As some of you may remember, I had previously worked on a "square" orifice nozzle for general experimentation. Further information and reading can be found here:
This nozzle has since been sent off for load testing to another forum user. Unfortunately, I did not feel much additional empirical testing was required to confirm that simply adding a square orifice to traditional nozzle geometry wouldn't change much in the way of print quality (though the extrudate was actually square, which was a nice result).
Up next: a nozzle designed with geometry scaled from a traditional extrusion die. The first photo is simply a CAD cross section of the overall design. The next photo is an actual cross section of our first attempt. The manufacturing method is EDM using electrodes cut on a high speed graphite mill. Tolerances are within 0.0005" using these methods. Additionally, surface finish is "perfect", at least perfectly consistent. Machine settings can manipulate how fine or course the finish is, as well as different grades of graphite (we use angstrofine, so most changes here will occur at the machine).
As you can see, right as the major ID begins, the path is a bit wider. This is due to electrode erosion, and the next sample will run additional electrodes to ensure the entire orifice is brought to size. Put simply, the inconsistency is not a manufacturing limitation, but rather having not validated the manufacturing process.
The theory is that this will assist in a) more consistent extrusion width b) less drool, and c) possibly an improved surface finish. Taking things a step further, if there are positive results samples will be vacuum hardened, and ultimately produced from Tungsten Carbide. One of the really great things about EDM, is it does not care about material hardness.
This is in active development, and I will be sure to share updates and progress. I expect the next photos to be actual print comparisons, and the next cross section to be completely straight/uniform. I expect to have to-spec sample by this Friday.
As an aside, the design concept was largely targeted toward pellet extrusion. Initial tests will be done with standard FDM extrusion setups, but high-detail pellet extrusion is the end goal.
I'd love to hear any opinions on this, including other possibilities given the manufacturing methods available.