First layer being printed with blemishes

[dougconran 1]

Not sure whether this is a printer problem or a Cura problem.  I have an Ultimaker 3 and am using Cura 4.4.0 as the slicer.  The filament I'm using is Ultimaker Sliver PLA (the one that came with the printer).  My main settings are:-

 

layer height : 0.2mm

Nozzle temp : 195 C

Bed temp     :  65 C

Initial layer Width : 120%

Initial layer speed : 18mm/s

Fan  :  Off (first layer)

 

I'm getting what appears to be the nozzle dragging the filament as it comes out of the nozzle but just in a couple of areas (see image).  I've raised both the bed temp and nozzle temp slightly (5 deg C) above normal because I was having a problem with some of the initial wall lines not sticking to the bed (as it happens, in the area of the blemishes).  The second layer was laid over the blemishes without a problem but on the third layer or so there was a bit of lifting of the print off the bed although it did not look like warping (for a start it was not lifting at any of the corners).

 

What is happening and what do I need to do to fix it?

 

TIA

Edited February 18, 2020 by dougconran

[gr5 2,167]

This isn't normally considered a problem as the layer above wil cover this up.

 

It's caused by overextrusion which is desirable on the bottom layer as a little overextrusion gets the part to stick better and having a part come loose can be a disaster.  Particularly on a UM3 you can get a head flood which takes an hour with a heat gun for an experienced person and often you need to replace some parts in the print head.

 

So the glass is not 100% pefrectly flat.  Plus if you used the glue stick that can create some height.  You only need about 0.1mm extra height to create these "blemishes".

 

The best way to get rid of them is to ONLY do manual leveling and to level on the fly with the 3 knobs while it's printing the brim.  To get rid of these blemishes will be very hard to do but if you see them then the glass is just a tiny bit too high (maybe half turn?  Maybe quarter turn?) on the nearest leveling screw.  But again, having the glass too low can be an epic disaster.

 

 

[gr5 2,167]

By the way, if your part is only one layer and this is both the top layer and the bottom layer then there is an "ironing" feature to fix these blemishes.  Look at all the cura "ironing" features.  I've never used it.  But ironing won't try to smooth internal, invisible layers, lol.  That would be a waste of time.

[dougconran 1]

36 minutes ago, gr5 said:

This isn't normally considered a problem as the layer above wil cover this up.

 

Thank you for the quick reply.  This is not a single layer print but, sadly, it is this bottom layer that will be visible and it is not practical to turn it over.  I'm not using a glue stick which is probably one of the reasons that I have to have the bed at a slightly higher temperature.

 

I can try (reluctantly!) to alter the level of the bed whilst printing but would prefer to see if I can solve the issue by other means to start with.

 

1.  I forgot to mention in my original post that my initial layer height is 0.27mm.  If I were to reduce this (to 0.2mm) and/or reduce the initial layer width do you think that would improve matters?

2.  I can also try moving the print to a different part of the build plate but it is quite a large print and so there is not too much scope for moving.

3.  I could raise the bed temperature.

4.  I could try printing on a raft which would make for a rather rough surface but could be acceptable.

 

Obviously I should just try each of these suggestions (and I will) but it would save time and filament (to say nothing of my sanity) if you could give me a few pointers.

 

Thanks again,

 

Doug

[geert_2 557]

If you look at the bottom, did it lift from the glass? Thus making a dent in the bottom?

 

If yes, it could be caused by dirty, greasy spots on the glass? Clean with isopropyl alcohol, and then a few times with pure hand-warm tap water only. (No soaps.)

 

A thinner bottom layer gives better bonding for me: 0.2mm is much better than 0.3mm. I guess because the material is squeezed more into the glass, and it has less room to escape sideways?

 

Then use a bonding-method for better adhesion. Some people use the glue-stick, some use dilluted wood glue, hairspray, 3D-LAC,... Find a method that works well for you, and that you like.

 

For PLA, I prefer my "salt method": wipe the glass with a tissue moistened with salt water. Gently keep wiping while it dries into a thin, almost invisible mist of salt. For PLA this increases bonding while hot, but gives absolutely no bonding when cold: models come off by themself. Then re-apply before the next print.

 

This works very well for my typical low, flat, long models. But it is not recommended for thin vertical models like lantern poles, or for high models with overhangs. Overhangs tend to curl up, and then the nozzle bangs into them. So these models might get knocked off, as the salt can not absorb shocks. Glue is better in absorbing shocks I guess.

 

For the full text, see here: (it is old, and I should probably update it, but it is still usefull)

https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals/

 

Bottom layer of part printed with the salt method: glossy, but with tiny pits from the salt. The second pic shows the mesh of a fan reflected in this bottom (I could not get bottom and reflection both in-focus, so they are separate pics).

 

Typical view of the glass:

 

Inverted prisms are the edge of what can be printed: some warp but can be completed. Some come off and produce spaghetti. The tiny bottom area and huge overhangs and warping forces are a hard test. Try such a model with all your bonding-methods while evaluating them.

 

Bottom with pits from the salt:

 

[dougconran 1]

37 minutes ago, geert_2 said:

If you look at the bottom, did it lift from the glass? Thus making a dent in the bottom?

Yes it did.  From what you are saying I think that it is very likely that the build plate needs a proper clean.  I have been wiping it but nowhere nearly as thoroughly as you are suggesting.

 

So, I will do a proper clean of the glass and play with the layer settings and see what joy I get.  Thank you both for your really quick and helpful suggestions.

 

Doug

[XYZDesignPro 70]

It appears you are using "Lines" for your top and bottom layer pattern.  Have you tried "Concentric"?  The head has fewer lifting and retractions.  In your case the pattern will just go around like a race track.  I find it both aesthetically pleasing and functional.

Also be sure there is nothing between the glass build plate and the aluminum heated plate.  Dirt or debris that might prevent proper leveling.

[gr5 2,167]

Well you didn't show us what the bottom of the part looked like (from the bottom).  You showed it from top view.  so I gave you the wrong answer.

 

First of all I didn't mean EVERY time you print you adjust the bottom layer - I meant just once or twice until you get this dialed in.

 

Second of all - I retract everything I said.  You didn't mention that the bottom looked bad (or at least there was no photo).  Maybe include that photo?

 

I'm guessing you have oil on the glass and it's not sticking.  Use glass cleaner.  See if that helps.

[gr5 2,167]

However once you show a photo of the bottom I may retract my second answer as well.  It's important to show a photo of the problem.

[dougconran 1]

My apologies, I obviously didn't have access to the underside whilst it was printing and didn't think to take another photo once it had finished.  Here is the underside (ignore the black markers, they are for a different purpose).

 

As suggested by  @geert_2 I have given the glass plate a thorough clean and am about to try again.  I will also try reducing the initial layer height from 0.27mm to 0.23mm.

[geert_2 557]

If that is the underside, I would level the bed closer to the nozzle. It is hard to see from this angle, but I think it is not flat enough to my taste.   :-)

 

I prefer the bottoms of my prints to look more like this, or like the above photos.

 

[dougconran 1]

1 hour ago, geert_2 said:

If that is the underside, I would level the bed closer to the nozzle. It is hard to see from this angle, but I think it is not flat enough to my taste.   🙂

 

Having cleaned the glass plate as you suggested I have another print on the go at the moment which is looking considerably better (almost, but not quite, perfect).  When you refer to '... not flat enough ...' are you referring to the level of the bed or the squishing of the filament (by the look of your photo you are referring to the filament).

 

The printer auto levels the bed, is there a setting somewhere where I can effectively get the nozzle closer to the bed?  Is that the  layer height or initial layer height setting?

[geert_2 557]

I was referring to the squishing of the filament indeed. I have two older UM2 printers with manual bed-adjustment, and I adjust it closer, so it is squished more. I prefer a nice glossy bottom, even if that causes a little bit of "elephant feet" sometimes. Not only does that stick better, but it makes watermark text in transparent materials (=inside the model, close to the bottom) easier to read.

 

In Cura, I usually set the first layer to 0.2mm. This too helps in giving a flatter bottom than 0.3mm, and gives better bonding.

 

I have no experience with UM3 or newer, so I can't say much about their procedures and their auto-leveling. I think you can switch it off, but I don't know if there is an in-between such as "auto-level to my prefered height"?

 

[dougconran 1]

On 2/19/2020 at 6:47 PM, geert_2 said:

In Cura, I usually set the first layer to 0.2mm. This too helps in giving a flatter bottom than 0.3mm, and gives better bonding.

 

I have the layer height set to 0.2mm and the initial layer height set to 0.27mm (the default height for 'Fast').  Are you saying that you have the layer height set to 0.3mm and the initial layer height set to 0.2mm, ie first layer THINNER than subsequent layers?  The help tip for initial layer height suggests that it should be thicker.

 

Also, I'm a bit baffled as to why the first layer should be thicker than subsequent layers AND the initial line width should be (recommended) 120% of the standard line width.  Isn't that, effectively, just increasing the width of the initial, squished, line even further?  Why not make the adjustment using just one setting?

[gr5 2,167]

The theory was that because the glass isn't perfectly flat - if you assume it has 0.1mm of vertical variation across the bed, then the bottom layer, if thicker than the variation, should be able to fill in the valleys and stay thin at the peaks (valleys and peaks of the glass bed).

 

In practice there is some pressure coming out of the nozzle and it can push down a bit on the bed and ride up and down the valleys and hills.  So even a layer height of 0.1mm works pretty well for the bottom layer.  I use the default bottom layer height but I have a friend who uses 0.1 for the bottom layer every time and he claims it works much better.

 

Either way works fine as far as I'm concerned.

 

[dougconran 1]

Thanks for that explanation, it was sort of what I'd thought but nice to have it confirmed.  That does, though, bring me on to another question as I'm still a bit confused about the purpose behind the 'layer height' setting and 'initial layer height' setting.  From what you are saying I deduce that the 'layer height' is the setting that determines the nozzle height above the build plate and thus the default height of each layer (I know that is obvious but bear with me!).  When the printer performs an auto levelling and moves the build plate up until it is just touching the nozzle does it treat that point as z = 0 and then add the (initial) layer height to that z or does it do what one effectively does when manually levelling and add the thickness of the card (0.1mm) to the z before adding the 'layer height'?  Intuitively it seems to me that if you do manual levelling you are, anyway, adding 0.1mm to the layer height for the initial layer.  If you then set the 'initial layer height' to, say' 0.27mm and 'layer height' to 0.2mm is the nozzle raised 0.37mm above the build plate for that first layer or 0.27mm above it or does it keep it at 0.2mm/0.3mm but squeeze out sufficient filament for an assumed nozzle height of 0.27/0.37mm.

 

I'm sorry, this probably all sounds rather confusing (it does to me) but I'm trying to understand just what the relationship between actual nozzle height and the height settings are.  I suppose I could look at the gcode but I wouldn't have a clue as to what I'd be looking for.

[tinkergnome 927]

3 hours ago, dougconran said:

When the printer performs an auto levelling and moves the build plate up until it is just touching the nozzle does it treat that point as z = 0 and then add the (initial) layer height to that z or does it do what one effectively does when manually levelling and add the thickness of the card (0.1mm) to the z before adding the 'layer height'?

 

• "nozzle is touching the build plate" is always treated as "z=0"  - no exceptions  (*)
• z-axis is moved to the "initial layer height" for the first layer... (0.27mm actual nozzle height in your example)
• ...and adds the amount of "layer height" to the actual nozzle height for all subsequent layers
• no magic, it's that simple

(*)

The manual leveling on Ultimaker printers (with the calibration card or a piece of paper) works no different. The thickness of the calibration card is compensated by the firmware, so that z=0 still means: "nozzle is touching the build plate".

The assumed thickness of the paper differs a bit between the printer models though... it's 0.1mm (piece of paper) for the UM2-series and 0.15mm (calibration card) for UM3 and S5.

 

 

The standard profiles in Cura are using a slightly thicker first layer. As @gr5 said - the intention is to level out unevenness of the build plate (there's no perfect even surface in the real world....).

The thicker (but fewer) lines on the first layer are there to increase adhesion (AFAIK). I don't know the actual physics behind this, but i know that Ultimaker material engineers do a lot of tests and i tend to trust their huge experiences in this case... 🙂

 

 

 

[dougconran 1]

On 2/22/2020 at 7:12 PM, tinkergnome said:

 

• "nozzle is touching the build plate" is always treated as "z=0"  - no exceptions  (*)
• z-axis is moved to the "initial layer height" for the first layer... (0.27mm actual nozzle height in your example)
• ...and adds the amount of "layer height" to the actual nozzle height for all subsequent layers
• no magic, it's that simple

That is a brilliantly clear, concise explanation of those settings - many thanks (and the rest of the comment is pretty good as well!)

[uncle_bob 21]

Hi

 

I have always been a big fan of hair spray on glass. It seems to be easier to get a thin / uniform layer onto the glass. Cleanup is done with a soak / rinse in hot water. I clean and re-coat the glass when things start to lift off. That might be a couple dozen prints using PLA.

 

Bob