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

Graham,

Snips, inserts below...

>In CCED, "Graham Stabler" <grezmos@...> wrote:
>I've lots of printer and scanner parts but I wanted to try and keep
>the ratios between the servo motor and the drive as they are,
>finding a set of pulleys etc of the right diameter might be a

challenge. That said if you find something of about the right size
<snip>

Makes sense. Keep as much of the "native intelligence" of the
printer as possible...

>As for the rest of your description; its pretty much as I imagined
>they might build it although I'm also not sure they bother having
>the gap at the sides of the build area, its raised up but there
>seemed to be some little fenders near the ends of the rollers. If
>the sides of the build box are beveled inwards any little bits of
>excess will fall in around the edges, the build platform lowers
>before printing anyway so it would not cause a problem.

Yes, the gap is a solution based on using cheap perspex as the
material, and not wanting to do a lot of extra edge
chamfer/detailing. One thing I HAVe thought about is whether the bin
material being plastic--as in your pumps and my perspex--will keep
the powder from "sliding" when the bin bottom is lowered? The shiny
steel shown in the Zcorp pics might be a "necessary" item?

>I'm not an overly big fan of using 4 leadscrews, I've never done it
>but it seems a recipe for problems potentially. You are using the
>grommets on your tubes and the fit between the piston and box as
>your linear bearings essentially, there is bound to be some
>rocking?

I've done it many times; including things not cnc related (platen
clamps). You see it on some wood planers as well. It works well, and
is easily adjustable for rocking and plane orientation. But one
could instead use two REAL linear bearings and one
leadscrew/actuator. Was thinking of a: Weekend-buy-the-perspex, get-
out-the-table-saw-and-glue-and-get-er-done kind of thing<G>

As for any unintended rocking; that's the reason fo rusing 4 screws:
any poor fit between the bin bottom and the bin sides will be
constrained to sideways motion. Likewise the fit of the tubes in
their grommets. The only vertical shift will be a component of the
relative movement VARIATION between these two "planes" moveing
sideways. And that's gonna be extremely small, considering all the
dimensions.

Put one hand above the other. Hold one end of a common string in
each hand. Move hands side-to side... You have to move quite a ways
before the distance vertically between your hands changes due to the
string constraint...

>If I use my piston idea I'll use single lead screws into nuts in the
>"con rod" as you describe, that seems a pretty good solution.
>This is the kind of pump I'm talking about:www.gifts2go.eu<snip>
>Obviously a proper built solution would be better in the long run.

Concern is for their round areas. The "snowplow" will be working
over an area (between the two) where no rise and fall can be
accomplished.
I'm visualising problems due to that with scatter, uneven layering
in the build area, and powder build up...

Which was basically why I detailed the perspex tank idea; I figured
for you that might end up being easier than the kluge of the pumps,
and should work well enough to keep working; rather than just being
a test of the concept?

>for the shake rattle and empty you could just add a door to the
>bottom of the tank one that only opens upwards, then just start
>prodding it with a solenoid.

Yes, I also thought about a "door". Not sure it's the best way to go
though...

Thank you for the fedback,

Ballendo