What causes this "stringing" and can my print recover from this?

3

Here's what it looks like enter image description here

This is the model thingiverse linky

It looks like it couldn't print the edge, but this happened many many hours after printing the brim.

This did not happen with my 1st attempt at this print. The last print lost adhesion and I had to scrap it. This time, adhesion looks good so not sure why this happened.

Printing with Monoprice Select V2 with ABS, sliced with Cura. 100C bed / 250C extruder. 15mm/s initial layer speed. 60 mm/s print speed.

Update It looks like the printer is starting to smooth it out like so. Still not sure if this will lead to an ok print or will fail because of this layer. And it seems the stringing area does not have a brim underneath it. Did Cura just not calculate the brim size correctly? enter image description here

Update2 Here's a few screenshots from Cura to show that the model is lying completely flat. cura1 cura2 cura3 I let the print go on overnight and here's where I stopped it top view side view It almost seems like the print shifted completely after printing the initial layer. Have you ever seen anything like this or is there anything in my Cura model that would make it do this?

kane

Posted 2019-01-04T00:08:32.683

Reputation: 449

1The strange thing is that all the models in the Thingiverse link have a perfect flat bottom, there should absolutely be no need for supports on that end. – 0scar – 2019-01-04T14:22:33.057

good that you had the print run on for a couple more hours, resulting in identifying layer shift. – Trish – 2019-01-04T20:07:25.727

Answers

3

No, your problem is not related to slicing, this is a hardware problem. Your complete print has shifted, this is called layer shift.

This could happen when the nozzle hits an obstruction while printing while the Y stepper continues. This could lead to skipping teeth on the belts, slipping of the pulley or missing steps. This results in printing over air as the print progresses. This manifests itself as stringing, but in fact is unsupported printing (in the air). In this case it is unrecoverable as the printer has lost the reference frame, it just continues to print with the new reference frame caused by the layer shift.

A Prusa MK3, or any printerboard using trinamic stepper drivers would be able to recover (if the belt and pulley are correctly attached, and steps are missed) as the skipping of steps is detected, in case of a Prusa MK3 the machine will re-home when it detects skipped steps and continue printing. See also this answer for more details.

Possible solutions are increasing the belt tension, increase the stepper torque by increasing the current through the stepper drivers or re-tighten the pulley on the stepper of the Y belt.

0scar

Posted 2019-01-04T00:08:32.683

Reputation: 25 570

1This seems like a reasonable explanation. To be honest, I don't understand everything you said, but I'm going to do some research on it – kane – 2019-01-04T18:59:42.147

In my Case a missing Set screw on the bed stepper would cause it to shift when it did a high speed transition from the back to the front of the piece. the small set screws were not particularly visible and its loss went unnoticed. – Kendrick – 2020-12-02T18:39:55.503

2

No, the print is lost.

First thoughts after Update 1

Your print will not perfectly recover from this stringing issue, which to me looks to be unsupported bridging. I postulate that your slicing seems to be made with the model not aligned flat on the bottom correctly.

The biggest indicator for this is, that the brim is passing right underneath the model, so in that area, the slicer did not detect the model touching the surface, which means it is considered floating.

Re-slice the model and check in layer view that you absolutely have the bottom touching to the sheet everywhere. Use the "lay flat" function (which should suffice) or enable at least 10% support to the build plate (which in this case should not be needed). Even though the model doesn't need this because the base is flat as to inspection, the last resort could be to move the item 0.1 mm into the sheet, cutting off any odd protrusion your slicer identifies that can result in parts of the object "floating" and demanding to bridge long ways into the unsupported nirvana.

New Thoughts/Revision after Update 2

After the new photos, it became apparent that it was not a slicing issue of a slightly angled print but a layer shift.

You will have to check the tension of your bed belt and if anything might have come into your bed movement. On my Ender 3 I had tried a cable chain, which did hinder Y-Axis movement - make sure that it has not even a movement of short snagging.

Make sure that your nozzle does not snatch on the print as it moves. Maybe activate Z-hopping.

Trish

Posted 2019-01-04T00:08:32.683

Reputation: 15 633

All models are perfectly flat, there should be no need for support for the bottom (other than the coin dispenser). – 0scar – 2019-01-04T14:25:19.950

@Trish this is a reasonable theory and something I'll look out for in the future. But please take a look at my updated photos. The model is laying flat and I even have supports enabled though I believe Oscar is right that it's not needed here. It almost looks like the print shifted y-axis after printing the initial layer – kane – 2019-01-04T18:31:17.083

1It was reasonable at the time we didn't had the new picture... layer shift can't be distinguished from bad slicing in the infancy at times. – Trish – 2019-01-04T18:48:54.013

@kane updated with a couple ideas what might be the cause of layer shift. bad cable chains or improperly installed ones can be a huge problem.. – Trish – 2019-01-04T20:11:18.393

@Trish I believe I identified the cause of the layer shift. I've posted it as a follow-up answer to this question – kane – 2019-01-08T18:07:35.787

2

Both @Oscar and @Trish have identified the problem in their answers. Upon further investigation, I believe I found the root of the problem.

The Monoprice Select V2 has what I think is an inherent design flaw with how its wires are routed. The wire can sometimes (1) get caught on the frame (when the y-axis is moving towards its maximum position), (2) get caught between the frame and the print bed preventing the y-axis from reaching the minimum position, and (3) it even hits the y-limit-switch sometimes.

Here's a backview of the printer where you can see problem (1) where the wire can get caught by the frame. You can also see the y-limit-switch and I saw first-hand when the wire bundle caught it, forcing another layer shift in my print. enter image description here

For problem (1) above, I found this solution seems to help thingiverse link

To resolve all of the wiring issues, you have to unwrap the wires and reroute them. People online say this voids the warranty.

The wire jamming doesn't always happen. But when you printer moves back and forth along the y-axis hundreds of times for a large print, there's a high probability it snags at some point. This is very frustrating after many hours of printing. And I'm thinking of getting another printer for this reason.

I should note that it looks like Monoprice's next version printer, the Monoprice Select Plus, doesn't seem like it would have this problem since the control unit is integrated and the wires don't seem like they would be in the way.

kane

Posted 2019-01-04T00:08:32.683

Reputation: 449

Snagging cables are a PITA... but nailed it (well, I was looking at a chain, but...) – Trish – 2019-01-08T18:08:11.500

hm, judging from the design... you don't need to remove the cable binders, if you are comfortable to unscrew all the screws... – Trish – 2019-01-09T12:38:36.683

@Trish What are you proposing? – kane – 2019-01-09T15:14:35.503

unscrew the backplate & rail on one side, then slip in the cable for the bed, then re-screw it. – Trish – 2019-01-09T15:25:30.267

Are you suggesting routing the wires to the heat bed under the backframe? – kane – 2019-01-09T15:28:32.427

yes, that would solve the snagging on that corner. – Trish – 2019-01-09T15:31:17.373

Let me look into this a bit later. I think I've already resolved issue (1) but your proposal could also resolve issue (3). I think it would exacerbate issue (2) though so I'll have to check. Also, I may have to unwrap cables so it would fit under the frame. I think it is too thick as it – kane – 2019-01-09T18:02:51.597

-3

There are many problems caused with this. It could be a faulty motors, an unlevel bed, a dirty nozzle, or even something as simple as using the wrong filament settings. It would be best to go through a checklist of things that might be wrong with your printer. It could also just be caused by the wear and tear of a really old printer.

superdog

Posted 2019-01-04T00:08:32.683

Reputation: 1

please be more specific. – Trish – 2019-01-04T20:05:22.523