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GerryH

holes/circles first layer

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Many of my 3d printed parts have smaller holes designed into the base.  Cura when printing the first layer prints the outer wall, then tries to print the circles inside the outer wall.  There's nothing connecting these circles and so they frequency don't stick.  Some other slicers print lines to connect the circles to the outer walls.  Is there a way to make Cura do this?  I've gotten so used to using Cura and have it tweaked just right for my work, I don't want to have to use another slicer for some parts.

 

This is an example of what I'd like to happen

Capture.GIF

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When you say "first layer" you mean "bottom layer", right?  So they should stick to the glass, right?  I guess I don't understand the question.  If they aren't sticking to the glass your nozzle is too far from the glass.

 

Maybe show a photo of what cura is doing.

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bottom layer/first layer.  I'm using PLA on buildtak with gluestick.  I don't have any problems on larger lines/circle, but these are 3 or 4 mm circle for screw holes.  I was just thinking that if the circle was attached to something, it would have a tendancy to move/not stick.

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Well isn't the circle attached to the build tak then?  It should stay in place until the print is done.  And then the circle should be attached to another one on the layer above, right?  And so on going upwards eventually connecting to the rest of the part.  Right?  Again, a photo of what it looks like in cura would be helpful both solid view and layer view.

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That's the problem, the circles sometimes don't stick, then the extruder drags them around until they fall off, but then you get some glob of PLA where you don't want it.

 

See how Cura prints the circles after the outer wall.  Compare that to the picture above.

 

I'm guessing this is just the way Cura slices.  Would be nice if there was an "anchor" feature for small features like this.

Capture2.GIF

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At the moment, Cura always prints walls and skin separately and given how the program is structured I can't see that being easily changed. However, I wonder if there is some scope for connecting the inner, circular walls to the outer walls with other walls. That would achieve similar results in terms of adhesion.

 

Personally, I have solved the small circle adhesion problem by printing first layer walls very slowly so I would not have any trouble printing your example above.

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You do not say what 1st layer speed you are using but you want 20mm/s for those circles and as @gr5 says an easy solution is to move the nozzle closer to the bed. If all else fails then you could design your part for the circles to start on layer 2 and then when finished cut out the 1st layer with a Stanley knife. Oh and to make things easy for adhesion print your 1st layer at 0.300 layer height

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8 hours ago, GerryH said:

That's the problem, the circles sometimes don't stick, then the extruder drags them around until they fall off

OH!  You should have said that in the first place, lol.  Instead of the 5th post.

 

Yeah.  As I said and as yellowshark said:  Move the nozzle closer to the print bed.  You aren't squishing the bottom layer enough.  I don't know what kind of printer you have.  On all Ultimaker printers you simply rotate the 3 leveling screws CCW as seen from below to move the glass bed up a bit.

 

Do you have a printer with a heated bed?  If you *do* have a heated bed 60C is good.  I don't think you need PVA glue on build tak - I think that might defeat the purpose a bit but your main problem is not enough "squish".  MUCH more details here:

 

 

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I do understand the problem, as I had that too in the very beginning, when printing on bare glass without any bonding aid, or when printing on a glue-layer that was too thick.

 

But if you try to solve this kind of bed adhesion problems in the slicer, it would create ugly lines through the bottom of your prints. I think it is best to optimise your bonding method, to make the small circles stick by themself.

 

It might be a good idea to post a few close-up photos of the underside, to see what exactly is the problem. For example: build-plate too far away, glue too thick,...

 

Since I started using my "salt method" (=wipe the glass with a tissue moistened with salt water) I don't have this problem anymore. But I think gr5's method (10% white wood glue in water) or neotko's hairspray method, or 3DLAC, or a thin layer of glue-stick wiped with a wet tissue afterwards, should also work well on the condition that the build-plate is at the correct level.

 

For the manual on the "salt method", see here:

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

 

When using a new bonding method, always stay with the printer for the first prints, and carefully watch if it works well, and what happens.

 

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This is a real question, and I ll say the reason is the low adhesion on the build plate resulting of the 'angle-dragging effect in the tiny circles'.

 

If you look at the filament on the build plate when a tiny circle (diameter < 4 mm) is printed, you can often see that the filament is 'dragged' by the latest filament exiting the nozzle, which is going in a direction sligtly different.

As the circle is made of tiny lines with a little angle between them (the meshes), the dragged effect is cumulative as after the first tiny angle there is almost at once a new deviation in the same way ... and so on

So the filament is moving 'inside' the circle and if the effect lasts there is a non adhesion of the circle.

 

You have not the same effect when there is an angle like in a square, as the new direction (at 90° form the preceding one) is lasting for a while. The filament in the new direction has the time to cool and stick to the plate, so the angle dragging effect occurs in this case only once during the first 0.1-0.2 mm and after it doesn-t move.

It is the same for the larger circles as the length of each mesh (and/or the angle between meshes is smaller) in the circle gives the time for the adhesion to prevail over the angle-dragged effect.

 

So the solutions would be :

1) lower the speed for the bottom layer, a kind of 'brutal force' solution

2) via a plugin lower the speed in the 1st layer for each movement in a wall with an extraction length below a certain value, indicating that the mesh is really tiny and there is a risk of angle-dragging

 

It would be fine if the team implement the second solution in CURA

 

 

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@smartavionics

the problem looks excatly the same but is your link for an existing plug-in ?

 

Furthermore i think this is mainly for the 1st layer as the adhesion is much better material on material than material on build plate .

The advantage is to modify only the first layer GCode

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Hello @JCD, the mod isn't a plugin, if accepted by the Cura devs it will be part of the slicer. The mod lets you specify a slowdown for small outlines on the first layer and also for all other layers (could be 100% if you only want a slowdown on the first layer).

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When you are not on the 1st layer it could be dangerous to sloww down the speed, specially when you begin the top layers, which may be above an empty zone (in an infill). If the speed is too slow the filament is not making a 'bridge'.

This bridge (even in low quality) is used to build the upper top layers above. Those layers hide the low quality of the bridge

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@JCD I like how you think.  I like how you pay attention.

 

What you call "angle dragging" I call the "liquid elastic effect".  I think of PLA as a liquid rubber band.  Like snot.  Like mucus.

 

Are you sure the bottom layer is the worst?  For me it seems like the bottom layer is the best and it gets worse on layers above and then as it gets farther from the heated bed it gets better again.  Do you have a printer with a heated glass bed?

 

You should look at "initial layer horizontal expansion" feature.  This value can be set to a negative value but that doesn't help you I suppose.  I think a bigger problem on my bottom layers is that I like to level such that the nozzle is a little "too close" to the glass which gives the bottom layer a little micro brim and is fixed with the "initial layer horizontal expansion" set to a negative value.

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@gr5

Yes I have a glass on my heated bed, but with PLA I use a bed temperature of 37° (with a really tiny spray of repositionable glue) with a brim to prevent

 

- The warping effect

- The 'Elephant Foot' effect you're describing (the higher the bed temp is, more elasticity the first layer (and a little the following layers above it) has and so naturally is leaking outside the model if there is no border)

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