Knob and crank builder

thingiverse

This is a dynamic knob and crank builder. Basically, measure the widest (round) part of the knob stem, then measure the flat part, figure out the shrinkage factor for your printer, and select styles, etc. This can generate a crank as well. See the Ryobi Drill Press Crank for an example derived using this. The default settings should make a knob for the RepRapDiscount LCD panel controller. The RepRapDiscount LCD panel knob depicted was printed in two colors on a single extruder using the M600 Marlin firmware experimental code. Version 2, updated 24-October-2013: stem dimensions on RepRapDiscount knob were inaccurate; changed sizing for medium and larger sizes to make a more reasonable size if the stem is small. Instructions To replace a knob, you need three measurements and one calibration datum. You really need a caliper that measures in millimeters. Harbor Freight sells one (in the US) for around $20. Measure the knob stem across the widest part of the stem. This would be the diameter of the stem if there was no flat part. Measure the knob stem from the flat part to the opposing round part. This needs to be accurate. Measure the height of the stem from the point where it would clear any obstacles. If there are screws below where the knob sits you may need to select the stem option or make the penetration less. Print a minimal knob first. This should be a small cube with the same stem fitting properties as a full knob. Use this to test the fit. You should need to push it on rather firmly. Sometimes the first layer is a bit spread out and needs to be pared down with a razor. If the fit just doesn't work, increase the shrinkage (default is 1.06). If it's too loose, decrease the shrinkage value. For larger stems you can drill out a set screw hole.