Re: [CAD_CAM_EDM_DRO] reprap build started

On Tue, Oct 11, 2011 at 6:25 PM, Jon Elson <elson@...> wrote:

> Alan wrote:
> > Kevin, Mike,
> >
> > What's the basic relationship of feeding stock to the travel in X &Y?
> >
> > Sounds like it would be a direct relationship. So one could calculate a
> > "feed distance" for the stock, and assign it to another axis to drive the
> > extruder (scaled, of course)...
> >
> > Seems like if the X axis needed to move 5" to lay down the filament, then
> 5"
> > of stock (or some scale of that) would need to be extruded at the same
> time.
> > Just like a "coordinated move"! Has someone already thought of that?
> >
> > I could see a little program that took normal Gcode, and generated the
> > "pseudo axis" for the coordinated move.
> >
> Since the filament fabricator has no Z axis, just a layer step size, one
> could assign the
> extruder drive to another axis, like Z (or U). Then, the G-code could
> be written to
> always move Z scaled by the sqrt(x*2 + Y*2) movement. This would give
> an acceleration
> ramp on the extruder that matches the acceleration of the X-Y table.
> The only thing this
> lacks is the pull-back each time the extruder needs to stop. That could
> also be written
> into the code.
>
> So, this could ALL be done in G-code, although it might end up being a
> LOT of lines.

There is a Z axis, how else would you move p by that layer step size?
Granted the Z axis doesn't move much on most prints, but it is there.

the extrusion rate is done all in g-code already, we use the E axis for the
extruder. I don't use multiple extruders at present, but I believe multiple
extruders are considered different tools and switched with an M code, but I
could be wrong about that (Multiple extruder support is fairly weak so far
in most RepRap firmware). The E axis g-code works just like any other, if
you send it the code G1 e100 it would extrude 100mm of filament. if you sent
g1 e-100 it would retract by 100mm. The slicer software knows your filament
diameter, the distance you are traveling, and the desired extrusion width
and height, and from those variables it knows how much filament it needs to
feed to get the volume of plastic required.

Interestingly, the nozzle diameter is not needed, since the volume of
plastic is based on the input size, not the output size. The output profile
will be the same with a .35mm nozzle and a .5mm nozzle at the same settings,
though there are practical limits.

As you note, the axis acceleration is synchronized by the firmware already,
so you can only move as fast as your slowest axis can move. For my machine
as it is currently configured, my limiting factor is the extruder, I can
reliably move at 125+mm/sec, but my extruder can only handle about 50mm/sec
(more accurately, I can extrude at a rate of about 7mm/second, which is what
I need to print at a 50mm/second feed rate). My next project will be to
figure that out what the limitation is and fix that, since I know people who
use the exact configuration I have and are printing well above 100mm/second.


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