Great!
- Thread starter Mibe
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Large footprint parts, especially ones that are boxy and tall tend to warp like crazy for me. By large, I mean bigger than 4-in x 4-in. It gets worse as the height gets above a 1/4-in or so. There are various fixes, like using ABS juice (ABS scrap dissolved in acetone) or Elmer's glue sticks on the perforated print bed or printing "walls" around the outside of your parts, but the better fix is to find a filament that doesn't warp, or that at least doesn't stress when it shrinks upon cooling.
Mike
Mike
bigseb
Alibre Super User
It helps to understand the physics behind the plastic. All the problems people experience with ABS are down to that plastics shrinkage. The larger the item you are printing the greater the overall change in size. Typical shrinkage value for ABS is 0.7% so if your item is ,say, 150mm long then the overall length delta from molten to solid is 1.05mm. The warping and cracking stems from the fact that your print is laid down layer by layer. The first layer cools as soon as it is extruded (think extreme temperature drop). The next layer is laid down on top of a cold layer, it also gets the shock cooling treatment. And so on and so on. By the time you're a few layers up the forces built up in the part are strong enough to either a) lift the part off the build platform or b) crack the part i.e layer delamination or c) both.MikeHenry said:
There are ways around this now that the theory is out of the way. Firstly your printer should be completely enclosed and preheated before printing. The warm chamber allows the ABS cool a bit more gradually and prevents the shock cooling I mentioned earlier. This is the number one step that will improve your prints dramatically. If your have an open print simply have a little perspex hood made that will encase the entire printer. My printer is open on the front and the top so I made a top cover from the polystyrene packing sheets that the printer came in and the front is covered with a clear plastic sheet. I printed covers for the grip handles and closed off the spool holders. ABS prints went from not working to amazing just by doing that. Its also wise to preheat the chamber before starting a print. I do this by enclosing the printer and leaving the HBP running for about 15 minutes before I start. A realistic chamber temp is about n50 degrees. 90 would be ideal though but your steppers might not work at that heat. The HBP should be set at about 90-95 degrees. The glass point of ABS is 100 degrees so any higher than 95 is simply going to ruin the print. And of course the lower the extruder temp the better for the initial temperature change. But be aware, go too low and your layers won't adhere properly. I stick to about 230 degrees, although I could probably drop it to 220.
Ultimately ABS has its pros and cons. The shrinkage is a definitely a con but can be dealt with once you understand the physics. FWIW, Stratasys printers don't differ much from other FFF printers. The main difference is that a) the printer has a fully enclosed print chamber, b) the chamber is heated to approx 90 degrees and c) the steppers are mounted outside the print chamber. Once you know that it is very easy to get professional results from a so-called consumer-grade product.
I keep meaning to play with things like infill density, dummy objects outside the part periphery, cover on the printer, etc. but just don't have the time to run tests on large prints since those also mean long print times.
Someone came up with a hack to allow PLA printing on the Zortrax M200 printer I have so I'll try that one of these days.
Mike
Someone came up with a hack to allow PLA printing on the Zortrax M200 printer I have so I'll try that one of these days.
Mike