DrawBot – Calibration

Calibrating my DrawBot was apparently important to its operation.  Who knew?!  If you’re following along at home, you’ll definitely want to check out Sandy Noble’s instructible on Polargraph calibration.  I’ll put my settings here, but they probably won’t be that helpful to you unless you’re using the same exact equipment and hardware as I am.

• Setup->MM per Rev = 50
• Based on the actual spool center diameter, this should be 47.  But, with some line wound onto the spool, it should be more like 54.  So, of course, I chose something that was neither.
• Setup->Steps Per Rev = 400
• While my stepper motors have 200 steps per revolution, Sandy’s controller software uses an interleaved step system, the steps must be doubled.
• Setup->Machine Width = 844
• Although the “Machine Width” is defined by Sandy as “The distance between the two closest points on the sprockets,” I used a different figure.¹  Since my machine uses spools, rather than sprockets, and the spools are unwound on the far side of the spool, I measured from the far edge of the spool’s core the the other far edge of the other spool’s core.  I figure this is probably the best measurement of the width of the line available to the machine.
• Setup->Machine Height = 848
• This is a relatively arbitrary specification given that my spools have about four times as much filament than I could use in my current configuration.  I intended this to be 844, but must have typed it in wrong.  :)
• Setup->Page Width = 216
• Rounded up from 215.9, which is 8.5 inches converted to millimeters.
• Setup->Page Height = 279
• Rounded from 279.4, which is 11 inches converted to millimeters.
• Setup->Pen Tip Size = 0.12
• With my 2′x4′x0.5″ board covered in butcher paper, I’ve marked out on the paper the locations of the various important lines for my machine.

1. Heaven forbid I do something normal, right? [↩]