Think I found a cure for curling

[PeteD3]

I am fairly new to 3d printing and have done a LOT of reading on how to best deal with curling. Printing with ABS plastic, I have found that masking tape provides a great surface for adhesion... however, when printing a large flat object, the heat of the plastic and the pull of shrinkage will still overcome the abilities of masking tape. At first I tried to simply raise the print above the platform in the software, before printing. I hoped it would add support material to the operation but it did not. It just printed a good raft them started to print my object up in the air.

So, using masking tape and turning the heated bed off, I have added a "rise pin", for lack of a better term, to my design. The pin is attached to nothing and is .2 inches tall by .06 diameter. This now causes the program to add support material between the raft and the real object. The pin I've added is just sacrificial. I find that by getting the flat print off the bed, it prevents curling. Even if the raft should curl slightly, that is absorbed within the support material as it is printed.

Printing the flat object atop of the support material seems to give it room to cool properly and away from the tape and bed, where it would otherwise cause problems and eventually curl.

I've attached a jpg to show what I mean. The pin is colored green for reference.

I hope I've explained this clearly. Feel free to ask any questions or make comments.

[RobH2]

This looks interesting. Do you have a few photos? I'm still a bit unclear about your exact workflow.

What I think you are doing is just raising a raft off of the bed by .2in (or do you mean mm) so that support is printed under the entire raft. Is that correct? If so, you may be able to raise your part in your slicer manually, to leave an air gap. That way you won't have to even mess with the pin. I'll try it in Simplify3D to see if that works.

[PeteD3]

Hi Rob, not raising the raft, but creating support structure between the raft and the flat face of my print. I would only say this is usefull when printing something large and flat... normally it would lie directly on the bed or raft but when there is that much plastic that close to the bed, it tends to curl. By getting the body of my object up and away from the bed, the problem has gone away. That little pin is .2 inches and forces the program to create support material between the raft and my printed object.

[old man emu]

Is this what you did?

Air Gap.jpg

Would you consider putting two or three more pegs under your object?

OME

[RobH2]

I haven't tested your theory yet but it makes a lot of sense. Curling and warping is generally worse on large, flat and thick parts. The upper layers begin to shrink while the bottom layers are still hot and expanded on the bed. This pulls the corners in. So, given your idea, a few issues are mitigated. First, the raft that I used is one layer thick. That's not going to curl and it provides "stick" to the bed. Secondly, the support that is created between the raft and the part allows for less shrinkage of their layers because they aren't as dense and there's likely more cooling air in there than is found in a typical raft. As you say, less heat from the bed reaches the part so the inclination to curl is lessened. I look forward to trying your idea.

Of course the support makes for a more messy bottom layer but that can be sanded smooth. And let's face it, I'd rather have a messy bottom layer to sand then to not be able to get a big part to print because it keeps warping. I once used diluted PVA glue on a bed so a large nylon part would stick. It was a tip I found on several websites. Nylon is very difficult to stick to anything. It worked perfectly but as the part cooled it actually cracked my expensive borosilicate glass. It cost $60 in glass to make that one part. I'm hoping this is a good way to print nylon.

Obviously, printing with a raft is not new and it's supposed to perform the same sort of thing. What's different is that "supports" are structurally a little different than raft. It might just be enough to be a good alternative. I use Simplify3D. It generated the part in the attached video. I'll test it later. I used 1 layer of raft and exaggerated the support material so it would be easier to see. But, it was easy and fast to do. I just used one small peg like you did to push the part up off of the bed plane so support would be triggered. I also had to change the support angle to "0" so it would put it everywhere.

[curious aardvark]

very clever. Obviously uses alot more plastic - but if that cuts down on buggered prints then probably saves time and plastic in the long run.

You also said you were printing with abs on a cold bed - or did I misread that part ?

I'm pretty much a total pla and other cold bed filament convert these days, but i do still have quite a lot of abs to use up.

[Marm]

This may help some of my rafting issues. On the XYZ, the slicer doesn't seem to do rafts quite right, and I can't ever get them to come off, which sorta defeats the purpose of a raft. Raising the object a mm or 2 before slicing and adding supports may solve some issues I might have.

On a side note, I have to manually add skirts to any builds that have "spires" (tall thin segments that the ABS doesn't cool enough to support layers above it). I add a 1 layer wide cylinder around my object to give the extruder something to do while it's letting the spire cool. Does use more filament than not, but far less than having a print fail 4 times right near the end.

[PeteD3]

Is this what you did?

Air Gap.jpg

Would you consider putting two or three more pegs under your object?

OME

I think I'm probably doing a horrible at being clear. What I am doing is simply adding a pin (any random minuscule object would do) so that something completely sacrificial exists between my object and the bed. So now, when it prints the raft, it will then first begin printing the sacrificial pin (which just floats below and away from the object by a hair) but which also forces the printer program to create support material as it prints the pin and before it gets to printing my object.... the effect is that it will begin printing my object on top of the support material, instead of directly on the bed or directly on a raft.

I hope that makes a little better sense.

Also, there would be no need to add more than one pin since one is all it takes to trick the printer into making support material. The pin doesn't actually hold anything.. it is just there to bring my flat item surface up and away from the bed.

[PeteD3]

very clever. Obviously uses alot more plastic - but if that cuts down on buggered prints then probably saves time and plastic in the long run.

You also said you were printing with abs on a cold bed - or did I misread that part ?

I'm pretty much a total pla and other cold bed filament convert these days, but i do still have quite a lot of abs to use up.

Yes, I am printing on a cold bed with masking tape added. If I heat the bed, the adhesive on the tape gets soft and allows it to pull away. The bond of tape is better with a cold bed. And yes, I am using ABS... I haven't gotten to using any PLA yet.

[PeteD3]

Here is a diagram that might help make this a bit more clear. On top is the drawing of my part with a pin added then below is a diagram of how it all would look being printed.

Attachment 3738