S3D to create a reduced-size first layer

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etotheipi
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S3D to create a reduced-size first layer

Post by etotheipi » Sat Apr 09, 2016 3:12 am

So, I have been printing fairly large box/prisms that curl a lot unless I use a really tight calibration (right now, PLA @ 215 C, bed @ 70 C, blue tape and glue). Of course the tight calibration means that there is more "squish" which spreads out the filament of the first layer more than the desired size. This effectively "dilates" the first print layer and makes a pretty sharp bottom edge. The rest of the box is perfect. What I want to do is "erode" the first layer by 0.5mm to offset the dilation, and it makes the most sense for the slicing engine to do it for me.

I use the terms "erosion" and "dilation" to mean what they do in image morphology: http://www.inf.u-szeged.hu/ssip/1996/mo ... ology.html

However, in Simplify3D, all I can find is "First Layer Width: 100%", which is scalar instead of constant, and I'm not even clear if it does both X/Y. Further, if I do multiple objects in one print, a global X/Y rescaling of the first layer as single object is going to be super wrong. An erosion of a constant value is exactly what is needed.

I have been hacking it with my SolidPython/OpenSCAD model, by chopping off the bottom 0.3mm of the box to be printed, and replacing it with a layer that is 0.5mm smaller on each side. It does do exactly what I want, but this is an ugly hack/workaround that won't work with more complex models. It really needs to be a feature of the slicing engine.

Anyone know a good way to achieve this? Or maybe I'm just missing an S3D setting?

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jimc
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Re: S3D to create a reduced-size first layer

Post by jimc » Sun Apr 10, 2016 1:25 am

if the first layer is squished too much then you need to change the bed to nozzle gap. you can do that right on the printer. first layer width has nothing to do with scaling. that is an extrusion multiplier that applies to the first layer only. its that actual extrusion width as a % of your regular extrusion width setting in the extruder tab. fiddling with that though to fix your issues is just a bandaid. you need to get that gap set right.

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Jules
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Re: S3D to create a reduced-size first layer

Post by Jules » Sun Apr 10, 2016 1:36 am

Yep, Jim's right - you're fighting way too hard.....reset that Starting Height to give yourself a normal sized first layer gap.

Another thing that might help.....you might be printing too hot.

PLA is a weird filament - it warps because there is a differential in temperature, and it stops warping once it cools off completely. So to keep it from warping, you want to cool it off just as fast as you possibly can. The hotter you print it, the hotter the bed temp, the more time it has to warp up on you while it cools off. To compensate for that, you are squishing the filament out the sides to try to give more surface area for adhesion, and that creates a little lip. So to deal with the lip, you are having to jump through hoops with your design.

It's good that you found a way to deal with it, but you can print PLA at lower temps, use a lot of adhesive, and just use your designs as you create them, with a normal sized first row. It will stick all over the plate (with enough adhesive) and yes, I did repeat myself. PLA warps, it needs adhesive for large surface area prints. I found that hairspray worked a lot better than gluestick, because we all try to be so damned delicate with the gluestick. :D

If you want to keep using gluestick, set up a grid pattern, one layer horizontally, one layer vertically, one layer horizontally - complete coverage.

And one other thing about PLA and printing large surface area low volume prints - PLA will continue to shrink and warp/twist after you have removed it from the plate, if you do not let it cool for a couple of hours while it is still attached to the plate. The glue holds it into the shape that you want it to be until it sets the shape.

I can also recommend the PEI surface for your borosilicate glass if you do not want to mess with adhesives. I print PLA all the time, with large surface area prints, on the PEI surface, and it holds without adhesive just fine. I still have to leave the print attached for a while, until it sets though - that's just the nature of PLA. ( Note: If you add PEI, you need to reset the Starting Height.)

Anyway, if you are willing to reset your starting height to a normal sized gap, I'd recommend trying a print at 205°C and 60°C. You might be able to get by with even less. (I used to have no trouble with PLA sticking at 50°C. But that required a lot of hairspray.) You can try cooling it off quicker by removing the fan guard on the bed fan. (Not the extruder fan, the one that points at the print.) It bumps up the cooling power exponentially.

And once you see the edge on a print start to curl up, kill the print, it's shot. Start over again with more adhesive. (Just keeps you from wasting a lot of filament while you figure out the correct amount.) :D

etotheipi
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Re: S3D to create a reduced-size first layer

Post by etotheipi » Sun Apr 10, 2016 3:14 pm

I appreciate the advice but I think two things are getting conflated.

I understand that the starting nozzle height is small which is responsible for the squish-out, but I mentioned that's intentional. I'm always happy to try to new things to get stuff to stick to not have the problem I stated, but I've spent years on this printer and my MBot Cube 2 before it, trying to find good adhesion techniques. It's a passive hobby for every 3d printer enthusiast. We've all battled this. I used to use canvas which was amazingly effective if you didn't mind the resulting bottom surface.

viewtopic.php?f=10&t=3443&e=0

But even when calibration is right, I wouldn't mind being able to adjust this to soften the bottom edges slightly, or compensate for a slightly-off calibration. We're talking about two different things:

(1) You say that I should re-raise the nozzle and find a different adhesion method (temps, bed surface type, etc).
(2) I say I already get the adhesion I want with the low nozzle, I just need to compensate for a side effect.

My request to erode the first layer is actually a really simple operation for slicing software, and then I'd my adhesion problems would be solved. It wouldn't surprise me if it existed somewhere. If it doesn't exist in slicing software, then I'm back to the drawing board and will be trying new things again (or programming an S3D plugin for it :D ). This really isn't such a crazy idea...

Also, I did think that 215/70 was pretty high for PLA, but for some reason S3D was preconfigured with that for M2 with PLA. When I tried it out the first time I was really happy with it. I will consider trying it with lower temps, which I know would reduce the warping. But I might find myself still preferring an eroded, tight first layer.

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Jules
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Re: S3D to create a reduced-size first layer

Post by Jules » Sun Apr 10, 2016 4:01 pm

If you prefer doing it that way, keep on keeping on..... :lol: (We're just offering alternatives for those who might be reading the thread but who are just getting started.) I don't know of any method for adjusting the width of the first layer extrusion in S3D other than that width multiplier which you already know about. Maybe if you checked on the S3D forum you might find something.

FWIW, you might want to try the PEI surface on a MIC6 plate....best combo I've found for adhesion. :D

etotheipi
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Re: S3D to create a reduced-size first layer

Post by etotheipi » Sun Apr 10, 2016 5:46 pm

Jules wrote:If you prefer doing it that way, keep on keeping on..... :lol: (We're just offering alternatives for those who might be reading the thread but who are just getting started.) I don't know of any method for adjusting the width of the first layer extrusion in S3D other than that width multiplier which you already know about. Maybe if you checked on the S3D forum you might find something.

FWIW, you might want to try the PEI surface on a MIC6 plate....best combo I've found for adhesion. :D
Fair enough. I encourage people to try a lot of different things. And I've seen a lot of people claim success with a technique that many others claimed didn't work for them. At some point, you find something that works for you and you stick with it :) In the case of my non-HBP MBot Cube 2, that was my canvas technique. I didn't care about the bottom surface of my prints, and it was flawless hold for PLA and moderate nylon prints (with cold platform!). With the HBP now, I've tried a few things and so far my configuration above gives me the most reliable adhesion. It still warps a little bit, but not enough to cause a problem. At some point I have to stop tinkering and just get things printed!

I actually did buy a PEI sheet, and I just haven't gotten around to trying it out. I knew I'd have to mess with the calibration afterwards, and I've been non-stop printing a set of (box-esque) prints that were going well and didn't want to mess with anything until I was done. Instead, I just replaced the bottom 0.3mm of the models with a slightly smaller box as described above, to get the right effect. Now everything comes out flawlessly.

If no one has seen this setting anywhere (Cura, Slic3r, S3D?) then I guess my next stop is the S3D forums. Thanks.

jsc
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Re: S3D to create a reduced-size first layer

Post by jsc » Sun Apr 10, 2016 7:41 pm

S3D introduced a horizontal size compensation parameter (in the Other tab) that will offset or inset model perimeters in the XY plane. You will want to make use of a custom first layer process if you want to do this.

etotheipi
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Re: S3D to create a reduced-size first layer

Post by etotheipi » Sun Apr 10, 2016 8:46 pm

jsc wrote:S3D introduced a horizontal size compensation parameter (in the Other tab) that will offset or inset model perimeters in the XY plane. You will want to make use of a custom first layer process if you want to do this.
Ooh this looks promising. The units are right and the name is as close as it gets :)

However I'm not clear how you assign different processes per layer in S3D. It's obvious/built-in in the temperature tab, but none of the others. Hints?

jsc
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Re: S3D to create a reduced-size first layer

Post by jsc » Sun Apr 10, 2016 11:38 pm

Create two processes. The first one will print from 0 to .20mm (or whatever your layer height is). The second will print from .20 on up. Advanced tab, Layer Modifications group.

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willnewton
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Re: S3D to create a reduced-size first layer

Post by willnewton » Mon Apr 11, 2016 12:45 pm

If I understand what you are getting at, when I need the same thing, I just use a .5mm chamfer on the bottom of the model. You can get your needed squish without the spreading. Pretty easy fix that allows you to squish down like crazy.

Also, I am a huge fan of blue tape, but in some cases where the pull is very strong, it will lift the tape, so you may want to try a different adhesion method for that print.

Not sure what your settings are, but maybe reducing the solid fill layers or infill density near the base will help, as well as rounding any sharp corners or breaking up long straight lines. These things will help lower the tension as the filament cools. Kinda depends on what your design looks like.
I'm finally back to where I started two days ago!

A thread with some stuff in it I update every once in a while. viewtopic.php?f=8&t=9
See some of my stuff http://www.thingiverse.com/willnewton/favorites

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