carl_m1968 wrote:When ABS cools after printing it shrinks approximately 8%, although this will vary somewhat depending on the particular ABS in use.
A blogger from Canada and an Internet message board as a source for the 8% figure? I'd take that one with a grain of salt.
Doing a quick search, this site quotes 4-6 thousandths for shrinkage on injection molding:
http://www.injectionmoldtips.com/shrinkage.html
This site gives shrinkage ranges for different flavors of ABS from 4-7 thousandths of an inch, per inch, which would be .4% to .7%:
http://ides.typepad.com/all_about_plast … of-ab.html
I wouldn't question a ballpark figure of a half percent, but 8%? That be an eighth of an inch on a 1.5 inch part and a half inch on a 6" part. Casual observation alone should be enough to question the source on that one. Yes?
I've been using 3D printing mainly for prototyping smaller parts under 2", with 100% infill, and have been regularly checking the results with calipers. To the extent the parts vary from spec, it's always on the large side, with slow and low settings producing the smallest tolerance issues. As near as I can tell, it's the inevitable banding effect of 3D printing that causes most of it. You're basically trying to fill a square hole with a round peg. The filament comes out round, gets smooshed flat, and the distance it gets smooshed depends on how much material is being flattened. If the flow rate is too high, it squishes out farther, making the part slightly larger than intended. If there's any shrinkage taking place, I haven't found it to be significant, but the flow rate can make enough of a difference in the quality of a print to make it worth adjusting. In playing around with it, if the top layer is overly rough and getting too much of a kind of waffle pattern, the flow rate needs to be tweeked down a bit. In any case, pardon me if I over reacted to your earlier post and came off as too much of a grouch. Hopefully the resulting discussions were at least a little bit productive.