Ugly Parametric Magnetic Effector

by rodsmith, published

Ugly Parametric Magnetic Effector by rodsmith Mar 9, 2018
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Quick Start

This Thing is a highly parametric effector for use with magnetic diagonal
rods on delta-style printers. It consists of three parts, each of which has
2 or 4 variants (in .stl form):

  • Effector-{hotend}-{probe|noprobe}.stl -- This is the effector itself.
    I provide versions for the E3D V6 (and clones) and for the Hexagon
    hotend. Both variants include versions with and without a mount for
    a bed probe, such as an inductive sensor.

  • Lock-{hotend}.stl -- This is a small triangular piece that locks the
    hot end in place.

  • FanDuct-{hotend}.stl -- This is an optional 180-degree fan duct for
    a 50mm centrifugal (aka "blower" or "radial") fan.

If you have an E3D V6, a clone of it, or a Hexagon hotend, you should be
able to print one set of three parts (or two parts, if you don't want to use
a part cooling fan) and go; however, you'll need to find a carriage with a
matching 51mm inter-ball distance to use the provided .stl files. If you
need to use the effector with a carriage that uses another inter-ball
spacing, you'll need to customize this effector, as described later.
Alternatively, you can look for a customizable carriage, such as
https://www.thingiverse.com/thing:932959, and modify it instead.

Non-Printed Parts

To use this effector, you'll need a number of non-printed parts, in addition
to the hot end:

  • 6x magball studs -- These are often sold with magnetic arms from vendors
    such as UltiBots and Filastruder. You'll normally use matching studs on
    the carriage.

  • 7x M3 nuts -- You need six nuts for the magball studs and one for the
    fan's mounting screw.

  • 2x - 4x M3x16 screws -- These are needed for the hot end fan. Optimum
    length depends on the fan's depth, but 16mm works for most fans.

  • 2x M3x6 screws -- These attach the fan duct to the effector.

  • 3x M3x10 screws -- These attach the locking nut to the effector. You may
    be able to get by with M3x8 screws, particularly on the Hexagon variant.

  • 1x M3x25 screw -- This screw attaches the centrifugal fan to its fan

  • Fans -- The Hexagon version uses a 25mm hot end fan, and the E3D V6
    version uses a 30mm fan. (These sizes match what comes with each hot end.)
    The part cooling duct is designed for a 50mm centrifugal fan.

Of course, if you don't use the part cooling fan duct, you won't need the
three screws or the nut associated with it.

Features & Caveats

I designed this effector with several goals in mind:

  • Parametric, to enable easy adaptation to different hot ends and diagonal
    rod spacing.

  • Support for a part-cooling fan.

  • Support for an inductive bed sensor. (This turned out not to work too
    well; see below.)

  • Designed for use with magnetic diagonal rods.

  • Low attachment point for diagonal rods, to maximize print height; but not
    so low that the view of the hot end's nozzle is seriously obstructed or
    that the heat block would come into near-direct contact with the
    effector's plastic.

  • No need for supports or rafts when printing. (The effector includes two
    concentric hollow cylinders that function as built-in supports for the top
    piece. These are easily removed after printing.)

This effector does meet these goals; however, there are several caveats:

  • The centrifugal fan protrudes significantly from the effector, which robs
    about 10mm of print area on one side. This figure may be greater or less
    for you. Using a 40mm centrifugal fan should reduce this loss; but the
    40mm fans I have are thicker than the 50mm fan I have, so this would
    require further tweaks to the design, likely including a wider inter-ball
    spacing to make room for the mounting screws.

  • In use on my printer, the bed sensor's trigger height varied significantly
    depending on the point on the bed being probed. This greatly reduced the
    bed sensor's usefulness, to the point that I switched to a Delta Smart
    Effector. Using Force-Sensitive Resistors (FSRs) under the print bed
    rather than an inductive sensor might have worked as well.

  • There seems to be no standardization of inter-ball spacing for magnetic
    diagonal rods. I used 51mm spacing to match an earlier effector design I
    tried. Thus, customization of the OpenSCAD file and rebuilding the .stl
    file, as described in the next section, or doing the equivalent for the
    carriage, may be necessary for most people.


I designed this effector to be highly parametric, so it's easy to customize
it. I used OpenSCAD (http://www.openscad.org), which is free software, so
you can customize this Thing quite easily with a minimal understanding of
OpenSCAD. The main file is Ugly-Parametric-Magnetic-Effector.scad; it
contains designs for all three parts. Variables that you're most likely to
want to change are on lines 6-48:

  • makeSensorMount -- Set this to true to build the effector with the
    sensor mount, or to false to omit the sensor mount.

  • makeWireTieDown -- Set this to true to add a half-torus above the hot
    end fan mount. I intended this for helping to secure wires, but it proved
    to get in the way more than help, at least for me. You might decide

  • recycleNum -- Set this to a number greater than 0 to add a recycling
    symbol and number on the effector and fan duct. Note that this feature
    requires the recycling_symbol.scad file from the OpenSCAD Recycling Symbol
    Library (https://www.thingiverse.com/thing:216963) to be in the same
    directory as the other .scad files.

  • ballDistance -- Set this value to match the ball spacing on your carriage.
    The ball spacing on the effector and carriage MUST match! Greater ball
    distances can increase stability, but too great and the ball mounts will
    physically detach from the main base and/or the ball mounts from different
    sides will begin to overlap.

  • baseLength -- Setting this shorter will bring the mounting balls closer to
    the hot end without changing the distance between parallel balls. Shorter
    baseLength values increase stability, but too short and the effector
    becomes structurally unsound and/or the ball studs won't fit in place.
    Also, a baseLength much shorter than the default of 51 makes it impossible
    to mount the fan duct to the effector. (Note that this variable sets the
    size of the triangle that forms the basis of the effector's base.) The
    baseLength and ballDistance values are normally similar -- they're both
    51mm in the default configuration and .stl files I provide.

  • makeEffector -- Set this to 1 to build the effector model with a Preview
    (F5) or Render (F6) operation.

  • makeLock -- Set this to 1 to build the lock model with a Preview (F5) or
    Render (F6) operation.

  • makeCentrifugalFanShroud -- Set this to 1 to build the fan duct model
    with a Preview (F5) or Render (F6) operation.

  • sensorDiameter -- This sets the inner diameter of the Z probe sensor

  • sensorBrimDiameter -- This sets the outer diameter of the Z probe sensor
    mount. It must be greater than sensorDiameter.

In addition, lines 27-29 include the .scad files that hold measurements of
the hot end; you must uncomment the line for the hot end you're using and
comment out the rest. If you want to build a version of this effector for
another hot end, you can create your own .scad file for it and include that
file. Use one of the existing hot end files as a model. I provide three
sample files, for the E3D V6, the Hexagon, and an effector that looked like
a Hexagon clone on eBay but that turned out to be quite different.

Additional variables in lines 6-103 may interest you if you have exotic
needs. The heFanSize variable, in the hot end .scad file, sets the size of
the fan used by the effector.

Work in Progress

I designed this effector for a homebrew Kossel XL; however, I was
unsatisifed with the performance of my inductive bed probe and so decided to
buy a Delta Smart Effector. Thus, I've abandoned this effector, at least for
the moment. I put a lot of work into it, though, and thought it might be of
interest to others -- particularly those who want to build delta printers
using Hexagon or more exotic hot ends. I have used this effector with both
an E3D V6 and the Hexagon not-really-a-clone. Although I've printed the
version for the genuine Hexagon to see that it fits, I've not actually
printed with it.

The main problem I had with the inductive bed probe is that, because of
varying effector tilt at different points on the bed, its readings were not
consistent, compared to actual nozzle height. This necessitated tedious
measurements to make the RepRapFirmware's G32 command produce good results,
and G29 never produced good results for me. You may have better luck with
force-sensitive resistors (FSRs) under the print bed, or simply doing manual
bed leveling. Perhaps another firmware, or a future version of
RepRapFirmware, will work better even with an inductive sensor. It's also
conceivable that other physical design aspects might improve the reliability
of an inductive sensor.

Shortly before buying my Smart Effector, I began experimenting with a design
to put a smaller 40mm box fan above the main body of the effector, so as to
recover the print area lost to the centrifugal fan. You can see what this
looks like by setting makeBoxFanShroud = 1 on line 19. I never printed (or
even completed) this design, since it looked ridiculously top-heavy and
would have blocked the hot end's filament entry hole. I've left the code in
the .scad file in case somebody else might want to modify it into something

Print Settings

Printer Brand:












This part should be rigid, so I recommend using at least three perimeters and 40% or better infill.

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This is great! I love how compact this is and that you incorporated a radial blower fan! Have you thought about adding more support to the arm between the effector ball ends and the main body? They look a little thin and may be the first spot to warp over time.
I'm excited to see the progress on this effector!

I'm glad you like the design. You can tweak it yourself in OpenSCAD. In particular, you can make a thicker base by increasing the baseLength parameter; however, this will also move the ball studs further from the center of the effector, which will reduce stability. Splitting those two effects into separate parameters would make sense, but as I've moved on to a Delta Smart Effector, as noted in the Thing's description, I'll leave it to others to make such improvements.