Who ate too much Pi?

Calibration, that’s what you need.  If you want to be the best, if you want to beat the rest, oh-ho-ho, calibration’s what you need.  I apologise to anyone too young to remember the TV programme Record Breakers but i couldn’t resist.  Calibration of my printer proceeds apace.  Today I’ve been checking the vertical movement of each carriage independently, and guess what?  If I command them all to move 100mm, they all move slightly different distances.  I think this is down to variations in printed pulley size, but this time I can compensate in the firmware.  So I measured the distance each carriage moved, and calculated the effective pulley diameter which would cause this movement.  That value replaces the nominal one in the firmware, and all is well.

Or it would be, except that I noticed that the value of pi I was using in the firmware was 3.1515926 which as everyone knows, is wrong (it should be 3.1415926).  Yes, if you are picky it should be 3.1415927, but frankly an error in the second decimal place is somewhat more important.  It’s not a huge error (around 0.3%), but it just shows that when you check everything, you should check EVERYTHING.  I wonder how many more little errors are lurking in the system?

Having changed possibly the most fundamental part of the calibration definitions, I now need to go back over the whole printer calibration routine, because the chances are that some of the other tweaks have actually been trying to mask these errors.  What fun.

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