Prints are too small?

First off, Hello! I've finally broken down and decided to ask some questions. Forgive me for being a 1 post wonder lol.

So i built a Prusa i3, first printer, first time messing with anything gcode related. Got it running! actually running great, dialed in wonderfully...
except for one tiny annoying problem. All of my prints are too small by roughly 1-2mm. I have no idea why. Phone cases WILL NOT fit, they try to, but the case is too small on just the x and y axes (havent really checked for the z). I know i can scale it up, but i'd much rather KNOW its going to print the correct size from the get-go. I've messed with the Marlin steps per mm, they were x:99.823 and y:99.027. Using 16T gears and a GT2 belt i figured i'd use the Repetier host belt calculator, it came out to be perfectly 100 even, so i put those numbers in...and i got bigger prints, but STILL too small. This is all of course after using a set of calipers to measure each axis for true distance traveled (x-100mm, y-100mm, z-50mm), but heres the real kicker...they were within .05-.1mm after doing the math and changing the Marlin stepper values, and i've done that many many times to make sure it was as mechanically accurate as possible. I had it truely moving 100mm exactly...but my prints were just too small :/ Belts are all very tight. any idea why this could be?

Here is some of my printer information:

Single aluminum plate
RAMPS 1.4
GT2 Belts and 16T Pulleys
MG Plus hot end w/ .35mm nozzle
Printing 1.75mm ABS
A4988 Pololu's


Could the Pololu's being turned down/up too far have any effect like this?

Thanks ahead of time!

Edited 1 time(s). Last edit at 12/31/2013 02:06AM by zachisparanoid.

ABS shrinks when it cools, which is also the cause of warping. Print a test part and figure out how much your filament shrinks in your machine. Find the scale setting in your favorite slicer and use it to compensate. Hopefully it is saved with the material profile so it gets applied automatically. I keep forgetting to look into this because it's been so long since I printed something that had to match up to something I didn't print.

This does make a lot of sense, i had pondered the idea before, but never really thought too far into it. I do greatly appreciate the input! i suppose scaling might just be the only way to go. I had also thought the models i'm finding online might have been a little small from the beginning. However i guess i'll just have to tinker with it a little more and get down to the bottom of it Thanks again!