Re: [CAD_CAM_EDM_DRO] Re: 3D printer fun with powder

David G. LeVine wrote:

> At 12:24 PM 6/21/2007, you wrote:
>
>>>Have you considered what is known as a doctor blade? Look up
>>>"Gravure Doctor Blade" on Google (WITH the quotes) to see a small
>>>number of references. Remove the quotes and see 95,000 of
>>>them! With a properly set up doctor blade, the speed should be less
>>>of an issue.
>>
>>A doctor blade is what is used in laser printers to provide a
>>very thin, even film of toner on the transfer roller. It is
>>usually a piece of stiff mylar, maybe .01" thick (.25 mm)
>>You'd need to spread an excess amount of the powder first, then
>>the doctor blade would sweep the powder level.
>>
>>Jon
>
>
> John, that is not what we are discussing, read about the gravure
> process and imagine a drum with no engraving present. The doctor
> blade will remove ALL the powder.

OK, in laser printers, at least, the term "doctor blade" is used
to level out and regulate the very thin layer of toner perticles
on the developer roller (I used the wrong term "transfer roller"
a couple days ago.) I looked up the "Gravure Doctor Blade"on
google and see that it is slightly different on a gravure press.
And, what you are trying to accomplish with the roller is quite
different than how a laser printer works. If you were trying to
use the roller to "lay down" a precise layer of particles onto
the top of the part being built, then a doctor blade could be
used to get the desired thickness of material on the roller.
This works on the laser printers because the toner is magnetic,
and the roller has magnets in it.

In Graham's machine, he is trying to use the roller to level the
dust. I can see a lot of ways this could go awry. I wonder if
a blade would work better, but the commercial units seem to use
the roller. But, there may be a non-obvious trick, like static
electricity, roller surface characteristics, etc.

Jon