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howardsmith

little indents on print in same place on each subsequent print

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I have a 3D model that prints out just fine but on each print it makes the same mistake(s)? whereby it leaves something of an indent in certain areas - there doesn't seem to be any reason why it should do that with regards the model - it's done using cad software and exported to .stl

5a331dee55a1e_IMG_20160607_1247431.thumb.jpg.282b45eac2fe431122c0ec28e5f34b19.jpg

You can see here two instances of it repeating. I thought it might be that the rods needed oiling until it occurred identically. I've oiled them anyway. I considered whether it was the bevel around the edge of the spokes but you can just see (if you squint) that there's an indent coming from the base upwards so it can't be that.

Any ideas? I printed these with default cura settings in PLA. If there any tips of advice in general also.

5a331dee55a1e_IMG_20160607_1247431.thumb.jpg.282b45eac2fe431122c0ec28e5f34b19.jpg

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It's not a part of the model in so far as geometry goes. It can't be anyway since it's a perfectly circular cylinder with protrusions. I've attached an image.

cura.thumb.png.325b5229785150916c297b8cf66c76aa.png

As I say it's odd because even at the base of the model where it should really just be a case of going round in circles it's making an indent in the same place every time.

Layer mode and xray seem fine, normal - nothing jumping out at me.

cura.thumb.png.325b5229785150916c297b8cf66c76aa.png

Edited by Guest

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That's the "z scar". It is where the outer most path starts and ends. You can see it in Cura in layer view also.

Anyway one fix is to print slower. Try 35mm/sec. Or if you are already at 35mm/sec try 25mm/sec. This assures less pressure in the head so less leakage while moving inward and outward from/to the outer edge.

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Ah. Okay... that makes some sense I suppose - I guess my problem is that the indentations or scars as you are calling them are replicated almost exactly from print to print that you'd think it was intentional. When you say I should be able to see this in layer mode I'm assuming you mean the path of the head and not the indentations itself? The path it takes does match up so you must be correct in saying it's z-scarring, but I guess my question is why is it always at these points in the model and not consistently all the way up?

I've taken the speed down to 25mm/sec from 30mm/sec but I'm already noticing it's started the indent on the base of the cylinder a quart of the way up as usual.

Is there any documentation on this? Maybe the depth of the cylinders walls should be thicker/thinner? etc... Actually I've been reading a guide on getting better prints and the z-scarring there seems to suggest it results in excess material that blobs. I have the opposite problem, little indentations in the print? Same thing or different?

Edited by Guest

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I'm not sure - I pretty much never get those Z scars. I know different temperature and different PLAs make a huge difference. I use expensive filament - mostly UM filament and Colorfab. Why not mess with temperature and/or speed while it's printing? It does not take long to change those 2 things in the TUNE menu.

I pretty much always slice with 2 shells. So if .4mm nozzle then .8mm shell width. Shell width must be an integral of nozzle size or you can get horrible results. With .8mm nozzle and larger I usually do 1 shell pass.

Also my infill speed is always identical - all my printing speeds (except for the main printing speed) are set to blank or zero such that they are all the same (e.g. inner sheel speed). Having different speeds will cause over or under extrusion on the outer layer right at the Z scar.

Are you using Cura 2.X? I haven't tried that lately and not sure if it has any z-scar bugs. Probably not.

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