Simplest toolpath from Skeinforge50

I'm trying to make a 2mm thick double shell with lots of penetrating holes as a case for a robot module, using ReplicatorG and Skeinforge50. If I could just get the toolpath generated to be the simplest possible, i.e. when it gets to a hole (gap in the shell) it just bridges to the other side of the hole, the surface of the shell would look fine. Instead what Skeinforge does is jump (create a long bridge) to the other side of the shell when it gets to the gap and after a lot of these jumps the surface of the shell is not nearly as smooth as it could be (not to mention the increase in print time). Is there any set of settings for Skeinforge that would force it not to make these large leaps and just create the simplest continuous perimeter?
many thanks,
cheers, ronmac

Could you give us pictures or drawings of what Skeinforge does and what you would like it to do? your post isn't easy to understand for a non-english language expert…

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François

Hi François....
Sorry to take so long to respond to your kind attention to my problem... I just realized I could have sent an alert email when you replied....

Here is a double shell model with holes as a test piece for the robot module shell I would like to create, . Here is the very reasonable toolpath (rendered in Mach3) showing the bridges as well as the extruded path. . And here is the result in a later test. .

My workaround has been to put cones behind the holes so that the surface is continuous and the cones form a drill-guide so that I can drill the shell at the right place (a drill guide keeps me from having to build a complicated jig to hold the shell in place while drilling). Here is a toolpath for a test model with this approach. . and here is the extruded result.

This is actually a pretty good solution, except when I want an odd shaped hole that would not be possible to drill, like the pyramid shape.

The machine I'm using to make the extrusion shown is a RepStrap I built myself, filling a small room in my basement.
The extruder is based on NopHead's HydraRaptor machine.

Before I came up with the cone depression workaround I build a simple model in GCode that extruded the outer shell and then the inner shell as I thought I wanted and discovered that the size of the filament heating chamber on my extruder is way too large, even with extensive retraction of the filament, to keep the bridged holes open with this technique.

So I guess I would still like to know if there is a way to tell Skeinforge to put a bridge across a hole when it gets to the end of either the inside or outside shell edge. (I hope this request is now clear... it is the difference between the toolpath with holes and the depression toolpath... the first one jumps (bridges) to the next continuous path and the second has some idea of inside and outside and creates shorter bridges (across holes).)
thanks again for your time..
cheers, ronmac

Hi again, François

I've included the STL model thinShellWithHolesSliced.stl this time. If we set Skeinforge Carve, Edge Width over Height to .45 with Layer Height .75mm you should get the toolpath shown in the MachToolpathShellWithHoles image. Here is a middle layer shown in Skeinlayer . The carve algorithm follows the perimeter of the shell until it gets to the starting point then bridges to the next closest perimeter starting point. Definitely the right thing to do but for it to extrude properly demands a better control of the filament than I have.

What I would like it to do is something like this . Carve treats the model as a single shell and bridges across gaps in the shell.
If you set Skeinforge Carve, Edge Width over Height to 2.0 with Layer Height .75mm you get this toolpath for the early layers until it encounters a gap, then stops producing GCode. All layers with a hole are empty layers.

So if there were a Skeinforge plugin (or settings) that allowed the holes in a single shell rendering to be treated as bridges and not errors that would be great.

many thanks again,
cheers, ronmac

Hi ronmacmedia!

ronmacmedia Wrote:
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> If I could just get the toolpath generated to be the
> simplest possible, i.e. when it gets to a hole
> (gap in the shell) it just bridges to the other
> side of the hole, the surface of the shell would
> look fine. Instead what Skeinforge does is jump
> (create a long bridge) to the other side of the
> shell when it gets to the gap and after a lot of
> these jumps the surface of the shell is not nearly
> as smooth as it could be

I am not sure to understand the difference you mean between bridges and long bridges… is it what we see in your DoubleShellSkeinforgeToolpath.jpg, non-printing moves across holes into the shell (when there are holes), and non-printing moves into your part, from an inner side to another?

If it's that we can't manage those non-printing moves with Skeinforge…

There is a direct relation between layer height and deposed filament width: the greater layer height is, the greater deposed filament is. 0.75mm layers are very too big to print a 2mm width part, you should try with very thinner layers, until you get a filling between your shells (the part should be stronger)… Perhaps this could have the side effect to correct your non-printing moves as in your IdealSingleShellToolpath.jpg?…

> If you set Skeinforge Carve, Edge Width over Height to 2.0 with Layer Height .75mm
> you get this toolpath for the early layers until it encounters a gap,
> then stops producing GCode. All layers with a hole are empty layers.

If Skeinforge sees there is no place to depose filament it don't depose it, this could explain (??) your empty layers (Caution: Skeinlayer frequently shows empty layers that are not really empty, just are Z intermediate moves between layers).

Playing with Edge Width over Height is not good to get deposed filament with too height layers (your 0.45 value for example), it should always be set to nearly it's default value (1.8).

That's all what I see for the moment!

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François