So it begins

Many people choose New Year’s Day to make resolutions; I’m going to get in early by starting this exercise in extraversion today.

One of my motivations is to put down in writing (etc.) the assorted project ideas running around inside my head. Foremost right now is my “build a better RepRap” project, so I’ll dive right in.

A little over 2 years ago I backed Brook Drumm’s KickStarter project and after some months wait I received my Printrbot LC kit. Since first powering it up I’ve made a couple of small modifications to the machine but I want More Awesomeness. I don’t want to sacrifice any of the capability I have now, which means I have to build a second 3D printer while leaving the first untouched. I now have pretty much all of the vitamins except the hotend, and it’s time to get more serious about assembly.

The new machine is to be based on nophead‘s Mendel90 design. My main design goal is improved print resolution and accuracy, building on the serious stability of the Mendel90 frame. Extra features I’m adding in support of this include

  • gear reduction (approx. 5:1) in X, Y, and Z drive, to trade off speed for resolution
  • belt reduction (2:1) in both X and Y, ditto
  • M6 1mm-pitch threaded rod for Z
  • T2.5 belts and pulleys; maybe GT2 2mm in some future iteration
  • gear reduction (approx. 5:1) and M6 1mm-pitch worm in extruder drive, to better match finest extrusion to finest axial motion
  • anti-backlash gears (printed) in each train

Ignoring microstepping for the moment, resolution comes out as:

  • X and Y: 200 step-per-rev motor, 51:10 gear, 16 tooth T2.5 pulley, 2:1 belt =>
    (200 step/rev x 51/10 x 2/1) / (16 t/rev x 2.5 mm/t) =>
    51 steps/mm, or 19.6 microns/step
  • Z: 200 step-per-rev motor, 51:10 gear, 1mm-pitch thread =>
    (200 step/rev x 51/10) / (1 mm/rev) =>
    1020 steps/mm, or 0.98 microns/step
  • extruder: 200 step-per-rev motor, 51:10 gear, 1mm-pitch thread, 3mm diameter filament, 0.4mm diameter nozzle =>
    (200 step/rev x 51/10) / (1 mm/rev) x (0.4 x 0.4)/(3 x 3) =>
    18.13 steps/mm extruded, or 55.15 microns/step

(I don’t plan to rely on microstepping for any increase in resolution, merely for smoothness and noise-reduction.)

I’ve seen a little mention of worm-drive extruders but not a lot about why they seem to have disappeared other than that they’re slow. Since I’m not initially concerned with speed I would like to find out what other disadvantages they have, and if I must I’ll find out by experimentation.

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