Re: 3D printing, powder spreading

Ted,

Thank you for sharing this. Helps immensely.

Ballendo

P.S. You mention having single raising/lowering screws. And than
follow that up with a comment about them being problematic. Would my
idea (tubed double screws) help in this area, based on your
experience?


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "laserted007" <thyde@...>
wrote:

>
> G, B & F -
> I have a particular model of the 3DP unit in question, and

although it

> is really simple technology, I will honor the manufacturer's

request

> that their trade secrets remain such. Given that, I can share a

lot of

> information still that one would find from open sources, such as

trade

> shows, discussion, and that which I have learned during my time

with it.

>
> Although MIT's patent lists compatibility with any loose powder,

and

> any binder, I have typically used a plaster dust for hi-res parts,

and

> a corn starch for lo-res or wax-cast parts.
>
> Our binder tank is not heated (I have the monochrome version), One
> important note is that the ink in the HP10 printhead is purged out
> when first inserted. The first few prints on a new head are a

little

> darker due to "black" residues, but after that you have to look

hard

> at the printing to see the mostly-clear binder being deposited.

It's

> also important to know the technologies that Epson and HP use in

their

> printheads - Epson uses piezo transducers to form the droplet,

while

> HP uses a heating pinpoint element. The thermal characteristic is

an

> important one.
>
> The manufacturer has spent considerable time fine tuning their
> binder/powder relationship, which is why they will charge $1200

for 80

> lbs of plaster, and $500 for a gallon of binder. Needless to say,

we

> won't be copying their formulae anytime soon for hobby purposes.

But

> we don't need to.
>
> After spending considerable $$$ on materials, we looked at

alternative

> options. First, we tested their plaster. It really is good quality
> molding plaster. We have replaced it on occasion (when we ran out)
> with good quality artistic molding plaster and had equal results.

We

> were also thinking dental alginate might be a good substitute, too.
> For the binder, while I by law had to post the MSDS sheets on my

wall,

> they weren't of too much help (and apparently trade secrets again)

but

> my chem background told me to use my nose first. There is nothing
> super-duper reactive in the binder, else it couldn't be handled in

an

> office environment, and the bullet points they use to sell the
> technology with would be inaccurate. The "nose" says think back to
> your grade school days and remember Elmer's brown liquid glue. Yup,
> natural horse glue, really thinned down. I'd expect that the
> manufacturer uses a synthetic version for shelf stability, but

recall

> where and how this technology was originally developed - (as the
> legend goes) a couple of MIT students with little $$$ and some dead
> ink-jet printers, probably printing whatever fluids they had at

hand

> in the kitchen.
>
> Ok, so you have your plaster, you have your horse glue, your HP
> printhead, 2 bins lifted and retracted by stepper motors on single
> center screws (really boring assembly and a b!tc# to perform
> maintenance on), and of course your rotating snowplow.
>
> After printing at a rate of about a half-inch per hour on a full

build

> area part (I typically print small things and often don't use the
> entire build area, so it's quicker than that), the videos stop

giving

> you information. This is where the major players in RP start to

have

> their "performance wars". FDM says that 3DP is messy and weak. 3DP
> says that FDM is hazardous (the older Dimension dissolvers, at

least -

> that's changed now too). LOM is an expensive waste, and SLA is just
> expensive. The new PolyReacts aren't proven. Thus the 3DP camp,
> doesn't advertise what you do next, too often....
>
> When the print is done, you leave it inside the printer for about

an

> hour. Newer versions of the cabinet are now slightly heated (about

80

> degrees) - and typically before, during and after printing.

(Explains

> the comment about the heated tanks). You can take a fresh

(or "Green"

> ) part out right away. You can also wreck it easily, too. Thin

walls

> (1.5mm or less) are very fragile at this point, and would likely

chip

> off. We usually wait the hour - there is a world of difference.
>
> After that time has passed, you "de-powder" - in two ways - first

you

> brush off (like an excavation dig) all the loose unused powder.

It's

> recycled back into the powder bin. This is where it gets messy. You
> can choose to vacuum it all off, and have a difficult time

reclaiming

> it, or you can brush it all over the place and spend more time
> cleaning your printer. (Note: powder with binder in it is NOT

reusable

> - thus if you have a bad or broken part, it goes into the trash.)

The

> second depowdering is inside the expensive "spray/vacuum booth"

they

> don't tell you about in the sales demo - overglorified vacuum

cleaner

> and airbrush. You get the majority of the powder off and leave it

in

> the printer. Then you move the part to the booth (cabinet, really)

and

> dust the rest off with the airbrush, or smaller bristle brushes.

Once

> again, powder without binder may be reclaimed.
>
> Although this part could be measured, colored, and looked at, you
> wouldn't want to pass it around the table. Still too fragile.

Thus, we

> fill the air inside with something. CA, Epoxy, wax are typical.

Yup,

> we even put CA into a spray gun. It's a commercially available kit
> from the manufacturer. Crazy. (I don't often use CA, as it forms a
> skin on the part and does not penetrate the part very much - about
> 1-2mm - but is good if you need it NOW.) I prefer a 2 part medium
> epoxy, such as MAS (though the manufacturer sells their own

version as

> well), but after trying lots of finish epoxies, the MAS gave me the
> best performance at a very good price. If you want to do investment
> casting, you'd infiltrate with wax (and use the cornstarch power
> instead. It works, you need to make a lot of patterns to get it

right

> the first time, though.)
>
> In retrospect, it appears that heat is a common theme for best
> performance in this technology - once the part comes out of the
> printer (hour wait), I put it into a 90 degree C convection oven

for

> about 20 minutes. Don't let it burn, just get really hot. After
> removal, I paint the epoxy on - the plaster wicks the epoxy in

quite

> deeply - about 12mm on a good fresh pull. I keep adding epoxy

until a

> shiny skin just starts to form on top - the part is "full". After

it's

> 24hr cure, you can sand, drill tap, mill, paint, bondo, throw,

drop,

> mail your part now. I even used plaster models in a skateboard

part we

> were making. Once you get this post-processing done correctly (it

is

> an acquired skill), the parts are extremely rigid. Note - if you
> "skin" the part with epoxy too much, you have to sand down epoxy,
> which is a challenge - a slightly rough texture during

infiltration is

> what you aim for, and a bit of finegrain sandpaper makes for a
> beautifully smooth finish afterwards.
>
> The best part of the technology, I think isn't that it makes cheap
> parts quickly - it's that it makes cheap PATTERNS quickly - yes, we
> can and do use the part right out of the printer as a prototype.
> Better than that, we can use the part as a pattern for making other
> parts, or different parts that an FDM can't do - such as

flexibles -

> just like you can get rigid casting agents from companies like
> Smooth-On, there is a 2-part polymer called Por-A-Mold which will
> infiltrate the plaster or cornstarch part. A well designed model
> (you're designing the 3d model for printing this time instead of
> dimensional accuracy) with the Por-A-Mold polymer will flex - very
> much like a CV boot or rubber ball - this time you aren't making a
> hard part, your're providing a surface for the polymer to bind to;

the

> powder/binder bonds disintegrate after the cure when you squish the
> finished part...
>
> Ted.
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo" <ballendo@>

wrote:

> >
> > Fernando,
> >
> > Excelent link. Worked for me. (Yahoo didn't break it up!)
> >
> > Thank you,
> >
> > Ballendo
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Fernando" <fer_mayrl@>
> > wrote:
> > >
> > > Graham,
> > > maybe if you get rid of the leading zero on the number. Here

is the

> > > complete link, it will most likely get truncated my yahoo, but

you

> > > know the drill of copy pasting it:
> > > http://patft.uspto.gov/netacgi/nph-Parser?
> > Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-
> > adv.htm&r=10&f=G&l=50&d=PALL&S1=6610429&OS=6610429&RS=6610429
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler"

<grezmos@>

> > > wrote:
> > > >
> > > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Fernando"

<fer_mayrl@>

> > wrote:
> > > > >
> > > > > What kind of binder are they using on the plaster that

hardens

> > so
> > > > quickly?
> > > > > Regards
> > > > > Fernando
> > > > >
> > > >
> > > > Web searches suggest that sugar water mixes are used with
> > plaster, I
> > > > think the tanks are slightly heated and also read that the

model

> > > > should ideally be left in situ for a while before disturbing

if

> > > possible.
> > > >
> > > > I couldn't find that patent, are you sure that was the full
> > number?
> > > >
> > > > Graham
> > > >
> > >
> >
>