DrawingBot in OpenSCAD

Background

Some time ago I decided to build a new project, and picked the DrawingBot by MakerC (https://www.thingiverse.com/thing:1517211). A bit of research also picked out the remixes by avanhanegem (https://www.thingiverse.com/thing:2058866) and henryarnold (https://www.thingiverse.com/thing:2349232) - their excellent ideas, designs and other contributions have all been considered in this re-design.

After looking at the original designs l decided that I wanted to make some changes - mostly to the idler pulleys and GT2 belt fixing, but also to tidy up a few loose ends that had irked me a little (e.g. limit switch fixing holes). Unfortunately I had no access to the original design files so had to make my own using OpenSCAD.

Design basics

My design is not as pretty as the originals, as I was too lazy to design the nice curves and neat linear bearing supports (mine are fixed with cable ties). The pieces are mostly straight-edged, albeit with nice curved corners.

The minimum requirements to implement the new bearing setup are: XY_carriage_base, XY_carriage_top, Y_back, Y_front, and base_slide. I used the original X-axis motor mounts and Z-carrier, and designed my own M3 knob to hold the pen (https://www.thingiverse.com/thing:2530144).

I have included a few extras, e.g. a servo arm that almost certainly will need to be modified to your own needs, as it was designed for my unbranded/unlabelled 9g servo. Note that it's almost impossible to print good servo shaft splines with an 0.4 nozzle, and in the end I modified a normal servo arm.

I have also included a source file for X-axis motor mounts, although I didn't use them myself - the originals are perfectly fit for purpose, so my file is only offered in case you wish to modify things in that area.

There is a file called support_tube.scad that generates a socket that can be glued to the existing X-axis motor mount on whichever side you prefer. This is used to locate the cable support that comes from the XY carriage. The Y-front OpenSCAD file gives an option whether or not to generate a support tube as part of the compilation (hopefully clear in the SCAD file).

Common definitions file

Note that almost all of the SCAD design files require the dimensions.scad file in the same directory to compile correctly. This file defines dimensions common to many parts, and also contains a number of modules used throughout the design.

Test files

There are 2 test files: horizontal_test_piece.scad and vertical_test_piece.scad, which allow you adjust values in the common file dimensions.scad without wasting too much plastic in the process. These cover things like hole diameters, the linear bearing locating grooves, captive nut holes and cable tie holes (I used 2.5mm x 100mm ties). The horizontal test piece is probably the most important one to get right.

The intention is that if you can get these pieces to print with all the dimensions correct for your components then all the other pieces will also be correct. Hopefully.

Alternative bearings

Flanged bearings:F604ZZ (qty. 10)

The bearings in the X carriage were mounted using M4 socket cap-head bolts - the screw heads have to be either narrow (like mine) or very flat, as the clearance between the screw head and the Y-axis rods is very small.

The assembly sequence for the XY-carriage was: M4 screw with threaded part pointing downwards, M4 washer, bearing with flange upwards, M4 washer, bearing with flange downwards, M4 washer, hole in X-carriage body, M4 washer, M4 Nylok nut.

A similar sequence was followed in the Y-axis back piece: M4 screw with threaded part pointing upwards, M4 washer, through first hole of the Y-axis back piece, M4 washer, bearing with flange downwards, M4 washer, bearing with flange upwards, M4 washer, through second hole of the Y-axis back piece, and into the M4 captive nut.

Print Settings

Printer:

G&C CoreXY

Rafts:

No

Resolution:

0.2

Infill:

33%

Notes:

Mine was printed using PLA at 0.2mm, with the exception of the base_slide, which I printed at 0.1mm for finer detail.

Support was "as necessary" - most parts don't require it, but things like the base_slide will need it.

Category: Robotics