The Z stop should have activated (not that I noticed it) but, because glass was on the bed and the new carriage is so thick (8mm), the heated bed was still forced down by the nozzle a good 3-4mm before hitting the carriage - and then the motor then made that awful grinding noise for a couple of seconds.

I'm trying to figure out how the home position has physically changed?  Something physical must have moved to create the change I guess?

As I didn't build the Malyan (it came boxed in 2 pieces that you just bolted together) I've not yet seen inside the enclosed X axis area that's responsible for the rise and fall of the rods.  The Malyan is fitted with nice chunky lead screws and I guess there's a collet that allows the axis to lift and fall?  Could this have skipped a thread?

Not my finest moment, and I was in the middle of a mammoth print run, so the timings not the best.   :slap:

Any ideas what's cause the change in home height?  Really hoping this is a fairly easy fix.   :-/

nate80

Just incase anyone's at all interested:  With the odd issues I've been experiencing I'm starting to become concerned that I might look a bit bonkers, but after spending 3 days investigating, educating myself with the specific in's and out's of the Malyan build, and recalibrating the 3D Printer, I haven't got a freeking clue as to what happened - because what happened is impossible.

The Z Axis end stop function (switch) works perfectly (tested, tested and re-tested) and it should have stopped the nozzle before it hit the bed.  I've actually spent a couple hours trying to replicate the issue and it's just not possible for the nozzle to continue pushing down into the bed as it did!  However, the reality is that the nozzle HAS dropped in height because the 3mm thick glass bed now doesn't fit beneath the nozzle when the auto home position is activated.

I've looked at every part of the build (frame/rods/carriage/lead screws/collets/bearings/bearing housings/extruder mount/extruder assembly etc.) and, even if a Z axis stepper motor clamp slipped and the threaded rod changed height, or even if the collet jumped (which also appears impossible), the home position wouldn't be affected in the slightest.  The nozzle is obviously attached to the X-Axis which is attached to a metal housing that is responsible for pressing down and activating the end stop switch.  If any part of the Z axis assembly got moved by the nozzle being forced down into the bed (which I'm 99% sure isn't the case) it wouldn't affect the home point in the slightest as the X Axis Metal Housing would still just ride down the Z Axis unit the metal housing hit the Z End Stop switch.  As I say, the metal housing is attached to the X Axis rods and that holds the extruder assembly, so the nozzle height in relation to the X Axis housing never changes.

So, I'm absolutely baffled and fed up trying to solve an impossible puzzle.  I'm going to design a bracket that raises the Z Axis End Stop switch by a few mm's and then test the printer to see if any damage was done.  I'm concerned the collet may have received some damage as there seems to be a squeak as the collet passes over a certain spot on the Z Axis lead screw, but other than that it appears to be working ok so far.

As far as the impossible issue I experience is concerned, I've not got a blinking clue.   :shrug:

shawdreamer

cant really give you a clear answer on what you had go wrong, seems bizarre by your description (tbh the only thing I could hazard a guess at is a intermittent failing z-stop switch or maybe a loose connection)

however, to avoid a similar occurrence you could consider converting your z-axis to a floating setup where the entire z-axis is separated from the z lead screw entire, that way even if the z winds down to its absolute minimum height once the nozzle strikes the print surface it cannot be forced further down by the z-axis motors.

Its essentially the same method used to correct a z-axis wobble issue so you should find plenty of designs on thingiverse that'll suit the M150.
Geeetech Prusa i3 pro-B (ABS Workhorse)
Pultur Prusa (my own design)
Poltur XL (my own "MUST BE BIGGER" design)
Poltur XL v.2 (my own "MUST BE BIGGER STILL, MUST USE EXTRUSION" design)
https://www.thingiverse.com/shawdreamer/designs

nate80

Monday,February 19, 2018, 09:58:37 #3 Last Edit: Monday,February 19, 2018, 10:01:21 by nate80
Hey S.D.  No, I really don't get it.  I feel like I've considered and triple checked every possible cause and come up empty.  Still, it did give me a perfect opportunity to learn more about the printer and its build, which is never a bad thing.

Happily there doesn't appear to be any damage.  I checked all parts that could have been affected for damage: the nozzle, the collets, both threaded rods, all Z/Y/X Axis Rods, Bearings, Bed Carriage, Heated Bed Plate and all screws and joints.  The Z Axis threaded rods do seem to have a bend in them and they bow slightly (they may well always have as I've never checked them before), and there were a few slightly loose screws that benefitted from tightening back up.  But that was it.

I did read that solid clamps between the Z Axis motors and lead rods was a bad idea and stops the rod being able to move side to side - which can cause the X Axis to fall out of alignment as it lifts up the rods.  The Malyan M150 uses solid metal clamps.  I wonder if changing this would make a noticeable or significant difference?

The floating extruder assembly is an interesting idea.  The Z Axis End Switch is working perfectly now so I'm just going to concentrate on getting my marathon print job done (a weeks worth at 10-16 hours a day).  I may replace some parts with upgrades (lead rods, Axis Rods, Bearings and Collets), but that's for another day.

Cheers

Nate