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JohnFox

Improving the bottom layer

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Any suggestions for improving the first layer, ( the object is shown upside down)? I watched the perimeter being printed and that looked OK but didn't see the rest of it.

Also what could be causing the oddities at the two corners?

I think the PLA is being squished down OK judging by the amount that is being pushed beyond the layer.

PLA, 210C, 0.12mm layer, bottom layer speed 30mm/sec

JFB_5815.thumb.jpg.614e570c3083d58532ec3339cae73781.jpg

JFB_5815.thumb.jpg.614e570c3083d58532ec3339cae73781.jpg

Edited by Guest

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To me it looks like the platform was a little to close to the nozzle. It starts putting too much material and then the material start to curl up on the sides.

It is not so easy to have the platform just right. That is why I use 0.3mm first layer but even then this might happen.

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I use a 0.3mm first layer as well.

Would it help to have a slower print speed for the first layer?

This problem on the bottom layer is my biggest problem at the moment. It takes quite a bit of work to sand away the grooves. The top layer is fine.

 

To me it looks like the platform was a little to close to the nozzle. It starts putting too much material and then the material start to curl up on the sides.

It is not so easy to have the platform just right. That is why I use 0.3mm first layer but even then this might happen.

 

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It's better to watch the first layer, so you can adjust some things if necessary. When the 'rippling' starts it will continue and only by adjusting it will change. By gently pushing the bed from the top or below you will see if the bottom layer improves or not. After that you can turn one or more of the bed screws underneath the bed.

Large surfaces are hard to get smooth! But if you get your leveling worked out and your nozzle clean on the outside it might improve a lot.

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I don't know your printer settings in Cura but I would assume that the first layer is already printed slower. But I don't think that the solution is in the print speed it is the amount of material coming out of the nozzle.

In principle you have conflicting requirements:

- You want to squash the first layer for better adhesion.

- You want to backup a bit to reduce elephant feed and these kind of ripples.

I the photo I see that some areas are almost homogeneously filled. You can get that effect when squashing the filament on the bed but you also get this rippling effect quite easily.

The larger the object the more difficult it gets since it also means that the bed needs to be 100% flat.

And the advise of a clean nozzle (from Peggyb) is a good one. Also if you squash to much your nozzle gets dirty on the outside within no time.

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Bed levelling and nozzle to bed distance are crucial in getting a decent 1st layer. When you have done it and think it is OK, it won’t be OK. You need to do it slowly, carefully and probably redo it several times.

For the nozzle to bed distance I have a calibration test routine, using a standard cube. I have a z-offset in the start gcode routine which makes it easy to adjust the nozzle to bed distance automatically and accurately. I use a binary chop style process to adjust the distance. On my printer I need a z-offset to allow for the glass plate; I do not know how it works on the UM2 with a glass plate. If you do not need a z-offset then just set it to 0.0. So…

Having set the distance during levelling using the standard sheet of paper, and assuming my z-offset is 7.1mm I will print the test cube (1st layer or 2 only).

Then I add 0.04 to the offset and print again

If 7.14 gives a better result then I add another 0.04

If 7.18 gives a better result then I add another 0.04 etc etc

If 7.22 gives a worse result then I subtract 0.02.

If 7.20 gives a better result than7.18 I will try 7.21, meaning either 7.20 or 7.21 is the correct offset

Referring to the above, if I find that 7.15 is worse then I go the other way, setting the offset to 7.10 etc etc

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And, printing thin layers is difficult for the 1st layer - set your 1st to .300 and once you have perfected it then if you need to go thinner give it a try.

I run my 1st layer at 20mm/s; go faster at your peril. Once the first layer is printed turn your bed temp down. I normally print my 1st layer at 65c and turn down to 50c, I have seen others that go lower. I assume you have your fans turned off for 1st layer.

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Just in the throes of doing some controlled tests on the bottom layer.

I'll try the 65C idea, makes some sense.

Not bothered about the elephants foot effect, it's the grooving that is the trouble.

 

And, printing thin layers is difficult for the 1st layer - set your 1st to .300 and once you have perfected it then if you need to go thinner give it a try.

I run my 1st layer at 20mm/s; go faster at your peril. Once the first layer is printed turn your bed temp down. I normally print my 1st layer at 65c and turn down to 50c, I have seen others that go lower. I assume you have your fans turned off for 1st layer.

 

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Yup I have suffered from elephant's foot but not for a long time. No doubt it will happen again. Not sure what causes it, probably too hot and/or too fast, or wrong nozzle to bed gap. I know when I did have the problem I reduced the horizontal dimension of the 1st layer by 0.5mm which removed the problem

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Just done some tests, no dramatic results.

I modified the first two layers of a test square, then went back to defaults afterwards. Printing PLA.

No visible difference between 20mm/sec and 30mm/sec

Possible change between 220C and 210C, (default)

No obvious improvement between 100%(default) and 110% extrusion rate

No obvious change between 60C bed( default) and 70C bed.

A minor improvement when using 225C nozzle AND 70C bed.

Similar result with 225C nozzle, 70C bed and 110% extrusion rate.

The biggest effect on the print quality was any alteration to bed height, with less than 1/4 turn of the screws making an obvious difference.

How does the UM2 zero the Z axis? Any minor fluctuation here would alter the quality of the first layer.

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Ok, well your point about a variation on the z axis homing could be a point although I do not think I have heard of that one. I will put that to one side for you to investigate. If your other layers are OK, you say the top layer is fine, then to my mind that points to the bed to nozzle distance - if you do not adjust it accurately you pic shows what you will get.

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The bed leveling (read also the absolute difference between nozzle and platform) plays a big role on the first layer. If the bed is too close the amount of material coming out the nozzle is too much so it will go somewhere. If it can not go to the side (one side has already printed material) it will curl up. And this is what it looks like curled up lines at certain places.

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Yes, I now think curling was the main problem. Trying to spread the material too wide.

 

The bed leveling (read also the absolute difference between nozzle and platform) plays a big role on the first layer. If the bed is too close the amount of material coming out the nozzle is too much so it will go somewhere. If it can not go to the side (one side has already printed material) it will curl up. And this is what it looks like curled up lines at certain places.

 

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I recognized the pattern of your artifact. I have seen it on my printer as well. Since I have a UMO I have to level the bed regularly (wood works with humidity) and sometimes I level to close and get the same pattern. It is always difficult to find out what a person means as bad.

The elephant feed at the bottom are usually not such a big issue they are easy to remove.

But the curling is of an other dimension if you want a nice looking bottom. When it is very bad the part could even detach from the printer bed before being finished. On the other hand you never get a solid looking plastic bottom you always see the 0.4mm pattern.

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