Problem in large print

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Problem in large print

Postby mhandley » Wed Apr 04, 2018 4:24 pm

So I printed this piece. It took 30 hours.
I was going to use it but I find that I need to reprint with slight changes
As you can see from the photos it had some problems that I would like to disappear
I'm printing with Hatchbox PLA with a raft and support on a painters tape bed, to which it was well adhered
6 solid inside outside top and bottom
I'm using Simplify3d

The first ridge is at 1" into the print right at the step up and then 3 more as the print progressed
It is really only visible on the 2 sides unless you are looking for it.

Any suggestions on this would be appreciated.
I was thinking that slowing down the print speed might help but I don't really know.

I'm not terribly savvy in the intricacies so please dumb down your suggestion for me ;)

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Re: Problem in large print

Postby zemlin » Thu Apr 05, 2018 9:49 pm

Are those X/Y shifts in the print, or ridges? Looks like shifting to me.
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Re: Problem in large print

Postby ednisley » Thu Apr 05, 2018 11:36 pm

mhandley wrote:only visible on the 2 sides

Do the ridges correspond to changes in the infill pattern on those layers? Previewing the G-Code may show something surprising happening on the interior of the model.

If you haven't calibrated the Extrusion Multiplier, then the ridges may show you where there's more plastic than the slicer expected. Over-extruding will exacerbate problems with high-solidity parts, as with your half-dozen perimeter threads forming a 2 mm plastic slab.

The nature of 3D printing produces surface artifacts you can see, but can't measure. When a smooth finish is vital, you must apply some post-processing / epoxy coating / high-fill priming / painting to hide the cough natural beauty of fused-filament construction.

Also, unless you absolutely must have a single unit, it's probably better to partition a huge model into smaller chunks for E-Z printing, then assemble the pieces with glue or screws. Not as heroic, but more reliable, which counts for a lot.

Or, as zemlin points out, the nozzle may be whacking a curled-up flange on the model and stalling the motors for a few steps. If that's happening, then you're going to end up partitioning the model, whether you want or not.
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Re: Problem in large print

Postby willnewton » Fri Apr 06, 2018 1:43 am

Are those lines diagonal? Are they occuring at the entry/exit points on the layers where the head is moving to a new perimeter or layer?

Sure, you can have an imperfect surface, but that ridge is a bit extreme.

As Ed says, you have a bit much plastic coming out. Also, check the print preview carefully, you can see things there that you can’t see with your naked eye, as they happen in the code. Many print issues are the result of gcode errors coming from the model itself, as the software chokes on a funky surface or leak in the model. Still others from the slicer itself as it tries to make something fit your print settings (such as layer height) and spits out a hairball instead.

You could be bumping the head and losing steps, but I would expect to see that in a corner or an isolated detail, not a long flat, but it could be happening in another part of the model and not showing up until later.

Also, you may want to try printing just areas of the print that need a specific fit or detail. You don’t need to print the entire thing to find out if a hole is in the right place. I make partial prints to test dimensions and hole locations all the time. I will make narrow slices through the model or dice the model up and just print areas that need to fit to a separate part. Much less waste and print time. Even spending an hour to print a test of detail is worth it vs. tossing out a 30 hour print made from a full roll of filament.

To help diagnose this ridge issue, just print a 1/4” thick slice of the full print as you test new settings. Also, you may want to see if you replicate the problem on a small print of a rectangle a few inches on a side using the exact same settings. This can help narrow things down to an issue with the model, the slicer, or the machine.
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