X, Y step calibration object with holes

Description

This object is for calculating the X and Y motor steps in a way that works better with horizontal expansion setting. The longer side is 45mm and the shorter side is 30mm. Holes are 20x20mm and 10x10mm. If you use horizontal expansion, you want it to be the same for holes and outer dimensions. If the hole dimension is A, then with expansion it is A2 = A-2He, and if outer dimension is B then its size will be B2 = B + 2He. So A2+B2 = A -2He + B -2He = A+B. And expansion is He = (B2-B-A2+A)/4. So calibrate X and Y steps so that the sum of one hole dimension and one outer dimension in that direrction to be right. For example, if you print it so that the longer side is along X, you will want to calibrate it so that Xout + Xbighole = 45+20=65mm, and Yout +Ybighole =30+20 = 50mm. New steps are then calculated this way: Xnew=Xold*(Xout + Xbighole)/(Xoutreal + Xbigholereal) and Ynew=Yold*(Yout + Ybighole)/(Youtreal + Ybigholereal) and the X expansion is Hx=(Xout - Xbighole -Xoutreal + Xbigholereal)/4 and Y expansion is Hy=(Yout - Ybighole -Youtreal + Ybigholereal)/4. But these expansion values are for old steps, so they have to be multiplied by Xold/Xnew and Yold/Ynew to be correct. This is close to 1 and the expansion values are usually quite low, so the old values are also usable. But the slicer I'm using (Cura 4.2.0) has only one expansion value (I don't know about others), so one has to calculate the mean value He= (Hx+Hy) / 2. This is a starting point value as everyone has different tolerances so for someone else's files you have to tweak the expansion sometimes to get the gap between the components right, but for your own prints that have been sized as they should come out in real life, it should do ok. If properly calibrated, your outer dimensions should be correct if you print this one again with calculated expansion and new steps and you should be able to push this cube into the bigger hole: http://www.thingiverse.com/thing:1278865 with a rather tight fit. For more accurate XY steps, you can also use this object: https://www.thingiverse.com/thing:3882150 but in the way described here, using its internal and external dimensions. It is slower to print as it is 150mmx150mm, but the x and y steps error is more accurately measured in bigger objects.

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