Brims vs Rafts?

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Gwhite
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Brims vs Rafts?

Post by Gwhite » Fri Sep 08, 2017 2:08 pm

I'm still getting warping on largish parts (anything over ~ 8 cm in length on the bed) using PLA & PETG. I've tried glue stick, hairspray & the factory polyimide on glass. I've played with the bed temperatures, first layer temperatures, etc. With large parts, experimentation is both filament & time consuming. It usually takes me one of two tries to get a design right anyway, and I can use those prototypes to continue learning. My long term plan includes adding an enclosure, but for now, I still need to be able to make prints that come out flat.

I think I need to start trying brims or rafts to avoid spending days chewing through entire spools of failed prints. I've removed rafts from some PLA prints done on a different printer, and didn't find it too onerous. I did a search, and there seems to be some thought that brims are easier to remove. Given how well my prints adhere to the build surface in the middle, the forces causing the warping at the corners must be considerable. I am a bit concerned that a brim (or even a raft) isn't really going to do the trick.

Thoughts & suggestions?

Thanks!

Phil
Posts: 193
Joined: Mon Sep 19, 2016 7:49 pm

Re: Brims vs Rafts?

Post by Phil » Fri Sep 08, 2017 2:41 pm

Can you post some pictures? It might have to do with the shape of your part. The first thing to try, though, is to make sure your bed is clean. Use acetone, or even plain glass cleaner, to get the surface REALLY clean. I have had failures due to finger/skin oils on the bed. Just the plain Kapton tape surface works well for me with PLA; no glue,etc.

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willnewton
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Re: Brims vs Rafts?

Post by willnewton » Fri Sep 08, 2017 4:06 pm

A brim will help and is easy to remove. It is a good solution for keeping things in place that have a lot of contact area with the bed, such as a box shape. 3-5 perimeter brim rings will solve most warping issues.

Another solution that works well is to add a dime sized feature that is centered at the outside corners. A two-layer "coin" will trim off very quickly and keep those corners in place.

A raft will solve most every other warping problem, but it is best used when you have small features in contact with the bed, such as a vertical rocket print resting on the tips of its fins. There can be some issues separating the raft from the print the larger the bottom layer contact area of your print gets, but a little settings tweaking can usually get it going. I tend to avoid rafts at all times, but sometimes you NEED that guarantee of adhesion, especially for long, high risk prints.

Ultimately, the best solution is to eliminate sharp corners and long narrow runs from your design, which are the source of most lifting issues. Corner fillets are your friend!

At times, I reach into the machine with the back side of a pair of metal tweezers and as soon as the head passes an ill-behaving corner, I apply some light pressure that is just enough to hold the corner in place and draw some heat out of the freshly laid plastic. After 2-3 passes and holds, the new extrusions are not strong enough to warp the corners I have "frozen" in place.

Lastly, if you are having corner issues, simply stop the print and solve the lifting issue before moving on with the rest of the print. These issues show up within the first few layers, so there is no need to continue being on the losing end of the deal. Spending hours producing multiple failed prints when you should have stopped after five minutes and spent a few minutes rethinking how to work within the limits of the machine and materials THEN restarting with a successful base to build from only cost you about 15 minutes to get back where you were before!

But you don't know what you don't know until you know it, so now you know. ;)
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/about

Gwhite
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Joined: Tue Jul 11, 2017 3:38 pm

Re: Brims vs Rafts?

Post by Gwhite » Fri Sep 08, 2017 5:25 pm

Phil wrote:Can you post some pictures? It might have to do with the shape of your part. The first thing to try, though, is to make sure your bed is clean. Use acetone, or even plain glass cleaner, to get the surface REALLY clean. I have had failures due to finger/skin oils on the bed. Just the plain Kapton tape surface works well for me with PLA; no glue,etc.
I can take pictures, but it will take a bit. All the prints have a basically rectangular footprint. I've had this issue with every large print I've tried. I have PETG fence brackets that have a 2 1/2" x 3" flat base, a rectangular block with holes for holding tools that is about 3" x 6", and the latest was a frame that supports the bottom of my power supply so I can hang it off the side of my bench. The contact to the bed on that is about 5/8" x 6". The ends lifted by about a half a mm.

If the prints are vaguely squarish, all four corners come up, but the power supply support frame is narrow in one dimension, so all I can see is that it is curled up at the ends. I originally printed the frame running front to back, and It seemed that I was getting worse warping in the back. Oddly enough, rotating the part 90 degrees to print in the X direction helped a lot, but I also dropped my bed temperature down from 75C to 70C. This was a test print in PLA. When I switched to PETG for the final version, I got a similar amount of warp.

I use denatured alcohol to clean my bed between every job when printing on the polyimide with PLA, and hairspray on the glass side for PETG. With PLA, I frequently have a battle getting my print loose from the polyimide. The hairspray lets go easily once it cools. I've had PETG prints on the polyimide side that wouldn't come loose even after several thermal cycle in the freezer, which is why I switched to hairspray on glass.

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insta
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Re: Brims vs Rafts?

Post by insta » Fri Sep 08, 2017 6:35 pm

That is way too hot of a bed for PLA. You want 56-60C.
Custom 3D printing for you or your business -- quote [at] pingring.org

Gwhite
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Re: Brims vs Rafts?

Post by Gwhite » Fri Sep 08, 2017 10:03 pm

I was actually using eSun PLA+, and +70C is at the top of the recommended range, which is why I dropped it from 75C. My original theory was that the stuff was cooling off too much, and the heat would help with that. I'm not quite sure what the mechanics are with too much heat, but my next attempt I will try 65C. Lots of folks seem to like a 65-70C bed temperature for the eSun stuff. For the PETG (HatchBox), I am running the bed at 87C which was recommended in Jules's thread on eSun PETG.

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willnewton
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Re: Brims vs Rafts?

Post by willnewton » Sun Sep 10, 2017 1:12 pm

esun PLA+ is totally fine with 50°C bed, been using it that way for a long time on my M2

it is also totally fine without a heated bed at all printed with a turnigy mini fabrikator.

Gwhite, knocking down the bed temp a few degrees at the time hoping that you will hit the magic temp that will work is not what is going to solve your problems.

Using one or several of these methods such as: Using a brim, adding fillets, adjusting your design, using dots in the corners, or a raft will. There is a reason these features were developed. If your car is out of gas, do you think changing the oil is gonna make it go? ;)
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/about

Gwhite
Posts: 257
Joined: Tue Jul 11, 2017 3:38 pm

Re: Brims vs Rafts?

Post by Gwhite » Sun Sep 10, 2017 2:26 pm

There are so many tinkerers out there working with different printers, filament brands, temperature profiles, build plate surfaces & secret sauces (like glue sticks & hairspray) that it's really hard to know which knob to turn (and in what direction). Throw in the different models everyone is printing, and it's a bewildering array of options. I just want to make stuff I can use without every model turning into a science project. I'm beginning to think that is a long ways off...

I keep seeing reports that so-and-so is getting wonderful results with no warping by using some combination without rafts or brims, but my attempts to duplicate them are less than thrilling. They often don't provide enough details to really duplicate what they are doing, or they fail to mention that their idea of a big model is 2" across. I also hear horror stories where somebody had to completely re-work their profile when they changed filament color... You can't tell if that's real, or if they failed to mention that it had been sitting around opened for 6 months in a humid environment.

I'm eventually hoping to mostly work in HatchBox PETG, and raising the bed temperature from 85 to 87 seemed to help that with warping, but I haven't had time to push it up further. It sounds like PLA wants to go colder, so I will try that on my next PLA print (coming up as soon as I finish the CAD work). It's a test print to check out the CAD model, so if it warps a bit I don't care. if I have to print anything crucial that is largish & needs to be flat, I'll play with a brim.

I've also heard that an enclosure helps a lot, and that is on my to-do list. Once I have that, I'll probably have to re-tune everything...

Fortunately, there are plenty of forums of fellow explorers to commiserate with. Thanks for the input!

b8smat
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Re: Brims vs Rafts?

Post by b8smat » Wed Nov 29, 2017 4:25 pm

For large prints (approx. 8" in X or Y) we have given up using any technique other than rafts. We use a 0.3mm airgap when using 0.2mm step height, and 0.2mm airgap with 0.1mm step height. Bed cooling fan is disabled. Bed is at 70C.

This has pretty much eliminated all warping issues with large prints.

Gwhite
Posts: 257
Joined: Tue Jul 11, 2017 3:38 pm

Re: Brims vs Rafts?

Post by Gwhite » Wed Nov 29, 2017 5:42 pm

I've found that the stock bed fan geometry is part of the problem. I'm printing rectangular parts roughly 3" square. At least with some really warpy PLA, reducing the cooling helps a lot, but I get to a point where the back sticks down just fine where it is shielded from the fan by the rest of the print. The front is constantly getting cooling, and still warps a bit.

I'm investigating fan shroud designs as a result...

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