Curing ABS "bow" Near the Bed

[Marshall]

So we've all probably dealt with this. My problems got worse now that it is winter, and the temp dropped in the area my Makergear M2 is located. I will be building a heated build chamber. (I will be writing a thread on that too, as you can pick up heated build chambers for free, if you do it right--it's an interesting chamber to say the least. )

Anyways. ABS contraction near the bed. It creates a "waist" within the first 4-8mm of height on cylindrical parts. Small parts of 12mm diameter, and parts 40mm diameter exhibiting this same bow profile from contraction. Right now I run my bed temp at 116°C with Kapton surface, MG black ABS, 241°C extrusion temp. If I run the bed at 110°, that 6° difference is all the difference between a first layer that bonds, and a first layer that sometimes pulls off. (An "O" shape ring gets strung into a "D" shape on layer 1, in other words.) So I'm sort of set with the 116° bed temp as it leads to 95% bonding success without monitoring the print starts.

I suspect the bow has to do with the temps near the bed being hotter, and creating a large temperature range in that area while printing.

I typically do not use 100% fill on anything. It's usually 10-30%. Here are some of my questions:

Will a higher % of infill cure this? I.E., 75%-100% on small parts that do not use much total filament?

How will perimeter outline counts affect this bow, is it better to use 3 perimeters vs 1, to help fight it?

Grid patterns?

Lastly, when I build my heated enclosure, will air temps in the chamber as high as 50-70°C help cure this with ABS? I almost assume the hotter the air, the more problem fixing I will achieve when printing parts with high contraction issues, since air is the only thing stealing temperature away while the height grows.

THANKS!

[Marshall]

No one have contraction issues with ABS?

[tenaja]

The hotter the build area, the less bowing you will see.

[Marshall]

Thanks. So 121°C bed temp it is, then. (About peak, in my current ambient air temp conditions.)

Have you noticed infill affecting the bow as much as the bed temps?

This might sound odd, strange, whatever, but what would a heated source of air do blowing on the part? I.E., a blow dryer set to high, but say arranged as a flexible "mini duct" unit going from hair dryer (or hot air gun), through the duct, to a printer fan location duct that is printer mounted, blowing a continuous hot air stream over the part as a fan would typically do with an ambient air stream. It would be flexible enough as to not interfere with movement of the printer. Anyone ever considered what this might do? My thoughts were possible elimination of a heated chamber altogether. Thoughts?

[Marshall]

UPDATE:

OK so I just watched the print to witness what is physically happening. I've tried this same part at the slowest of speeds, faster speeds, and layer heights from 0.15mm to 0.185mm. With the 0.185mm layer height I just sat and watched, the cylinder is building up from the start OK. For example maybe the first 4-5 layers. I have the perimeter set for the most outside accuracy, IE., Inside-to-Outside perimeter. Well, after the first few layers, I start to witness the nozzle overhanging the edge while it's performing the final perimeter. Once I start seeing this, I start looked at the level of the part horizontally to look at the top level. What I see is the edge being higher than the rest of the print, and each loop the extruder travels, I see that slightly curled outer edge being pushed down and flexing while the latest layer is being applied, On and on it goes. This has to be the reason for the "waist" like appearance at the outside, and after 12mm or so it has had enough extra plastic laid to absorb the difference into the structure.

Does this directly explain anything? The print is still going. I could post a photo when it's finished.

[dorgeman]

I can't say for sure if this is the reason for what you are seeing, but here are some things that might be worth thinking about...

I print mostly with ABS on a heated bed without a heated build chamber. I have a silicone heater attached to a thin sheet of aluminum. On top of that is a sheet of borosilicate glass with hairspray on it. I mention all of that because physical printer differences might explain some differences in behavior. My printer is located in an area that is not that carefully heated/cooled - so one might expect the winter temps to change how it behaves - but they have not.

My general goal is to print the first layer just a bit above the glass transition temperature of the plastic I am using. This takes a little experimentation because glass transition is more of a range for ABS rather than a specific temperature - and it varies from spool to spool. That all said, I expect you are way above the glass transition temperature. My first layer is in the mid to upper 90s measured by a thermistor between the silicone heater and the aluminum. At layer 2, I drop the temperature to slightly below the glass transition temperature. My second layer (and all layers after) are at the mid to upper 80s.

If I don't drop the temperature below Tg after the first layer, each progressive layer stays too soft to properly support the next layer, and all sorts of strange deformation take place. Some of those look very much like what you described. The first layer needs to be higher so that the part will stick to the bed. Printing ABS the way I describe above, I almost never get any warp or curl to the parts. I sometimes can see a very slight narrowing near the base (I think related to the changing bed temperature) but I have to look really carefully to detect it. More perimeters and higher percentage infill will make warping more likely, but I often print 3 perimeters and 30% infill without any problems. Perimeters and infill do not seem to have any impact on the slight narrowing near the base. When the bed cools down to room temperature, the parts pop off the bed on their own.

I don't know if any of that will help you, but take it for what it is worth.

[zapta]

No one have contraction issues with ABS?

ABS is problematic in general in open frame printers. Try to enclose it somehow and in cold weather preheat the bed before you start printing.