Hole size calibration

thingiverse

This is a test print for determining hole size adjustment. This is my solution to the problem that when you calibrate the printer fir accurate external dimensions, the holes are of wrong size- in my case they are too small. This can have many causes, such as wrong handling of holes by the slicer program, over-extrusion, thermal shrinkage and slight shift of hole position between layers resulting in hole edges partly covering up the hole from a different side in each layer. To use this, you print it at 100% size in X and Y, and without any raft or brim. Z size can be thicker and then it will be more accurate, but more material will be used, and having at least 5 layers would be nice to account for hole shift between layers. Then, you measure the resulting holes with calipers and enter both theoretical holes and actual holes into a spreadsheet, and do linear regression (LINEST should be English equivalent of REGLINP) where real holes are the "X" and theoretical are "Y". this returns the gain a and zero offset b, that gives you a function Y=aX + b with which you can calculate the size a hole has to be in the 3d file (Y), so that it comes out the size you want (X). This way you can have this spreadsheet open and quickly convert the holes to the right size. Different materials and different slicer programs will likely have different hole size changing properties, and adding some tolerance would also be a good idea if the hole will have something inserted in it, but now it doesn't have to be so big. Also polygonal holes will probably behave differently (as slicer can use arc commands in gcode if supported), this is why it has square holes as well. Edit: If your a is close to 1 and b is fairly consistent, you should use a slicer that has "Horizontal expansion" setting and use this object instead: https://www.thingiverse.com/thing:3967147 More in the object description, but it does save you from resizing all holes manually.