A basic structure and mechansim Re: 3D printing, powder spreading

Graham,

Thank you for the additional details.

A quick thought: Cheap and/or thrown-away desktop scanners are now
widely available over here (They're in all the thrift stores for a
few bucks). these would be a cheap sources for an additional axis of
travel with belts and guides...

I've been thinking mostly about the lift and let-down aspects; the
powder tanks. I'm thinking that this whole thing is even easier than
I thought. See if this makes sense:

One large "tank" over all; For conversation purposes; let's say it's
about an 11" x 19" rectangle in plan and is made of 3mm perspex
stock.

We'll make it fairly tall so there will be space under it when the
source and build tanks are made up and fitted within.

These two tanks are made of five sheets of perspex (two longer sides
and three crosspieces--2 ends and a middle). All sized so that there
is a single or double thickness of space between their width and the
larger catch tank. ( This inner double "hole" box is about 10-1/2"
wide x 17 long x build depth plus a couple inches) of 3mm perspex.

By using multiple small and/or angled strips to mount the inner two-
hole box to the outer catch box, we allow a place for the snowplow
roller ends. This will also let the powder at the edges fall into
this crack and to the catch basin below.

Now we cut two bottom plates such that with a perimeter of vinyl or
silicone split tubing, each forms a moving bottom for the build and
source "tank". Seems this would be a "good enough" seal, seeing as
how it's all sitting inside of the bigger "catch box" anyways. (May
not even need this kind of seal. plaster kinda "cakes" anyways; this
being a point of experimentation...)

Now we've got one big box with two equally-sized holes (and a 2 x 11
spillway at one end). Our two smaller movable-bottom "boxes" top
surface is our build surface.

The plates that form the bottom will be leadscrew moved. Less
engineering to use 4 leadscrews per bottom; but we can get away with
4. I'm choosing to use 6. I'l support the build area bottom with 4
leadscrew pillars, and the source/supply bin with two. Why will
become apparent in a few paragraphs... We need to keep our
leadscrews from getting covered with powder so we'll actually use
tubular pillars in the catch basin area, with a circular seal where
each one passes through the catch basin bottom. Think hexapod
actuator; and you'll see where I'm going with this...

So we have two bottoms, let's deal with the easier one first. We can
simply glue two hollow tubes to its bottom surface, and provide
matching holes in the catch basin bottom.

Now if we put a leadscrew nut at the far end (bottom) of each of
these two tubes, we can mount steppers on a plate set away from the
catch basin bottom --and parallel to it-- so that only the hollow
rods are exposed to the dust of the powder.

This stepper mounting plate would be held in position by the sides
and rear of the larger catch basin panels. That's why we made
them "relatively tall" in the description above.(I'd put a partial
panel at the sides of the front too. Cutaway so you can get into
clean out--and re-use--the powder.

Either drive two steppers at once, or set up a belt between the two
LS's so that the "actuators" (like those in a hexapod) can extend
and retract moving the bottom plate of the supply/source powder bin.

BTW, these don't need to be fancy steppers or fancy drives. We're
only gonna move .0035 or .007 or so every 15-25 seconds or so!

FWIW, we don't even need steppers... We could use a solenoid
operated escapement to effect the turning of the leaadscrews.
Simple. Effective (would have to be reversible.)

It'd almost be faster to build than to describe!<G>

Fnctional description:
The bin bottom has a tube glued to it. At the bottom of the tube is
a round plastic nut (could be A/B, but probably not necessary). the
nut is fastened AT the bottom of the tube. The tube and nut go
through a "grommeted/sealed" hole in the bottom of the catch basin.
The stepper/leadscrew goes through its mounting plate upwards
towards the tube and nut.

The spacing between the stepper mounting plate, catch basin bottom,
and source bin bottom is adjust to minimise wasted length (to keep
the tube and screws as short as possible in balance with being able
to get int anre-use the powder). And The tube/leadscrew length
itself will need to be adjusted towards this goal.

Now we get to the BUILD bin bottom. I'd put four posts on this one
because of something I saw on the Zcorp website. It said that after
the build the bin "shakes" the part and it LOOKEd like the powder
level was lowered during this operation...

So I got to thinking; If we rocked the bottom panel back-and-forth
after the building process... Not only would that shake it free of
the powder, it would ALSO allow the powder to fall out the bottom
directly into the catch bin for re-use!

Now you could do this with the two post approach I just described
for the source bin. It might even be eaiser to engineer, since the
two rods won't change distance as the thing rocks... But I think I
want/need something more predictable and stable for the build side.
By using 4 posts, we're gonna have easy adjustability for the "fall"
of the build plane through the build.

FWIW, I don't think this is as critical for the source side; but
using 4 supports/actuators there also is not too tough if needs be.
Anyways, we'll leave that part of the design up to those who wish to
pursue it.

Use pivots where the rods meet the build bin bottom. And realise
that if you tilt the plate very much the horizontal distance
(between actuators) will change. This is something that will need
some attention if the rocking and dumping action after build is
desired.

So we set up four actuators and their Leadscrews and drivers. Again
simple. But a bit more complexity needed if we're gonna actuate them
in not-unified ways to rock the bottom plate. So give that some
thought.
(I've gotta add that although the "rock-and-drop" presents a few
challenges design-wise; I think it will be REALLY useful and helpful
to keep the powder re-usable and contained.) And so IMO it's worth
the extra effort.

I think this whole arrangement could be made over a weekend, and
would provide the basis for the printer aspect to follow. You'd
adjust the overall box size to work with your printer carriage
dimensions.

Add a top "flange" plate to the catch basin outer box. And set up
your "snowplow" on the printer carriage.

I'm thinking that 5-1/4" disk drive steppers would be sufficient for
the raising and lowering of the two powder bin bottoms, using 1/4-20
or so leadscrews.

I didn't describe the entire catch box required for total
containment. But if you have the parts in place that I DID describe
the required additional panels will be obvious, and do-able.

Hope this helps,

Ballendo






--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler"
<grezmos@...> wrote:

>
> Fernando, yes it was the leading zero causing the problem, I

worked it

> out but it was too late.
>
> I use http://ep.espacenet.com/ for looking at patents its really

good

> and now allows pdf download.
>
> Ballendo,
>
> I've only been working on this a week really and I didn't even
> consider looking at patents as the basic operation is just an

inkjet

> printer. I'm going to do the powder height adjustment with a pair

of

> pumps used for inflatable beds, the big syringe type. It will

limit

> my build size but provides two cylinders with close fitting pistons
> for very little money.
>
> For binder have a look in the patent, it mentions a few adhesives

in

> the recipes section. I'll be happy to wet plaster with ink or

water

> to start with just to prove it works.
>
> The printer I have is a HP deskjet 1360. The gantry is now

mounted on

> some linear bearings, I'm going to use a dual cable drive (a la
> photocopier) to get it moving, that way I can make the drive roller
> the same size as the paper roller and its also much cheaper than

belts

> and pulleys. I'm using a 7 strand stainless plastic coated wire
> bought from a tackle shop as the cable.
>
> Graham
>