forcing bridging

I am trying to print an object with a recessed bolt hole. The larger hole for the bolt head is printed first with the narrower shaft hole above it. In my openscad source code I put a 1 layer membrane between these two diameters so that the smaller hole would not be printed in mid air. Skeinforge properly sliced it, but it did not consider this membrane to be bridging - it did a normal solid fill. I would have preferred that it use my bridge settings for this layer. Is there some trick to forcing this, or at least fooling skeinforge into thinking bridging is necessary?

Can you share your openscad code for us to understand better what you are trying?

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François

Here is a simplified example. The two objects are identical except that the one over the origin has a membrane. Obviously with this simple example the objects can be flipped over, but for a more complex object this might not be possible.

module x() {
	difference() {
		cylinder(r=5, h=10, center=true, $fn=30);
		translate([0, 0, 2.5])
			cylinder(r=2, h=5.1, center=true, $fn=30);
		translate([0, 0, -2.5])
			cylinder(r=4, h=5.1, center=true, $fn=30);
	}
}

translate([15, 0, 0]) x();

union() {
	x();
	cylinder(r=4, h=0.3, center=true);
}

I think you have a reason to print the "larger hole" first, your part inversed there would be no print difficulty or support needed.

Recently I made a part very similar to yours, printed "larger hole first", without your membrane, with a support. I understand that you use a membrane to avoid a support, is this that? with good parameters, a support can have no connexion with vertical walls, just must be detached from the horizontal bridge… But I think I don't answer your question…

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François

using support is definitely an option. In the actual part being printed, the large hole is fairly deep. I thought it would be difficult to remove the support.

It's not a big deal - with the solid infill the print was very successful. I'm just thinking of the more general case where I might want to do something like this on a larger scale where bridging might be more important.