Grilled Cheese Sandwich (Base Warping Issue)

[tachyio 0]

Hi Guys,

I'm trying to solve the dreaded grilled cheese sandwich problem, I notice it happens on long rectangular parts that are either symmetrical or assymetrical, and less so on rounded, cube-shaped and generally symmetrical parts.

Here's a photo of the warpage:

I have several ideas on how to counteract this apart from a heated build platform, but I'm not sure if they will work - so I will be testing them out after this current print finishes.

I am printing with Cura RC2, at 220C, 0.2mm layer height, 50mm/sec

Theorized Countermeasures:

1. Increase the thickness of the bottom layer from 0.6mm to 2.0mm - my hope is that this would provide less shrinkage-space for the material, and reduce the intensity of warping

2. Print a thick raft that would hopefully provide more adhesion and spread-out the forces from cooling

3. Slow down layer 0 even more, currently at 12mm/sec

I have done other prints with Cura RC2 and they all have minimal warpage, hard to discern anyway so its as good as not being there. But this particular rectangular piece that I'm printing out for a camera part is particularly irritating.

Cura Prints so Far: https://plus.google.com/photos/104220463645938697004/albums/5738998358660985857

3D Model of the Part I'm trying to print: https://plus.google.com/photos/104220463645938697004/albums/5739490261864478145

Any ideas would be much appreciated, thanks! =)

[Daid 306]

Actually, with a part this big, the layers on top of the first layer also pull up the layers causing the warping.

A simple solution is the cut-away 1 layer discs. See:

http://www.thingiverse.com/thing:17612

for an example. Uses a lot less material then a raft, and is easier to remove.

[tachyio 0]

Hmm okay I'll give that a go. Ultimaker is having issues again so I'm fixing them, printed well for 2 days and then it had a very bad jam...

So if its one layer and I'm printing the first layer at 0.3mm, I just add 0.3mm thick discs to the 3d model using my CAD program?

I don't see an option for discs in Cura, thanks Daid! =)

[joergen 2]

Hmm okay I'll give that a go. Ultimaker is having issues again so I'm fixing them, printed well for 2 days and then it had a very bad jam...

So if its one layer and I'm printing the first layer at 0.3mm, I just add 0.3mm thick discs to the 3d model using my CAD program?

I don't see an option for discs in Cura, thanks Daid! =)

The first layer thickness has virtually no influence on the warping, since it is a function of all layers that follow on top of if and all have different stages of cooling (the lowest is the coolest, and they get gradually warmer closer to the print head. PLA has a glass transition temperature of 58C, and until it reaches this temperature, it does shrink, and especially with those chunky square objects, the corners see a strong pull in XY from the layers above, and hence the corners lift off... there is almost no way to prevent that, since the shrink-force is WAY stronger than the adhesion to whatever substrate you are using... even if you get a great adhesion to say blue tape, the curling force will simply lift the blue tape off. the only way around is keeping the part above the glass transition temperature with a heated bed (at 70C), or simply live with curly bottoms, or cut/sand them off (it helps to reduce the amount of plastic used for the bottom greatly, think how lego pieces are from underneath, the less PLA volume you have, the less shrinkage you will see). the disks daid mentioned are something you need to add to your 3D model yourself.

[thomix 0]

The stress in the object that causes the warpage builds up over length so longer distances cause more stress. You can reduce this by cutting in your model, for instance make a hole in the center.

[tachyio 0]

Hmm okay I shall redesign my part to incorporate holes in the bottom to use less material

One other thing though, my Ultimaker just started randomly shutting down during prints. The error is a serial write-timeout-error. It's never happened before. Anyone know what's up with it? Everything else is fine though, extrusion, x-y accuracy,temp control...but it just STOPS mid-way through a print.

:/ I am jinxed...

Cura Console Error Message:

https://plus.google.com/photos/10422046 ... 1129241778

 

[Daid 306]

Odd. After the "writeTimeoutError" happens, can you still connect to the Ultimaker or does it completely stop working? Or do you need to unplug the USB to get it working again?

Also, you could check if there are power-safe settings enabled on USB. This seems to cause problems for some people.

[alaris2 1]

I've added a one layer thick rectangle extending 3-4mm from each corner of any item I don't want to lift off the bed (to the model). it seems to work quite well. it's a bit like a raft I suppose, but more manly..

[tachyio 0]

Daid > Nope cannot reconnect, have to disconnect usb then reconnect usb, then reconnect in software. Most likely software related, gone now that I've restarted the PC.

Alaris > I've added these 1-layer circles, hope it works! https://plus.google.com/photos/104220463645938697004/albums/5739490261864478145/5740154749355539954

Here's a stress simulation of the part: https://plus.google.com/photos/104220463645938697004/albums/5739490261864478145/5740156859240514514

Also I've edited my part to give it a more cool 3d-printed feel, yeaahh

[tachyio 0]

Haha! Yeah I read somewhere that rafts are for girls lol! Must have been the Ultimaker Wiki...can't remember.

[IRobertI 520]

Haha! Yeah I read somewhere that rafts are for girls lol! Must have been the Ultimaker Wiki...can't remember.

Probably from Florian's post here

http://techwall.net/analyzing-your-first-print

 

[tachyio 0]

Good News! =)

No warping!

I'm printing this with comb, so I don't get fuzzy hairs all over it.

https://plus.google.com/photos/104220463645938697004/albums/5739490261864478145/5740199138427957922

[alaris2 1]

that's the way - circles look even more cool than squares. how did you do the funky stress simulation thing btw?

[tachyio 0]

Okay I uploaded the part to Thingiverse.com!

http://www.thingiverse.com/thing:22791

 

that's the way - circles look even more cool than squares. how did you do the funky stress simulation thing btw?

It's design is a culmination of some of the suggestions posted here such as adding circles, reducing bulk volume, etc

Solidworks 2010 and later has a built in stress simulation module. It's under tools, Simulation Xpress.

Just set fixtures (parts that don't move, like the floor, or a bolted portion) and then specify where the loads will be. Next, choose a material. I used high-impact acrylic for the simulation, since I couldn't find PLA in the list. But my goal was to see where the stress was, rather than see if the part would fail - since failure can be determined after I print it, but to design the trusses, I needed to know where to add them to minimize flex and improve strength.

[tachyio 0]

I've added a one layer thick rectangle extending 3-4mm from each corner of any item I don't want to lift off the bed (to the model). it seems to work quite well. it's a bit like a raft I suppose, but more manly..

Hi Alaris, what software do you use to modify STL files?

[alaris2 1]

ahh, I wonder if I can download Solidworks free edition maybe. I'll look into that - don't really want to switch 3D model tools yet again since the learning curve takes so much time.

I try to modify before I export as STL, I'm using hexagon right now on account of the speed and ease of use but it only exports, not imports STL which is mildly annoying.

it beats the pants off 123D which was the only other free contender to the title that I knew of. I've used everything from 3D studio max through to Rhino and some exotic modellers I've forgotten the names of now. 123D will let you load and modify STL, but it takes a long time and doesn't play nice with other apps - if I had an STL from thingiverse I'd probably go this route.

for 'copying' I use a 3D scanner, David, meshlab, post fixup in hexagon and then on to repg, then finally Cura and printrun.

it's an awful long tool chain, but no one tool does all of what I need ;(

[tachyio 0]

Have you tried Autodesk 123D Catch Beta? It's a Cloud-Based 3d scanner. It actually works quite well, though not as expected - it works better with lousy data than with good data. I think primarily because it was meant to be used by tourists shakily holding cameras and snapping off multiple views of the same object, haha! It's free too, I gave it a go over the weekend, and it seems to work about 75% of the time.

=)