What caused this 'shifting' when printing?

[metrons]

Filament drive?

[metrons]

So, here is my latest dud print...pulley screws glued in and this time i printed with the seam running down the fox's back (that actually turned out really well, no little nibs anywhere really).

anyway...its still printing these little shifts and they're in the exact same spot as everything else...i'm out of ideas now. the pulley screws didn't fix anything, at least they're glued in though.

this is the 3rd time i've tried printing this piece now. i will say, the shifting IS there, but its not as bad as the other prints. its still awful but not as bad...what the fudge is causing this. . . . . . . . . . . .

[jsc]

Filament drive means the thing that holds the hot end in place. One of these: http://www.thingiverse.com/thing:433292
Print at a high infill in ABS.

Do you have this shifting issue with all prints, or just that fox? Is the STL for the fox available? I could check it out.

[metrons]

Hey jcs.

Here is the gcode file. Will that work?

https://www.dropbox.com/s/rievoy01x8a6o ... gcode?dl=0

I can try printing that filament piece tonight for sure.

It doesn't do the shifting for all prints. It's random or something. But it does do the shifting tty he same when it does shift.

[jsc]

I took a look at your gcode file. One thing that jumps out at me is that this model has some serious overhangs, and you are printing without supports. My hypothesis is that you are getting massive edge curling on those overhangs and the nozzle is getting caught up at those layers. Hard to tell exactly, but it does look like your layer shifts occur at locations where the overhangs are most severe: the lower one where the bottom arch joins up, and the upper one where the tail and body hook up.

My suggestions would be to enable supports for this model, and make sure you are using 100% fan after the first layer. If you do see any curling even then, try using a desk fan blowing over the whole bed as well. This is assuming you are printing in PLA.

[ednisley]

But it does do the shifting tty he same when it does shift.

The G-Code file suggests that the three shifts occur on layers where the nozzle path bridges an opening in the layer just below it:

• Coin slot near layer 45
• Base opening near layer 87
• Internal tail-body join near layer 256

The video of your extruder shows that the hot end flops around in the mount; that must be an absolutely rigid joint. Because of that loose joint, the entire hot end will shift when the nozzle bumps against a slight discontinuity, which happens whenever it crosses a gap. It'll maintain the same position until the next jolt, at which point it'll shift again.

Models that don't include bridges will (probably) work fine, because they don't apply any particular force to the nozzle. Any model with a bridge will (probably) produce a predictable failure at the layer(s) just after the opening.

I don't know why the extruder would be that loose. Perhaps:

• The hot end overheated / melted the mount
• A severe impact deformed the plastic
• There's a tolerance mismatch of epic proportion

The most straightforward fix would be to simply epoxy (*) the hot end in place, but that's rather permanent. Replacing the plastic mount will ensure the hot end has the correct alignment as well as a rigid position.

(*) Using steel-filled JB Weld, not the clear low-temperature resin epoxy:
http://www.jbweld.com/product/j-b-weld/

[jsc]

I didn't notice that you had posted the video that Ed refers to. If what he noticed is accurate (haven't watched the video), then that is definitely your problem. I would dismount everything, inspect the mount carefully to make sure there are no cracks and verify what is causing the floppiness, and fix it up enough to print yourself a new one. Check both the filament drive (which I linked to earlier) and the extruder mount itself, which it screws into. "eburt" on thingiverse has a sturdier model of that part as well. Remember to use ABS, as PLA will just soften with the heat.

[metrons]

I cant thank everyone enough. i'd be absolutely lost without this awesome forum.

i'm printing this as we speak. if this prints ok i'll swap it out.

http://www.thingiverse.com/thing:433292/#files

Thanks for that info ednisley. i'm not sure how you find the gaps in the gcode. but i believe i understand what is happening. i have this hollow shape and its creating issues with the extruder as it has basically empty space to extrude on? i wish i had a visual example of what you mean. i THINK i get it what you're saying though.

I wonder if i printed this upright would that solve some issues? trying this mount to print first. updates in a shortly. cheers!

[jsc]

Simplify3D has a built in gcode previewer, so you can see what the print will look like. Move the sliders at the bottom to walk through your print.

Ed is referring to the same thing I was pointing out, which is that your model has serious overhangs (parts where it is trying to print over mostly empty air). As a rule of thumb, you can safely print up to 45 degrees from vertical, and maybe up to 60 degrees with some sagging. Above that, you should enable supports, which are structures intended to give your model something to print on that need to be removed when the print is complete. The way Simplify3D generates them, they are usually pretty easy to remove, but that can vary. Check out my Simplify3D doc http://jinschoi.github.io/simplify3d-docs/ for a walkthrough on the process.

Speaking of support, you will need to enable support to print out that filament drive as well, as I recall...

[ednisley]

how you find the gaps in the gcode

Being that type of guy, I always preview the nozzle path for every model: that helps to either avoid problems or show me something I should have noticed before it went wrong. [grin]

Slic3r now has a tool path preview function, but http://gcode.ws/ provides far more detail about both the overall model and each layer.

Here's the layer two down from the internal tail-body join:

Two layers below bridge

FoxxyBack - G-Code Layer 254.png (259.96 KiB) Viewed 9747 times

One layer below the bridge:

One layer below bridge

FoxxyBack - G-Code Layer 255.png (267.98 KiB) Viewed 9747 times

The bridge:

Bridge layer

FoxxyBack - G-Code Layer 256.png (257.28 KiB) Viewed 9747 times

Your M2 ticks along at a layer per minute, giving the plastic plenty of time to cool between passes. The sharp tips of those horns have an enormous amount of overhang on each successive layer, so the nozzle will tend to pull the thread back from the void and bend the tip upward, where it will cool and whack the nozzle head-on as it passes by in the other direction while bridging the gap. The impact with a cool and solid plastic obstruction repositions the loose-and-floppy hot end.

The same sort of thing happens just above the other gaps, but, to judge from the exterior shift, this looks to be the worst.

A rigidly mounted hot end whacking a large-enough discontinuity can stall the X / Y steppers and produce a layer shift, which is what we all thought was going on here. Layers due to lost steps tend to be inset on one side and protruding on the other, which isn't quite what your pictures show, but now you know what to look for.

The motors can also lose steps if the firmware applies more acceleration than the motors can deliver, which happens only if the acceleration settings exceed the hardware capabilities. You (well, I) generally figure that out when a seemingly harmless model fails at the same point, without any other plausible explanations. The only cure is to back off the XY acceleration by factors of two, but that's not called for here: we see smoke curling out of the barrel.