3D printer configuration of the Engravograph-based CNC mill
Updated 6 May 2012
While any 3-axis CNC machine can be converted to use as a 3D printer,
the Engravograph-based milling machine seemed most appropriate. An
extruder
experiences almost no force pushing back on it when it dispenses molten
plastic, so machine rigidity is much less important than during milling
operations. The Engravograph-based mill had too much backlash in the Z
axis when cutting harder materials, and also has a larger range of
motion in all
axes. I devoted the 4-axis controller to this machine so that the
additional axis would be available to control and extruder. I purchased
a used Stepstruder Mark 6 on eBay for my 3D printing needs. It consists
of a stepper motor with a filament feeding disc and a heated nozzle
that melts ABS filament and dispenses it in a controlled diameter over
a range of selectable rates. Dispensing the filament using a stepper
motor rather than a DC motor has the advantages that the rate can be
continuously adjusted and that the filament can be withdrawn by a few
steps when necessary to avoid unintended oozing of molten plastic. I
chose to control the extruder head temperature using a simple and
inexpensive ($15) PID controller that I found also on eBay - noticing a
pattern here? I go to eBay pretty frequently for my parts. As an aside,
always also check Amazon and any other vendors you think could also
sell the parts you need, just to have a good idea for bargain market
prices. The PID is not controlled through software, but its adjustment
time is several minutes and I did not see the use of adding any
interface between the extruder heater and the computer. I am using
black ABS filament with a diameter of 1.75 mm. The extruded filament
diameter is 0.45 mm. I have found so far that setting my extruder to
245 C is about right to dispense sticky, molten plastic. This is in the
range that I have also seen others use as published on-line.
Getting back to my difficulty with control software, I quickly realized
that adding the Stepstruder was not as easy as writing G-code with the
additional instruction to also squirt plastic. Using Mach3, the
Stepstruder is treated as a fourth mechanical axis. Any physical
movement of the milling tool head is an interpolation between the X,Y,
and Z axes so that all motions end at the same time. If the extruder
axis is instructed to take a particular number of steps during this
time, it too will take these steps in such a way that it ends when the
other axes movements also end. Changing the rate of the extruder
changes the amount of extruded plastic, so some careful thinking is
required to make it work correctly. At this point I am just starting to
read about others' implementation of 3D printing using Mach3. The ratio
of mechanical motion to extruded plastic length has worked well at
about 200:1, which is explained by the ratio of filament diameter
to extruded plastic diameter, which is about 15:1. Since volume is
conserved, pi*R1^2*L1=pi*R2^2*L2, so that L2=L1*15^2 = 225*L1. I still
need to calibrate the extruder so that Mach 3 correctly accounts for
millimeters of extruded plastic.
I have hand-written G-code to crease a few simple objects so far such
as a spiral of plastic appropriately sized to produce a ring for my
wife. She is now somewhat of a fan of my 3D printing efforts. I made
sure to create some rings using conventional machining of aluminum and
brass and engraved her name on a metal plate when I started this
project as well. Making jewelry and keepsakes seems to go a long way in
terms of support of all the time I spend on this hobby at home.
Links (Newest efforts first) - Videos and images included
Air Assist Cone
Plastic Eagle
My 3D printer making my first 3D part!
Picture
1 of first 3D Part
Picture
2 of first 3D Part
G
Code for the part (hand written)
G
Code for 3D printing a ring