Re: [CAD_CAM_EDM_DRO] Making a rapid prototyper

On Tuesday 01 August 2006 12:28, Alan Marconett wrote:

> HI Sebastien,
>
> I found and mentioned the RepRap project on this list just last week! A
> bit after the bevy of posts on self-replication of a few weeks ago.
>

I ran across your post after sending out my email, I hadn't finished reading
the backlog.

> I hadn't seen the 2nd generation RP head, just the first. Sounds like a
> step forward! I'll give it some study. (I wish you'd publish PDF's.)
>

I assume you want an engineering drawing of the extruder head, in pdf format?
I'll see about doing one up; the CAD parts are being done in ArtOfIllusion
(AoI), a free rendering program. AoI is a good program, but it can't output
technical drawings. The renderings on
http://reprapdoc.voodoo.co.nz/bin/view/Main/Version2OfThePolymorphExtrusionHead
are from AoI. The plastic parts in the photographs were printed by Adrian
Bowyer's Stratsys rapid prototyper - the stratsys used .stl files from AoI.
(Adrian's the project lead.)

Since I'm trying to use my mill to machine an extruder head, I'll put up the
g-code and related files that other folk with CNC mills will be able to use.
Neil Gershenfeld, of MIT's Fab Lab, wrote this bit of code for converting .stl
files into .g code - we may find it useful for this and for other projects:

http://web.media.mit.edu/~neilg/fab/dist/cam.py

I'd also like to put up .dxf files of the thing, which will happen soon after
I buy and start using a CAD program - either varicad or something else that
will work under linux/linux+wine. Any suggestions for linux-friendly CAD
programs?

> RepRap is using lower temp materials then I was considering. We recently
> purchased a ProtoPulsion Dimension SST RP, and it uses ABS "wire". I'm
> told it melts at about 165C, a little warmer! And, the inside of the
> enclosure for the RP is heated. Lovely machine!
>
> How hard is the Poly material you're using when it's cooled? The ABS is
> fairly hard. And the .07" ABS wire (1.77mm) comes on spools already (no
> need to make your own PolyMorph rods! I'm told I can have the tail-ends of
> the spools; they leave quite a bit on them in the magazines.
>

We've looked at using ABS, but the lower temperature thermoplastics may be
better for our purpose, since we can recycle them with a double boiler and a
ladle. Anything that melts over 100C is much harder to process. These are
the stuff that we're thinking about using:

http://reprapdoc.voodoo.co.nz/bin/view/Main/ThermoPlastic

We're probably going to stick with spools of 3mm diameter filament of some
thermoplastic, caprolactone or something else. Forrest Higgs has done some
good work on extruding 3mm filament, written up here:
http://reprap.blogspot.com/2006/07/new-wrinkle-on-capa-filament.html

Often, feedstock for rp machines can be expensive - over at a university I
know, parts from their printer cost them about $6/cubic inch! For
comparison, solvay sent me a 20kg bag of polycaprolactone (CAPA 6800) pellets
for about $5/kilo.

CAPA 6800 has an elastic modulus of 440, a yield stress of 16 Mpa, a Shore A
hardness of 94, and a Shore B hardness of 50, according to:
www.solvaycaprolactones.com/.../attachments/a.Props.___Processing_of_CAPA_Thermoplastics_ADS.pdf
I'm just parroting here, I don't know beans about material science, and
couldn't tell you how it compares to delrin or ABS. Also, most numerical
data is going to be for a solid ingot or rod of plastic - when I have a rod
made from filaments, I'll try to make relevant measurements.

Also, we'd like to source our thermoplastics or biopolymers from plant starch
or something similar, as opposed to from petroleum. However, we'll look into
making our own plastic after the 1.0 release.

> I've designed and have been building a "Baby PCB Router", which at 12" x
> 12" x 12" high overall might be an appropriate size to take an extrusion
> head. It's currently designed with a 3.25" x 5" tooling plate on the Z
> axis, and I have a bracket for DeWalt DW670 trim router mounted on it.
>

It sounds perfect. The extruder head is 20-25 cm tall, and you may need an
adapter plate to hold it. If a mill can move a dremel around, it can move an
extruder around. (It should be possible to build an adapter plate sockets
into a collet on a bridgeport and holds our fiddly little extruder head, so
that people with big machines could do this too.)

> Although I'm currently implementing USB with the PIC 18F4550 uP, my Step4
> controller program runs under DOS. I don't yet have a convenient driver
> for USB under DOS. And I am a LONG way from getting Step4 ported over to
> Windoz (if ever). I am investigating USB-CNC, a windoz controller program.
> The extruder control program could run as a windoz program as well! All
> we'd need would be some simple handshake between the two processes (I
> think, help me here).
>

If it is easy, we'll have a command line switch so that the reprap controller
software also works with parallel port + emc controlled machine tools. Our
controller is java based - it will work under linux, osx, windows.

> I think "self replication" is a long way off (Star Trek, NG), I'm simply
> interested in being able to explore a new fabrication method.
>

I agree with you. I have no idea how to fabricate a microcontroller.
Possible a microfluidic plate with conductive/semiconductive plastic in the
channels, for a hand-waving solution. Once we get the 1.0 release out the
door, we'll worry about esoteric stuff like that. More usefully and
realistically, the gang has looked at printing circuit boards out of
conductive materials and thermoplastic. Right now, it's silly to work on
that.

> Have you considered a two-material extrusion head? The SST also has a dual
> extrude head; the second material is a water-soluble structural support
> material.
>

Yeah, we'll have some kind of a support material going for the 1.0 or 1.1
release, along with a higher diameter orifice for thermoplastic to make a
bulk feed head. Every new material we add to the feedstock bus makes it
heavier and more complicated (especially if it means another motor). I wrote
up some thoughts on materials in an evening or so:
http://reprapdoc.voodoo.co.nz/bin/view/Main/MaterialsScience
I'd enjoy hearing what folks would suggest,
[ ...especially in a form I can copy and paste into the wiki ;) ]

> A sintering head would really be making progress! I know nothing about the
> process, but expect it needs higher heat and pressure that a hobbyist can
> easily handle. Please prove me wrong!
>

You can sinter clay (like your tea cup or a rp fabricated object from extruded
kaolin slurry), precious metal clay, or aluminum slurry in a kiln or furnace.
Extruding the material requires a syringe in a squeezing mechanism or a
peristaltic pump clipped onto a feedline ending in a syringe tip, so that is
very easy.

If you want to make carbide lathe tool bits inserts, you'll need a pressurized
mold in a furnace. That is hard. Luckily, most objects won't need to be
pressurized when they are sintered.

There's some work out there on putting down a layer of material, sintering it
with a laser, putting down another layer, etc. We'll worry about it later.

> Can't we make the extruder out of METAL? Would that make it smaller and
> more compact? I'd also consider a stepper motor for the drive. As I
> mentioned, I'm really not targeting self-replication. I'd make the best
> use of materials available to me.
>

Yes. If you have a mill, it makes more sense to make the extruder out of
metal. For the reprap project, we need to be able to make the extruder out
of thermoplastic and a drilled out brass bolt made with a lathe. (We only
need a crude lathe based on a hand drill or rotary tool:
http://staff.bath.ac.uk/ensab/replicator/Downloads/Afghan_lathe/Afghan_Lathe.html
I'd suggest using a real lathe if you have one.)
This way, we can make copies of the reprap using a reprap and a rotary tool.
If we cannot, it's not truly self-replicating, and we haven't met our project
requirements. (The assumption is that the user does not have a mill or
ECM/EDM head, but does have a reprap or repstrap and a spool of
thermoplastic.)

If you do design a smaller extruder out of metal, the reprap group would be
very interested to hear about it and would gladly host the files and
write-up; drop me an email or log onto to objects.reprap.org and upload the
info.

> Alan KM6VV
> Central coast, CA, USA
> SherlineCNC list
>

Eventually, not today but by 3 years from now we hope, we'll be making loaner
extrusion heads/repraps, and sending them out to folk who want to make their
own machine, and would be willing to make their own loaner extrusion
heads/repraps.

-Sebastien Bailard
reprap.org