Printrbot Tensioner

As a followup to my post about making printable models from PDF part diagrams, here is a replacement Printrbot tensioner I made using that method. (The original did not need to be replaced; I just chose this part as a simple test case. It’s working great.)

The original tensioner is assembled from two laser-cut wood parts, numbered 21 and 22 in the Printrbot Simple’s diagram. I exported the patterns per the process described in the post linked above and combined them using the following OpenSCAD script. Note that part 22 has a partly recessed socket for a hex nut, which I exported separately.

module part_22() {
	difference() {
		
		// Part 22, with bolt holes
		linear_extrude(height=6) import("part-22.dxf");
		
		// Subtract the hex nut socket from part 22
		translate([398.15 - 394.29, 525.66 - 489.21, 3])
		linear_extrude(height=3) import("part-22-hex.dxf");
	}
}

module part_21() {
	// Part 21, not including hole through which 22 goes
	linear_extrude(height=6) import("part-21-solid.dxf");
}

union() {
	part_22();
	translate([0, 36, 458.88 - 462.4]) rotate([90, 0, 0]) part_21();
}

The parts are aligned using positions reported for each feature in LibreOffice. The actual position on the page doesn’t matter; only the difference between them is used to get things centered.

The STL exported from this script could be used to make an exact replacement for the original assembly. Instead, I imported it into SketchUp using the SketchUp STL plugin and made a few changes to simplify the part and make it easier to print without supports. This is the final version published on Thingiverse.

Posted on Tuesday, February 11th, 2014.

Mystic Crystal

Printed a sphere inside a tiny cube. How cool is that?

With this plain translucent plastic, the inner contours are visible when the object is backlit. I think this has pretty cool artistic potential.

Posted on Wednesday, January 29th, 2014.

Making Printable Models from Parts Diagrams

Printrbot provides part diagrams of the laser-cut wood parts included with their printer kits. These diagrams are useful if you want to save even more on the cost of a kit by having the parts cut yourself. Alternatively, you can use these patterns to print replacement parts for your Printrbot using your Printrbot. Here’s a roundabout way to convert the part diagrams to printable models using only free software.

First, download a parts diagram from the Printrbot Support page for your printer. Here is the diagram for my printer (PDF).

Open the PDF in LibreOffice. For this example, I’ll convert part 16, the cooling fan mount. Select the part, including holes, but not including the “16” label:

Select Export… from the File menu. Check Selection and choose EPS as the file type to export.

Be sure mm is selected as the unit in the EPS Options window. Click OK.

Convert the EPS file to DXF format using pstoedit:

pstoedit -dt -f dxf:"-polyaslines -mm" part16.eps part16.dxf

(There may be friendlier tools available to convert PDF or EPS files to DXF. DXF is needed because it is the only 2D format understood by OpenSCAD, which is used in the next step to extrude the outline into three dimensions. Printrbot part diagrams are available as DXF drawings, but I think it requires a bit more CAD expertise to extract individual parts from those files.)

Use OpenSCAD to import the DXF drawing and give it depth:

linear_extrude(height=6) import("part16.dxf");

Finally, to get a printable STL file, select Compile and Render from OpenSCAD’s Design menu, then Export as STL… from the same menu. Here’s the result positioned in RepetierHost, ready to print:

Another thing to try would be to use OpenSCAD to union an assembly of multiple parts into a model you could print as a single piece for greater rigidity and ease of maintenance. You might also customize the model to accomodate different components. This article on using fasteners with printed parts is worth a look for useful design tips, too.

Posted on Friday, January 24th, 2014.

A Fan Fix

At some point the other day I peeled the sticker off the center of the cooling fan on my Printrbot extruder. I think in so doing I must have budged the solder where the wires enter the fan: last night I realized the fan wasn’t running, regardless of setting. So, this morning I pulled my multimeter out of cold storage (no, really – it is cold in the garage) and verified current was reaching the fan. I was happy to confirm the fan was at fault, and not some connection on the circuit board.

A quick trip to Unicorn Electronics for an identical replacement, and we’re back in action!

The cooling fan helps ensure plastic emerging from the extruder solidifies quickly. Actually, as a test I printed several items earlier this week with it turned off, and didn’t notice a difference in output – perhaps it is more important when the ambient temperature is higher.

Posted on Thursday, January 23rd, 2014.

Building OpenSCAD from Source

OpenSCAD is a useful tool for 3D modeling. You create models in OpenSCAD by writing scripts composed of commands like cube or rotate to instantiate and manipulate shapes. Furthermore, you can combine shapes using constructive solid geometry operations like union or difference. So it is not a substitute for interactive modeling, but a tool for writing programs to generate models from input. For example, Thingiverse Customizer uses OpenSCAD.

I use OpenSCAD with Linux Mint, where it is readily available via the Software Manager. However, the version available there is not the latest. Furthermore, the downloadable version of the latest release on the OpenSCAD web site does not run on my laptop, due to an unnecessarily strict glibc version dependency. So, rather than muck around with a bunch of different versions, I decided to just build the latest code available from Github. Happily, the build instructions work. Here’s a step-by-step summary for Linux (assumes you have git installed):

# download the code
git clone https://github.com/openscad/openscad.git

# enter the downloaded directory
cd openscad

# download MCAD part library, stored as a separate repository
git submodule update --init

# download and compile other dependencies (tools and libraries)
# - might take a while depending how many are already installed
scripts/uni-get-dependencies.sh
scripts/uni-build-dependencies.sh

# compile Openscad
qmake
make

Now you can run openscad from that directory, or run sudo make install to install the app for systemwide access.

Posted on Wednesday, January 22nd, 2014.

PrintrBot Assembly Notes

The Printrbot Simple’s assembly instructions are published online as a photo-illustrated guide. Having recently assemble my own Printrbot, I thought I would share a few comments and tips for the benefit of anyone else about to build one.

First, and most generally, it’s worth reading through the instructions before you begin building to get a sense of how everything it will fit together. At the very least, look at the photos for the next step before you proceed with the current step to see how the current step will look when done.

Find the right tool for the job of separating the laser-cut plywood parts (step 2). I did not settle on a safe and consistent cutting method until I tried the chisel-tip blade pictured at right. (Simply snapping the parts apart by hand is possible, but discouraged due to the possibility of splitting or snapping the parts themselves.) This advice may soon be moot since I understand Printrbot plans to transition to all-aluminum construction.

The zip ties securing the Z axis drive rod coupler (step 40) pass very close to wires from the circuit board. I wrapped a piece of tape around the zip tie nubs to prevent them from accidentally yanking wires as the rod rotates. Careful grouping and routing of wires is general good practice to avoid interference with moving parts.

Last but most important: once you’ve finished the assembly, but before you run the printer for the first time, examine the 3″ bolt installed on the back of the extruder carraige in step 30. This is the Z stopper. Its job is to hit the Z end stop switch on the base of the printer (nut and black box at right in the picture above) just before the extruder tip hits the print bed (at left in the picture above). Make sure it is threaded in far enough to do so! Otherwise, the extruder tip will be driven into the print bed when the printer attempts to find its “home” location by descending until the Z stop is triggered.

Posted on Wednesday, January 22nd, 2014.